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LDC1312, LDC1314
SNOSCZ0A – DECEMBER 2014 – REVISED MARCH 2018
LDC1312, LDC1314 Multi-Channel 12-Bit Inductance to Digital Converter (LDC) for
Inductive Sensing
1 Features
3 Description
•
•
•
The LDC1312 and LDC1314 are 2- and 4-channel,
12-bit inductance to digital converters (LDCs) for
inductive sensing solutions. With multiple channels
and support for remote sensing, the LDC1312 and
LDC1314 enable the performance and reliability
benefits of inductive sensing to be realized at minimal
cost and power. The products are easy to use, only
requiring that the sensor frequency be within 1 kHz
and 10 MHz to begin sensing. The wide 1 kHz to 10
MHz sensor frequency range also enables use of
very small PCB coils, further reducing sensing
solution cost and size.
•
•
•
•
•
•
•
Easy-to-Use – Minimal Configuration Required
Up to 4 Channels With Matched Sensor Drive
Multiple Channels Support Environmental and
Aging Compensation
Remote Sensor Position of >20 cm Supports
Operation In Harsh Environments
Pin-Compatible Medium and High-Resolution
Options:
– LDC1312/4: 2/4-ch 12-Bit LDC
– LDC1612/4: 2/4-ch 28-Bit LDC
Supports Wide Sensor Frequency Range of 1 kHz
to 10 MHz
Power Consumption:
– 35 µA Low Power Sleep Mode
– 200 nA Shutdown Mode
2.7 V to 3.6 V Operation
Multiple Reference Clocking Options:
– Included Internal Clock For Lower System
Cost
– Support for 40 MHz External Clock For Higher
System performance
Immunity to DC Magnetic Fields and Magnets
2 Applications
•
•
•
•
•
•
•
•
Knobs in Consumer, Appliances, and Automotive
Linear and Rotational Encoders
Buttons in Home Electronics, Wearables,
Manufacturing, and Automotive
Keypads in Manufacturing and Appliances
Slider Buttons in Consumer Products
Metal Detection in Industrial and Automotive
POS and EPOS
Flow Meters in Consumer and Appliances
Simplified Schematic
3.3 V
SD
GPIO
IN0B
Core
GND
IN1A
IN1B
SDA
I 2C
I 2C
Peripheral
SCL
ADDR
Sensor 1
PACKAGE
BODY SIZE (NOM)
WSON-12
4 mm × 4 mm
LDC1314
WQFN-16
4 mm × 4 mm
(1) For all available packages, see the orderable addendum at
the end of the datasheet.
Measurement Precision vs. Target Distance
2.25
VDD
GPIO
INTB
Target
PART NUMBER
LDC1312
VDD
IN0A
Sensor 0
Device Information(1)
2.5
MCU
CLKIN
Target
The LDC1312 and LDC1314 are easily configured via
an I2C interface. The two-channel LDC1312 is
available in a WSON-12 package and the fourchannel LDC1314 is available in a WQFN-16
package.
3.3 V
LDC1312
40 MHz
The LDC1312 and LDC1314 offer well-matched
channels, which allow for differential and ratiometric
measurements. This enables designers to use one
channel
to
compensate
their
sensing
for
environmental and aging conditions such as
temperature, humidity, and mechanical drift. Given
their ease of use, low power, and low system cost
these products enable designers to greatly improve
on existing sensing solutions and to introduce brand
new sensing capabilities to products in all markets,
especially consumer and industrial applications.
Inductive sensing offers better performance,
reliability, and flexibility than competitive sensing
technologies at lower system cost and power.
3.3 V
GND
Measurement Precision (µm)
1
2
1.75
1.5
1.25
1
0.75
0.5
0.25
Copyright © 2016, Texas Instruments Incorporated
0
0
10%
20%
30%
40%
50%
60%
Sensing Range (Target Distance / ‡SENSOR)
70%
D001
1
An IMPORTANT NOTICE at the end of this data sheet addresses availability, warranty, changes, use in safety-critical applications,
intellectual property matters and other important disclaimers. PRODUCTION DATA.
LDC1312, LDC1314
SNOSCZ0A – DECEMBER 2014 – REVISED MARCH 2018
www.ti.com
Table of Contents
1
2
3
4
5
6
7
Features ..................................................................
Applications ...........................................................
Description .............................................................
Revision History.....................................................
Pin Configuration and Functions .........................
Specifications.........................................................
1
1
1
2
3
4
6.1
6.2
6.3
6.4
6.5
6.6
6.7
4
4
4
4
5
6
7
Absolute Maximum Ratings ......................................
ESD Ratings ............................................................
Recommended Operating Conditions.......................
Thermal Information .................................................
Electrical Characteristics...........................................
Switching Characteristics - I2C .................................
Typical Characteristics ..............................................
Detailed Description .............................................. 9
7.1
7.2
7.3
7.4
7.5
Overview ................................................................... 9
Functional Block Diagram ......................................... 9
Feature Description................................................... 9
Device Functional Modes........................................ 11
Programming........................................................... 12
7.6 Register Maps ......................................................... 14
8
Application and Implementation ........................ 31
8.1 Application Information............................................ 31
8.2 Typical Application ................................................. 47
9 Power Supply Recommendations...................... 51
10 Layout................................................................... 52
10.1 Layout Guidelines ................................................. 52
10.2 Layout Example .................................................... 52
11 Device and Documentation Support ................. 53
11.1
11.2
11.3
11.4
11.5
11.6
11.7
11.8
Device Support......................................................
Documentation Support ........................................
Related Links ........................................................
Receiving Notification of Documentation Updates
Community Resources..........................................
Trademarks ...........................................................
Electrostatic Discharge Caution ............................
Glossary ................................................................
53
53
53
53
53
54
54
54
12 Mechanical, Packaging, and Orderable
Information ........................................................... 54
4 Revision History
NOTE: Page numbers for previous revisions may differ from page numbers in the current version.
Changes from Original (December 2014) to Revision A
Page
•
Changed ESD values from 1000 to 2000 and from 250 to 750 on both packages................................................................ 4
•
Added logic levels for ADDR, INTB, and SD pins. ................................................................................................................. 5
•
Changed description of clocking architecture for improved clarity. ..................................................................................... 10
•
Changed register names and field names from CHx_NAME and NAME_CHx to NAMEx. ................................................ 14
•
Added instructions on setting registers with both R and R/W fields..................................................................................... 14
•
Changed register names from DATA_CHx to DATAx; and CHx_ERR_YY field names to ERR_YYx. ............................... 15
•
Changed ERR_AE field description on DATA0, DATA1, DATA2 and DATA3 tables. ......................................................... 15
•
Changed register names from RCOUNT_CHx to RCOUNTx; and CHx_RCOUNT field names to RCOUNTx .................. 17
•
Changed register names from OFFSET_CHx to OFFSETx; and CHx_OFFSET field names to OFFSETx ...................... 18
•
Changed register names from SETTLECOUNT_CHx to SETTLECOUNTx; and CHx_SETTLECOUNT field names to
SETTLECOUNTx ................................................................................................................................................................. 19
•
Changed Address of SETTLECOUNT0 and SETTLECOUNT1 were not correct on table. ................................................ 20
•
Changed register names from CLOCK_DIVIDERS_CHx to CLOCK_DIVIDERSx; CHx_FIN_DIVIDER field names to
FIN_DIVIDERx, and CHx_FREF_DIVIDER field names to FREF_DIVIDERx. ................................................................... 21
•
Changed CHx_UNREADCONV field names to UNREADCONVx ...................................................................................... 23
•
Changed register names from DRIVE_CURRENT_CHx to DRIVE_CURRENTx; CHx_IDRIVE field names to
IDRIVEx, and CHx_INIT_IDRIVE to INIT_IDRIVEx ............................................................................................................ 28
•
Changed Application Information section for clarity, and provided additional information on device configuration and
operation. ............................................................................................................................................................................. 31
•
Added instructions for using an oscilloscope to configure sensor drive current .................................................................. 42
•
Changed description of clocking usage for clarity. .............................................................................................................. 43
•
Changed reference frequency limits from < to ≤ .................................................................................................................. 44
•
Changed to a ≥ symbol in the Clock Configuration Requirements table. ............................................................................ 44
2
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SNOSCZ0A – DECEMBER 2014 – REVISED MARCH 2018
5 Pin Configuration and Functions
CLKIN
3
10
ADDR
4
INTB
SD
IN3A
IN2B
IN2A
15
14
13
IN1B
11
IN1A
3
10
IN0B
4
9
IN0A
1
IN0B
SDA
2
9
IN0A
CLKIN
5
8
GND
ADDR
6
7
VDD
DAP
IN3B
12
SCL
DAP
8
IN1A
GND
11
7
2
VDD
SDA
6
IN1B
SD
12
5
1
INTB
SCL
16
DNT and RGH Packages
Top View
LDC1314 WQFN-16
LDC1312 WSON-12
Pin Functions
PIN
NAME
NO.
TYPE (1)
DESCRIPTION
SCL
1
I
SDA
2
I/O
CLKIN
3
I
External Reference Clock input. Tie this pin to GND if internal oscillator is used.
4
I
I2C Address selection pin: when ADDR=L, I2C address = 0x2A, when ADDR=H, I2C address =
0x2B. This input must not be allowed to float.
5
O
Configurable Interrupt output pin. Push-pull output; does not require pullup.
6
I
Shutdown input: set SD = L for normal operation, set SD=H for inactive mode. This input must
not be allowed to float.
VDD
7
P
Power Supply
GND
8
G
Ground
IN0A
9
A
External LC sensor 0 connection
IN0B
10
A
External LC sensor 0 connection
IN1A
11
A
External LC sensor 1 connection
IN1B
12
A
External LC sensor 1 connection
IN2A
13
A
External LC sensor 2 connection (LDC1314 only)
IN2B
14
A
External LC sensor 2 connection (LDC1314 only)
IN3A
15
A
External LC sensor 3 connection (LDC1314 only)
IN3B
16
A
External LC sensor 3 connection (LDC1314 only)
DAP
N/A
ADDR
INTB
SD
DAP (2)
(1)
(2)
I2C Clock input. Open drain output; requires resistive pullup to logic high level.
I2C Data input/output. Open drain output; requires resistive pullup to logic high level.
Connect to Ground
I = Input, O = Output, P=Power, G=Ground, A=Analog
There is an internal electrical connection between the exposed Die Attach Pad (DAP) and the GND pin of the device. Although the DAP
can be left floating, for best performance the DAP should be connected to the same potential as the device's GND pin. Do not use the
DAP as the primary ground for the device. The device GND pin must always be connected to ground.
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6 Specifications
6.1 Absolute Maximum Ratings
MIN
MAX
UNIT
5
V
VDD
Supply Voltage Range
Vi
Voltage on any pin
-0.3
VDD+0.3
V
IA
Input current on any INx pin
-8
8
mA
ID
Input current on any Digital pin
-5
5
mA
Tj
Junction Temperature
-55
150
°C
Tstg
Storage temperature range
-65
150
°C
(1)
Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings
only, which do not imply functional operation of the device at these or any other conditions beyond those indicated under Recommended
Operating Conditions. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.
6.2 ESD Ratings
VALUE
UNIT
LDC1312 in WSON-12 package
V(ESD)
Electrostatic discharge
Human-body model (HBM), per ANSI/ESDA/JEDEC JS-001 (1)
±2000
Charged-device model (CDM), per JEDEC specification JESD22C101 (2)
±750
Human-body model (HBM), per ANSI/ESDA/JEDEC JS-001 (1)
±2000
Charged-device model (CDM), per JEDEC specification JESD22C101 (2)
±750
V
LDC1314 in WQFN-16 package
V(ESD)
(1)
(2)
Electrostatic discharge
V
JEDEC document JEP155 states that 500-V HBM allows safe manufacturing with a standard ESD control process.
JEDEC document JEP157 states that 250-V CDM allows safe manufacturing with a standard ESD control process.
6.3 Recommended Operating Conditions
Unless otherwise specified, all limits ensured for TA = 25°C, VDD = 3.3 V
MIN
NOM
MAX
UNIT
VDD
Supply Voltage
2.7
3.6
V
TA
Operating Temperature
-40
125
°C
6.4 Thermal Information
THERMAL METRIC (1)
RθJA
(1)
4
Junction-to-ambient thermal resistance
LDC1312
LDC1314
WSON (DNT)
WQFN (RGH)
12 PINS
16 PINS
50
38
UNIT
°C/W
For more information about traditional and new thermal metrics, see the Semiconductor and IC Package Thermal Metrics application
report.
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SNOSCZ0A – DECEMBER 2014 – REVISED MARCH 2018
6.5 Electrical Characteristics
Unless otherwise specified, all limits ensured for TA = 25°C, VDD = 3.3 V. See
(1)
(2)
MIN (3)
TYP (4)
MAX (3)
PARAMETER
TEST CONDITIONS
UNIT
VDD
Supply Voltage
TA = -40°C to +125°C
IDD
Supply Current (not including
sensor current) (5)
ƒCLKIN = 10 MHz
IDDSL
Sleep Mode Supply Current (5)
SLEEP_MODE_EN = b1
35
60
µA
ISD
Shutdown Mode Supply
Current (5)
SD = VDD
0.2
1
µA
ISENSORMAX
Sensor Maximum Current drive
RP
Sensor RP
HIGH_CURRENT_DRV = b0
DRIVE_CURRENTx = 0xF800
IHDSENSORMAX
High current sensor drive mode:
Sensor Maximum Current
RP_HD_MIN
Minimum sensor RP
ƒSENSOR
Sensor Resonance Frequency
VSENSORMAX
Maximum oscillation amplitude
(peak)
NBITS
Number of bits
POWER
2.7
3.6
V
(6)
2.1
mA
SENSOR
1.5
1
HIGH_CURRENT_DRV = b1
DRIVE_CURRENT0 = 0xF800
Channel 0 only
TA = -40°C to +125°C
CIN
Sensor Pin input capacitance
mA
Ω
250
0.001
10
MHz
1.8
V
12
RCOUNTx ≥ 0x0400
Maximum Channel Sample Rate
kΩ
6
RESET_DEV.OUTPUT_GAIN=b00
ƒCS
mA
100
single active channel continuous
conversion, SCL=400 kHz
13.3
bits
kSPS
4
pF
DIGITAL PIN LEVELS
VIL
Low voltage threshold (ADDR
and SD)
VIH
High voltage threshold (ADDR
and SD)
VOL
INTB low voltage output level
VOH
INTB high voltage output level
0.3*VDD
V
0.7*VDD
V
3mA sink current
0.4
V
2.4
V
REFERENCE CLOCK
ƒCLKIN
External Reference Clock Input
Frequency (CLKIN)
CLKINDUTY_MIN
External Reference Clock
minimum acceptable duty cycle
(CLKIN)
40%
External Reference Clock
maximum acceptable duty cycle
(CLKIN)
60%
CLKINDUTY_MAX
VCLKIN_LO
CLKIN low voltage threshold
VCLKIN_HI
CLKIN high voltage threshold
(1)
(2)
(3)
(4)
(5)
(6)
TA = -40°C to +125°C
2
40
MHz
0.3*VDD
0.7*VDD
V
V
Electrical Characteristics Table values apply only for factory testing conditions at the temperature indicated. Factory testing conditions
result in very limited self-heating of the device such that TJ = TA. No guarantee of parametric performance is indicated in the electrical
tables under conditions of internal self-heating where TJ > TA. Absolute Maximum Ratings indicate junction temperature limits beyond
which the device may be permanently degraded, either mechanically or electrically.
Register values are represented as either binary (b is the prefix to the digits), or hexadecimal (0x is the prefix to the digits). Decimal
values have no prefix.
Limits are ensured by testing, design, or statistical analysis at 25°C. Limits over the operating temperature range are ensured through
correlations using statistical quality control (SQC) method.
Typical values represent the most likely parametric norm as determined at the time of characterization. Actual typical values may vary
over time and will also depend on the application and configuration. The typical values are not tested and are not guaranteed on
shipped production material.
I2C read/write communication and pull-up resistors current through SCL, SDA not included.
