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LDC2112, LDC2114
SNOSD15B – DECEMBER 2016 – REVISED APRIL 2017
LDC2112, LDC2114 Inductive Touch Solution for Low-Power HMI Button Applications
1 Features
3 Description
•
Inductive sensing technology enables touch button
design for human machine interface (HMI) on a wide
variety of materials such as metal, glass, plastic, and
wood, by measuring small deflections of conductive
targets. The sensor for an inductive touch system is a
coil that can be implemented on a small PCB located
behind the panel and protected from the environment.
Inductive sensing solution is insensitive to humidity or
non-conductive contaminants such as oil and dirt. It is
able to automatically correct for any deformation in
the conductive targets.
1
•
•
•
•
•
•
•
•
•
Low Power Consumption:
– One Button: 6 µA at 0.625 SPS
– Two Buttons: 72 µA at 20 SPS
Configurable Button Scan Rates:
– 0.625 SPS to 80 SPS
Force Level Measurement of Touch Buttons
Independent Channel Operation:
– Two Channels for LDC2112
– Four Channels for LDC2114
Integrated Algorithms to Enable:
– Adjustable Force Threshold per Button
– Environmental Shift Compensation
– Simultaneous Button Press Detection
Supports Independent Operation without MCU
Robust EMI Performance:
– Allows for CISPR 22 and CISPR 24
Compliance
Operating Voltage Range: 1.8 V ± 5%
Temperature Range: –40 °C to +85 °C
Interface:
– I2C
– Dedicated Logic Output per Channel
2 Applications
Touch Buttons and Force Level Measurements on
Different Materials, Including Metal, Plastic, and
Glass for:
•
•
Consumer Electronics:
– Smartphones
– Smart Watches and Other Wearable Devices
– Smart Speakers
– Tablets/PCs
– Virtual Reality Headsets
– Sound Bars
Industrial Applications:
– Televisions
– Handheld Devices
– Home Appliances
– HMI Panels and Keypads
The LDC2112/LDC2114 is a multi-channel low-noise
inductance to digital converter with integrated
algorithms to implement inductive touch applications.
The device employs an innovative LC resonator that
offers high rejection of noise and interference. The
LDC2112/LDC2114 can reliably detect material
deflections of less than 200 nm.
The LDC2112/LDC2114 includes an ultra-low power
mode intended for power on/off buttons in battery
powered applications.
The LDC2112/LDC2114 is available in a 16-pin
DSBGA or TSSOP package. The 0.4 mm pitch
DSBGA package has a very small 1.6 × 1.6 mm
nominal body size with a maximum height of 0.4 mm.
The 0.65 mm pitch TSSOP package has a 5.0 × 4.4
mm nominal body size with a maximum height of 1.2
mm.
Device Information(1)
PART NUMBER
PACKAGE
BODY SIZE (NOM)
LDC2112/LDC2114
DSBGA (16)
1.6 mm × 1.6 mm
LDC2112/LDC2114
TSSOP (16)
5.0 mm × 4.4 mm
(1) For all available packages, see the orderable addendum at
the end of the data sheet.
Simplified Schematic
VDD
LDC2114
OUT0
Digital
Algorithm
IN0
OUT1
OUT2
OUT3
IN1
IN2
Resonant
Circuit
Driver
Inductive
Sensing Core
INTB
Logic
LPWRB
IN3
COM
I2C
SCL
SDA
GND
Copyright © 2016, Texas Instruments Incorporated
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.
LDC2112, LDC2114
SNOSD15B – DECEMBER 2016 – REVISED APRIL 2017
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
5
6.1
6.2
6.3
6.4
6.5
6.6
6.7
6.8
5
5
5
5
6
7
7
8
Absolute Maximum Ratings ......................................
ESD Ratings..............................................................
Recommended Operating Conditions.......................
Thermal Information ..................................................
Electrical Characteristics...........................................
Digital Interface .........................................................
I2C Interface ..............................................................
Typical Characteristics ..............................................
Detailed Description ............................................ 10
7.1
7.2
7.3
7.4
Overview .................................................................
Functional Block Diagram .......................................
Feature Description.................................................
Device Functional Modes........................................
10
10
11
15
7.5 Register Maps ......................................................... 15
8
Application and Implementation ........................ 28
8.1 Application Information............................................ 28
8.2 Typical Application .................................................. 38
9 Power Supply Recommendations...................... 40
10 Layout................................................................... 40
10.1 Layout Guidelines ................................................. 40
10.2 Layout Example .................................................... 40
10.3 DSBGA Light Sensitivity ...................................... 41
11 Device and Documentation Support ................. 42
11.1
11.2
11.3
11.4
11.5
11.6
11.7
11.8
Documentation Support .......................................
Related Links ........................................................
Receiving Notification of Documentation Updates
Community Resources..........................................
Trademarks ...........................................................
Electrostatic Discharge Caution ............................
Export Control Notice ...........................................
Glossary ................................................................
42
42
42
42
42
42
42
43
12 Mechanical, Packaging, and Orderable
Information ........................................................... 43
4 Revision History
Changes from Revision A (January 2017) to Revision B
Page
•
Changed unit of Data set-up time from µs to ns (typo) ......................................................................................................... 7
•
Changed Multi-Channel and Single-Channel Operation ...................................................................................................... 11
•
Added LDC2112 to Register EN – Address 0x0C Table...................................................................................................... 19
Changes from Original (December 2016) to Revision A
•
2
Page
Changed Advance Information to Production Data Release.................................................................................................. 1
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Copyright © 2016–2017, Texas Instruments Incorporated
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SNOSD15B – DECEMBER 2016 – REVISED APRIL 2017
5 Pin Configuration and Functions
LDC2112
16-Pin DSBGA
Top View (Bumps Down)
1
A
B
C
2
NC
NC
3
IN0
IN1
INTB
ADDR
LPW
VDD
LDC2112
16-Pin TSSOP
Top View
SDA
4
GND
NC
GND
COM
SCL
1
16
SCL
GND
2
15
OUT0
LPWRB
3
14
SDA
VDD
4
13
OUT1
LDC2112
OUT1
RB
D
COM
INTB
5
12
NC
NC
6
11
ADDR
NC
7
10
GND
IN1
8
9
IN0
OUT0
Pin Functions - LDC2112
PIN
NAME
DSBGA NO.
TSSOP NO.
C1
4
D1
2
A4
10
INTB
B2
LPWRB
VDD
I/O (1)
DESCRIPTION
P
Power supply
G
Ground (2)
5
O
Interrupt output
Polarity can be configured in Register 0x11.
C2
3
I
Normal / Low Power Mode select
Set LPWRB to VDD for Normal Power Mode or ground for Low Power Mode.
COM
D2
1
A
Common return current path for all LC resonator sensors
A capacitor should be connected from this pin to GND. Refer to Setting COM
Pin Capacitor.
IN0
A3
9
A
Channel 0 LC sensor input
IN1
A2
8
A
Channel 1 LC sensor input
OUT0
D4
15
O
Channel 0 logic output
Polarity can be configured in Register 0x1C.
OUT1
C4
13
O
Channel 1 logic output
Polarity can be configured in Register 0x1C.
ADDR
B3
11
I
I2C address
When ADDR = Ground, I2C address = 0x2A. When ADDR = VDD, I2C address =
0x2B.
SCL
D3
16
I
I2C clock
SDA
C3
14
I/O
I2C data
A1
7
B1
6
—
No connect
Leave them floating.
B4
12
GND
NC
(1)
(2)
I = Input, O = Output, P=Power, G=Ground, A=Analog
Both pins should be connected to the system ground on the PCB.
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LDC2112, LDC2114
SNOSD15B – DECEMBER 2016 – REVISED APRIL 2017
www.ti.com
LDC2114
16-Pin DSBGA
Top View (Bumps Down)
A
B
1
2
3
4
IN2
IN1
IN0
GND
IN3
OUT3
INTB
LDC2114
16-Pin TSSOP
Top View
OUT2
COM
1
16
SCL
GND
2
15
OUT0
LPWRB
3
14
SDA
VDD
4
13
OUT1
LDC2114
C
VDD
LPW
SDA
OUT1
RB
D
GND
COM
SCL
OUT0
INTB
5
12
OUT2
IN3
6
11
OUT3
IN2
7
10
GND
IN1
8
9
IN0
Pin Functions - LDC2114
PIN
NAME
DSBGA NO.
TSSOP NO.
C1
4
D1
2
A4
10
INTB
B2
LPWRB
VDD
I/O (1)
DESCRIPTION
P
Power supply
G
Ground (2)
5
O
Interrupt output
Polarity can be configured in Register 0x11.
C2
3
I
Normal / Low Power Mode select
Set LPWRB to VDD for Normal Power Mode or ground for Low Power Mode.
COM
D2
1
A
Common return current path for all LC resonator sensors
A capacitor should be connected from this pin to GND. Refer to Setting COM Pin
Capacitor.
IN0
A3
9
A
Channel 0 LC sensor input
IN1
A2
8
A
Channel 1 LC sensor input
IN2
A1
7
A
Channel 2 LC sensor input
IN3
B1
6
A
Channel 3 LC sensor input
OUT0
D4
15
O
Channel 0 logic output
Polarity can be configured in Register 0x1C.
OUT1
C4
13
O
Channel 1 logic output
Polarity can be configured in Register 0x1C.
OUT2
B4
12
O
Channel 2 logic output
Polarity can be configured in Register 0x1C.
OUT3
B3
11
O
Channel 3 logic output
Polarity can be configured in Register 0x1C.
SCL
D3
16
I
I2C clock
SDA
C3
14
I/O
GND
(1)
(2)
4
I2C data
I2C address = 0x2A.
I = Input, O = Output, P=Power, G=Ground, A=Analog
Both pins should be connected to the system ground on the PCB.
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SNOSD15B – DECEMBER 2016 – REVISED APRIL 2017
6 Specifications
6.1 Absolute Maximum Ratings
Over operating temperature range unless otherwise noted. (1)
MIN
VDD
MAX
UNIT
2.2
V
V
Supply voltage
Voltage on SCL, SDA
–0.3
3.6
Voltage on any other pin
–0.3
2.2 (2)
V
TJ
Junction temperature
–40
85
℃
TSTG
Storage temperature
–65
125
°C
VI
(1)
(2)
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.
Maximum voltage across any two pins (not including SCL or SDA) is VDD + 0.3 V.
6.2 ESD Ratings
VALUE
V(ESD)
(1)
(2)
Electrostatic
discharge
Human body model (HBM), per ANSI/ESDA/JEDEC JS-001 (1)
±1000
Charged device model (CDM), per JEDEC specification JESD22C101 (2)
±250
UNIT
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
Over operating temperature range unless otherwise noted.