Sensor inductor: 2 layer, 32 turns/layer, 14 mm diameter, PCB inductor with L=19.4 µH, RP=5.7 kΩ at 2 MHz Sensor capacitor: 330 pF
1% COG/NP0 Target: Aluminum, 1.5 mm thickness Channel = Channel 0 (continuous mode) ƒCLKIN = 40 MHz, FIN_DIVIDER0 = b0000,
FREF_DIVIDER0 = 0x0001, RCOUNT0 = 0xFFFF, SETTLECOUNT0 = 0x0100, RP_OVERRIDE = b1, AUTO_AMP_DIS = b1,
DRIVE_CURRENT0 = 0x9800
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Electrical Characteristics (continued)
Unless otherwise specified, all limits ensured for TA = 25°C, VDD = 3.3 V. See (1)
TEST CONDITIONS (2)
PARAMETER
ƒINTCLK
Internal Reference Clock
Frequency range
TCf_int_μ
Internal Reference Clock
Temperature Coefficient mean
MIN (3)
TYP (4)
MAX (3)
UNIT
35
43.4
55
MHz
-13
ppm/°C
TIMING CHARACTERISTICS
tWAKEUP
Wake-up Time from SD high-low
transition to I2C readback
tWD-TIMEOUT
Sensor recovery time (after
watchdog timeout)
2
5.2
ms
ms
6.6 Switching Characteristics - I2C
Unless otherwise specified, all limits ensured for TA = 25°C, VDD = 3.3 V
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
VOLTAGE LEVELS
VIH
Input High Voltage
VIL
Input Low Voltage
0.7ˣVDD
VOL
Output Low Voltage (3mA sink
current)
HYS
Hysteresis
V
0.3ˣVDD
V
0.4
V
0.1ˣVDD
V
I2C TIMING CHARACTERISTICS
ƒSCL
Clock Frequency
10
tLOW
Clock Low Time
1.3
μs
tHIGH
Clock High Time
0.6
μs
tHD;STA
Hold Time (repeated) START
condition
0.6
μs
tSU;STA
Set-up time for a repeated START
condition
0.6
μs
tHD;DAT
Data hold time
0
μs
tSU;DAT
Data setup time
100
ns
tSU;STO
Set-up time for STOP condition
0.6
μs
tBUF
Bus free time between a STOP
and START condition
1.3
μs
tVD;DAT
Data valid time
0.9
μs
tVD;ACK
Data valid acknowledge time
0.9
μs
tSP
Pulse width of spikes that must be
suppressed by the input filter (1)
50
ns
(1)
After this period, the first clock
pulse is generated
400
kHz
This parameter is specified by design and/or characterization and is not tested in production.
SDA
tLOW
tf
tHD;STA
tr
tf
tr
tBUF
tSP
SCL
tSU;STA
tHD;STA
tHIGH
tHD;DAT
START
tSU;STO
tSU;DAT
STOP
REPEATED
START
START
Figure 1. I2C Timing
6
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6.7 Typical Characteristics
Common test conditions (unless specified otherwise): Sensor inductor: 2 layer, 32 turns/layer, 14 mm diameter, PCB inductor
with L=19.4 µH, RP=5.7 kΩ at 2 MHz; Sensor capacitor: 330 pF 1% COG/NP0; Target: Aluminum, 1.5 mm thickness; Channel
= Channel 0 (continuous mode); ƒCLKIN = 40 MHz, FIN_DIVIDER0 = 0x1, FREF_DIVIDER0 = 0x001, RCOUNT0 = 0xFFFF,
SETTLECOUNT0 = 0x0100, RP_OVERRIDE = 1, AUTO_AMP_DIS = 1, DRIVE_CURRENT0 = 0x9800
3.25
3.25
IDD CH0 Current (mA)
3.225
3.2
IDD CH0 Current (mA)
VDD = 2.7 V
VDD = 3 V
VDD = 3.3 V
VDD = 3.6 V
3.175
3.15
3.125
3.1
3.2
3.15
3.1
-40°C
-20°C
0°C
25°C
3.075
3.05
-40
-20
0
20
40
60
Temperature (°C)
80
100
3.05
2.7
120
2.8
Includes 1.57 mA sensor coil current
-40°C to +125°C
Figure 2. Active Mode IDD vs. Temperature
3.3
3.4
3.5
3.6
D004
Figure 3. Active Mode IDD vs. VDD
VDD = 2.7 V
VDD = 3 V
VDD = 3.3 V
VDD = 3.6 V
-40°C
-20°C
60
0°C
25°C
50°C
85°C
100°C
125°C
55
45
40
35
50
45
40
35
30
25
-40
3.1
3.2
VDD (V)
65
Sleep Current (µA)
Sleep Current (µA)
50
3
Includes 1.57 mA sensor coil current
60
55
2.9
D003
50°C
85°C
100°C
125°C
30
-20
0
20
40
60
Temperature (°C)
80
100
25
2.7
120
2.8
2.9
3
D005
3.1
3.2
VDD (V)
3.3
3.4
3.5
3.6
D006
-40°C to +125°C
Figure 4. Sleep Mode IDD vs. Temperature
Figure 5. Sleep Mode IDD vs. VDD
1.4
1
0.8
0.6
0.4
0.2
0
-40
-40°C
-20°C
1.4
Shutdown Current (µA)
Shutdown Current (µA)
1.2
1.6
VDD = 2.7 V
VDD = 3 V
VDD = 3.3 V
VDD = 3.6 V
0°C
25°C
50°C
85°C
100°C
125°C
1.2
1
0.8
0.6
0.4
0.2
-20
0
20
40
60
Temperature (°C)
80
100
120
0
2.7
2.8
2.9
D007
3
3.1
3.2
VDD (V)
3.3
3.4
3.5
3.6
D008
-40°C to +125°C
Figure 6. Shutdown Mode IDD vs. Temperature
Figure 7. Shutdown Mode IDD vs. VDD
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Typical Characteristics (continued)
Common test conditions (unless specified otherwise): Sensor inductor: 2 layer, 32 turns/layer, 14 mm diameter, PCB inductor
with L=19.4 µH, RP=5.7 kΩ at 2 MHz; Sensor capacitor: 330 pF 1% COG/NP0; Target: Aluminum, 1.5 mm thickness; Channel
= Channel 0 (continuous mode); ƒCLKIN = 40 MHz, FIN_DIVIDER0 = 0x1, FREF_DIVIDER0 = 0x001, RCOUNT0 = 0xFFFF,
SETTLECOUNT0 = 0x0100, RP_OVERRIDE = 1, AUTO_AMP_DIS = 1, DRIVE_CURRENT0 = 0x9800
43.41
43.4
VDD = 2.7 V
VDD = 3 V
VDD = 3.3 V
VDD = 3.6 V
43.38
43.37
43.36
43.35
43.34
43.33
43.32
-40
0°C
25°C
50°C
85°C
100°C
125°C
43.39
43.38
43.37
43.36
43.35
43.34
43.33
-20
0
20
40
60
Temperature (°C)
80
100
120
2.8
2.9
3
3.1
3.2
VDD (V)
3.3
3.4
3.5
3.6
D010
Data based on 1 unit
Figure 8. Internal Oscillator Frequency vs. Temperature
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43.32
2.7
D009
-40°C to +125°C
8
-40°C
-20°C
43.4
Internal Oscillator (MHz)
Internal Oscillator (MHz)
43.39
Figure 9. Internal Oscillator Frequency vs. VDD
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7 Detailed Description
7.1 Overview
The LDC1312/LDC1314 is an inductance-to-digital converter (LDC) that measures the oscillation frequency of
multiple LC resonators. The device outputs a digital value that is proportional to frequency, with 12 bits of
measurement resolution. This frequency measurement can be converted to an equivalent inductance, or mapped
to the movement of an conductive object. The LDC1312/LDC1314 supports a wide range of inductance and
capacitor combinations with oscillation frequencies varying from 1 kHz to 10 MHz with equivalent parallel
resistances as low as 1.0 kΩ. The device includes a stable internal reference to reduce overall system cost, while
also providing the option to drive a clean external oscillator for improved measurement noise. The conversion
time of the LDC1312/LDC1314 is configurable per channel, where longer conversion times provide higher
effective resolution.
The LDC1312/LDC1314 is configured through a 400-kbit/s I2C bus and includes the ADDR input pin to select an
address. The power supply of the device ranges from 2.7 V to 3.6 V. The only external components necessary
for operation are the supply bypassing capacitors and I2C pull-ups.
7.2 Functional Block Diagram
40 MHz
40 MHz
CLKIN
VDD
SD
INTB
fREF
IN0A
IN0B
Resonant
Circuit
Driver
IN1B
VDD
IN0A
Resonant
Circuit
Driver
Core
Resonant
Circuit
Driver
I2C
fIN
SDA
SCL
SD
INTB
fREF
IN0B
fIN
IN1A
CLKIN
IN3A
IN3B
Resonant
Circuit
Driver
Core
SDA
I2C
SCL
ADDR
ADDR
GND
GND
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Figure 10. Block Diagrams for the LDC1312 (Left) and LDC1314 (Right)
The LDC1312/LDC1314 is composed of front-end resonant circuit drivers, followed by a multiplexer that
sequences through the active channels, connecting them to the core that measures and digitizes the sensor
frequency (ƒSENSOR). The core uses a reference frequency (ƒREF) to measure the sensor frequency. ƒREF is
derived from either the internal reference clock (oscillator), or an externally supplied clock. The digitized output
for each channel is proportional to the ratio of ƒSENSOR/ƒREF. The I2C interface is used to support device
configuration and to transmit the digitized frequency values to a host processor. The LDC can be placed in an
inactive shutdown mode to reduce current consumption by setting the SD pin to VDD. The INTB pin may be
configured to notify the host of changes in system status.
7.3 Feature Description
7.3.1 Multi-Channel and Single Channel Operation
The LDC1312/LDC1314 provides flexibility in channel sampling. It can continuously convert on any available
single channel or automatically sequence conversions across multiple channels. When operated in multi-channel
mode, the LDC sequentially samples the selected channels. In single channel mode, the LDC continuously
samples only the selected channel.
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Feature Description (continued)
At the end of each conversion in single channel mode, or after converting all selected channels when in multichannel mode, the LDC1312/LDC1314 can be configured to assert the INTB pin to indicate completion of the
conversion.
Refer to Multi-Channel and Single Channel Operation for details on the LDC1312/LDC1314 channel functionality
and configuration.
7.3.2 Adjustable Conversion Time
The LDC1312/LDC1314 conversion provides a tradeoff between measurement resolution and conversion
interval. Longer conversion intervals have higher measurement resolution. The conversion interval can be
configured from 3.2 µs to >26.2 ms with 16 bits of resolution. Note that it is possible to configure the conversion
interval to be shorter than the time required to read back the DATAx registers. The LDC1312/LDC1314 supports
per-channel adjustment of the conversion interval by setting the RCOUNTx register.
Refer to Sensor Conversion Time for details on the LDC1312/LDC1314 configuration and details on the setting
conversion interval.
7.3.3 Digital Signal Gain
The LDC1312/LDC1314 output resolution is 12 bits, but the internal signal path supports 16 bits of output
resolution by use of the GAIN setting.
Refer to Digital Signal Gain for details on the configuration and details on the setting conversion interval.
7.3.4 Sensor Startup and Glitch Configuration
For minimum noise, the sensor measurement should be performed after the sensor amplitude has stabilized. The
LDC1312/LDC1314 provides an adjustable sensor startup timing per channel. The timing can be varied from 1.2
µs to >26.2 ms by setting the SETTLECOUNTx register. Sensors with lower resonant frequencies or higher Qs
may require additional time to stabilize.
Refer to Settling Time for details on the LDC1312/LDC1314 configuration and details on the setting conversion
interval.
The LDC1312/LDC1314 can be configured with a faster sensor activation, or to use a lower current sensor
activation. Refer to Sensor Activation for details on this capability.
The LDC1312/LDC1314 provides an internal filter to attenuate interference from external noise sources. Refer to
Input Deglitch Filter for information on configuration on the deglitch filter.
7.3.5 Reference Clock
Optimum LDC1312/LDC1314 performance requires a clean reference clock. This reference frequency is
equivalent to the reference voltage of an Analog-to-Digital converter. The LDC1312/LDC1314 provide an internal
reference oscillator with a typical frequency of 43 MHz. This internal oscillator has good stability, with a typical
temperature coefficient of -13 ppm/°C. For applications requiring higher resolution or improved performance
across temperature, an external reference frequency can be applied to the CLKIN input.
The LDC1312/LDC1314 provides digital dividers for the ƒCLK and the sensor inputs to adjust the effective
frequency measured by the LDC core. The dividers provide flexibility in system design, so that the full range of
sensor frequencies can be supported with a wide range of ƒCLK. Each channel has a dedicated divider
configuration. Higher reference frequencies provide a higher sample rate for a given resolution.
Refer to Reference Clock for details on clocking requirements, configuration, and divider setup.
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Feature Description (continued)
7.3.6 Sensor Current Drive Control
The lossy characteristic of the sensors used for inductive sensing require injection of energy to maintain a
constant sensor amplitude. The LDC1312/LDC1314 provides this energy by driving an AC current matching the
sensor resonant frequency across the LC sensor. To achieve optimum performance, it is necessary to set the
current drive so that the sensor amplitude is within the range of 1.2 VP to 1.8 VP. Each channel current drive is
set independently between 16 µA and 1.6 mA by setting the corresponding IDRIVEx register field. The
LDC1312/LDC1314 can also automatically determine the appropriate sensor current drive, and even dynamically
adjust the sensor current by use of the RP_OVERRIDE_EN function.
Refer to Sensor Current Drive Configuration for detailed information on configuration of the sensor drive.
7.3.7 Device Status Monitoring
The LDC1312/LDC1314 can monitor attached sensors and can report on device status and sensor status via the
I2C interface. Reported conditions include:
• Sensor Amplitude outside of optimum range
• Sensor unable to oscillate
• New conversion data available
• Conversion errors
Use of this monitoring functionality can alert the system MCU of unexpected conditions such as sensor damage.
Refer to Device Status Registers for more information.
7.4 Device Functional Modes
7.4.1 Startup Mode
When the LDC powers up, it enters into Sleep Mode and will wait for configuration. Once the device is
configured, exit Sleep Mode and begin conversions by setting CONFIG.SLEEP_MODE_EN to b0.
It is recommended to configure the LDC while in Sleep Mode. If a setting on the LDC needs to be changed,
return the device to Sleep Mode, change the appropriate register, and then exit Sleep Mode.
7.4.2 Sleep Mode (Configuration Mode)
Sleep Mode is entered by setting the CONFIG.SLEEP_MODE_EN register field to 1. While in this mode, the
device configuration is retained, but the device does not perform conversions. To enter Normal mode to perform
conversions, set the CONFIG.SLEEP_MODE_EN register field to 0. After setting CONFIG.SLEEP_MODE_EN to
b0, sensor activation for the first conversion will begin after 16,384÷ƒINT elapses. Refer to Clocking Architecture
for more information on the device timing.
While in Sleep Mode the I2C interface is functional so that register reads and writes can be performed. Entering
Sleep Mode will clear all conversion results, any error conditions, and de-assert the INTB pin.
For applications which do not require continuous conversions, returning the device to Sleep mode after
completion and readback of the desired number of conversions can provide power consumption savings. Refer
to the TI Applications Note Power Reduction Techniques for the LDC131x/161x for Inductive Sensing for more
information.
7.4.3 Normal (Conversion) Mode
When operating in the normal (conversion) mode, the LDC is repeatedly sampling the frequency of the sensor(s)
and generating sample outputs for the active channel(s) based on the device configuration.
7.4.4 Shutdown Mode
When the SD pin is set to high, the LDC will enter Shutdown Mode. Shutdown Mode is the lowest power state.
To exit Shutdown Mode and enter Sleep Mode, set the SD pin to low. Entering Shutdown Mode will return all
registers to their default state.
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Device Functional Modes (continued)
While in Shutdown Mode, no conversions are performed. In addition, entering Shutdown Mode will clear any
error condition and de-assert the INTB pin (when de-asserted, INTB will be actively driven high). While the
device is in Shutdown Mode, is not possible to read to or write from the device via the I2C interface.
It is permitted to change the ADDR pin setting while in Shutdown Mode.
7.4.4.1 Reset
The device can be reset by writing to RESET_DEV.RESET_DEV. Any active conversion will stop and all
registers will return to their default values. This register bit will always return 0b when read.