MIN
NOM
MAX
UNIT
VDD
Supply voltage
1.71
1.89
V
TJ
Junction temperature
–40
85
°C
6.4 Thermal Information
LDC2112/LDC2114
THERMAL METRIC (1)
DSBGA
TSSOP
UNIT
16 PINS
16 PINS
RθJA
Junction-to-ambient thermal resistance
81.8
105.1
°C/W
RθJC(top)
Junction-to-case (top) thermal resistance
0.4
40.3
°C/W
RθJB
Junction-to-board thermal resistance
18.2
50.2
°C/W
ΨJT
Junction-to-top characterization parameter
0.3
3.6
°C/W
ΨJB
Junction-to-board characterization
parameter
18
49.6
°C/W
(1)
For more information about traditional and new thermal metrics, see the Semiconductor and IC Package Thermal Metrics application
report.
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LDC2112, LDC2114
SNOSD15B – DECEMBER 2016 – REVISED APRIL 2017
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6.5 Electrical Characteristics
Over operating temperature range unless otherwise noted. VDD = 1.8 V, TJ = 25 °C.
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
1.71
1.8
1.89
V
POWER
VDD
Supply voltage
IDDNP
Normal power mode supply current
(4 channels) (1) (2) (3)
4 channels, 40 SPS per channel,
1 ms sampling window per channel,
LPWRB = VDD
IDDNP
Normal power mode supply current
(2 channels) (1) (2)
2 channels, 40 SPS per channel,
1 ms sampling window per channel,
LPWRB = VDD
0.26
mA
IDDLP
Low power mode supply
current (1) (2)
1 channel, 1.25 SPS per channel,
1 ms sampling window per channel,
LPWRB = Ground
9
µA
IDDSB
Standby supply current
No button active (EN = 0x00)
5
0.49
mA
7
µA
SENSOR
ISENSOR,
MAX
Registers SENSORn_CONFIG: RPn = 0
Sensor maximum current drive
(4)
2.5
mA
RP,
MIN
Sensor minimum parallel resonant
impedance
350
Ω
RP,
MAX
Sensor maximum parallel resonant
impedance
10
kΩ
fSENSOR
Sensor resonant frequency
QSENSOR,
MIN
Sensor minimum quality factor
QSENSOR,
MAX
Sensor maximum quality factor
VSENSOR,
PP
CIN
1
30
MHz
5
30
Sensor oscillation peak-to-peak
voltage
Measured on the INn
reference to COM.
(4)
pins with
Sensor input pin capacitance
0.9
V
17
pF
CONVERTER
SRNP,
MIN
Minimum normal power mode scan
rate (5)
LPWRB = VDD
7
10
13
SPS
SRNP,
MAX
Maximum normal power mode scan
rate (5)
LPWRB = VDD
56
80
104
SPS
SRLP, MIN
Minimum low power mode scan
rate (5)
LPWRB = Ground
0.438
0.625
0.813
SPS
SRLP, MAX
Maximum low power mode scan
rate (5)
LPWRB = Ground
3.5
5
6.5
SPS
Resolution
Data code width
(1)
(2)
(3)
(4)
(5)
6
12
Bits
Sensor configuration: LSENSOR = 0.85 µH, CSENSOR = 58 pF, QSENSOR = 11, RP = 0.7 kΩ.
I2C communication and pull-up resistors current is not included.
Four-channel supply current is applicable to LDC2114 only.
The italic n is the channel index, i.e., n = 0 or 1 for LDC2112; n = 0, 1, 2, or 3 for LDC2114.
For typical distribution of the scan rates, refer to Figure 9.
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SNOSD15B – DECEMBER 2016 – REVISED APRIL 2017
6.6 Digital Interface
Over operating temperature range unless otherwise noted. VDD = 1.8 V, TJ = 25 °C. Pins: LPWRB, INTB, OUT0, OUT1,
OUT2, OUT3, and ADDR.
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
VOLTAGE LEVELS
VIH
Input high voltage
VIL
Input low voltage
0.8 × VDD
VOH
Output high voltage
ISOURCE = 400 µA
VOL
Output low voltage
ISINK = 400 µA
IL
Digital input leakage current
V
0.2 × VDD
0.8 × VDD
V
V
0.2 × VDD
V
500
nA
MAX
UNIT
–500
6.7 I2C Interface
MIN
TYP
VOLTAGE LEVELS
VIH
Input high voltage
VIL
Input low voltage
VOL
Output low voltage
HYS
Hysteresis (1)
0.7 × VDD
V
3 mA sink current
0.3 × VDD
V
0.2 × VDD
V
0.05 × VDD
V
I2C TIMING CHARACTERISTICS
fSCL
Clock frequency
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 set-up 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)
400
After this period, the first
clock pulse is generated.
kHz
This parameter is specified by design and/or characterization and is not tested in production.
SDA
tLOW
tf
tHD;STA
tf
tr
tr
tBUF
tSP
SCL
tSU;STA
tHD;STA
tHIGH
tHD;DAT
START
tSU;STO
tSU;DAT
REPEATED
START
STOP
START
Figure 1. I2C Timing Diagram
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LDC2112, LDC2114
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6.8 Typical Characteristics
Over recommended operating conditions unless specified otherwise. VDD = 1.8 V, TJ = 25 °C.
One channel enabled with a button sampling window of 1 ms unless specified otherwise.
1600
800
10 SPS
20 SPS
40 SPS
80 SPS
1200
1000
800
600
400
600
500
400
300
200
200
100
0
0
0
1
2
3
4
5
6
Sensor RP (k:)
7
8
9
10
0
3
4
5
6
Sensor RP (k:)
7
8
9
10
D011
160
0.625 SPS
1.25 SPS
2.5 SPS
5 SPS
25
150
Average Supply Current (PA)
Average Supply Current (PA)
2
Figure 3. Supply Current vs Sensor RP for Normal Power
Mode. Sensor Frequency = 3.6 MHz. Two Channels Enabled.
30
20
15
10
5
VDD = 1.71 V
VDD = 1.8 V
VDD = 1.89 V
140
130
120
110
100
90
80
-40
0
0
1
2
3
4
5
6
Sensor RP (k:)
7
8
9
10
0
20
40
Temperature (qC)
60
80
100
D003
Figure 5. Supply Current vs Temperature. Sensor RP = 650
Ω, Scan Rate = 40 SPS.
160
9
150
8
Standby Current (PA)
140
130
120
110
100
VDD = 1.71 V
VDD = 1.8 V
VDD = 1.89 V
7
6
5
4
90
80
1.7
-20
D002
Figure 4. Supply Current vs Sensor RP for Low Power Mode.
Sensor Frequency = 3.6 MHz.
Average Supply Current (PA)
1
D001
Figure 2. Supply Current vs Sensor RP for Normal Power
Mode. Sensor Frequency = 3.6 MHz. Four Channels
Enabled.
-40qC
-25qC
1.75
1.8
VDD (V)
0qC
25qC
1.85
85qC
1.9
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3
-40
-20
0
D004
Figure 6. Supply Current vs VDD. Sensor RP = 650 Ω, Scan
Rate = 40 SPS.
8
10 SPS
20 SPS
40 SPS
80 SPS
700
Average Supply Current (PA)
Average Supply Current (PA)
1400
20
40
Temperature (qC)
60
80
100
D005
Figure 7. Standby Current vs Temperature
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SNOSD15B – DECEMBER 2016 – REVISED APRIL 2017
Typical Characteristics (continued)
One channel enabled with a button sampling window of 1 ms unless specified otherwise.
450
9
400
8
7
Occurrences
Standby Current (PA)
350
6
5
300
250
200
150
100
4
-40qC
-25qC
3
1.7
0qC
25qC
85°C
50
0
1.75
1.8
VDD (V)
1.85
1.9
D006
Figure 8. Standby Current vs VDD
-12 -11 -10 -9 -8 -7 -6 -5 -4 -3 -2 -1 0
Percentage Offset ( )
1
2
3
4
D007
Figure 9. Scan Rate Distribution at 30 °C
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7 Detailed Description
7.1 Overview
The LDC2112/LDC2114 is a multi-channel, low-noise, high-resolution inductance to digital converter (LDC)
optimized for inductive touch applications. Button presses form micro-deflections in the conductive targets which
cause frequency shifts in the resonant sensors. The LDC2112/LDC2114 can measure such frequency shifts and
determine when button presses have occurred. With adjustable sensitivity per input channel, the
LDC2112/LDC2114 can reliably operate with a wide range of physical button structures and materials. The high
resolution measurement enables the implementation of force level buttons. The LDC2112/LDC2114 incorporates
customizable post-processing algorithms for enhanced robustness.
The LDC2112/LDC2114 can operate in an ultra-low power mode for optimal battery life, or can be toggled into a
higher scan rate for more responsive button press detection for game play or other low latency applications. The
LDC2112/LDC2114 is operational from –40 °C to +85 °C with a 1.8 V ± 5% power supply voltage.
The LDC2112/LDC2114 is configured through 400 kHz I2C. Button presses can be reported through the I2C
interface or with configurable polarity dedicated push-pull outputs. Besides the LC resonant sensors, the only
external components necessary for operation are supply bypassing capacitors and a COM pin capacitor to
ground.
7.2 Functional Block Diagram
VDD
LDC2112
Digital
Algorithm
OUT0
OUT1
IN0
Resonant
Circuit
Driver
Inductive
Sensing Core
INTB
Logic
LPWRB
IN1
COM
ADDR
I2C
SCL
SDA
GND
Copyright © 2016, Texas Instruments Incorporated
Figure 10. Block Diagram of LDC2112
10
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Functional Block Diagram (continued)
VDD
LDC2114
OUT0
OUT1
Digital
Algorithm
IN0
OUT2
OUT3
IN1
Resonant
Circuit
Driver
IN2
Inductive
Sensing Core
INTB
Logic
LPWRB
IN3
SCL
I2C
COM
SDA
GND
Copyright © 2016, Texas Instruments Incorporated
Figure 11. Block Diagram of LDC2114
7.3 Feature Description
7.3.1 Multi-Channel and Single-Channel Operation
The LDC2112 provides two independent sensing channels; the LDC2114 provides four independent sensing
channels. In the following sections, some parameters, such as DATAn and SENSORn_CONFIG, contain a
channel index n. In those instances, n = 0 or 1 for LDC2112, and n = 0, 1, 2, or 3 for LDC2114.