7.5 Programming
The LDC1312/4 device uses an I2C interface to access control and data registers. The recommended
configuration procedure is to put the device into Sleep Mode, set the appropriate registers, and then enter
Normal Mode. Conversion results must be read while the device is in Normal Mode. Setting the device into
Shutdown mode will reset the device configuration.
7.5.1 I2C Interface Specifications
The LDC1312/4 use I2C for register access with a maximum speed of 400 kbit/s. The device registers are 16 bits
wide, and so a repeated start is used to access the 2nd byte of data. This sequence follows the standard I2C 7bit
slave address followed by an 8 bit pointer register byte to set the register address. Refer to Figure 11 and
Figure 12 for proper protocol diagrams. The device does not use I2C clock stretching.
When the ADDR pin is set low, the device I2C address is 0x2A; when the ADDR pin is set high, the I2C address
is 0x2B. The ADDR pin setting can be changed while the device is in Shutdown Mode to select the alternate I2C
address.
1
9
1
9
SCL
A6
SDA
A5
A4
A3
A2
A1
A0 R/W
Start by
Master
R7
R6
R5
Ack by
Slave
Frame 1
Serial Bus Address Byte
from Master
1
9
R4
R3
R2
R1
R0
Ack by
Slave
Frame 2
Slave Register
Address
1
9
SCL
SDA
D15 D14 D13 D12 D11 D10 D9
Frame 3
Data MSB from
Master
D8
D7
Ack by
Slave
D6
D5
D4
D3
D2
Frame 4
Data LSB from
Master
D1
D0
Ack by
Slave
Stop by
Master
Figure 11. I2C Write Register Sequence
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Programming (continued)
1
9
1
9
SCL
A6
SDA
A5
A4
A3
A2
A1
A0 R/W
Start by
Master
R7
R6
R5
Ack by
Slave
Frame 1
Serial Bus Address Byte
from Master
1
R4
R3
R2
R1
R0
Ack by
Slave
Frame 2
Slave Register
Address
1
9
9
1
9
SCL
A6
SDA
A5
A4
A3
A2
A1
D15 D14 D13 D12 D11 D10 D9
A0 R/W
Start by
Master
Ack by
Slave
Frame 4
Data MSB from
Slave
Frame 3
Serial Bus Address Byte
from Master
D8
D7
D6
Ack by
Master
D5
D4
D3
D2
Frame 5
Data LSB from
Slave
D1
D0
Nack by Stop by
Master Master
Figure 12. I2C Read Register Sequence
7.5.2 Pulses on I2C
The I2C interface of the LDC is designed to operate with the standard I2C transactions detailed in the I2C
specification; however it is not suitable for use in an I2C system which supports early termination of transactions.
A STOP condition or other early termination occurring before the normal end of a transaction (ACK) is not
supported and may corrupt that transaction and/or the following transaction. The device is also sensitive to any
(extraneous) pulse on SDA during the SCL low period of the first bit position of the i2c_address byte. To ensure
proper LDC operation, the master device should not transmit this type of waveform. An example of an
unsupported I2C waveform is shown in Figure 13. Any such pulses should not have a duration which exceeds
the device tSP specification.
AVOID SDA PULSE
AFTER START
SDA
SCL
START
ADDR
Figure 13. Example of SDA Pulse Between I2C START and ADDR Which Must be Avoided by the I2C
Master
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7.6 Register Maps
7.6.1 Register List
Fields indicated with Reserved must be written only with indicated value, otherwise improper device operation
may occur. The R/W column indicates the Read-Write status of the corresponding field. A ‘R/W’ entry indicates
read and write capability, a ‘R’ indicates read-only, and a ‘W’ indicates write-only.
For registers with R and R/W fields, write the reset value to the field when setting the R/W fields.
Figure 14. Register List
ADDRESS
0x00
0x02
0x04
0x06
0x08
0x09
NAME
DATA0
DATA1
DATA2
DATA3
RCOUNT0
RCOUNT1
DEFAULT VALUE
0x0000
0x0000
0x0000
0x0000
0x0080
0x0080
DESCRIPTION
Channel 0 Conversion Result and Error Status
Channel 1 Conversion Result and Error Status
Channel 2 Conversion Result and Error Status (LDC1314 only)
Channel 3 Conversion Result and Error Status (LDC1314 only)
Reference Count setting for Channel 0
Reference Count setting for Channel 1
0x0A
0x0B
0x0C
0x0D
0x0E
0x0F
0x10
0x11
0x12
0x13
0x14
0x15
0x16
0x17
0x18
0x19
0x1A
0x1B
0x1C
0x1E
0x1F
0x20
0x21
0x7E
0x7F
RCOUNT2
RCOUNT3
OFFSET0
OFFSET1
OFFSET2
OFFSET3
SETTLECOUNT0
SETTLECOUNT1
SETTLECOUNT2
SETTLECOUNT3
CLOCK_DIVIDERS0
CLOCK_DIVIDERS1
CLOCK_DIVIDERS2
CLOCK_DIVIDERS3
STATUS
ERROR_CONFIG
CONFIG
MUX_CONFIG
RESET_DEV
DRIVE_CURRENT0
DRIVE_CURRENT1
DRIVE_CURRENT2
DRIVE_CURRENT3
MANUFACTURER_ID
DEVICE_ID
0x0080
0x0080
0x0000
0x0000
0x0000
0x0000
0x0000
0x0000r_
0x0000
0x0000
0x0000
0x0000
0x0000
0x0000
0x0000
0x0000
0x2801
0x020F
0x0000
0x0000
0x0000
0x0000
0x0000
0x5449
0x3054
Reference Count setting for Channel 2. (LDC1314 only)
Reference Count setting for Channel 3.(LDC1314 only)
Offset value for Channel 0
Offset value for Channel 1
Offset value for Channel 2 (LDC1314 only)
Offset value for Channel 3 (LDC1314 only)
Channel 0 Settling Reference Count
Channel 1 Settling Reference Count
Channel 2 Settling Reference Count (LDC1314 only)
Channel 3 Settling Reference Count (LDC1314 only)
Reference and Sensor Divider settings for Channel 0
Reference and Sensor Divider settings for Channel 1
Reference and Sensor Divider settings for Channel 2 (LDC1314 only)
Reference and Sensor Divider settings for Channel 3 (LDC1314 only)
Device Status Report
Error Reporting Configuration
Conversion Configuration
Channel Multiplexing Configuration
Reset Device
Channel 0 sensor current drive configuration
Channel 1 sensor current drive configuration
Channel 2 sensor current drive configuration (LDC1314 only)
Channel 3 sensor current drive configuration (LDC1314 only)
Manufacturer ID
Device ID
14
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7.6.2 Address 0x00, DATA0
Figure 15. Address 0x00, DATA0
15
ERR_UR0
14
ERR_OR0
13
ERR_WD0
12
ERR_AE0
11
7
6
5
4
3
10
9
8
1
0
DATA0[11:0]
2
DATA0[11:0]
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset
Table 1. Address 0x00, DATA0 Field Descriptions
Bit
Field
Type
Reset
Description
15
ERR_UR0
R
0
Channel 0 Conversion Under-range Error Flag
Cleared by reading the bit.
14
ERR_OR0
R
0
Channel 0 Conversion Over-range Error Flag
Cleared by reading the bit.
13
ERR_WD0
R
0
Channel 0 Conversion Watchdog Timeout Error Flag
Cleared by reading the bit.
12
ERR_AE0
R
0
Channel 0 Conversion Amplitude Error Flag.
Cleared by reading the bit.
DATA0[11:0]
R
0x000
Channel 0 Conversion Result
11:0
7.6.3 Address 0x02, DATA1
Figure 16. Address 0x02, DATA1
15
ERR_UR1
14
ERR_OR1
13
ERR_WD1
12
ERR_AE1
11
7
6
5
4
3
10
9
8
1
0
DATA1[11:0]
2
DATA1[11:0]
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset
Table 2. Address 0x02, DATA1 Field Descriptions
Bit
Field
Type
Reset
Description
15
ERR_UR1
R
0
Channel 1 Conversion Under-range Error Flag
Cleared by reading the bit.
14
ERR_OR1
R
0
Channel 1 Conversion Over-range Error Flag
Cleared by reading the bit.
13
ERR_WD1
R
0
Channel 1 Conversion Watchdog Timeout Error Flag
Cleared by reading the bit.
12
ERR_AE1
R
0
Channel 1 Conversion Amplitude Error Flag
Cleared by reading the bit.
DATA1[11:0]
R
0x000
Channel 1 Conversion Result
11:0
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7.6.4 Address 0x04, DATA2 (LDC1314 only)
Figure 17. Address 0x04, DATA2
15
ERR_UR2
14
ERR_OR2
13
ERR_WD2
12
ERR_AE2
11
7
6
5
4
3
10
9
8
1
0
DATA2[11:0]
2
DATA2[11:0]
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset
Table 3. Address 0x04, DATA2 Field Descriptions
Bit
Field
Type
Reset
Description
15
ERR_UR2
R
0
Channel 2 Conversion Under-range Error Flag
Cleared by reading the bit.
14
ERR_OR2
R
0
Channel 2 Conversion Over-range Error Flag
Cleared by reading the bit.
13
ERR_WD2
R
0
Channel 2 Conversion Watchdog Timeout Error Flag
Cleared by reading the bit.
12
ERR_AE2
R
0
Channel 2 Conversion Amplitude Error Flag
Cleared by reading the bit.
DATA2[11:0]
R
0x000
Channel 2 Conversion Result
11:0
7.6.5 Address 0x06, DATA3 (LDC1314 only)
Figure 18. Address 0x06, DATA3
15
ERR_UR3
14
ERR_OR3
13
ERR_WD3
12
ERR_AE3
11
7
6
5
4
3
10
9
8
1
0
DATA3 [11:0]
2
DATA3 [11:0]
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset
Table 4. Address 0x06, DATA3 Field Descriptions
Bit
Field
Type
Reset
Description
15
ERR_UR3
R
0
Channel 3 Conversion Under-range Error Flag
Cleared by reading the bit.
14
ERR_OR3
R
0
Channel 3 Conversion Over-range Error Flag
Cleared by reading the bit.
13
ERR_WD3
R
0
Channel 3 Conversion Watchdog Timeout Error Flag
Cleared by reading the bit.
12
ERR_AE3
R
0
Channel 3 Conversion Amplitude Error Flag
Cleared by reading the bit.
DATA3[11:0]
R
0x000
Channel 3 Conversion Result
11:0
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7.6.6 Address 0x08, RCOUNT0
Figure 19. Address 0x08, RCOUNT0
15
14
13
12
11
10
9
8
3
2
1
0
RCOUNT0
7
6
5
4
RCOUNT0
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset
Table 5. Address 0x08, RCOUNT0 Field Descriptions
Bit
15:0
Field
Type
Reset
Description
RCOUNT0
R/W
0x0080
Channel 0 Reference Count Conversion Interval Time
0x0000-0x0004: Reserved
0x0005-0xFFFF: Conversion Time (tC0) = (RCOUNT0×16)/ƒREF0
7.6.7 Address 0x09, RCOUNT1
Figure 20. Address 0x09, RCOUNT1
15
14
13
12
11
10
9
8
3
2
1
0
RCOUNT1
7
6
5
4
RCOUNT1
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset
Table 6. Address 0x09, RCOUNT1 Field Descriptions
Bit
15:0
Field
Type
Reset
Description
RCOUNT1
R/W
0x0080
Channel 1 Reference Count Conversion Interval Time
0x0000-0x0004: Reserved
0x0005-0xFFFF: Conversion Time (tC1)= (RCOUNT1×16)/ƒREF1
7.6.8 Address 0x0A, RCOUNT2 (LDC1314 only)
Figure 21. Address 0x0A, RCOUNT2
15
14
13
12
11
10
9
8
3
2
1
0
RCOUNT2
7
6
5
4
RCOUNT2
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset
Table 7. Address 0x0A, RCOUNT2 Field Descriptions
Bit
15:0
Field
Type
Reset
Description
RCOUNT2
R/W
0x0080
Channel 2 Reference Count Conversion Interval Time
0x0000-0x0004: Reserved
0x0005-0xFFFF: Conversion Time (tC2)= (RCOUNT2ˣ16)/ƒREF2
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7.6.9 Address 0x0B, RCOUNT3 (LDC1314 only)
Figure 22. Address 0x0B, RCOUNT3
15
14
13
12
11
10
9
8
3
2
1
0
RCOUNT3
7
6
5
4
RCOUNT3
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset
Table 8. Address 0x0B, RCOUNT3 Field Descriptions
Bit
15:0
Field
Type
Reset
Description
RCOUNT3
R/W
0x0080
Channel 3 Reference Count Conversion Interval Time
0x0000-0x0004: Reserved
0x0005-0xFFFF: Conversion Time (tC3)= (RCOUNT3ˣ16)/ƒREF3
7.6.10 Address 0x0C, OFFSET0
Figure 23. Address 0x0C, OFFSET0
15
14
13
12
11
10
9
8
3
2
1
0
OFFSET0
7
6
5
4
OFFSET0
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset
Table 9. OFFSET0 Field Descriptions
Bit
15:0
Field
Type
Reset
Description
OFFSET0
R/W
0x0000
Channel 0 Conversion Offset
ƒOFFSET0 = (OFFSET0÷216)׃REF0
7.6.11 Address 0x0D, OFFSET1
Figure 24. Address 0x0D, OFFSET1
15
14
13
12
11
10
9
8
3
2
1
0
OFFSET1
7
6
5
4
OFFSET1
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset
Table 10. Address 0x0D, OFFSET1 Field Descriptions
Bit
15:0
18
Field
Type
Reset
Description
OFFSET1
R/W
0x0000
Channel 1 Conversion Offset
ƒOFFSET1 = (OFFSET1÷216)׃REF1
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7.6.12 Address 0x0E, OFFSET2 (LDC1314 only)
Figure 25. Address 0x0E, OFFSET2
15
14
13
12
11
10
9
8
3
2
1
0
OFFSET2
7
6
5
4
OFFSET2
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset
Table 11. Address 0x0E, OFFSET2 Field Descriptions
Bit
15:0
Field
Type
Reset
Description
OFFSET2
R/W
0x0000
Channel 2 Conversion Offset
ƒOFFSET_2 = (OFFSET2÷216)׃REF2
7.6.13 Address 0x0F, OFFSET3 (LDC1314 only)
Figure 26. Address 0x0F, OFFSET3
15
14
13
12
11
10
9
8
3
2
1
0
OFFSET3
7
6
5
4
OFFSET3
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset
Table 12. Address 0x0F, OFFSET3 Field Descriptions
Bit
15:0
Field
Type
Reset
Description
OFFSET3
R/W
0x0000
Channel 3 Conversion Offset
ƒOFFSET3 = (OFFSET3÷216)׃REF3
7.6.14 Address 0x10, SETTLECOUNT0
Figure 27. Address 0x10, SETTLECOUNT0
15
14
13
12
11
SETTLECOUNT0
10
9
8
7
6
5
4
3
SETTLECOUNT0
2
1
0
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset
Table 13. Address 0x10, SETTLECOUNT0 Field Descriptions
Bit
15:0
Field
Type
Reset
Description
SETTLECOUNT0
R/W
0x0000
Channel 0 Conversion Settling
The LDC will use this settling time to allow the LC sensor to
stabilize before initiation of a conversion on Channel 0.
If the amplitude has not settled prior to the conversion start, an
Amplitude error will be generated if reporting of this type of error
is enabled.
0x0000: Settle Time (tS0)= 32 ÷ ƒREF0
0x0001: Settle Time (tS0)= 32 ÷ ƒREF0
0x0002 - 0xFFFF: Settle Time (tS0)= (SETTLECOUNT0ˣ16) ÷
ƒREF0
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7.6.15 Address 0x11, SETTLECOUNT1
Figure 28. Address 0x11, SETTLECOUNT1
15
14
13
12
11
SETTLECOUNT1
10
9
8
7
6
5
4
3
SETTLECOUNT1
2
1
0
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset
Table 14. Address 0x11, SETTLECOUNT1 Field Descriptions
Bit
15:0
Field
Type
Reset
Description
SETTLECOUNT1
R/W
0x0000
Channel 1 Conversion Settling
The LDC will use this settling time to allow the LC sensor to
stabilize before initiation of a conversion on a Channel 1.