The LDC2112's two available channels are always enabled in Normal Power Mode. The LDC2112 sequentially
samples both channels at the configured scan rate. Either channel can be independently enabled in Low Power
Mode by setting the LPENn (n = 0 or 1) bit fields in Register EN (Address 0x0C).
Any of the LDC2114’s four available channels can be independently enabled by setting the ENn and LPENn (n =
0, 1, 2, or 3) bit fields in Register EN (Address 0x0C). The low-power-enable bit LPENn only takes effect if the
corresponding ENn bit is also set. If only one channel is set active, the LDC2114 periodically samples the single
active channel at the configured scan rate. When several channels are set active, the LDC2114 operates in
multi-channel mode, and it sequentially samples the active channels at the configured scan rate. Each channel of
the LDC2114 can be independently enabled in Low Power Mode and Normal Power Mode.
7.3.2 Button Output Interfaces
Button events may be reported by using two methods. The first method is to monitor the OUTn pins (n = 0, 1, 2,
or 3), which are push-pull outputs and can be used as interrupts to a micro-controller. The polarities of these pins
are programmable through Register OPOL_DPOL (Address 0x1C). Any button press or error condition is also
reported by the push-pull interrupt pin, INTB. Its polarity is configurable through Register INTPOL (Address
0x11). Any assertion of INTB is cleared upon reading Register STATUS (Address 0x00). Each push-pull output
must be assigned to a dedicated general-purpose input pin on the micro-controller to avoid potential current
fights.
The second method is by use of the LDC2112/LDC2114’s I2C interface. The Register OUT (Address 0x01)
contains the fields OUT0, OUT1, OUT2, and OUT3, which indicate when a button press has been detected. For
more advanced button press measurements, the output DATAn registers (n = 0, 1, 2, or 3, Addresses 0x02
through 0x09), which are 12-bit two’s complements, can be retrieved for all active buttons, and processed on a
micro-controller. A valid button push is represented by a positive value. The polarity is configurable in Register
OPOL_DPOL (Address 0x1C). The DATAn values can be used to implement multi-level buttons, where the data
value is correlated to the amount of force applied to the button.
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Feature Description (continued)
7.3.3 Programmable Button Sensitivity
The GAINn registers (Addresses 0x0E, 0x10, 0x12, and 0x14) enable sensitivity enhancement of individual
buttons to ensure consistent behavior of different mechanical structures. The sensitivity has a 64-level gain factor
for a normalized gain between 1 and 232. Each gain step increases the gain by an average of 9%.
The gain required for an application is primarily determined by the mechanical rigidity of each individual button.
The individual gain steps are listed in the Gain Table.
7.3.4 Baseline Tracking
The LDC2112/LDC2114 incorporates a baseline tracking algorithm to automatically compensate for any slow
change in the sensor output caused by environmental variations, such as temperature drift. The baseline tracking
is configured independently for Normal Power Mode and Low Power Mode. For more information, refer to
Tracking Baseline.
7.3.5 Integrated Button Algorithms
The LDC2112/LDC2114 features several algorithms that can mitigate false button detections due to mechanical
non-idealities. The algorithms look for correlated button responses, for example, similar or opposite responses
between two neighboring buttons, to determine if there is any undesirable mechanical crosstalk. For more
information, refer to Mitigating False Button Detections.
7.3.6 I2C Interface
The LDC2112/LDC2114 features an I2C Interface that can be used to program the internal registers and read
channel data. Before reading the OUT (Address 0x01) or channel DATAn (n = 0, 1, 2 or 3, Addresses 0x02
through 0x05) registers, the user should always read Register STATUS (Address 0x00) first to lock the data. The
LDC2112/LDC2114 supports burst mode with auto-incrementing register addresses.
For the write sequence, there is a special handshake process that has to take place to ensure data integrity. The
sequence of register write is illustrated as follows:
• Set CONFIG_MODE (Register RESET, Address 0x0A) bit = 1 to start the register write session
• Poll for RDY_TO_WRITE (Register STATUS, Address 0x00) bit = 1
• I2C write to configure registers
• Set CONFIG_MODE (Register RESET, Address 0x0A) bit = 0 to terminate the register write session
After CONFIG_MODE is de-asserted, the new scan cycle will start in less than 1 ms. The waveform of the above
process is shown in Figure 12.
25 ms scan cycle
25 ms scan cycle
Sampling
Sampling
CONFIG_MODE
< 1 ms
(Register RESET)
RDY_TO_WRITE
(Register STATUS)
Program registers only after
confirming RDY_TO_WRITE = 1
Figure 12. Timing Diagram Representing the States of the CONFIG_MODE and RDY_TO_WRITE Bits for
an I2C Write Handshake
7.3.6.1 Selectable I2C Address (LDC2112 Only)
The LDC2112 provides an I2C address select pin, ADDR. Connecting this pin to ground will set the LDC2112 I2C
address to 0x2A. Connecting ADDR to VDD will set the LDC2112 I2C address to 0x2B.
The LDC2114 has a fixed I2C address of 0x2A.
12
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Feature Description (continued)
7.3.6.2 I2C Interface Specifications
The maximum speed of the I2C interface is 400 kHz. This sequence uses the standard I2C 7-bit slave address
followed by an 8-bit pointer to set the register address. For both write and read, the address pointer will autoincrement as long as the master acknowledges.
1
9
1
9
SCL
SDA
A6
A5
A4
A3
A2
A1
A0
R/W
D7
Start by
Master
D6
D5
D4
D3
D2
D1
D0
Ack
by
Slave
Ack
by
Slave
Frame 1
Serial Bus Address Byte
from Master
Frame 2
Slave Register Address
1
9
SCL
(continued)
SDA
(continued)
D7
D6
D5
D4
D3
D2
D1
D0
Stop by
Master
Ack
by
Slave
Frame 3
Data Byte
Figure 13. I2C Sequence of Writing a Single Register
1
9
1
9
SCL
SDA
A6
A5
A4
A3
A2
A1
A0
R/W
Start by
Master
D7
D6
D5
D4
D3
D2
D1
D0
Ack
by
Slave
Ack
by
Slave
Frame 1
Serial Bus Address Byte
from Master
Frame 2
Slave Register Address (ADDR) from
Master
1
9
1
9
SCL
(continued)
SDA
(continued)
D7
D6
D5
D4
D3
D2
D1
D7
D0
D6
D5
D4
D3
D2
Ack
by
Slave
D1
D0
Ack
by
Slave
Frame 3
Data Byte to
Register ADDR
Frame 4
Data Byte to
Register ADDR+1
1
9
SCL
(continued)
SDA
(continued)
D7
D6
D5
D4
D3
D2
D1
D0
Ack
by
Slave
Stop by
Master
Frame N+3
Data Byte to Register
ADDR+N
Figure 14. I2C Sequence of Writing Consecutive Registers
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Feature Description (continued)
1
9
1
9
SCL
SDA
A6
A5
A4
A3
A2
A1
A0
R/W
D7
D6
D5
D4
D3
D2
D1
D0
Ack
by
Slave
Start by
Master
Ack
by
Slave
Frame 1
Serial Bus Address Byte
from Master
Frame 2
Slave Register Address from Master
1
1
9
9
SCL
(continued)
SDA
(continued)
A6
A5
A4
A3
A2
A1
A0
D7
R/W
D6
D5
D4
D3
D2
D1
D0
No Ack
by
Master
Ack
by
Slave
Repeat
Start by
Master
Frame 3
Serial Bus Address Byte
from Master
Stop
by
Master
Frame 4
Data Byte from Slave
Figure 15. I2C Sequence of Reading a Single Register
1
9
1
9
SCL
SDA
A6
A5
A4
A3
A2
A1
A0
R/W
Start by
Master
D7
D6
D5
D4
D3
D2
D1
D0
Ack
by
Slave
Ack
by
Slave
Frame 1
Serial Bus Address Byte
from Master
Frame 2
Slave Register Address (ADDR) from
Master
1
9
1
9
SCL
(continued)
SDA
(continued)
A6
A5
A4
A3
A2
A1
A0
D7
R/W
Repeat
Start by
Master
D6
D5
D4
D3
D2
D1
D0
Ack
by
Master
Ack
by
Slave
Frame 3
Serial Bus Address Byte
from Master
Frame 4
Data Byte from Slave Register ADDR
1
9
1
9
SCL
(continued)
SDA
(continued)
D7
D6
D5
D4
D3
D2
D1
D7
D0
D6
D5
D4
D3
D2
D1
No Ack
by
Master
Ack
by
Master
Frame 5
Data Byte from Slave Register ADDR+1
D0
Stop
by
Master
Frame N+4
Data Byte from Slave Register
ADDR+N
Figure 16. I2C Sequence of Reading Consecutive Registers
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Feature Description (continued)
7.3.6.3 I2C Bus Control
The LDC2112/LDC2114 cannot drive the I2C clock (SCL), i.e. it does not support clock stretching. In the unlikely
event where the SCL is stuck LOW, power cycle any device that is holding the SCL to activate its internal PowerOn Reset (POR) circuit. If the LDC is connected to the same power supply as that device, there will be about 66
ms set-up time before the LDC becomes active again. For more information, refer to Defining Power-On Timing.
If the data line (SDA) is stuck LOW, the I2C master should send nine clock pulses. The device that is holding the
bus LOW should release it sometime within those nine clocks. If not, then power cycle to clear the bus.
The LDC2112/LDC2114 has built-in monitors to check that the device is currently working. In the unlikely event
of a device fault, the device state will be reset internally, and all the registers will be reset with default settings.
For system robustness, it is recommended to check the value of a modified register periodically to monitor the
device status and reload the register settings if needed.
7.4 Device Functional Modes
The LDC2112/LDC2114 supports two power modes of operation, a Normal Power Mode for active sampling at
10, 20, 40, or 80 SPS, and a Low Power Mode for reduced current consumption at 0.625, 1.25, 2.5, or 5 SPS.
Refer to Configuring Button Scan Rate for details.
7.4.1 Normal Power Mode
When the LPWRB input pin is set to VDD, all enabled channels operate in Normal Power Mode. Each channel
can be enabled independently through Register EN (Address 0x0C). For the electrical specification of Normal
Power Mode Scan Rate, refer to Electrical Characteristics.