If the amplitude has not settled prior to the conversion start, an
Amplitude error will be generated if reporting of this type of error
is enabled.
0x0000: Settle Time (tS1)= 32 ÷ ƒREF1
0x0001: Settle Time (tS1)= 32 ÷ ƒREF1
0x0002 - 0xFFFF: Settle Time (tS1)= (SETTLECOUNT1ˣ16) ÷
ƒREF1
7.6.16 Address 0x12, SETTLECOUNT2 (LDC1314 only)
Figure 29. Address 0x12, SETTLECOUNT2
15
14
13
12
11
SETTLECOUNT2
10
9
8
7
6
5
4
3
SETTLECOUNT2
2
1
0
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset
Table 15. Address 0x12, SETTLECOUNT2 Field Descriptions
Bit
15:0
20
Field
Type
Reset
Description
SETTLECOUNT2
R/W
0x0000
Channel 2 Conversion Settling
The LDC will use this settling time to allow the LC sensor to
stabilize before initiation of a conversion on Channel 2.
If the amplitude has not settled prior to the conversion start, an
Amplitude error will be generated if reporting of this type of error
is enabled.
0x0000: Settle Time (tS2)= 32 ÷ ƒREF2
0x0001: Settle Time (tS2)= 32 ÷ ƒREF2
0x0002 - 0xFFFF: Settle Time (tS2)= (SETTLECOUNT2ˣ16) ÷
ƒREF2
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7.6.17 Address 0x13, SETTLECOUNT3 (LDC1314 only)
Figure 30. Address 0x13, SETTLECOUNT3
15
14
13
12
11
SETTLECOUNT3
10
9
8
7
6
5
4
3
SETTLECOUNT3
2
1
0
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset
Table 16. Address 0x13, SETTLECOUNT3 Field Descriptions
Bit
15:0
Field
Type
Reset
Description
SETTLECOUNT3
R/W
0x0000
Channel 3 Conversion Settling
The LDC will use this settling time to allow the LC sensor to
stabilize before initiation of a conversion on Channel 3.
If the amplitude has not settled prior to the conversion start, an
Amplitude error will be generated if reporting of this type of error
is enabled
0x0000: Settle Time (tS3)= 32 ÷ ƒREF3
0x0001: Settle Time (tS3)= 32 ÷ ƒREF3
0x0002 - 0xFFFF: Settle Time (tS3)= (SETTLECOUNT3ˣ16) ÷
ƒREF3
7.6.18 Address 0x14, CLOCK_DIVIDERS0
Figure 31. Address 0x14, CLOCK_DIVIDERS0
15
7
14
13
FIN_DIVIDER0
12
11
6
4
3
FREF_DIVIDER0
10
9
8
FREF_DIVIDER0
2
1
RESERVED
5
0
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset
Table 17. Address 0x14, CLOCK_DIVIDERS0 Field Descriptions
Bit
Field
Type
15:12
FIN_DIVIDER0
R/W
11:10
RESERVED
R/W
9:0
FREF_DIVIDER0
R/W
Reset
Description
0000
Channel 0 Input Divider
Sets the divider for Channel 0 input. Must be set to ≥2 if the
Sensor frequency is ≥ 8.75MHz
b0000: Reserved. Do not use.
FIN_DIVIDER0 ≥ b0001:
ƒin0 = ƒSENSOR0/FIN_DIVIDER0
00
Reserved. Set to b00.
0x000
Channel 0 Reference Divider
Sets the divider for Channel 0 reference. Use this to scale the
maximum conversion frequency.
0x000: Reserved. Do not use.
FREF_DIVIDER0 ≥ 0x001:
ƒREF0 = ƒCLK/FREF_DIVIDER0
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7.6.19 Address 0x15, CLOCK_DIVIDERS1
Figure 32. Address 0x15, CLOCK_DIVIDERS1
15
7
14
13
FIN_DIVIDER1
12
11
6
4
3
FREF_DIVIDER1
10
9
8
FREF_DIVIDER1
2
1
RESERVED
5
0
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset
Table 18. Address 0x15, CLOCK_DIVIDERS1 Field Descriptions
Bit
Field
Type
15:12
FIN_DIVIDER1
R/W
11:10
RESERVED
R/W
9:0
FREF_DIVIDER1
Reset
Description
0000
Channel 1 Input Divider
Sets the divider for Channel 1 input. Used when the Sensor
frequency is greater than the maximum FIN.
b0000: Reserved. Do not use.
FIN_DIVIDER1 ≥ b0001:
ƒin1 = ƒSENSOR1÷FIN_DIVIDER1
00
Reserved. Set to b00.
0x000
Channel 1 Reference Divider
Sets the divider for Channel 1 reference. Use this to scale the
maximum conversion frequency.
0x000: Reserved. Do not use.
FREF_DIVIDER1 ≥ 0x001:
ƒREF1 = ƒCLK÷FREF_DIVIDER1
R/W
7.6.20 Address 0x16, CLOCK_DIVIDERS2 (LDC1314 only)
Figure 33. Address 0x16, CLOCK_DIVIDERS2
15
7
14
13
FIN_DIVIDER2
12
11
6
4
3
FREF_DIVIDER2
10
9
8
FREF_DIVIDER2
2
1
RESERVED
5
0
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset
Table 19. Address 0x16, CLOCK_DIVIDERS2 Field Descriptions
Bit
Field
Type
Reset
Description
15:12
FIN_DIVIDER2
R/W
0000
Channel 2 Input Divider
Sets the divider for Channel 2 input. Must be set to ≥2 if the
Sensor frequency is ≥ 8.75MHz.
b0000: Reserved. Do not use.
FIN_DIVIDER2 ≥ b0001:
ƒIN2 = ƒSENSOR2÷FIN_DIVIDER2
11:10
RESERVED
R/W
00
Reserved. Set to b00.
FREF_DIVIDER2
R/W
0x000
Channel 2 Reference Divider
Sets the divider for Channel 2 reference. Use this to scale the
maximum conversion frequency.
0x000: Reserved. Do not use.
FREF_DIVIDER2 ≥ 0x001:
ƒREF2 = ƒCLK÷FREF_DIVIDER2
9:0
22
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7.6.21 Address 0x17, CLOCK_DIVIDERS3 (LDC1314 only)
Figure 34. Address 0x17, CLOCK_DIVIDERS3
15
7
14
13
FIN_DIVIDER3
12
11
6
4
3
FREF_DIVIDER3
10
9
8
FREF_DIVIDER3
2
1
RESERVED
5
0
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset
Table 20. Address 0x17, CLOCK_DIVIDERS3
Bit
Field
Type
Reset
Description
15:12
FIN_DIVIDER3
R/W
0000
Channel 3 Input Divider
Sets the divider for Channel 3 input. Must be set to ≥2 if the
Sensor frequency is ≥ 8.75MHz.
b0000: Reserved. Do not use.
FIN_DIVIDER3 ≥ b0001:
ƒIN3 = ƒSENSOR3÷FIN_DIVIDER3
11:10
RESERVED
R/W
00
Reserved. Set to b00.
FREF_DIVIDER3
R/W
0x000
Channel 3 Reference Divider
Sets the divider for Channel 3 reference. Use this to scale the
maximum conversion frequency.
0x000: reserved
FREF_DIVIDER3 ≥ 0x001:
ƒREF3 = ƒCLK÷FREF_DIVIDER3
9:0
7.6.22 Address 0x18, STATUS
Figure 35. Address 0x18, STATUS
15
14
13
ERR_UR
12
ERR_OR
6
DRDY
5
4
ERR_CHAN
7
RESERVED
RESERVED
11
ERR_WD
10
ERR_AHE
9
ERR_ALE
8
ERR_ZC
3
2
1
0
UNREADCON UNREADCONV UNREADCONV UNREADCONV
V0
1
2
3
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset
Table 21. Address 0x18, STATUS Field Descriptions
Bit
Field
Type
Reset
Description
ERR_CHAN
R
00
Error Channel
Indicates which channel has generated a Flag or Error. Once
flagged, any reported error is latched and maintained until either
the STATUS register or the DATAx register corresponding to the
Error Channel is read.
b00: Channel 0 is source of flag or error.
b01: Channel 1 is source of flag or error.
b10: Channel 2 is source of flag or error (LDC1314 only).
b11: Channel 3 is source of flag or error (LDC1314 only).
13
ERR_UR
R
0
Conversion Under-range Error
b0: No Conversion Under-range error was recorded since the
last read of the STATUS register.
b1: An active channel has generated a Conversion Under-range
error. Refer to STATUS.ERR_CHAN field to determine which
channel is the source of this error.
12
ERR_OR
R
0
Conversion Over-range Error
b0: No Conversion Over-range error was recorded since the last
read of the STATUS register.
b1: An active channel has generated a Conversion Over-range
error. Refer to STATUS.ERR_CHAN field to determine which
channel is the source of this error.
15:14
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Table 21. Address 0x18, STATUS Field Descriptions (continued)
Bit
Field
Type
Reset
Description
11
ERR_WD
R
0
Watchdog Timeout Error
b0: No Watchdog Timeout error was recorded since the last
read of the STATUS register.
b1: An active channel has generated a Watchdog Timeout error.
Refer to STATUS.ERR_CHAN field to determine which channel
is the source of this error.
10
ERR_AHE
R
0
Sensor Amplitude High Error
b0: No Amplitude High error was recorded since the last read of
the STATUS register.
b1: An active channel has generated an Amplitude High error this occurs when the sensor amplitude is above a nominal 1.8 V.
It is recommended to reduce the corresponding sensor IDRIVEx
setting. Refer to STATUS.ERR_CHAN field to determine which
channel is the source of this error.
9
ERR_ALE
R
0
Sensor Amplitude Low Error
b0: No Amplitude Low error was recorded since the last read of
the STATUS register.
b1: An active channel has generated an Amplitude Low error this occurs when the sensor amplitude is below a nominal 1.2 V.
Refer to STATUS.ERR_CHAN field to determine which channel
is the source of this error.
8
ERR_ZC
R
0
Zero Count Error
b0: No Zero Count error was recorded since the last read of the
STATUS register.
b1: An active channel has generated a Zero Count error. Refer
to STATUS.ERR_CHAN field to determine which channel is the
source of this error.
7
Reserved
R
0
Reserved. Reads 0.
6
DRDY
R
0
Data Ready Flag
b0: No new conversion result was recorded in the STATUS
register.
b1: A new conversion result is ready. When in Single Channel
Conversion, this indicates a single conversion is available. When
in sequential mode, this indicates that a new conversion result
for all active channels is now available.
5:4
24
Reserved
R
00
Reserved. Reads 00b.
3
UNREADCONV0
R
0
Channel 0 Unread Conversion
b0: No unread conversion is present for Channel 0.
b1: An unread conversion is present for Channel 0.
Read Register DATA0 to retrieve conversion results.
2
UNREADCONV1
R
0
Channel 1 Unread Conversion
b0: No unread conversion is present for Channel 1.
b1: An unread conversion is present for Channel 1.
Read Register DATA1 to retrieve conversion results.
1
UNREADCONV2
R
0
Channel 2 Unread Conversion
b0: No unread conversion is present for Channel 2.
b1: An unread conversion is present for Channel 2.
Read Register DATA2 to retrieve conversion results (LDC1314
only)
0
UNREADCONV3
R
0
Channel 3 Unread Conversion
b0: No unread conversion is present for Channel 3.
b1: An unread conversion is present for Channel 3.
Read Register DATA3 to retrieve conversion results (LDC1314
only)
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7.6.23 Address 0x19, ERROR_CONFIG
Figure 36. Address 0x19, ERROR_CONFIG
15
UR_ERR2OUT
14
OR_ERR2OUT
13
WD_
ERR2OUT
12
AH_ERR2OUT
11
AL_ERR2OUT
10
9
RESERVED
8
7
UR_ERR2INT
6
OR_ERR2INT
5
WD_ERR2INT
4
AH_ERR2INT
3
AL_ERR2INT
2
ZC_ERR2INT
1
Reserved
0
DRDY_2INT
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset
Table 22. Address 0x19, ERROR_CONFIG
Bit
Field
Type
Reset
Description
15
UR_ERR2OUT
R/W
0
Under-range Error to Output Register
b0: Do not report Under-range errors in the DATAx registers.
b1: Report Under-range errors in the DATAx.ERR_URx register
field corresponding to the channel that generated the error.
14
OR_ERR2OUT
R/W
0
Over-range Error to Output Register
b0: Do not report Over-range errors in the DATAx registers.
b1: Report Over-range errors in the DATAx.ERR_ORx register
field corresponding to the channel that generated the error.
13
WD_ ERR2OUT
R/W
0
Watchdog Timeout Error to Output Register
b0: Do not report Watchdog Timeout errors in the DATAx
registers.
b1: Report Watchdog Timeout errors in the DATAx.ERR_WDx
register field corresponding to the channel that generated the
error.
12
AH_ERR2OUT
R/W
0
Amplitude High Error to Output Register
b0:Do not report Amplitude High errors in the DATAx registers.
b1: Report Amplitude High errors in the DATAx.ERR_AEx
register field corresponding to the channel that generated the
error.
11
AL_ERR2OUT
R/W
0
Amplitude Low Error to Output Register
b0: Do not report Amplitude High errors in the DATAx registers.
b1: Report Amplitude High errors in the DATAx.ERR_AEx
register field corresponding to the channel that generated the
error.
10:8
Reserved
R/W
00
Reserved. Set to b00.
7
UR_ERR2INT
R/W
0
Under-range Error to INTB
b0: Do not report Under-range errors by asserting INTB pin and
STATUS register.
b1: Report Under-range errors by asserting INTB pin and
updating STATUS.ERR_UR register field.
6
OR_ERR2INT
R/W
0
Over-range Error to INTB
b0: Do not report Over-range errors by asserting INTB pin and
STATUS register.
b1: Report Over-range errors by asserting INTB pin and
updating STATUS.ERR_OR register field.
5
WD_ERR2INT
R/W
0
Watchdog Timeout Error to INTB
b0: Do not report Watchdog errors by asserting INTB pin and
STATUS register.
b1: Report Watchdog Timeout errors by asserting INTB pin and
updating STATUS.ERR_WD register field.
4
AH_ERR2INT
R/W
0
Amplitude High Error to INTB
b0: Do not report Amplitude High errors by asserting INTB pin
and STATUS register.
b1: Report Amplitude High errors by asserting INTB pin and
updating STATUS.ERR_AHE register field.
3
AL_ERR2INT
R/W
0
Amplitude Low Error to INTB
b0: Do not report Amplitude Low errors by asserting INTB pin
and STATUS register.
b1: Report Amplitude Low errors by asserting INTB pin and
updating STATUS.ERR_ALE register field.
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Table 22. Address 0x19, ERROR_CONFIG (continued)
Bit
Field
Type
Reset
Description
2
ZC_ERR2INT
R/W
0
Zero Count Error to INTB
b0: Do not report Zero Count errors by asserting INTB pin and
STATUS register.
b1: Report Zero Count errors by asserting INTB pin and
updating STATUS. ERR_ZC register field.
1
Reserved
R/W
0
Reserved. Set to b0.
0
DRDY_2INT
R/W
0
Data Ready Flag to INTB
b0: Do not report Data Ready Flag by asserting INTB pin and
STATUS register.
b1: Report Data Ready Flag by asserting INTB pin and updating
STATUS. DRDY register field.
7.6.24 Address 0x1A, CONFIG
Figure 37. Address 0x1A, CONFIG
15
14
ACTIVE_CHAN
7
INTB_DIS
13
SLEEP_MODE
_EN
12
RP_OVERRID
E_EN
5
4
6
HIGH_CURRE
NT_DRV
11
10
SENSOR_ACTI AUTO_AMP_DI
VATE_SEL
S
3
9
REF_CLK_SR
C
8
RESERVED
1
0
2
RESERVED
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset
Table 23. Address 0x1A, CONFIG Field Descriptions
Bit
Field
Type
Reset
Description
ACTIVE_CHAN
R/W
00
Active Channel Selection
Selects channel for continuous conversions when
MUX_CONFIG.AUTOSCAN_EN is 0.
b00: Perform continuous conversions on Channel 0
b01: Perform continuous conversions on Channel 1
b10: Perform continuous conversions on Channel 2 (LDC1314
only)
b11: Perform continuous conversions on Channel 3 (LDC1314
only)
13
SLEEP_MODE_EN
R/W
1
Sleep Mode Enable
Enter or exit low power Sleep Mode.
b0: Device is active.
b1: Device is in Sleep Mode.