7.4.2 Low Power Mode
When the LPWRB input pin is set to Ground, only the low-power-enabled channels are active. Each channel can
be enabled independently to operate in Low Power Mode through Register EN (Address 0x0C). For a channel to
operate in the Low Power Mode, both the LPENn and ENn bits (n is the channel index) must be set to 1. The
Low Power Mode allows for energy-saving monitoring of button activity. In this mode, the device is in an inactive
power-saving state for the majority of the time. Lower scan rates correspond to lower current consumption. In
addition, the individual button sampling window should be set to the lowest effective setting (this is system
dependent, but typically 0.8 to 1 ms). For the electrical specification of the configurable Low Power Mode Scan
Rate, refer to Electrical Characteristics.
If a channel is operational in both Low Power Mode and Normal Power Mode, it is recommended to toggle the
LPWRB pin only after the button associated with that channel is released.
7.4.3 Configuration Mode
Before configuring any register settings, the device must be put into the configuration mode first. Setting
CONFIG_MODE = 1 through Register RESET (Address 0x0A) stops data conversion and holds the device in
configuration mode. Any device configuration changes can then be made. The current consumption in this mode
is typically 0.3 mA. After all changes have been written, set CONFIG_MODE = 0 for normal operation. Refer to
I2C Interface for more information.
7.5 Register Maps
Registers indicated with Reserved must be written only with indicated values. Improper device operation may
occur otherwise.
Table 1. Register List
ADDRESS
NAME
DEFAULT VALUE
0x00
STATUS
0x00
DESCRIPTION
Device status
0x01
OUT
0x00
Channel output logic states
0x02
DATA0_LSB
0x00
The lower 8 bits of the Button 0 data (Two’s complement)
0x03
DATA0_MSB
0x00
The upper 4 bits of the Button 0 data (Two’s complement)
0x04
DATA1_LSB
0x00
The lower 8 bits of the Button 1 data (Two’s complement)
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Register Maps (continued)
Table 1. Register List (continued)
16
ADDRESS
NAME
DEFAULT VALUE
DESCRIPTION
0x05
DATA1_MSB
0x00
The upper 4 bits of the Button 1 data (Two’s complement)
0x06
DATA2_LSB
0x00
The lower 8 bits of the Button 2 data (Two’s complement)
0x07
DATA2_MSB
0x00
The upper 4 bits of the Button 2 data (Two’s complement)
0x08
DATA3_LSB
0x00
The lower 8 bits of the Button 3 data (Two’s complement)
0x09
DATA3_MSB
0x00
The upper 4 bits of the Button 3 data (Two’s complement)
0x0A
RESET
0x00
Reset device and register configurations
0x0B
RESERVED
0x00
Reserved. Set to 0x00
0x0C
EN
0x10 (LDC2112)
0x1F (LDC2114)
Enable channels and low power modes
0x0D
NP_SCAN_RATE
0x01
Normal Power Mode scan rate
0x0E
GAIN0
0x28
Gain for Channel 0 sensitivity adjustment
0x0F
LP_SCAN_RATE
0x02
Low Power Mode scan rate
0x10
GAIN1
0x28
Gain for Channel 1 sensitivity adjustment
0x11
INTPOL
0x01
Interrupt polarity
0x12
GAIN2
0x28
Gain for Channel 2 sensitivity adjustment
0x13
LP_BASE_INC
0x05
Low power base increment
0x14
GAIN3
0x28
Gain for Channel 3 sensitivity adjustment
0x15
NP_BASE_INC
0x03
Normal power base increment
0x16
BTPAUSE_MAXWIN
0x00
Baseline tracking pause and Max-win
0x17
LC_DIVIDER
0x03
LC oscillation frequency divider
0x18
HYST
0x08
Hysteresis for threshold
0x19
TWIST
0x00
Anti-twist
0x1A
COMMON_DEFORM
0x00
Anti-common and anti-deformation
0x1B
RESERVED
0x00
Reserved. Set to 0x00
0x1C
OPOL_DPOL
0x0F
Output polarity
0x1D
RESERVED
0x00
Reserved. Set to 0x00
0x1E
CNTSC
0x55
Counter scale
0x1F
RESERVED
0x00
Reserved. Set to 0x00
0x20
SENSOR0_CONFIG
0x04
Sensor 0 cycle count, frequency, RP range
0x21
RESERVED
0x00
Reserved. Set to 0x00
0x22
SENSOR1_CONFIG
0x04
Sensor 1 cycle count, frequency, RP range
0x23
RESERVED
0x00
Reserved. Set to 0x00
0x24
SENSOR2_CONFIG
0x04
Sensor 2 cycle count, frequency, RP range
0x25
FTF0
0x02
Sensor 0 fast tracking factor
0x26
SENSOR3_CONFIG
0x04
Sensor 3 cycle count, frequency, RP range
0x27
RESERVED
0x00
Reserved. Set to 0x00
0x28
FTF1_2
0x50
Sensors 1 and 2 fast tracking factors
0x29
RESERVED
0x00
Reserved. Set to 0x00
0x2A
RESERVED
0x00
Reserved. Set to 0x00
0x2B
FTF3
0x01
Sensor 3 fast tracking factor
0xFC
MANUFACTURER_ID_LSB
0x49
Manufacturer ID lower byte
0xFD
MANUFACTURER_ID_MSB
0x54
Manufacturer ID upper byte
0xFE
DEVICE_ID_LSB
0x01 (LDC2112)
0x00 (LDC2114)
Device ID lower byte
0xFF
DEVICE_ID_MSB
0x20
Device ID upper byte
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7.5.1 Individual Register Listings
Fields indicated with ‘Reserved’ must be written only with indicated values. Improper device operation may occur
otherwise. The R/W column indicates the Read-Write status of the corresponding field. An ‘R/W’ entry indicates
read and write capability, an ‘R’ indicates read-only, and a ‘W’ indicates write-only.
Before reading the OUT (Address 0x01) or channel DATAn registers (n = 0, 1, 2, or 3, Addresses 0x02 through
0x09), the user should always read the STATUS register (Address 0x00) first to lock the data. The
LDC2112/LDC2114 supports burst mode with auto-incrementing register addresses.
Table 2. Register STATUS – Address 0x00
BIT
FIELD
TYPE
RESET
DESCRIPTION
7
OUT_STATUS
R
0
Output Status
Logic OR of output bits from Register OUT (Address 0x01). This field
is cleared by reading this register.
6
CHIP_READY
R
1
Chip Ready Status
b0: Chip not ready after internal reset.
b1: Chip ready after internal reset.
5
RDY_TO_WRITE
R
0
Ready to Write
Indicates if registers are ready to be written. See I2C Interface for
more information.
b0: Registers not ready.
b1: Registers ready.
4
MAXOUT
R
0
Maximum Output Code
Indicates if any channel output data reaches the maximum value
(+0x7FF or –0x800). Cleared by a read of the status register.
b0: No maximum output code.
b1: Maximum output code.
3
FSM_WD
R
0
Finite-State Machine Watchdog Error
Reports an error has occurred and conversions have been halted.
Cleared by a read of the status register.
b0: No error in finite-state machine.
b1: Error in finite-state machine.
2
LC_WD
R
0
LC Sensor Watchdog Error
Reports an error when any LC oscillator fails to start. Cleared by a
read of the status register.
b0: No error in LC oscillator initialization.
b1: Error in LC oscillator initialization.
1
TIMEOUT
R
0
Button Timeout
Reports when any button is asserted for more than 50 seconds.
Cleared by a read of the status register.
b0: no timeout error.
b1: timeout error.
0
REGISTER_FLAG
R
0
Register Integrity Flag
Reports if any register's value has an unexpected change. Cleared by
a read of the status register.
b0: No unexpected register change.
b1: Unexpected register change.
Table 3. Register OUT – Address 0x01
BIT
FIELD
TYPE
RESET
DESCRIPTION
7:4
RESERVED
R
0000
Reserved. Set to b0000.
3
OUT3
R
0
Output Logic State for Channel 3 (LDC2114 Only)
b0: No button press detected on Channel 3.
b1: Button press detected on Channel 3.
2
OUT2
R
0
Output Logic State for Channel 2 (LDC2114 Only)
b0: No button press detected on Channel 2.
b1: Button press detected on Channel 2.
1
OUT1
R
0
Output Logic State for Channel 1
b0: No button press detected on Channel 1.
b1: Button press detected on Channel 1.
0
OUT0
R
0
Output Logic State for Channel 0
b0: No button press detected on Channel 0.
b1: Button press detected on Channel 0.
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Table 4. Register DATA0_LSB – Address 0x02
BIT
FIELD
TYPE
RESET
7:0
DATA0[7:0]
R
0000 0000 The lower 8 bits of Channel 0 data (Two’s complement).
DESCRIPTION
Table 5. Register DATA0_MSB – Address 0x03
BIT
FIELD
TYPE
RESET
DESCRIPTION
7:4
RESERVED
R
0000
Reserved.
3:0
DATA0[11:8]
R
0000
The upper 4 bits of Channel 0 data (Two’s complement).
BIT
FIELD
7:0
DATA1[7:0]
Table 6. Register DATA1_LSB – Address 0x04
TYPE
RESET
DESCRIPTION
R
0000 0000 The lower 8 bits of Channel 1 data (Two’s complement).
Table 7. Register DATA1_MSB – Address 0x05
BIT
FIELD
TYPE
RESET
DESCRIPTION
7:4
RESERVED
R
0000
Reserved.
3:0
DATA1[11:8]
R
0000
The upper 4 bits of Channel 1 data (Two’s complement).
Table 8. Register DATA2_LSB – Address 0x06
BIT
FIELD
TYPE
RESET
7:0
DATA2[7:0]
R
0000 0000 The lower 8 bits of Channel 2 data (Two’s complement).
(LDC2114 Only)
DESCRIPTION
Table 9. Register DATA2_MSB – Address 0x07
BIT
FIELD
TYPE
RESET
DESCRIPTION
7:4
RESERVED
R
0000
Reserved.
3:0
DATA2[11:8]
R
0000
The upper 4 bits of Channel 2 data (Two’s complement).
(LDC2114 Only)
Table 10. Register DATA3_LSB – Address 0x08
BIT
FIELD
TYPE
RESET
7:0
DATA3[7:0]
R
0000 0000 The lower 8 bits of Channel 3 data (Two’s complement).
(LDC2114 Only)
DESCRIPTION
Table 11. Register DATA3_MSB – Address 0x09
BIT
FIELD
TYPE
RESET
DESCRIPTION
7:4
RESERVED
R
0000
Reserved.
3:0
DATA3[11:8]
R
0000
The upper 4 bits of Channel 3 data (Two’s complement).
(LDC2114 Only)
Table 12. Register RESET – Address 0x0A
BIT
FIELD
TYPE
RESET
DESCRIPTION
7:5
RESERVED
R/W
000
Reserved. Set to b000.