12
RP_OVERRIDE_EN
R/W
0
Sensor RP Override Enable
Provides control over Sensor current drive used during the
conversion time for Ch. x, based on the programmed value in
the IDRIVEx field. Refer to Automatic IDRIVE Setting with
RP_OVERRIDE_EN for details.
b0: Override off
b1: RP Override on
11
SENSOR_ACTIVATE_SEL
R/W
1
Sensor Activation Mode Selection
Set the mode for sensor initialization. Refer to Sensor Activation
for details.
b0: Full Current Activation Mode – the LDC will drive maximum
sensor current for a shorter sensor activation time.
b1: Low Power Activation Mode – the LDC uses the value
programmed in DRIVE_CURRENTx during sensor activation to
minimize power consumption.
10
AUTO_AMP_DIS
R/W
0
Automatic Sensor Amplitude Correction Disable
Setting this bit will disable the automatic Amplitude correction
algorithm and stop the updating of the INIT_IDRIVEx field.
b0: Automatic Amplitude correction enabled.
b1: Automatic Amplitude correction is disabled. Recommended
for precision applications.
15:14
26
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Table 23. Address 0x1A, CONFIG Field Descriptions (continued)
Bit
Field
Type
Reset
Description
9
REF_CLK_SRC
R/W
0
Select Reference Frequency Source
b0: Use Internal oscillator as reference frequency.
b1: Reference frequency is provided from CLKIN pin.
8
RESERVED
R/W
0
Reserved. Set to b0.
7
INTB_DIS
R/W
0
INTB Disable
b0: INTB pin will be asserted when status register updates.
b1: INTB pin will not be asserted when status register updates. If
this mode is selected, the INTB pin level will be high.
6
HIGH_CURRENT_DRV
R/W
0
High Current Sensor Drive
b0: The LDC will drive all channels with normal sensor current
(1.5mA max).
b1: The LDC will drive channel 0 with current >1.5mA.
This mode is not supported if AUTOSCAN_EN = b1 (multichannel mode).
RESERVED
R/W
00 0001
Reserved. Set to b00’0001.
5:0
7.6.25 Address 0x1B, MUX_CONFIG
Figure 38. Address 0x1B, MUX_CONFIG
15
AUTOSCAN_E
N
7
14
13
RR_SEQUENCE
12
11
10
RESERVED
9
8
6
4
3
2
1
DEGLITCH
0
5
RESERVED
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset
Table 24. Address 0x1B, MUX_CONFIG Field Descriptions
Bit
Field
Type
Reset
Description
15
AUTOSCAN_EN
R/W
0
Auto-Scan Mode Enable
b0: Continuous conversion on the single channel selected by
CONFIG.ACTIVE_CHAN register field.
b1: Auto-Scan conversions as selected by
MUX_CONFIG.RR_SEQUENCE register field.
14:13
RR_SEQUENCE
R/W
00
Auto-Scan Sequence Configuration
Configure multiplexing channel sequence. The LDC will perform
a single conversion on each channel in the sequence selected,
and then restart the sequence continuously.
b00: Ch0, Ch1
b01: Ch0, Ch1, Ch2 (LDC1314 only)
b10: Ch0, Ch1, Ch2, Ch3 (LDC1314 only)
b11: Ch0, Ch1
12:3
RESERVED
R/W
00 0100
0001
Reserved. Set to 00 0100 0001.
2:0
DEGLITCH
R/W
111
Input Deglitch Filter Bandwidth
Select the lowest setting that exceeds the maximum sensor
oscillation frequency.
b001: 1.0 MHz
b100: 3.3 MHz
b101: 10 MHz
b111: 33 MHz
7.6.26 Address 0x1C, RESET_DEV
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Figure 39. Address 0x1C, RESET_DEV
15
RESET_DEV
14
7
6
13
12
11
10
9
OUTPUT_GAIN
3
2
RESERVED
5
4
8
RESERVED
1
0
RESERVED
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset
Table 25. Address 0x1C, RESET_DEV Field Descriptions
Bit
Field
Type
Reset
Description
15
RESET_DEV
R/W
0
Device Reset
Write b1 to reset the device. Will always readback 0.
14:11
RESERVED
R/W
0000
Reserved. Set to b0000.
10:9
OUTPUT_GAIN
R/W
00
Output Gain Control
00: Gain = 1 (0 bits shift)
01: Gain = 4 (2 bits shift)
10: Gain = 8 (3 bits shift)
11: Gain = 16 (4 bits shift)
8:0
RESERVED
R/W
0x000
Reserved. Set to b0 0000 0000.
7.6.27 Address 0x1E, DRIVE_CURRENT0
Figure 40. Address 0x1E, DRIVE_CURRENT0
15
7
14
13
IDRIVE0
12
11
6
5
4
3
INIT_IDRIVE0
10
9
INIT_IDRIVE0
8
2
1
0
RESERVED
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset
Table 26. Address 0x1E, DRIVE_CURRENT0 Field Descriptions
Bit
28
Field
Type
Reset
Description
15:11
IDRIVE0
R/W
0 0000
Channel 0 L-C Sensor Drive Current
This field sets the Sensor Drive Current used during the settling
+ conversion time of Channel 0 sensor.
RP_OVERRIDE_EN bit must be set to 1.
10:6
INIT_IDRIVE0
R
0 0000
Channel 0 Sensor Current Drive
This field stores the Initial Drive Current measured during the
initial Amplitude Calibration phase. It is updated after each
Amplitude Correction phase of the sensor conversion if
AUTO_AMP_DIS=0.
When writing to DRIVE_CURRENT0, set this field to b0 0000.
5:0
RESERVED
R/W
00 0000
Reserved. Set to b00 0000
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7.6.28 Address 0x1F, DRIVE_CURRENT1
Figure 41. Address 0x1F, DRIVE_CURRENT1
15
7
14
13
IDRIVE1
12
11
6
5
4
3
INIT_IDRIVE1
10
9
INIT_IDRIVE1
8
2
1
0
RESERVED
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset
Table 27. Address 0x1F, DRIVE_CURRENT1 Field Descriptions
Bit
Field
Type
Reset
Description
15:11
IDRIVE1
R/W
0 0000
Channel 1 L-C Sensor Drive Current
This field sets the Sensor Drive Current used during the settling
+ conversion time of Channel 0 sensor.
RP_OVERRIDE_EN bit must be set to 1.
10:6
INIT_IDRIVE1
R
0 0000
Channel 1 Sensor Current Drive
This field stores the Initial Drive Current calculated during the
initial Amplitude Calibration phase. It is updated after each
Amplitude Correction phase of the sensor conversion if
AUTO_AMP_DIS=0.
When writing to DRIVE_CURRENT1, set this field to b0 0000.
5:0
RESERVED
-
00 0000
Reserved
7.6.29 Address 0x20, DRIVE_CURRENT2 (LDC1314 only)
Figure 42. Address 0x20, DRIVE_CURRENT2
15
7
14
13
IDRIVE2
12
11
6
5
4
3
INIT_IDRIVE2
10
9
INIT_IDRIVE2
8
2
1
0
RESERVED
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset
Table 28. Address 0x20, DRIVE_CURRENT2 Field Descriptions
Field
Type
Reset
Description
15:11
Bit
IDRIVE2
R/W
0 0000
Channel 2 L-C Sensor Drive Current
This field sets the Sensor Drive Current used during the settling
+ conversion time of Channel 0 sensor.
RP_OVERRIDE_EN bit must be set to 1.
10:6
INIT_IDRIVE2
R
0 0000
Channel 2 Sensor Current Drive
This field stores the Initial Drive Current calculated during the
initial Amplitude Calibration phase. It is updated after each
Amplitude Correction phase of the sensor conversion if
AUTO_AMP_DIS=0.
When writing to DRIVE_CURRENT2, set this field to b0 0000.
5:0
RESERVED
–
00 0000
Reserved
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7.6.30 Address 0x21, DRIVE_CURRENT3 (LDC1314 only)
Figure 43. Address 0x21, DRIVE_CURRENT3
15
14
13
IDRIVE3
12
11
6
5
4
3
7
INIT_IDRIVE3
10
9
INIT_IDRIVE3
8
2
1
0
RESERVED
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset
Table 29. DRIVE_CURRENT3 Field Descriptions
Bit
Field
Type
Reset
Description
15:11
IDRIVE3
R/W
0 0000
Channel 3 L-C Sensor Drive Current
This field sets the Sensor Drive Current used during the settling
+ conversion time of Channel 0 sensor.
RP_OVERRIDE_EN bit must be set to 1.
10:6
INIT_IDRIVE3
R
0 0000
Channel 3 Sensor Current Drive
This field stores the Initial Drive Current calculated during the
initial Amplitude Calibration phase.It is updated after each
Amplitude Correction phase of the sensor conversion if
AUTO_AMP_DIS =0.
When writing to DRIVE_CURRENT3, set this field to b0 0000.
5:0
RESERVED
–
00 0000
Reserved
7.6.31 Address 0x7E, MANUFACTURER_ID
Table 30. Address 0x7E, MANUFACTURER_ID Field Descriptions
Bit
15:0
Field
Type
Reset
MANUFACTURER_ID
R
0101 0100 Manufacturer ID = 0x5449
0100 1001
Description
7.6.32 Address 0x7F, DEVICE_ID
Figure 44. Address 0x7F, DEVICE_ID
15
14
13
12
11
10
9
8
3
2
1
0
DEVICE_ID
7
6
5
4
DEVICE_ID
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset
Table 31. Address 0x7F, DEVICE_ID Field Descriptions
30
Bit
Field
Type
Reset
7:0
DEVICE_ID
R
0011 0000 Device ID = 0x3054
0101 0100
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8 Application and Implementation
NOTE
Information in the following applications sections is not part of the TI component
specification, and TI does not warrant its accuracy or completeness. TI’s customers are
responsible for determining suitability of components for their purposes. Customers should
validate and test their design implementation to confirm system functionality.
8.1 Application Information
8.1.1 Conductive Objects in a Time-Varying EM Field
An AC current flowing through an inductor will generate an AC magnetic field. If a conductive material, such as a
metal object, is brought into the vicinity of the inductor, the magnetic field will induce a circulating current (eddy
current) on the surface of the conductor.
Conductive
Target
Eddy
Current
d
Figure 45. Conductor in AC Magnetic Field
The eddy current is a function of the distance, size, and composition of the conductor. The eddy current
generates its own magnetic field, which opposes the original field generated by the sensor inductor. This effect is
equivalent to a set of coupled inductors, where the sensor inductor is the primary winding and the eddy current in
the target object represents the secondary inductor. The coupling between the inductors is a function of the
sensor inductor, and the resistivity, distance, size, and shape of the conductive target. The resistance and
inductance of the secondary winding caused by the eddy current can be modeled as a distance dependent
resistive and inductive component on the primary side (coil). Figure 45 shows a simplified circuit model of the
sensor and the target as coupled coils.
8.1.2 L-C Resonators
An EM field can be generated using an L-C resonator, or L-C tank. One topology for an L-C tank is a parallel RL-C construction, as shown in Figure 46.
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Application Information (continued)
Distance-dependent coupling
M(d)
Eddy
Current
CPAR
Distance (d)
Target Resistance
Coil Series
Resistance (Rs)
I
RP(d)
L(d)
CPAR + CTANK
Parallel Electrical
Model, L-C Tank
Copyright © 2016, Texas Instruments Incorporated
Figure 46. Electrical Model of the L-C Tank Sensor
A resonant oscillator can be constructed by combining a frequency selective circuit (resonator) with a gain block
in a closed loop. The criteria for oscillation are: (1) loop gain > 1, and (2) closed loop phase shift of 2π radians.
The R-L-C resonator provides the frequency selectivity and contributes to the phase shift. At the resonance
frequency, the impedance of the reactive components (L and C) cancels, leaving only RP, the lossy (resistive)
element in the circuit. The voltage amplitude is maximized at this frequency. The RP can be used to determine
the sensor drive current for a given oscillation amplitude. A lower RP requires a larger sensor current to maintain
a constant oscillation amplitude. The sensor oscillation frequency is given by:
1
¦SENSOR
2S LC
1
Q
2
5 10
9
Q LC
|
1
2S LC
where:
•
•
C is the sensor capacitance (CSENSOR + CPARASITIC)
L is the sensor inductance
(1)
The value of Q can be calculated by:
Q
RP
C
L
where:
•
32
RP is the AC parallel resistance of the LC resonator at the operating frequency
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Application Information (continued)
Texas Instruments' WEBENCH design tool can be used for coil design, in which the parameter values for RP, L
and C are calculated. See http://www.ti.com/webench.
RP is a function of target distance, target material, and sensor characteristics. Figure 47 shows an example of RP
variation based on the distance between the sensor and the target. The graph represents a 14 mm diameter
PCB coil (23 turns, 4 mil trace width, 4 mil spacing between traces, 1 oz. copper thickness, on FR4 material).
This curve is a typical response where the target distance scales based on the sensor size and the sensor RP
scales based on the free-space of the inductor.
18
16
14
RP (kΩ)
12
10
8
6
4
2
0
0
1
2
3
4
5
Distance (mm)
6
7
8
Figure 47. Example RP vs. Distance with a 14 mm PCB Coil and 2 mm Thick Stainless Steel Target
It is important to configure the sensor current drive so that the sensor will still oscillate at the minimum RP value
(which typically occurs with maximum target interaction). As an example, if the closest target distance in a
system with the response shown in Figure 47 is 1mm, then the sensor current drive needs to support a RP value
is 5 kΩ. Both the minimum and maximum RP conditions should have oscillation amplitudes that are within the
device operating range. See section Sensor Current Drive Control for details on setting the current drive.
The inductance that is measured by the LDC is:
1
L(d) Linf M(d)
(2S ¦SENSOR )2 C
where:
•
•
•
•
•
L(d) is the measured sensor inductance, for a distance d between the sensor coil and target
Linf is the inductance of the sensing coil without a conductive target (target at infinite distance)
M(d) is the mutual inductance
ƒSENSOR = sensor oscillation frequency for a distance d between the sensor coil and target
C = CSENSOR + CPARASITIC
(3)
Figure 48 shows an example of variation in sensor frequency and inductance as a function of distance for a 14
mm diameter PCB coil (23 turns, 4 mil trace width, 4 mil spacing between traces, 1 oz copper thickness, FR4
material). The frequency and inductance graphs will scale based on the sensor free-space characteristics, and
the target distance scales based on the sensor diameter.
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Application Information (continued)
4
24
Target D = 1 x coil ‡
3.5
21
3
18
2.5
15
2
12
1.5
Inductance (µH)
Sensor Frequency (MHz)
Target D = 0.5 x coil ‡
9
Sensor Frequency (MHz)
Inductance (µH)
1
0
1
2
3
4
6
5 6 7 8 9 10 11 12 13 14
Target Distance D (mm)
D011
Figure 48. Example Sensor Frequency, Inductance vs. Target Distance
with 14 mm PCB Coil and 1.5 mm Thick Aluminum Target
The Texas Instruments Application Notes LDC Sensor Design and LDC Target Design provide more information
on construction of sensors and targets charactersitics to consider based on system requirements.
8.1.3 Multi-Channel and Single Channel Operation
The multi-channel package of the LDC enables the user to save board space and support flexible system design.
For example, temperature drift can often cause a shift in component values, resulting in a shift in resonant
frequency of the sensor. Using a second sensor as a reference or in a differential configuration provides the
capability to cancel out temperature shifts and other environmental variations. When operated in multi-channel
mode, the LDC sequentially samples the selected channels - only one channel is active at any time while the
other selected channels are held in an inactive state. In single channel mode, the LDC samples a single channel,
which is selectable. Refer to Inactive Channel Sensor Connections for more details on inactive channels.
Inactive channels have the corresponding INAx and INBx pins tied to ground. The following table shows the
registers and values that are used to configure either multi-channel or single channel modes.