FULL_RESET
R/W
0
Device Reset
b0: Normal operation.
b1: Resets the device and register configurations. All registers will be
returned to default values. Normal operation will not resume until
STATUS:CHIP_READY = 1.
RESERVED
R/W
000
Reserved. Set to b000.
CONFIG_MODE
R/W
0
Configuration Mode
b0: Normal operation.
b1: Holds the device in configuration mode (no data conversion), but
maintains current register configurations. Any device configuration
changes should be made with this bit set to 1. After all configuration
changes have been written, set this bit to 0 for normal operation.
4
3:1
0
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Table 13. Register EN – Address 0x0C
BIT
FIELD
TYPE
RESET
DESCRIPTION
7
LPEN3
R/W
0
Channel 3 Low-Power-Enable (LDC2114 Only)
b0: Disable Channel 3 in Low Power Mode.
b1: Enable Channel 3 in Low Power Mode. EN3 must also be set
to 1.
6
LPEN2
R/W
0
Channel 2 Low-Power-Enable (LDC2114 Only)
b0: Disable Channel 2 in Low Power Mode.
b1: Enable Channel 2 in Low Power Mode. EN2 must also be set
to 1.
5
LPEN1
R/W
0
Channel 1 Low-Power-Enable
b0: Disable Channel 1 in Low Power Mode.
b1: Enable Channel 1 in Low Power Mode. EN1 must also be set
to 1.
4
LPEN0
R/W
1
Channel 0 Low-Power-Enable
b0: Disable Channel 0 in Low Power Mode.
b1: Enable Channel 0 in Low Power Mode. EN0 must also be set
to 1.
3
EN3 (LDC2114)
R/W
1
Channel 3 Enable (LDC2114 Only)
b0: Disable Channel 3.
b1: Enable Channel 3.
RESERVED (LDC2112)
R
0
Reserved. Set to b0. (LDC2112 Only)
EN2 (LDC2114)
R/W
1
Channel 2 Enable (LDC2114 Only)
b0: Disable Channel 2.
b1: Enable Channel 2.
RESERVED (LDC2112)
R
0
Reserved. Set to b0. (LDC2112 Only)
EN1 (LDC2114)
R/W
1
Channel 1 Enable (LDC2114 Only)
b0: Disable Channel 1.
b1: Enable Channel 1.
RESERVED (LDC2112)
R
0
Reserved. Set to b0. (LDC2112 Only)
For LDC2112, Channel 1 is always enabled.
EN0 (LDC2114)
R/W
1
Channel 0 Enable (LDC2114 Only)
b0: Disable Channel 0.
b1: Enable Channel 0.
RESERVED (LDC2112)
R
0
Reserved. Set to b0. (LDC2112 Only)
For LDC2112, Channel 0 is always enabled.
2
1
0
Table 14. Register NP_SCAN_RATE – Address 0x0D
BIT
FIELD
TYPE
RESET
DESCRIPTION
7:2
RESERVED
R/W
b00 0000
Reserved. Set to b00 0000.
1:0
NPSR
R/W
01
Normal Power Mode Scan Rate
Refer to Configuring Button Scan Rate for more information.
b00: 80 SPS
b01: 40 SPS (Default)
b10: 20 SPS
b11: 10 SPS
BIT
FIELD
TYPE
RESET
DESCRIPTION
7:6
RESERVED
R/W
00
Reserved. Set to b00.
5:0
GAIN0
R/W
b10 1000
Gain for Channel 0
Refer to the Gain Table for detailed configuration.
Table 15. Register GAIN0 – Address 0x0E
Table 16. Register LP_SCAN_RATE – Address 0x0F
BIT
FIELD
TYPE
RESET
DESCRIPTION
7:2
RESERVED
R/W
b00 0000
Reserved. Set to b00 0000.
1:0
LPSR
R/W
10
Low Power Mode Scan Rate
Refer to Configuring Button Scan Rate for more information.
b00: 5 SPS
b01: 2.5 SPS
b10: 1.25 SPS (Default)
b11: 0.625 SPS
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Table 17. Register GAIN1 – Address 0x10
BIT
FIELD
TYPE
RESET
DESCRIPTION
7:6
RESERVED
R/W
00
Reserved. Set to b00.
5:0
GAIN1
R/W
b10 1000
Gain for Channel 1
Refer to the Gain Table for detailed configuration.
Table 18. Register INTPOL – Address 0x11
BIT
FIELD
TYPE
RESET
DESCRIPTION
7:3
RESERVED
R/W
b0 0000
Reserved. Set to b0 0000.
INTPOL
R/W
0
Interrupt Polarity
b0: Set INTB pin polarity to active low.
b1: Set INTB pin polarity to active high.
RESERVED
R/W
01
Reserved. Set to b01.
2
1:0
Table 19. Register GAIN2 – Address 0x12
BIT
FIELD
TYPE
RESET
DESCRIPTION
7:6
RESERVED
R/W
00
Reserved. Set to b00.
5:0
GAIN2
R/W
b10 1000
Gain for Channel 2 (LDC2114 Only)
Refer to the Gain Table for detailed configuration.
Table 20. Register LP_BASE_INC – Address 0x13
BIT
FIELD
TYPE
RESET
DESCRIPTION
7:3
RESERVED
R/W
b0 0000
Reserved. Set to b0 0000.
2:0
LPBI
R/W
b101
Baseline Tracking Increment in Low Power Mode
Refer to Tracking Baseline for more information. Valid values:
[b000:b111].
b101: LPBI = 5 (Default)
Table 21. Register GAIN3 – Address 0x14
BIT
FIELD
TYPE
RESET
DESCRIPTION
7:6
RESERVED
R/W
00
Reserved. Set to b00.
5:0
GAIN3
R/W
b10 1000
Gain for Channel 3 (LDC2114 Only)
Refer to the Gain Table for detailed configuration.
Table 22. Register NP_BASE_INC – Address 0x15
BIT
FIELD
TYPE
RESET
DESCRIPTION
7:3
RESERVED
R/W
b0 0000
Reserved. Set to b0 0000.
2:0
NPBI
R/W
b011
Baseline Tracking Increment in Normal Power Mode
Refer to Tracking Baseline for more information. Valid values:
[b000:b111].
b011: NPBI = 3 (Default)
Table 23. Register BTPAUSE_MAXWIN – Address 0x16
BIT
20
FIELD
TYPE
RESET
DESCRIPTION
7
BTPAUSE3
R/W
0
Baseline Tracking Pause for Channel 3 (LDC2114 Only)
Pauses baseline tracking for Channel 3 when OUT3 is asserted.
Refer to Tracking Baseline for more information.
b0: Normal baseline tracking for Channel 3 regardless of OUT3
status. (Default)
b1: Pauses baseline tracking for Channel 3 when OUT3 is
asserted.
6
BTPAUSE2
R/W
0
Baseline Tracking Pause for Channel 2 (LDC2114 Only)
Pauses baseline tracking for Channel 2 when OUT2 is asserted.
Refer to Tracking Baseline for more information.
b0: Normal baseline tracking for Channel 2 regardless of OUT2
status. (Default)
b1: Pauses baseline tracking for Channel 2 when OUT2 is
asserted.
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Table 23. Register BTPAUSE_MAXWIN – Address 0x16 (continued)
BIT
FIELD
TYPE
RESET
DESCRIPTION
5
BTPAUSE1
R/W
0
Baseline Tracking Pause for Channel 1
Pauses baseline tracking for Channel 1 when OUT1 is asserted.
Refer to Tracking Baseline for more information.
b0: Normal baseline tracking for Channel 1 regardless of OUT1
status. (Default)
b1: Pauses baseline tracking for Channel 1 when OUT1 is
asserted.
4
BTPAUSE0
R/W
0
Baseline Tracking Pause for Channel 0
Pauses baseline tracking for Channel 0 when OUT0 is asserted.
Refer to Tracking Baseline for more information.
b0: Normal baseline tracking for Channel 0 regardless of OUT0
status. (Default)
b1: Pauses baseline tracking for Channel 0 when OUT0 is
asserted.
3
MAXWIN3
R/W
0
Max-Win Algorithm Setting for Channel 3 (LDC2114 Only)
Refer to Resolving Simultaneous Button Presses (Max-Win) for
more information.
b0: Exclude Channel 3 from the max-win group. (Default)
b1: Include Channel 3 in the max-win group.
2
MAXWIN2
R/W
0
Max-Win Algorithm Setting for Channel 2 (LDC2114 Only)
Refer to Resolving Simultaneous Button Presses (Max-Win) for
more information.
b0: Exclude Channel 2 from the max-win group. (Default)
b1: Include Channel 2 in the max-win group.
1
MAXWIN1
R/W
0
Max-Win Algorithm Setting for Channel 1
Refer to Resolving Simultaneous Button Presses (Max-Win) for
more information.
b0: Exclude Channel 1 from the max-win group. (Default)
b1: Include Channel 1 in the max-win group.
0
MAXWIN0
R/W
0
Max-Win Algorithm Setting for Channel 0
Refer to Resolving Simultaneous Button Presses (Max-Win) for
more information.
b0: Exclude Channel 0 from the max-win group. (Default)
b1: Include Channel 0 in the max-win group.
Table 24. Register LC_DIVIDER – Address 0x17
BIT
FIELD
TYPE
RESET
DESCRIPTION
7:3
RESERVED
R/W
b0 0000
Reserved. Set to b0 0000.
2:0
LCDIV
R/W
b011
LC Oscillation Frequency Divider
The frequency divider sets the button sampling window in
conjunction with SENCYCn. Valid values: [b000:b111].
Refer to Programming Button Sampling Window for more
information.
b011: LCDIV = 3 (Default)
BIT
FIELD
TYPE
RESET
DESCRIPTION
7:4
RESERVED
R/W
b0000
Reserved. Set to b0000.
3:0
HYST
R/W
b1000
Hysteresis
Defines the hysteresis for button triggering threshold. Valid values:
[b0000:b1111].
Hysteresis = HYST × 4
b1000: HYST = 8, Hysteresis = 32 (Default)
Refer to Setting Button Triggering Threshold for more information.
Table 25. Register HYST – Address 0x18
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Table 26. Register TWIST – Address 0x19
BIT
FIELD
TYPE
RESET
DESCRIPTION
7:3
RESERVED
R/W
b0 0000
Reserved. Set to b0 0000.
2:0
ANTITWIST
R/W
b000
Anti-Twist
When set to 0, the anti-twist algorithm is not enabled.
When greater than 0, all buttons are enabled for the anti-twist
algorithm. The validation of all buttons is void if any button’s DATA
is negative by a threshold.
Anti-twist Threshold = ANTITWIST × 4.
Refer to Overcoming Case Twisting (Anti-Twist) for more
information.
Table 27. Register COMMON_DEFORM – Address 0x1A
BIT
FIELD
TYPE
RESET
DESCRIPTION
7
ANTICOM3
R/W
0
Anti-Common Algorithm Setting for Channel 3 (LDC2114 Only)
Refer to Eliminating Common-Mode Change (Anti-Common) for
more information.
b0: Exclude Channel 3 from the anti-common group. (Default)
b1: Include Channel 3 in the anti-common group.
6
ANTICOM2
R/W
0
Anti-Common Algorithm Setting for Channel 2 (LDC2114 Only)
Refer to Eliminating Common-Mode Change (Anti-Common) for
more information.
b0: Exclude Channel 2 from the anti-common group. (Default)
b1: Include Channel 2 in the anti-common group.
5
ANTICOM1
R/W
0
Anti-Common Algorithm Setting for Channel 1
Refer to Eliminating Common-Mode Change (Anti-Common) for
more information.
b0: Exclude Channel 1 from the anti-common group. (Default)
b1: Include Channel 1 in the anti-common group.
4
ANTICOM0
R/W
0
Anti-Common Algorithm Setting for Channel 0
Refer to Eliminating Common-Mode Change (Anti-Common) for
more information.
b0: Exclude Channel 0 from the anti-common group. (Default)
b1: Include Channel 0 in the anti-common group.
3
ANTIDFORM3
R/W
0
Anti-Deform Algorithm Setting for Channel 3 (LDC2114 Only)
Refer to Mitigating Metal Deformation (Anti-Deform) for more
information.
b0: Exclude Channel 3 from the anti-deform group. (Default)
b1: Include Channel 3 in the anti-deform group.
2
ANTIDFORM2
R/W
0
Anti-Deform Algorithm Setting for Channel 2 (LDC2114 Only)
Refer to Mitigating Metal Deformation (Anti-Deform) for more
information.
b0: Exclude Channel 2 from the anti-deform group. (Default)
b1: Include Channel 2 in the anti-deform group.
1
ANTIDFORM1
R/W
0
Anti-Deform Algorithm Setting for Channel 1
Refer to Mitigating Metal Deformation (Anti-Deform) for more
information.
b0: Exclude Channel 1 from the anti-deform group. (Default)
b1: Include Channel 1 in the anti-deform group.
0
ANTIDFORM0
R/W
0
Anti-Deform Algorithm Setting for Channel 0
Refer to Mitigating Metal Deformation (Anti-Deform) for more
information.
b0: Exclude Channel 0 from the anti-deform group. (Default)
b1: Include Channel 0 in the anti-deform group.
Table 28. Register OPOL_DPOL – Address 0x1C
22
BIT
FIELD
TYPE
RESET
DESCRIPTION
7
OPOL3
R/W
0
Output Polarity for OUT3 Pin (LDC2114 Only)
b0: Active low (Default)
b1: Active high
6
OPOL2
R/W
0
Output Polarity for OUT2 Pin (LDC2114 Only)
b0: Active low (Default)
b1: Active high
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Table 28. Register OPOL_DPOL – Address 0x1C (continued)
BIT
FIELD
TYPE
RESET
DESCRIPTION
5
OPOL1
R/W
0
Output Polarity for OUT1 Pin
b0: Active low (Default)
b1: Active high
4
OPOL0
R/W
0
Output Polarity for OUT0 Pin
b0: Active low (Default)
b1: Active high
3
DPOL3
R/W
1
Data Polarity for Channel 3 (LDC2114 Only)
b0: DATA3 decreases as fSENSOR3 increases.
b1: DATA3 increases as fSENSOR3 increases. (Default)
2
DPOL2
R/W
1
Data Polarity for Channel 2 (LDC2114 Only)
b0: DATA2 decreases as fSENSOR2 increases.
b1: DATA2 increases as fSENSOR2 increases. (Default)
1
DPOL1
R/W
1
Data Polarity for Channel 1
b0: DATA1 decreases as fSENSOR1 increases.
b1: DATA1 increases as fSENSOR1 increases. (Default)
0
DPOL0
R/W
1
Data Polarity for Channel 0
b0: DATA0 decreases as fSENSOR0 increases.
b1: DATA0 increases as fSENSOR0 increases. (Default)
Table 29. Register CNTSC – Address 0x1E (1)
(1)
BIT
FIELD
TYPE
RESET
DESCRIPTION
7:6
CNTSC3
R/W
01
Counter Scale for Channel 3 (LDC2114 Only)
Refer to Scaling Frequency Counter Output for more information.
b00: CNTSC3 = 0
b01: CNTSC3 = 1 (Default)
b10: CNTSC3 = 2
b11: CNTSC3 = 3
5:4
CNTSC2
R/W
01
Counter Scale for Channel 2 (LDC2114 Only)
Refer to Scaling Frequency Counter Output for more information.
b00: CNTSC2 = 0
b01: CNTSC2 = 1 (Default)
b10: CNTSC2 = 2
b11: CNTSC2 = 3
3:2
CNTSC1
R/W
01
Counter Scale for Channel 1
Refer to Scaling Frequency Counter Output for more information.
b00: CNTSC1 = 0
b01: CNTSC1 = 1 (Default)
b10: CNTSC1 = 2
b11: CNTSC1 = 3
1:0
CNTSC0
R/W
01
Counter Scale for Channel 0
Refer to Scaling Frequency Counter Output for more information.
b00: CNTSC0 = 0
b01: CNTSC0 = 1 (Default)
b10: CNTSC0 = 2
b11: CNTSC0 = 3
The Counter Scale sets a scaling factor for the internal frequency counter to avoid data overflow. The formula for calculating counter
scale is CNTSCn = LCDIV + ceiling(log2 (0.0861×(SENCYCn+1)/fSENSORn)), n = 0, 1, 2, or 3, where LCDIV and SENCYCn are the
exponential and linear scalers that set the number of sensor oscillation cycles, fSENSORn is the sensor frequency in MHz.
Table 30. Register SENSOR0_CONFIG – Address 0x20
BIT
7
FIELD
TYPE
RESET
DESCRIPTION
RP0
R/W
0
Channel 0 Sensor RP Range Select
Set based on the actual sensor RP physical parameter.
RP = 1/RS × L/C
where RS is the AC series resistance in the LC resonator, L is the
inductance, and C is the capacitance.
Refer to Designing Sensor Parameters for more information.
b0: 350Ω ≤ RP ≤ 4kΩ (Default)
b1: 800Ω ≤ RP ≤ 10kΩ
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Table 30. Register SENSOR0_CONFIG – Address 0x20 (continued)
BIT
FIELD
TYPE
RESET
DESCRIPTION
6:5
FREQ0
R/W
00
Channel 0 Sensor Frequency Range Select
Refer to Designing Sensor Parameters for more information.
b00: 1 MHz to 3.3 MHz (Default)
b01: 3.3 MHz to 10 MHz
b10: 10 MHz to 30 MHz
b11: Reserved
4:0
SENCYC0
R/W
b0 0100
Channel 0 Sensor Cycle Count
SENCYC0 sets the Channel 0 button sampling window in
conjunction with LCDIV.
Refer to Programming Button Sampling Window for more
information.
Table 31. Register SENSOR1_CONFIG – Address 0x22
BIT
FIELD
TYPE
RESET
DESCRIPTION
RP1
R/W
0
Channel 1 Sensor RP Range Select
Set based on the actual sensor RP physical parameter.
RP = 1/RS × L/C
where RS is the AC series resistance in the LC resonator, L is the
inductance, and C is the capacitance.
Refer to Designing Sensor Parameters for more information.
b0: 350 Ω ≤ RP ≤ 4 kΩ (Default)
b1: 800 Ω ≤ RP ≤ 10 kΩ
6:5
FREQ1
R/W
00
Channel 1 Sensor Frequency Range Select
Refer to Designing Sensor Parameters for more information.
b00: 1 MHz to 3.3 MHz (Default)
b01: 3.3 MHz to 10 MHz
b10: 10 MHz to 30 MHz
b11: Reserved
4:0
SENCYC1
R/W
b0 0100
Channel 1 Sensor Cycle Count
SENCYC1 sets the Channel 1 button sampling window in
conjunction with LCDIV.
Refer to Programming Button Sampling Window for more
information.
7
Table 32. Register SENSOR2_CONFIG – Address 0x24
BIT
FIELD
TYPE
RESET
DESCRIPTION
RP2
R/W
0
Channel 2 Sensor RP Range Select (LDC2114 Only)
Set based on the actual sensor RP physical parameter.
RP = 1/RS × L/C
where RS is the AC series resistance in the LC resonator, L is the
inductance, and C is the capacitance.
Refer to Designing Sensor Parameters for more information.
b0: 350 Ω ≤ RP ≤ 4 kΩ (Default)
b1: 800 Ω ≤ RP ≤ 10 kΩ
6:5
FREQ2
R/W
00
Channel 2 Sensor Frequency Range Select (LDC2114 Only)
Refer to Designing Sensor Parameters for more information.
b00: 1 MHz to 3.3 MHz (Default)
b01: 3.3 MHz to 10 MHz
b10: 10 MHz to 30 MHz
b11: Reserved
4:0
SENCYC2
R/W
b0 0100
Channel 2 Sensor Cycle Count (LDC2114 Only)
SENCYC2 sets the Channel 2 button sampling window in
conjunction with LCDIV.
Refer to Programming Button Sampling Window for more
information.
7
24
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Table 33. Register FTF0 – Address 0x25
BIT
FIELD
TYPE
RESET
DESCRIPTION
7:3
RESERVED
R/W
b0 0000
Reserved. Set to b0 0000.
2:1
FTF0
R/W
01
Fast Tracking Factor for Channel 0
Defines baseline tracking speed for negative values of DATA0.
Refer to Tracking Baseline for more information.
b00: FTF0 = 0
b01: FTF0 = 1 (Default)
b10: FTF0 = 2
b11: FTF0 = 3
RESERVED
R/W
0
Reserved. Set to b0.
0
Table 34. Register SENSOR3_CONFIG – Address 0x26
BIT
FIELD
TYPE
RESET
DESCRIPTION
RP3
R/W
0
Channel 3 Sensor RP Range Select (LDC2114 Only)
Set based on the actual sensor RP physical parameter.
RP = 1/RS × L/C
where RS is the AC series resistance in the LC resonator, L is the
inductance, and C is the capacitance.