Channel 0
Sensor
Activation
Channel 0
Conversion
Channel
switch delay
Channel 1
Conversion
Channel 1
Sensor
Activation
Channel
switch delay
Channel 0
Sensor
Activation
Channel 0
Channel 1
Figure 49. Multi-Channel Mode Sequencing
34
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Application Information (continued)
Active Channel
Sensor Signal
Sensor
Activation
Conversion
Conversion
Conversion
Amplitude
Correction
Amplitude
Correction
Amplitude
Correction
Figure 50. Single-Channel Mode Sequencing
Table 32. Single and Multi-Channel Configuration Registers
MODE
REGISTER
VALUE (1)
FIELD
00 = chan 0
CONFIG, addr 0x1A
01 = chan 1
ACTIVE_CHAN [15:14]
10 = chan 2
Single channel
11 = chan 3
MUX_CONFIG addr 0x1B
AUTOSCAN_EN [15]
0 = continuous conversion on a
single channel (default)
MUX_CONFIG addr 0x1B
AUTOSCAN_EN [15]
1 = continuous conversion on
multiple channels
MUX_CONFIG addr 0x1B
RR_SEQUENCE [14:13]
00 = Ch0, Ch 1
Multi-channel
01 = Ch0, Ch 1, Ch 2
10 = Ch0, CH1, Ch2, Ch3
(1)
Channels 2 and 3 are only available for LDC1314
The digitized sensor measurement for each channel (DATAx) represents the ratio of the sensor frequency to the
reference frequency. The data outputs represent the 12 MSBs of a 16-bit result. With the FIN_DIVIDER set to 1
and OFFSET set to 0, the sensor frequency can be calculated from:
'$7$[ ¦REFx
¦ sensorx
(4)
212
The following table illustrates the registers that contain the fixed point sample values for each channel.
Table 33. LDC1314/1312 Sample Data Registers
CHANNEL
(1)
REGISTER
FIELD NAME [BITS(S) ]
VALUE
0
DATA0, addr 0x00
DATA0 [11:0]
12 bit conversion results
0x000 = sensor under range
condition
0xfff = sensor over range
condition
1
DATA1, addr 0x02
DATA1 [11:0]
12 bit conversion results.
0x000 = sensor under range
condition
0xfff = sensor over range
condition
2
DATA2, addr 0x04
DATA2 [11:0]
12 bit conversion result.
0x000 = sensor under range
condition
0xfff = sensor over range
condition
(1)
Channels 2 and 3 available for LDC1314 only.
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Table 33. LDC1314/1312 Sample Data Registers (continued)
CHANNEL
(1)
3
REGISTER
FIELD NAME [BITS(S) ]
VALUE
DATA3, addr 0x06
DATA3 [11:0]
12 bit conversion result.
0x000 = sensor under range
condition
0xfff = sensor over range
condition
DATAx = DATAx_MSB×65536 + DATAx_LSB
(5)
8.1.3.1 Data Offset
An offset value may be subtracted from each DATA value to compensate for a frequency offset or maximize the
dynamic range of the sample data. The offset values should be < ƒSENSORx_MIN / ƒREFx. Otherwise, the offset
might be so large that it masks the LSBs which are changing.
Table 34. Frequency Offset Registers
CHANNEL
REGISTER
(1)
FIELD [ BIT(S) ]
VALUE
0
OFFSET0, addr 0x0C
OFFSET0 [ 15:0 ]
ƒOFFSET0 = OFFSET0 × (ƒREF0/216)
1
OFFSET1, addr 0x0D
OFFSET1 [ 15:0 ]
ƒOFFSET1 = OFFSET1 × (ƒREF1/216)
2
OFFSET2, addr 0x0E
OFFSET2 [ 15:0 ]
ƒOFFSET2 = OFFSET2 × (ƒREF2/216)
3
OFFSET3, addr 0x0F
OFFSET3 [ 15:0 ]
ƒOFFSET3 = OFFSET3 × (ƒREF3/216)
The sensor frequency can be determined by:
¦SENSORx
DATAx
§
&+[B),1B',9,'(5 ¦REFx ¨ (12 OUTPUT_GAIN)
©2
CHx_OFFSET ·
¸
216
¹
where:
•
•
•
DATAx = Conversion result from the DATAx register
OFFSETx = Offset value set in the OFFSETx register
OUTPUT_GAIN = output multiplication factor set in the RESET_DEVICE.OUTPUT_GAIN register
(6)
8.1.3.2 Digital Signal Gain
Internally, the LDC measures inductance shifts with 16 bits of resolution, while the conversion output word width
is only 12 bits. For systems in which the sensor signal variation is less than 25% of the full scale range, the LDC
can report conversion results with higher resolution by setting the Output Gain. The Output Gain is applied to all
device channels. An output gain can be used to apply a 2-bit, 3-bit, or 4-bit shift to the output code for all
channels, providing an effectively higher measurement resolution. When the Gain function is used, additional
LSBs of the conversion word are reported, while the corresponding number of MSBs are not reported.
To avoid data corruption issues, use the Output Gain function (Data Offset ) to shift the output codes to prevent
toggling of the shifted MSBs.
Table 35. Output Gain Register
CHANNEL
(1)
All
(1)
(1)
36
REGISTER
RESET_DEV, addr
0x1C
FIELD [ BIT(S) ]
EFFECTIVE
RESOLUTION (BITS)
VALUES
OUTPUT RANGE
OUTPUT_GAIN [ 10:9 ] 00 (default): Gain =1 (0
bits shift)
12
100% full scale
01: Gain = 4 (2 bits left
shift)
14
25% full scale
10: Gain = 8 (3 bits left
shift)
15
12.5% full scale
11 : Gain = 16 (4 bits left
shift)
16
6.25% full scale
Channels 2 and 3 are only available for LDC1314
Channels 2 and 3 are available for LDC1314 only.
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Example: If the conversion result for a channel is 0x07A3, with OUTPUT_GAIN=0x0, the reported output code is
0x07A. If OUTPUT_GAIN is set to 0x3 in the same condition, then the reported output code is 0x7A3. The
original 4 MSBs (0x0) are no longer accessible. Figure 51 illustrates the segments of the 16-bit sample that is
reported for each possible gain setting.
MSB
Conversion result
LSB
15
12
11
Output_gain = 0x3
7
4
3
0
11
Output_gain = 0x2
0
11
Output_gain = 0x1
Output_gain = 0x0
(default)
8
0
11
0
11
0
11
0
Data available in DATA_MSB_CHx.DATA_CHx [11:0]
Figure 51. Conversion Data Output Gain
8.1.4 Sensor Conversion Time
The LDC1312/LDC1314 provides a configurable conversion time by setting an internal register. The conversion
interval can be configured across a range of 1.2 µs to >26.2 ms with 16 bits of resolution. Note that it is possible
to configure the conversion interval to be significantly shorter than the time required to readback the DATAx
registers; when configured in this manner, older conversions for a channel are overwritten when new conversion
data is completed for each channel. The conversion interval is set in multiples of the reference clock period by
setting the RCOUNTx register value. The conversion time for any channel x is:
tCx = (RCOUNTx × 16 + 4) /fREFx
(7)
In general, a longer conversion time will provide a higher resolution inductance measurement. The reference
count value should be chosen to support both the required sample rate and the necessary resolution. Refer to
the TI Application Note Optimizing L Measurement Resolution for the LDC1312 and LDC1314 for more
information.
Table 36. Conversion Time Configuration Registers, Channels 0 - 3 (1)
CHANNEL
(1)
REGISTER
FIELD
CONVERSION TIME
0
RCOUNT0, addr 0x08
RCOUNT0 [15:0]
(RCOUNT0×16)/fREF0
1
RCOUNT1, addr 0x09
RCOUNT1 [15:0]
(RCOUNT1×16)/fREF1
2
RCOUNT2, addr 0x0A
RCOUNT2 [15:0]
(RCOUNT2×16)/fREF2
3
RCOUNT3, addr 0x0B
RCOUNT3 [15:0]
(RCOUNT3×16)/fREF3
Channels 2 and 3 are available only for LDC1314.
The typical channel switch delay time between the end of conversion and the beginning of sensor activation of
the subsequent channel is:
Channel Switch Delay = 692 ns + 5 / fref
(8)
The deterministic conversion time of the LDC allows data polling at a fixed interval. A data ready flag (DRDY)
can assert the INTB pin for use in interrupt driven system designs (see the STATUS register description in
Register Maps).
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8.1.4.1 Settling Time
When the LDC sequences through the channels in multi-channel mode, the dwell time interval for each channel
is the sum of 3 parts: sensor activation time + conversion time + channel switch delay.
The sensor activation time is the amount of settling time required for the sensor oscillation amplitude to stabilize,
as shown in Figure 49. The settling wait time is programmable and should be set to a value that is long enough
to allow stable oscillation. The settling wait time for channel x is given by:
tSx = (SETTLECOUNTx ×16)/ƒREFx
(9)
Table 37 illustrates the registers and values for configuring the settling time for each channel.
Table 37. Settling Time Register Configuration
REGISTER
FIELD
CONVERSION TIME (2)
0
SETTLECOUNT0, addr 0x10
SETTLECOUNT0 ['15:0]
(SETTLECOUNT0×16)/fREF0
1
SETTLECOUNT1, addr 0x11
SETTLECOUNT1 [15:0]
(SETTLECOUNT1×16)/fREF1
2
SETTLECOUNT2, addr 0x12
SETTLECOUNT2 [15:0]
(SETTLECOUNT2×16)/fREF2
3
SETTLECOUNT3, addr 0x13
SETTLECOUNT3 [15:0]
(SETTLECOUNT3×16)/fREF3
(1)
(2)
Channels 2 and 3 are available only in the LDC1314.
ƒREFx is the reference frequency configured for the channel.
CHANNEL
(1)
The SETTLECOUNTx for any channel x must satisfy:
SETTLECOUNTx ≥ QSENSORx × ƒREFx / (16 × ƒSENSORx)
where:
•
•
•
Q
RP
ƒSENSORx = Sensor Frequency of Channel x
ƒREFx = Reference frequency for Channel x
QSENSORx = Quality factor of the sensor on Channel x. The sensor Q can be calculated with:
C
L
(10)
(11)
Round the result to the next highest integer (for example, if Equation 10 recommends a minimum value of 6.08,
program the register to 7 or higher).
L, RP and C values can be obtained by using Texas Instrument’s WEBENCH® for the coil design.
8.1.4.2 Sensor Activation
The LDC1312/LDC1314 provides option to either reduce the sensor activation time or to reduce the device
current consumption during the sensor activation time.
This can reduce the sensor activation time for higher-Q sensors by driving the maximum sensor drive current
during the sensor settling time. The maximum sensor drive current is nominally 1.56 mA. Sensors already
configured to use the maximum drive current setting (IDRIVEx = b11111) will see no change in operation based
on this setting.
This mode is selected by setting SENSOR_ACTIVATE_SEL to 0.
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Full Current Activation
settle time
Low Power Activation settle
time
Sensor Amplitude
Time
Figure 52. Sensor Full Current Activation vs. Low Power Activation
8.1.5 Sensor Current Drive Configuration
The registers listed in Table 38 are used to control the sensor drive current so that the sensor signal amplitude is
within the optimum range of 1.2 VP to 1.8 VP (sensor amplitudes outside this optimum range can be reported in
the status register - refer to Device Status Registers ). The device can still convert with sensor amplitudes lower
than 0.6 VP, however the conversion noise will increase with lower sensor amplitudes. Below 0.6 VP the sensor
oscillations may not be stable or may completely stop and the LDC will stop converting. If the current drive
results in the oscillation amplitude greater than 1.8 V, the internal ESD clamping circuit will become active. This
may cause the sensor frequency to shift so that the output values no longer represent a valid system state.
Figure 53 shows the block diagram of the sensor driver. Each channel has an independent setting for the IDRIVE
current used to set the sensor oscillation amplitude.
IDRIVE
Sensor 0
IN0A
IN0B
Chan 0
Driver
Sensor 1
IN1A
IN1B
Chan 1
Driver
Measurement Core
Sensor 2
IN2A
IN2B
Chan 2
Driver
Sensor 3
IN3A
IN3B
Chan 3
Driver
Figure 53. LDC1314 Sensor Driver Block Diagram
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Table 38. Current Drive Control Registers
CHANNEL
(1)
REGISTER
FIELD [ BIT(S) ]
CONFIG, addr 0x1A
VALUE
SENSOR_ACTIVATE_SEL [11]
Sets current drive for sensor activation.
Recommended value is b0 (Full Current
mode).
RP_OVERRIDE_EN [12]
Set to b1 for normal operation (RP
Override enabled)
AUTO_AMP_DIS [10]
Disables Automatic amplitude correction.
Set to b1 for normal operation (disabled)
CONFIG, addr 0x1A
HIGH_CURRENT_DRV [6]
b0 = normal current drive (1.5 mA)
b1 = Increased current drive (> 1.5 mA)
for Ch 0 in single channel mode only.
Cannot be used in multi-channel mode.
DRIVE_CURRENT0, addr 0x1E
IDRIVE0 [15:11]
Drive current used during the settling and
conversion time for Ch. 0 (auto-amplitude
correction must be disabled and RP over
ride=1 )
INIT_IDRIVE0 [10:6]
Initial drive current stored during autocalibration. Not used for normal operation.
IDRIVE1 [15:11]
Drive current used during the settling and
conversion time for Ch. 1 (auto-amplitude
correction must be disabled and RP over
ride=1 )
INIT_IDRIVE1 [10:6]
Initial drive current stored during autocalibration. Not used for normal operation.
IDRIVE2 [15:11]
Drive current used during the settling and
conversion time for Ch. 2 (auto-amplitude
correction must be disabled and RP over
ride=1 )
INIT_IDRIVE2 [10:6]
Initial drive current stored during autocalibration. Not used for normal operation.
IDRIVE3 [15:11]
Drive current used during the settling and
conversion time for Ch. 3 (auto-amplitude
correction must be disabled and RP over
ride=1 )
INIT_IDRIVE3 [10:6]
Initial drive current stored during autocalibration. Not used for normal operation.
All
0
0
DRIVE_CURRENT1, addr 0x1F
1
DRIVE_CURRENT2, addr 0x20
2
DRIVE_CURRENT3, addr 0x21
3
(1)
Channels 2 and 3 are available for LDC1314 only.
If the RP value of the sensor attached to Channel x is known, Table 39 can be used to select the 5-bit value to be
programmed into the IDRIVEx field for the channel. If the measured RP (at maximum spacing between the
sensor and the target) falls between two of the table values, use the current drive value associated with the lower
RP from the table. All channels that use an identical sensor/target configuration can use the same IDRIVEx
value. The appropriate sensor drive current can be calculated with:
IDRIVE = πVP ÷ 4RP
(12)
Table 39. Optimum Sensor RP Ranges for Sensor IDRIVEx Setting.
IDRIVEx Register Field Value
40
Nominal Sensor
Current (µA)
Minimum Sensor RP Maximum Sensor RP
(kΩ)
(kΩ)
0
b00000
16
60.0
90.0
1
b00001
18
51.8
77.6
2
b00010
20
44.6
66.9
3
b00011
23
38.4
57.6
4
b00100
28
33.7
49.7
5
b00101
32
29.5
42.8
6
b00110
40
23.6
36.9
7
b00111
46
20.5
31.8
8
b01000
52
18.1
27.4
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Table 39. Optimum Sensor RP Ranges for Sensor IDRIVEx Setting. (continued)
IDRIVEx Register Field Value
Nominal Sensor
Current (µA)
Minimum Sensor RP Maximum Sensor RP
(kΩ)
(kΩ)
9
b01001
59
16.1
23.6
10
b01010
72
13.1
20.4
11
b01011
82
11.5
17.6
12
b01100
95
9.92
15.1
13
b01101
110
8.57
13.0
14
b01110
127
7.42
11.2
15
b01111
146
6.46
9.69
16
b10000
169
5.58
8.35
17
b10001
195
4.83
7.20
18
b10010
212
4.45
6.21
19
b10011
244
3.86
5.35
20
b10100
297
3.17
4.61
21
b10101
342
2.76
3.97
22
b10110
424
2.22
3.42
23
b10111
489
1.93
2.95
24
b11000
551
1.71
2.54
25
b11001
635
1.48
2.19
26
b11010
763
1.24
1.89
27
b11011
880
1.07
1.63
28
b11100
1017
0.93
1.40
29
b11101
1173
0.80
1.21
30
b11110
1355
0.70
1.05
31
b11111
1563
0.60
0.90
Sensors with RP greater than 90 kΩ can be driven by placing a 100 kΩ resistor in parallel with the sensor
inductor to reduce the effective RP.