Refer to Designing Sensor Parameters for more information.
b0: 350 Ω ≤ RP ≤ 4 kΩ (Default)
b1: 800 Ω ≤ RP ≤ 10 kΩ
6:5
FREQ3
R/W
00
Channel 3 Sensor Frequency Range Select (LDC2114 Only)
Refer to Designing Sensor Parameters for more information.
b00: 1 MHz to 3.3 MHz (Default)
b01: 3.3 MHz to 10 MHz
b10: 10 MHz to 30 MHz
b11: Reserved
4:0
SENCYC3
R/W
b0 0100
Channel 3 Sensor Cycle Count (LDC2114 Only)
SENCYC3 sets the Channel 3 button sampling window in
conjunction with LCDIV.
Refer to Programming Button Sampling Window for more
information.
7
Table 35. Register FTF1_2 – Address 0x28
BIT
FIELD
TYPE
RESET
DESCRIPTION
7:6
FTF2
R/W
01
Fast Tracking Factor for Channel 2 (LDC2114 Only)
Defines baseline tracking speed for negative values of DATA2.
Refer to Tracking Baseline for more information.
b00: FTF2 = 0
b01: FTF2 = 1 (Default)
b10: FTF2 = 2
b11: FTF2 = 3
5:4
FTF1
R/W
01
Fast Tracking Factor for Channel 1
Defines baseline tracking speed for negative values of DATA1.
Refer to Tracking Baseline for more information.
b00: FTF1 = 0
b01: FTF1 = 1 (Default)
b10: FTF1 = 2
b11: FTF1 = 3
3:0
RESERVED
R/W
b0000
Reserved. Set to b0000.
Table 36. Register FTF3 – Address 0x2B
BIT
FIELD
TYPE
RESET
DESCRIPTION
7:2
RESERVED
R/W
b00 0000
Reserved. Set to b00 0000.
1:0
FTF3
R/W
01
Fast Tracking Factor for Channel 3 (LDC2114 Only)
Defines baseline tracking speed for negative values of DATA3.
Refer to Tracking Baseline for more information.
b00: FTF3 = 0
b01: FTF3 = 1 (Default)
b10: FTF3 = 2
b11: FTF3 = 3
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Table 37. Register MANUFACTURER_ID_LSB – Address 0xFC
BIT
FIELD
TYPE
RESET
DESCRIPTION
7:0
MANUFACTURER_ID [7:0]
R
0x49
Manufacturer ID [7:0]
Table 38. Register MANUFACTURER_ID_MSB – Address 0xFD
BIT
FIELD
7:0
MANUFACTURER_ID [15:8] R
TYPE
RESET
DESCRIPTION
0x54
Manufacturer ID [15:8]
Table 39. Register DEVICE_ID_LSB – Address 0xFE
BIT
FIELD
TYPE
RESET
DESCRIPTION
7:0
DEVICE_ID [7:0]
R
0x01
(LDC2112)
Device ID [7:0]
0x00
(LDC2114)
Table 40. Register DEVICE_ID_MSB – Address 0xFF
26
BIT
FIELD
TYPE
RESET
DESCRIPTION
7:0
DEVICE_ID [15:8]
R
0x20
Device ID [15:8]
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7.5.1.1 Gain Table for Registers GAIN0, GAIN1, GAIN2, and GAIN3
Table 41. GAINn Bit Values in Decimal and Corresponding Normalized Gain Factors
BIT VALUE IN DECIMAL
NORMALIZED GAIN FACTOR
BIT VALUE IN DECIMAL
NORMALIZED GAIN FACTOR
0
1.0
32
16
1
1.0625
33
17
2
1.1875
34
19
3
1.3125
35
21
4
1.4375
36
23
5
1.5625
37
25
6
1.6875
38
27
7
1.8125
39
29
8
2.0
40
32
9
2.125
41
34
10
2.375
42
38
11
2.625
43
42
12
2.875
44
46
13
3.125
45
50
14
3.375
46
54
15
3.625
47
58
16
4.0
48
64
17
4.25
49
68
18
4.75
50
76
19
5.25
51
84
20
5.75
52
92
21
6.25
53
100
22
6.75
54
108
23
7.25
55
116
24
8.0
56
128
25
8.5
57
136
26
9.5
58
152
27
10.5
59
168
28
11.5
60
184
29
12.5
61
200
30
13.5
62
216
31
14.5
63
232
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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
The LDC2112/LDC2114 supports multiple buttons. Each button can be configured in various ways for optimal
operation.
8.1.1 Theory of Operation
An AC current flowing through an inductor will generate an AC magnetic field. If a conductive material, such as a
metal object, is in close proximity to the inductor, the magnetic field will induce circulating eddy currents on the
surface of the conductor. The eddy currents are a function of the distance, size, and composition of the
conductor. If the conductor is deflected toward the inductor as shown in Figure 17, more eddy currents will be
generated.
Figure 17. Metal Deflection
The eddy currents create their own magnetic field, which opposes the original field generated by the inductor.
This effect reduces the effective inductance of the system, resulting in an increase in sensor frequency.
Figure 18 shows the inductance and frequency response of an example sensor with a diameter of 14 mm. As the
sensitivity of an inductive sensor increases with closer targets, the conductive plate should be placed quite close
to the sensor—typically 10% of the sensor diameter for circular coils. For rectangular or race-track-shaped coils,
the target to sensor distance should typically be less than 10% of the shorter side of the coil.
28
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Application Information (continued)
7
5
4.75
6
4.5
5.5
4.25
Sensor Inductance (μH)
4
Sensor Frequency (MHz)
5
4.5
3.75
4
3.5
3.5
Sensor Frequency (MHz)
Sensor Inductance (μH)
6.5
3.25
3
0
1
2
3
4
5
6
7
8
Distance between Sensor and Target (mm)
9
3
10
D010
Figure 18. Sensor Inductance and Frequency vs Target Distance. Sensor Diameter = 14 mm
The output DATAn registers (Addresses 0x02 through 0x09) of the LDC2112/LDC2114 contain the processed
values of the changes in sensor frequencies.
8.1.2 Designing Sensor Parameters
Each inductive touch button uses an LC resonator sensor, as illustrated in Figure 19, where L is the inductor, C
is the capacitor, and RS is the AC series resistance of the sensor at the frequency of operation. The key
parameters of the LC sensor include frequency, effective parallel resistance RP, and quality factor Q. These
parameters must be within the ranges as specified in the Sensor section of the Electrical Characteristics table.
Note that the effective RP and Q changes when the conductive target is in place.
L
C
RS
Figure 19. LC Resonator
The LC sensor frequency, as defined by the equation below, must be between 1 MHz and 30 MHz.
1
fSENSOR
2S LC
(1)
The sensor quality factor, as defined by the equation below, must be between 5 and 30.
QSENSOR
1
RS
L
C
(2)
The series resistance can be represented as an equivalent parallel resistance, RP, which is given by
L
RP
RS C
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Application Information (continued)
L
RP
C
Figure 20. Equivalent Parallel Circuit
RP can be viewed as the load on the sensor driver. This load corresponds to the current drive needed to maintain
the oscillation amplitude. RP must be between 350 Ω and 10 kΩ.
In summary, the LDC2112/LDC2114 requires that the sensor parameters are within the following ranges when
the conductive target is present:
• 1 MHz ≤ fSENSOR ≤ 30 MHz
• 5 ≤ Q ≤ 30
• 350 Ω ≤ RP ≤ 10 kΩ
8.1.3 Setting COM Pin Capacitor
The COM pin requires a bypass capacitor to ground. The capacitor should be a low ESL, low ESR type. CCOM
must be sized so that the following relationship is valid for all channels.
100 × CSENSORn / QSENSORn < CCOM < 1250 × CSENSORn / QSENSORn
(4)
The value of QSENSORn when the sensor is at the minimum target distance should be used. The maximum
acceptable value for CCOM is 20 nF. The CCOM range for a particular sensor configuration can be obtained with
the Spiral_Inductor_Designer tab of the LDC Calculations Tool.
8.1.4 Defining Power-On Timing
The low power architecture of the LDC2112/LDC2114 makes it possible for the device to be active all the time.
When not being used, the LDC2112/LDC2114 can operate in Low Power Mode with a single standby power
button, which typically consumes less than 10 µA. If additional power-saving is desired, or in the rare event
where a power-on reset becomes necessary (see I2C Interface), the output data will become ready after 50 ms
startup time, about 1 ms optional register loading time, and two sampling windows for all active channels. The
power-on timing of the LDC2112/LDC2114 is illustrated in Figure 21 below.
Only Channels 0 and 1 are enabled. Scan rate: 40 SPS.
25 ms scan cycle
25 ms scan cycle
66 ms startup time
Sampling
Sampling
VDD
IN0
IN1
Events
Power up
DATA is ready
after all active channels
finish two conversions.
66 ms startup time is
independent of scan rate.
Figure 21. Power-On Timing
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Application Information (continued)
8.1.5 Configuring Button Scan Rate
The LDC2112/LDC2114 periodically samples all active channels at the selected scan rate. The device can
operate at eight different scan rates to meet various power consumption requirements, where a lower scan rate
achieves lower power consumption. In Normal Power Mode, the scan rate can be programmed to 80, 40, 20, or
10 SPS through Register NP_SCAN_RATE (Address 0x0D). In Low Power Mode, the scan rate can be
programmed to 5, 2.5, 1.25, or 0.625 SPS through Register LP_SCAN_RATE (Address 0x0F). The mode is
selected by setting the LPWRB pin to VDD (Normal Power) or ground (Low Power). In either mode, each button
can be independently enabled through a bit in Register EN (Address 0x0C). For typical distribution of the scan
rates, refer to Figure 9.
Table 42. Button Scan Rates
SCAN RATE (SPS)
LPSR (0x0F) SETTING
NPSR (0x0D) SETTING
LPWRB PIN SETTING
0.625
b11
Not Applicable
Ground
1.25
b10
Not Applicable
Ground
2.5
b01
Not Applicable
Ground
5
b00
Not Applicable
Ground
10
Not Applicable
b11
VDD
20
Not Applicable
b10
VDD
40
Not Applicable
b01
VDD
80
Not Applicable
b00
VDD
8.1.6 Programming Button Sampling Window
The button sampling window is the actual duration per scan cycle for active data sampling of the sensor
frequency. It is programmed with the exponential parameter, LCDIV, in Register LC_DIVIDER (Address 0x17),
and the individual linear sensor cycle counter SENCYCn (n = 0, 1, 2, or 3) in Registers SENSORn_CONFIG (n =
0, 1, 2, or 3, Addresses 0x20, 0x22, 0x24, 0x26). For most touch button applications, the button sampling
window should be set to between 1 ms and 8 ms. The recommended minimum sensor conversion time is 1 ms.