Sensors which have a wide range of RP may require more than one current drive setting across the range of
operation - the current would need to be dynamically set based on the target position. Note that some highresolution applications will experience an output code offset when the current drive is changed. Another
approach for systems which have a wide range of RP is to place a discrete resistor in parallel with the inductor to
limit the range of RP variation in the system. This will also reduce the sensor Q, and so may not be feasible for
some implementations.
8.1.5.1 Inactive Channel Sensor Connections
The LDC1312/LDC1314 ties the INAx and INBx pins for all channels to ground by ~10 Ω except for the active
channel; in Sleep and Shutdown modes there are no active channels and so all channels are tied to ground. By
grounding the channels, potential interactions between sensors are minimized. For multi-channel sequencing,
only the active channel is driven with the IDRIVE current during the conversion time; once the conversion for the
specific channel completes, the sensor is tied to ground to shut off the sensor, and the next sensor is activated.
For systems which do not use all sensor channels, it is acceptable to leave the unused INAx and INBx pins NoConnect.
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8.1.5.2 Automatic IDRIVE Setting with RP_OVERRIDE_EN
The LDC1312/LDC1314 can automatically determine the appropriate sensor current drive when entering Active
Mode. For the majority of applications, it is recommended to program a fixed current drive for consistent
measurement performance. The automatic sensor amplitude setting is useful for initial system prototyping if the
sensor amplitude is unknown. When this function is enabled, the LDC attempts to find the IDRIVEx setting which
results in a sensor amplitude between 1.2 VP and 1.8VP. For systems which have a large variation in target
interaction, the LDC1312/LDC1314 may select a current drive setting which has poorer repeatability over the
range of target interactions. In addition, measurement repeatability will be poorer with different sensor current
drives. To enable the automatic sensor amplitude, set RP_OVERRIDE to b0.
The following sequence uses auto-calibration to configure sensor drive current for a sensor with an unknown RP:
1. Set target at the maximum planned operating distance from the sensor.
2. Place the device into SLEEP mode by setting CONFIG.SLEEP_MODE_EN to b0.
3. Program the desired values of SETTLECOUNT and RCOUNT values for the channel.
4. Enable auto-calibration by setting RP_OVERRIDE_EN to b0.
5. Take the device out of SLEEP mode by setting CONFIG.SLEEP_MODE_EN to b1.
6. Allow the device to perform at least one measurement, with the target stable (fixed) at the maximum
operating range.
7. Read the channel current drive value from the appropriate DRIVE_CURRENTx register (addresses 0x1e,
0x1f, 0x20, or 0x21), in the INIT_DRIVEx field (bits 10:6). Save this value.
8. During startup for normal operating mode, write the value saved from the INIT_DRIVEx bit field into the
IDRIVEx bit field (bits 15:11).
9. During normal operating mode, the RP_OVERRIDE_EN should be set to b1 for a fixed current drive.
If the current drive results in the oscillation amplitude greater than 1.8 V, the internal ESD clamping circuit will
become active. This may cause the sensor frequency to shift so that the output values no longer represent a
valid system state. If the current drive is set at a lower value, the SNR performance of the system will decrease,
and at near zero target range, oscillations may completely stop, and the output sample values will be all zeroes.
If there are significant differences in the sensor construction for different channels, then this process should be
repeated for each channel.
8.1.5.3 Determining Sensor IDRIVE for an Unknown Sensor RP Using an Oscilloscope
If the sensor RP is not known, probing the sensor amplitude with an oscilloscope can be used set IDRIVEx.
An iterative process of adjusting the drive current setting while monitoring the signal amplitude on INAx or INBx
to ground is sufficient. Simply move the sensor target to the farthest planned operating distance from the sensor,
and measure the channel amplitude after the amplitude has stabilized. If the sensor amplitude is less than 1.5
VP, increase the channel IDRIVE setting. If the sensor amplitude settles to greater than 1.75 VP, decrease the
channel IDRIVE setting. If there are significant differences in the sensor construction for different channels, then
this process should be repeated for each channel.
8.1.5.4 Sensor Auto-Calibration Mode
The LDC includes a sensor current Auto-calibration mode which can be dynamically set the sensor drive current.
The auto-amplitude correction attempts to maintain the sensor oscillation amplitude between 1.2V and 1.8V by
adjusting the sensor drive current between conversions.
This functionality is enabled by setting AUTO_AMP_DIS to b0, and applies to all active channels. The
INIT_IDRIVEx register field will be updated with the current drive value as the sensor current drive setting
changes. The value of the INIT_IDRIVEx register field matches the setting of the IDRIVEx register field. For
example, an INIT_IDRIVEx field with b10001 corresponds to a current drive of 195 µA.
When auto-amplitude correction is active, the output data may experience offsets in the channel output code due
to adjustments in drive current. Due to these offsets, Auto-amplitude correction is generally not recommended for
use in high precision applications.
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8.1.5.5 Channel 0 High Current Drive
Channel 0 provides a high sensor current drive mode to drive sensor coils with a typical drive current >3.5 mA.
This feature can be used to drive sensors with an RP lower than 350 Ω. Set the HIGH_CURRENT_DRV field to
b1 to enable this mode. This drive mode is only available on Channel 0, and can only be enabled in single
channel mode (AUTOSCAN_EN = 0).
8.1.6 Clocking Architecture
Optimum LDC1312/LDC1314 performance requires a clean reference clock with a limited frequency range. The
device provides digital dividers for the ƒCLK and the sensor inputs. The dividers provide flexibility in system
design, so that the full range of sensor frequencies can be supported with available fCLK. Each channel has a
dedicated divider configuration. Higher reference frequencies provide a higher sample rate for a given resolution.
Figure 54 shows the clock dividers and multiplexers of the LDC.
IN0A
fSENSOR0
Sensor 0
CH0
Driver
÷ FIN_DIVIDER0
(0x14)
fIN0
CH1
Driver
÷ FIN_DIVIDER1
(0x15)
fIN1
CH2
Driver
÷ FIN_DIVIDER2(1)
(0x16)
fIN2
CH3
Driver
÷ FIN_DIVIDER3(1)
(0x17)
fIN3(1)
IN0B
IN1A
fSENSOR1
Sensor 1
IN1B
fIN
IN2A(1)
Sensor 2(1)
fSENSOR2(1)
(1)
IN2B(1)
IN3A(1)
Sensor 3(1)
fSENSOR3(1)
IN3B
fCLKIN
(1)
CONFIG (0x1A)
MUX_CONFIG (0x1B)
CLKIN
fINT
÷ FREF_DIVIDER0
(0x14)
fREF0
÷ FREF_DIVIDER1
(0x15)
fREF1
Measurement
Core
Data
Output
Int. Osc.
REF_CLK_SRC
(0x1A)
fREF
÷
FREF_DIVIDER2(1)
(0x16)
fREF2(1)
÷
FREF_DIVIDER3(1)
(0x17)
fREF3(1)
Figure 54. Clocking Diagram
(1) LDC1314 only
In Figure 54, the key clocks are ƒINx, ƒREFx, and ƒCLK. ƒCLK is selected from either the internal clock source or
external clock source (CLKIN). The frequency measurement reference clock, ƒREF, is derived from the ƒCLK
source.
The internal oscillator is highly stable across temperature and is suitable for most LDC1312/4 applications.
Applications requiring matched performance across multiple LDC1312/4 devices and/or requiring higher longterm stability may need an external oscillator. Note that some internal functions, such as watchdog timers,
always use ƒINT for timing.
The ƒINx clock is derived from sensor frequency for channel x, ƒSENSORx. ƒREFx and ƒINx must meet the
requirements listed in Table 40, depending on whether ƒCLK (reference clock) is the internal or external clock.
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Table 40. Clock Frequency Requirements
REFERENCE
SOURCE
MODE (1)
Multi-Channel
Single-Channel
(1)
(2)
VALID ƒREFx
RANGE
Internal
ƒREFx ≤ 55 MHz
External
ƒREFx ≤ 40 MHz
Either external or
internal
ƒREFx ≤ 35 MHz
VALID ƒINx
RANGE
SET
FIN_DIVIDERx to
≥ b0001
< ƒREFx /4
(2)
VALID
VALID RCOUNTx
SETTLECOUNTx
SETTINGS
SETTINGS
>3
>8
Channels 2 and 3 are only available for LDC1314
If ƒSENSOR ≥ 8.75 MHz, then FIN_DIVIDERx must be ≥ 2
Table 41 shows the clock configuration registers. Each input channel has a dedicated configuration which can be
set independently.
Table 41. Clock Configuration Registers
CHANNEL (1)
REGISTER
FIELD
VALUE
ƒCLK = Reference
Clock Source
CONFIG, addr 0x1A
REF_CLK_SRC [9]
b0 = internal oscillator is used as the
reference clock
b1 = external clock source is used as the
reference clock
0
ƒREF0
CLOCK_DIVIDERS0,
addr 0x14
FREF_DIVIDER0 [9:0]
ƒREF0 = ƒCLK / FREF_DIVIDER0
1
ƒREF1
CLOCK_DIVIDERS1,
addr 0x15
FREF_DIVIDER1 [9:0]
ƒREF1 = ƒCLK / FREF_DIVIDER1
2
ƒREF2
CLOCK_DIVIDERS2,
addr 0x16
FREF_DIVIDER2 [9:0]
ƒREF2 = ƒCLK / FREF_DIVIDER2
3
ƒREF3
CLOCK_DIVIDERS3,
addr 0x17
FREF_DIVIDER3 [9:0]
ƒREF3 = ƒCLK / FREF_DIVIDER3
0
ƒIN0
CLOCK_DIVIDERS0,
addr 0x14
FIN_DIVIDER0 [15:12]
ƒIN0 = ƒSENSOR0 / FIN_DIVIDER0
1
ƒIN1
CLOCK_DIVIDERS1,
addr 0x15
FIN_DIVIDER1 [15:12]
ƒIN1 = ƒSENSOR1 / FIN_DIVIDER1
2
ƒIN2
CLOCK_DIVIDERS2,
addr 0x16
FIN_DIVIDER2 [15:12]
ƒIN2 = ƒSENSOR2 / FIN_DIVIDER2
3
ƒIN3
CLOCK_DIVIDERS3,
addr 0x17
FIN_DIVIDER3 [15:12]
ƒIN3 = ƒSENSOR3 / FIN_DIVIDER3
All
(1)
CLOCK
Channels 2 and 3 are only available for LDC1314
8.1.7 Input Deglitch Filter
The input deglitch filter suppresses EMI and ringing above the sensor frequency. It does not impact the
conversion result as long as its bandwidth is configured to be above the maximum sensor frequency. The input
deglitch filter can be configured in MUX_CONFIG.DEGLITCH register field as shown in Table 42. This setting
applies to all channels. For optimal performance, it is recommended to select the lowest setting that exceeds the
highest sensor oscillation frequency for all selected channels. For example, if the maximum sensor frequency is
2.8 MHz, choose MUX_CONFIG.DEGLITCH = b100 (3.3 MHz).
Table 42. Input Deglitch Filter Register
CHANNEL
(1)
44
(1)
MUX_CONFIG.DEGLITCH REGISTER VALUE
DEGLITCH FREQUENCY
ALL
b001
1.0 MHz
ALL
b100
3.3 MHz
ALL
b101
10 MHz
ALL
b011
33 MHz
Channels 2 and 3 are available for LDC1314 only.
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8.1.8 Device Status Registers
The LDC1312/LDC1314 can monitor and report on conversion results and the status of attached sensors using
the registers listed in Table 43.
Table 43. Status Registers
CHANNEL (1)
(1)
REGISTER
FIELDS [ BIT(S) ]
VALUES
All
STATUS, addr 0x18
Refer to Register Maps section
12 fields are available that
for a description of the individual
contain various status bits [ 15:0 ]
status bits.
All
ERROR_CONFIG, addr 0x19
12 fields are available that are
Refer to Register Maps section
used to configure error reporting [ for a description of the individual
15:0 ]
error configuration bits.
Channels 2 and 3 are available for LDC1314 only.
See the STATUS (Table 21) and ERROR_CONFIG (Table 22) register descriptions in the Register Map section.
These registers can be configured to trigger an interrupt on the INTB pin for certain events. The following
conditions must be met:
1. The error or status register must be unmasked by enabling the appropriate register bit in the
ERROR_CONFIG register.
2. The INTB function must be enabled by setting CONFIG.INTB_DIS to 0.
When a bit field in the STATUS register is set, the entire STATUS register content is held until read or until the
DATAx register is read. Reading also de-asserts INTB. After first starting conversions in active mode, the first
read of STATUS should performed be after assertion of INTB.
Interrupts are cleared by one of the following events:
1. Entering Sleep Mode
2. Power-on reset (POR)
3. Device enters Shutdown Mode (SD is asserted)
4. S/W reset
5. I2C read of the STATUS register: Reading the STATUS register will clear any error status bit set in STATUS
along with the ERR_CHAN field and de-assert INTB
Setting register CONFIG.INTB_DIS to b1 disables the INTB function and holds the INTB pin high.
The TI Application Note LDC1312, LDC1314, LDC1612, LDC1614 Sensor Status Monitoring provides detailed
information on sensor status reporting.
8.1.9 Multi-Channel Data Readback
When in multi-channel mode, the LDC1312/LDC1314 alternates conversions on all selected channels. After each
channel conversion completes, the conversion results for that channel overwrites the previous conversion results
with the new data.
When the device completes a conversion on the last channel in the selected group, the device will pull INTB low
if DRDY2INT is set to 1. At this time, the conversion results should be retrieved via the I2C bus.
If the device is put into Sleep mode or Shutdown mode, all DATAx registers are cleared of conversion data.
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Results of Delays in reading after INTB assertion
Channel 0
Conversion N
Channel 1
Conversion N
Channel 0
Conversion N+1
Channel 1
Conversion N+1
Channel 0
Channel 1
Case 1: No Data Loss
INTB
I2C
x
I2C transaction #1: read
Data N-1
& INTB deassert
x
I2C Transaction #2 reads:
Channel 0 conversion N
Channel 1 conversion N
I2C read
#2
x
x
Case 2: Data Loss
INTB
I2C
I2C Transaction #2 reads:
Channel 0 conversion N+1
Channel 1 conversion N
x
I2C transaction #1: read
Data N-1
& INTB deassert
I2C read
#2
Channel 0 Conversion N was overwritten
when conversion N+1 for Channel 0
completed
x
x
x
Case 3: Data Loss
INTB
I2C
I2C Transaction #2 reads:
Channel 0 conversion N+1
Channel 1 conversion N+1
x
I2C transaction #1: read
Data N-1
& INTB deassert
I2C read
#2
x
x
x
INTB assert
INTB assert with
Chan 0 conversion N
Chan 1 conversion N
completion of Conversion complete and available in
complete and available in
N-1
Register 0x00
Register 0x02
Channel 0 Conversion N was overwritten when
Conversion N+1 completed
Channel 1 Conversion N is overwritten when
Conversion N+1 completed
Time
Chan 0 conversion N+1
complete and available in
Register 0x00
Figure 55. Data Readback Timing
The STATUS register (Address 0x18) flags UNREADCONVx monitor the accesses to the DATAx registers.
When the DATAx register is read, the corresponding UNREADCONVx flag is cleared.
As shown in Figure 55 , if the I2C data readback is delayed, then it is possible to lose older, unread conversion
results. Monitoring the UNREADCONVx flags are useful to assess whether data loss is occurring.
A delayed read of previous conversion results can produce the condition in which reading the STATUS register
immediately after INTB asserts shows that Channel 0 has no unread data (where the UNREADCONV0 flag is 0),
but other channels do have unread data indicated by the corresponding UNREADCONVx flags.
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8.2 Typical Application
8.2.1 System Sensing Functionality
Inductive sensing provides a wide range of system advantages that no other technology can provide - contactless measurement, resistance to dirt/dust/water, immunity to external magnets, remote sensor positioning,
inexpensive and robust sensors, and high resolution measurement of relative movement.
The LDC1312/LDC1314 can be used to sense a wide range of applications for measuring a variety of target
movement:
• Angular Measurement: refer to 1-Degree Dial Reference Design for an example implementation.
• Linear Position Sensing: details on sensor and target construction are available in LDC1612/LDC1614 Linear
Position Sensing Application Note. For absolute positioning needs, it is recommended to use a differential 2
channel construction.
• Encoder Knob: refer to Inductive Sensing 32-Position Encoder Knob Reference Design for an example
system implementation.
• Inductive buttons using snap-domes: refer to 16-Button Inductive Keypad Reference Design for an example
system implementation.
8.2.2 Example Application
Example of a multi-channel implementation using the LDC1312. This example is representative of an axial
displacement application, in which the target movement is perpendicular to the plane of the coil. The second
channel can be used to sense proximity of a second target, or it can be used for environmental compensation by
connecting a reference coil.
3.3 V
3.3 V
LDC1312
MCU
CLKIN
40 MHz
SD
GPIO
INTB
GPIO
IN0A
Target
VDD
VDD
IN0B
Sensor 0
Core
GND
IN1A
Target
SDA
I 2C
IN1B
ADDR
Sensor 1
I 2C
Peripheral
SCL
3.3 V
GND
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Figure 56. Example Multi-Channel Application - LDC1312
8.2.3 Design Requirements
Design example in which Sensor 0 is used for proximity measurement and Sensor 1 is used for temperature
compensation. WEBENCH coil designer tool used to create sensor. System measurement requirements:
• Target distance = 1.0 mm
• Distance resolution = 0.2 µm
• Target diameter = 10 mm
• Target material = stainless steel (SS416)
• Number of PCB layers for the coil = 2
• The application requires 1 kSPS ( TSAMPLE = 1.00 ms)
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Typical Application (continued)
8.2.4 Detailed Design Procedure
1.
2.
3.
4.
5.
6.
7.
8.
48
The target distance, resolution and diameter are used as inputs to WEBENCH to design the sensor coil, The
resulting coil design is a 2 layer coil, with an area of 2.5 cm2, diameter of 17.7 mm, and 39 turns. The values
for RP, L and C are: RP = 6.6 kΩ, L = 43.9 µH, C = 100 pF.
Using the L and C to determine ƒSENSOR = 1/2π√(LC) = 1/2π√(43.9*10-6 * 100*10-12) = 2.4 MHz
With a system reference clock of 40 MHz applied to the CLKIN pin allows flexibility for setting the internal
clock frequencies. The sensor coil is connected to channel 0 (IN0A and IN0B pins).
After powering on the LDC, it will be in Sleep Mode. Program the registers as follows (this example sets
registers for channel 0 only; channel 1 registers can use equivalent configuration):
Set the dividers for Channel 0.
a. Because the sensor frequency is less than 8.75 MHz, the sensor divider can be set to 1, which means
setting field FIN_DIVIDER0 to 0x1. By default, ƒIN0 = ƒSENSOR = 2.4 MHz.
b. The design constraint for ƒREF0 is > 4 × ƒSENSOR. The 40 MHz reference frequency satisfies this
constraint, so the reference divider can be set to 1. This is done by setting the FREF_DIVIDER0 field to
0x01.
c. The combined value for Chan. 0 divider register (0x14) is 0x1002.
Program the settling time for Channel 0. The calculated Q of the coil is 10 (see Multi-Channel and Single
Channel Operation).
a. SETTLECOUNT0 ≥ Q × fREF0 / (16 × fSENSOR0) → 5.2, rounded up to 6. To provide margin to account for
system tolerances, a higher value of 10 is chosen.
b. Register 0x10 should be programmed to a minimum of 10.
c. The settle time is: (10 x 16)/20,000,000 = 8 µs
d. The value for SETTLECOUNT0 register (0x10) is 0x000A.
The channel switching delay is ~1 μs for fREF = 20 MHz (see Multi-Channel and Single Channel Operation)
Set the conversion time by the programming the reference count for Channel 0. The budget for the
conversion time is : TSAMPLE – settling time – channel switching delay = 1000 – 8 – 1 = 991 µs
a. To determine the conversion time register value, use the following equation and solve for RCOUNT0:
Conversion Time (tC0)= (RCOUNT0ˣ16)/fREF0.
b. This results in RCOUNT0 having a value of 1238 decimal (rounded down)
c. Set the RCOUNT0 register (0x08) to 0x04D6.
Use the default values for the ERROR_CONFIG register (address 0x19). By default, no interrupts are
enabled
Sensor drive current: to set the IDRIVE0 field value, read the value from Figure 52 using RP = 6.6 kΩ. In this
case IDRIVE0 value should be set to 18 (decimal). The INIT_DRIVE0 current field should be set to 0x00.
The combined value for the DRIVE_CURRENT0 register (addr 0x1E) is 0x9000.
Program the MUX_CONFIG register
a. Set the AUTOSCAN_EN to b1 bit to enable sequential mode
b. Set RR_SEQUENCE to b00 to enable data conversion on two channels (channel 0, channel 1)
c. Set DEGLITCH to b100 to set the input deglitch filter bandwidth to 3.3MHz, the lowest setting that
exceeds the oscillation tank frequency.
d. The combined value for the MUX_CONFIG register (address 0x1B) is 0x820C
Finally, program the CONFIG register as follows:
a. Set the ACTIVE_CHAN field to b00 to select channel 0.
b. Set SLEEP_MODE_EN field to b0 to enable conversion.
c. Set RP_OVERRIDE_EN to b1 to disable auto-calibration.
d. Set SENSOR_ACTIVATE_SEL = b0, for full current drive during sensor activation
e. Set the AUTO_AMP_DIS field to b1 to disable auto-amplitude correction
f. Set the REF_CLK_SRC field to b1 to use the external clock source.
g. Set the other fields to their default values.
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Typical Application (continued)
h. The combined value for the CONFIG register (address 0x1A) is 0x1601.
We then read the conversion results for channel 0 and channel 1 every 1.00 ms from register addresses
0x00 and 0x02.
8.2.5 Recommended Initial Register Configuration Values
Based on the example configuration in section Detailed Design Procedure, the following register write sequence
is recommended:
Table 44. Recommended Initial Register Configuration Values (Single-Channel Operation)
ADDRESS
VALUE
REGISTER NAME
COMMENTS
0x08
0x04D6
RCOUNT0
Reference count calculated from timing requirements (1 kSPS) and
resolution requirements
0x10
0x000A
SETTLECOUNT0
Minimum settling time for chosen sensor
0x14
0x1002
CLOCK_DIVIDERS0 FIN_DIVIDER0 = 1, FREF_DIVIDER0 = 2
0x19
0x0000
ERROR_CONFIG
Can be changed from default to report status and error conditions
0x1B
0x020C
MUX_CONFIG
Enable Channel 0 in continuous mode, set Input deglitch bandwidth to
3.3MHz
0x1E
0x9000
DRIVE_CURRENT0
Sets sensor drive current on channel 0
0x1A
0x1601
CONFIG
Select active channel = ch 0, disable auto-amplitude correction and autocalibration, enable full current drive during sensor activation, select
external clock source, wake up device to start conversion. This register
write must occur last because device configuration is not permitted while
the LDC is in active mode.
Table 45. Recommended Initial Register Configuration Values (Multi-Channel Operation)
ADDRESS
VALUE
REGISTER NAME
COMMENTS
0x08
0x04D6
RCOUNT0
Reference count calculated from timing requirements (1
kSPS) and resolution requirements
0x09
0x04D6
RCOUNT1
Reference count calculated from timing requirements (1
kSPS) and resolution requirements
0x10
0x000A
SETTLECOUNT0
Minimum settling time for chosen sensor
0x11
0x000A
SETTLECOUNT1
Minimum settling time for chosen sensor
0x14
0x1002
CLOCK_DIVIDERS0
FIN_DIVIDER0 = 1, FREF_DIVIDER0 = 2
0x15
0x1002
CLOCK_DIVIDERS_1
FIN_DIVIDER1 = 1, FREF_DIVIDER1 = 2
0x19
0x0000
ERROR_CONFIG
Can be changed from default to report status and error
conditions
0x1B
0x820C
MUX_CONFIG
Enable Ch 0 and Ch 1 (sequential mode), set Input deglitch
bandwidth to 3.3MHz
0x1E
0x9000
DRIVE_CURRENT0
Sets sensor drive current on ch 0
0x1F
0x9000
DRIVE_CURRENT1
Sets sensor drive current on ch 1
0x1A
0x1601
CONFIG
Disable auto-amplitude correction and auto-calibration,
enable full current drive during sensor activation, select
external clock source, wake up device to start conversion.
This register write must occur last because device
configuration is not permitted while the LDC is in active
mode.
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8.2.6 Application Curves
Common Test Conditions (unless specified otherwise):
• Sensor inductor: 2 layer, 32 turns/layer, 14mm diameter, PCB inductor with L=19.4 µH, RP=5.7 kΩ at 2 MHz
• Sensor capacitor: 330 pF 1% COG/NP0
• Target: Aluminum, 1.5 mm thickness
• Channel = Channel 0 (continuous mode)
• ƒCLKIN = 40 MHz, FIN_DIVIDERx = 0x01, FREF_DIVIDERx = 0x001
• RCOUNT0 = 0xFFFF, SETTLECOUNT0 = 0x0100
• RP_OVERRIDE = 1, AUTO_AMP_DIS = 1, DRIVE_CURRENT0 = 0x9800
3500
2.5
2.25
Measurement Precision (µm)
Output Code - DATA_CH0 (DEC)
Average Code (DEC)
3000
2500
Target Distance =
0.5 x coil diameter
2000
Target Distance =
1 x coil diameter
1500
1.75
1.5
1.25
1
0.75
0.5
0.25
1000
0
20%
40%
60%
Target Distance / ‡SENSOR
80%
100%
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0
0.1
0.2
D012
Figure 57. Typical Output Code vs. Target Distance (0 to
14mm)
50
2
0.3
0.4
0.5
Target Distance / ‡SENSOR
0.6
0.7
D013
Figure 58. Measurement Precision in Distance vs. Target
Distance (0 to 10mm)
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8.2.7 Inductor Self-Resonant Frequency
Every inductor has a distributed parasitic capacitance, which is dependent on construction and geometry. At the
Self-Resonant Frequency (SRF), the reactance of the inductor cancels the reactance of the parasitic
capacitance. Above the SRF, the inductor will electrically appear to be a capacitor. Because the parasitic
capacitance is not well-controlled or stable, it is recommended that: ƒSENSOR < 0.8 × fSR.
175.0
150.0
Ls (µH)
125.0
100.0
75.0
50.0
25.0
0.0
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
Frequency (MHz)
Figure 59. Example Coil Inductance vs. Frequency
In Figure 59, the inductor has a SRF at 6.38 MHz; therefore the inductor should not be operated above 0.8×6.38
MHz, or 5.1 MHz.
9 Power Supply Recommendations
•
•
The LDC requires a voltage supply within 2.7 V and 3.6 V. A multilayer ceramic X7R bypass capacitor of 1 μF
between the VDD and GND pins is recommended. If the supply is located more than a few inches from the
LDC, additional capacitance may be required in addition to the ceramic bypass capacitor. A ceramic capacitor
with a value of 10 μF is a typical choice.
The optimum placement of bypass capacitors is closest to the VDD and GND terminals of the device. Care
should be taken to minimize the loop area formed by the bypass capacitor connection, the VDD pin, and the
GND pin of the IC. See Figure 60 for a layout example.
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10 Layout
10.1 Layout Guidelines
Avoid long traces between the sensor and the LDC - higher frequency sensors may need to be placed closer to
the device to minimize noise. The INAx and INBx traces should be routed as differential pairs - run the traces in
parallel and close together. Lower trace impedances (even well below 100 Ω) are acceptable, as they reduce any
parasitic inductance.
The sensor capacitor should be placed close to the inductor to minimize the sensor RP.
Do not place filled planes underneath or between the sensor layers. If the sensor is placed in a plane, there
should be a gap of at least 20% of a sensor diameter between the plane and the outermost coil of the sensor.
There should not be any continuous ring of conductors encircling the sensor. This can be managed with a small
cut in the conductor.
Refer to the TI Application Note LDC Sensor Design for more information on sensor design and optimization.
10.2 Layout Example
Figure 60 shows an example layout for the LDC1312, including a pair of sensor.
Figure 60. Example PCB Layout
52
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SNOSCZ0A – DECEMBER 2014 – REVISED MARCH 2018
11 Device and Documentation Support
11.1 Device Support
11.1.1 Development Support
For related links, see the following:
• Texas Instruments' WEBENCH tool: http://www.ti.com/webench
11.2 Documentation Support
11.2.1 Related Documentation
For related documentation, refer to the following:
• LDC1000 Temperature Compensation SNAA212
• LDC Sensor Design SNOA930
• LDC1612/LDC1614 Linear Position Sensing Application Note SNOA931
• Optimizing L Measurement Resolution for the LDC1312 and LDC1314 SNOA945
• Power Reduction Techniques for the LDC131x/161x for Inductive Sensing SNOA949
• Optimizing L Measurement Resolution for the LDC161x and LDC1101 SNOA950
• Inductive Sensing Touch-On-Metal Buttons Design Guide SNOA951
• LDC Target Design SNOA957
• LDC1312, LDC1314, LDC1612, LDC1614 Sensor Status Monitoring SNOA959
• 16 Button Inductive Touch Stainless Steel Keypad Reference Design
• Inductive Sensing 32-Position Encoder Knob Reference Design
• 16-Button Inductive Keypad Reference Design
• 1-Degree Dial Reference Design
11.3 Related Links
The table below lists quick access links. Categories include technical documents, support and community
resources, tools and software, and quick access to sample or buy.
Table 46. Related Links
PARTS
PRODUCT FOLDER
SAMPLE & BUY
TECHNICAL
DOCUMENTS
TOOLS &
SOFTWARE
SUPPORT &
COMMUNITY
LDC1312
Click here
Click here
Click here
Click here
Click here
LDC1314
Click here
Click here
Click here
Click here
Click here
11.4 Receiving Notification of Documentation Updates
To receive notification of documentation updates, navigate to the device product folder on ti.com. In the upper
right corner, click on Alert me to register and receive a weekly digest of any product information that has
changed. For change details, review the revision history included in any revised document.
11.5 Community Resources
The following links connect to TI community resources. Linked contents are provided "AS IS" by the respective
contributors. They do not constitute TI specifications and do not necessarily reflect TI's views; see TI's Terms of
Use.
TI E2E™ Online Community TI's Engineer-to-Engineer (E2E) Community. Created to foster collaboration
among engineers. At e2e.ti.com, you can ask questions, share knowledge, explore ideas and help
solve problems with fellow engineers.
Design Support TI's Design Support Quickly find helpful E2E forums along with design support tools and
contact information for technical support.
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11.6 Trademarks
E2E is a trademark of Texas Instruments.
WEBENCH is a registered trademark of Texas Instruments.
All other trademarks are the property of their respective owners.
11.7 Electrostatic Discharge Caution
These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam
during storage or handling to prevent electrostatic damage to the MOS gates.
11.8 Glossary
SLYZ022 — TI Glossary.
This glossary lists and explains terms, acronyms, and definitions.
12 Mechanical, Packaging, and Orderable Information
The following pages include mechanical, packaging, and orderable information. This information is the most
current data available for the designated devices. This data is subject to change without notice and revision of
this document. For browser-based versions of this data sheet, refer to the left-hand navigation.
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PACKAGE OPTION ADDENDUM
www.ti.com
10-Dec-2020
PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package Pins Package
Drawing
Qty
Eco Plan
(2)
Lead finish/
Ball material
MSL Peak Temp
Op Temp (°C)
Device Marking
(3)
(4/5)
(6)
LDC1312DNTR
ACTIVE
WSON
DNT
12
4500
RoHS & Green
SN
Level-1-260C-UNLIM
-40 to 125
LDC1312
LDC1312DNTT
ACTIVE
WSON
DNT
12
250
RoHS & Green
SN
Level-1-260C-UNLIM
-40 to 125
LDC1312
LDC1314RGHR
ACTIVE
WQFN
RGH
16
4500
RoHS & Green
SN
Level-1-260C-UNLIM
-40 to 125
LDC1314
LDC1314RGHT
ACTIVE
WQFN
RGH
16
250
RoHS & Green
SN
Level-1-260C-UNLIM
-40 to 125
LDC1314
(1)
The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2)
RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance
do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may
reference these types of products as "Pb-Free".
RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption.
Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of
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