Longer conversion time can be used to achieve better signal-to-noise ratio if needed. If multiple channels are
enabled, the active channels will sample sequentially, as illustrated in Figure 22.
Button Sampling Window: set by
LCDIV, SENCYCn, and fSENSORn
IN0
IN1
IN2
IN3
Scan Rate: set by NPSR,
LPSR, and LPWRB pin
Figure 22. Configurable Scan Rate and Button Sampling Window
The LDC2112/LDC2114 is designed to work with LC resonator sensors with oscillation frequencies ranging from
1 MHz to 30 MHz. The exact definition of the button sampling window is given by the equation below.
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Number of Sensor Oscillation Cycles
Sensor Frequency
Button Sampling Window
128 u SENCYCn 1 u 2LCDIV
tSAMPLE
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fSENSORn
,n
0, 1, 2, or 3
where:
•
•
•
tSAMPLE is the button sampling window in µs,
SENCYCn and LCDIV are the linear and exponential scalers that set the number of sensor oscillation cycles, and
fSENSORn is the sensor frequency in MHz.
(5)
In the equation above, LCDIV (0 to 7, default 3) is the exponential LC divider that sets the approximate ranges
for all channels, and SENCYCn (0 to 31, default 4) is the linear sensor cycle scaler that fine-tunes each
individual channel. Together they set the number of sensor oscillation cycles used to determine the button
sampling window.
For example, if the LC sensor frequency is 9.2 MHz, and it is desirable to get 1 ms button sampling window, then
this can be achieved by setting SENCYCn = 17 and LCDIV = 2.
Alternatively, from the button sampling window and sensor frequency, the LCDIV can be read off from Figure 23.
For example, 1 ms button sampling window and 9.2 MHz sensor frequency intersect at the region where LCDIV
= 2. Then SENCYCn can be calculated accordingly.
30
Maximum Sensor Frequency (MHz)
LCDIV=7
25
LCDIV=6
20
LCDIV=5
15
LCDIV=4
10
LCDIV=3
LCDIV=2
5
LCDIV=1
LCDIV=0
0
0
1
2
3
4
5
6
7
Button Sampling Window (ms)
8
9
D008
Figure 23. LCDIV as a Function of Sensor Frequency and Button Sampling Window
8.1.7 Scaling Frequency Counter Output
The LDC2112/LDC2114 requires this internal frequency counter scaler to be set based on the button sampling
window to avoid data overflow. The scaler in Register CNTSC (Address 0x1E) must be set by the following
formula:
CNTSCn
§
0.0861u SENCYCn 1 ·
LCDIV ceiling ¨¨ log2
¸¸ , n
fSENSORn
©
¹
0, 1, 2, or 3
where:
•
•
•
32
CNTSCn is the internal frequency counter scaler,
SENCYCn and LCDIV are the linear and exponential scalers that set the number of sensor oscillation cycles, and
fSENSORn is the sensor frequency in MHz.
(6)
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8.1.8 Setting Button Triggering Threshold
Every material shows some hysteresis when it deforms then returns to the original state. The amount of
hysteresis is a function of material properties and physical parameters, such as size and thickness. This feature
modifies the hysteresis of the button signal threshold according to different materials and various button shapes
and sizes. Hysteresis can be programmed in Register HYST (Address 0x18). By default, the button triggering
hysteresis is set to 32. The nominal button triggering threshold is 128. With hysteresis, the effective on-threshold
is 128 + 32 = 160. This means if the DATAn (n = 0, 1, 2, or 3) reaches 160, the LDC considers that as a button
press. When the DATAn decreases to 128 – 32 = 96, the LDC considers the button to be released.
ThresholdON 128 Hysteresis
(7)
ThresholdOFF
128 Hysteresis
(8)
OUTn
High=Button
Press Detected
Low=No Button
Press Detected
DATAn
ThresholdOFF
128
ThresholdON
Figure 24. Button Triggering Threshold with Hysteresis. Output Polarity: Active High
8.1.9 Tracking Baseline
The LDC2112/LDC2114 automatically tracks slow changes in the baseline signal and compensates for
environmental drifts and variations. In Normal Power Mode, the effective baseline increment per scan cycle
(BINCNP) can be determined by Equation 9:
BINCNP
2NPBI
72
where:
•
NPBI is the Normal Power Baseline Increment index that can be configured in Register NP_BASE_INC (Address
0x15).
(9)
In Low Power Mode, the effective baseline increment per scan cycle (BINCLP) can be determined by
Equation 10:
BINCLP
2LPBI
9
where:
•
LPBI the Low Power Baseline Increment index that can be configured in Register LP_BASE_INC (Address 0x13).
(10)
As a result of baseline tracking, a button press with a constant force only lasts for a finite amount of time. The
duration of a button press is defined by Equation 11 (DATAn > ThresholdON).
DATAn ThresholdOFF
Duration of Button Press
BINC
where:
•
•
•
Duration of Button Press is the number of scan cycles that the channel is asserted,
DATAn is the button signal at the beginning of a press, and
BINC is the baseline increment per scan cycle.
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Button Released
Baseline
DATAn
Baseline Increment
Fast tracking if DATAn is
negative
Figure 25. Baseline Tracking in the Presence of a Button Press
The baseline tracking for a particular channel can be paused when the channel output is asserted. This is
achieved by setting the corresponding BTPAUSE bit in Register BTPAUSE_MAXWIN (Address 0x16) to b1.
If DATAn is negative, the tracking speed will be scaled by the fast tracking factor as specified in Registers FTF0
(Address 0x25), FTF1_2 (Address 0x28), or FTF3 (Address 0x2B). The scaling factors for various FTFn settings
are shown in Table 43.
BINC (DATAn < 0) = Fast_Tracking_Factor_n × BINC (DATAn > 0)
(12)
Table 43. Fast Tracking Factor Settings
FTFn Setting
Fast Tracking Factor
b00
1
b01
4
b10
8
b11
16
8.1.10 Mitigating False Button Detections
The LDC2112/LDC2114 offers several algorithms that can mitigate false button detections due to mechanical
non-idealities associated with groups of buttons. These are listed below.
8.1.10.1 Eliminating Common-Mode Change (Anti-Common)
This algorithm eliminates false detection when a user presses the middle of two or more buttons, which could
lead to a common-mode response on multiple buttons. All the buttons can be individually enabled to have this
feature by programming Register COMMON_DEFORM (Address 0x1A).
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Common-mode change
to both Buttons 0 and 1.
Button 0
Button 1
Intentional Press
of Button 1
DATA
Threshold = 128+Hysteresis
Time
Button 0
OUTPUT without
Anti-common
(High = Button
Press Detected)
Button 1
Time
Button 0
OUTPUT with
Anti-common
(High = Button
Press Detected)
Button 1
Time
Figure 26. Illustration of the Anti-Common Feature
8.1.10.2 Resolving Simultaneous Button Presses (Max-Win)
This algorithm enables the system to select the button pressed with maximum force when multiple buttons are
pressed at the same time. This could happen when two buttons are physically very close to each other, and
pressing one causes a residual reaction on the other. Buttons can be individually enabled to join the “max-win”
group by configuring Register BTPAUSE_MAXWIN (Address 0x16).
Intentional Press of Button 0 Intentional Press of
with coupled response of
Button 1
Button 1
Button 0
Button 1
DATA
Threshold = 128+Hysteresis
Time
Button 0
OUTPUT
without Max-Win
(High = Button
Press Detected)
Button 1
Time
Button 0
OUTPUT with
Max-Win
(High = Button
Press Detected)
Button 1
Time
Figure 27. Illustration of the Max-Win Feature
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8.1.10.3 Overcoming Case Twisting (Anti-Twist)
The anti-twist algorithm reduces the likelihood of false detection when the case is twisted, which could cause
unintended mechanical activation of the buttons, or an opposite reaction in two adjacent buttons. When this
algorithm is enabled, detection of button presses is suppressed if any button’s output data is negative by a
configurable threshold. The anti-twist algorithm can be enabled by configuring Register TWIST (Address 0x19).
Twisting effect of
Buttons 0 and 1.
Button 0
Button 1
Intentional Press of
Button 1.
DATA
Threshold = 128+Hysteresis
Time
Button 0
OUTPUT without
Anti-twist
(High = Button
Press Detected)
Button 1
Time
Button 0
OUTPUT with
Anti-twist
(High = Button
Press Detected)
Button 1
Time
Figure 28. Illustration of the Anti-Twist Feature
8.1.10.4 Mitigating Metal Deformation (Anti-Deform)
This function filters changes due to metal deformation in the vicinity of one or more buttons. Such metal
deformation can be accidentally caused by pressing a neighboring button that does not have sufficient
mechanical isolation. The user can specify which buttons to join the anti-deform group by configuring Register
COMMON_DEFORM (Address 0x1A).
8.1.11 Reporting Interrupts for Button Presses and Error Conditions
INTB, the LDC2112/LDC2114 interrupt pin, is asserted when a button press or an error condition occurs. The
default polarity is active low and can be configured through Register INTPOL (Address 0x11).
Figure 29 shows the LDC2112/LDC2114 response to a single button press on Channel 0. At the end of the
button sampling window following a press of Button 0, the OUT0 pin and INTB pin are asserted. The
OUT_STATUS bit changes from 0 to 1, and remains so until a read of the STATUS register clears it. The OUTn
(n = 0, 1, 2, or 3) and INTB pins are asserted until the end of the button sampling window following the release of
the button.
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OUTn DQG ,17% DUH SURJUDPPHG WR ³$FWLYH /RZ´. Scan Rate: 40 SPS.
25 ms scan cycle
25 ms scan cycle
Sampling
25 ms scan cycle
Sampling
Sampling
OUT0
Pin
INTB
Pin
STATUS
Register
Events
Button 0
pressed
OUT0 and
INTB asserted,
OUT_STATUS
bit asserted
Reading the Status
Register clears the
OUT_STATUS bit.
Button 0
released
OUT0 de-asserted
Figure 29. Timing Diagram of a Single Button Press
Figure 30 shows the LDC2112/LDC2114 response to multiple button presses. In this example, after Button 0 is
pressed, the OUT0 pin is asserted. After that, Button 1 is also pressed, following which Button 0 is released. The
OUT0 pin is de-asserted and OUT1 pin asserted at the end of the next button sampling window. The INTB pin
remains continuously asserted as long as at least one of the buttons is pressed. The OUT_STATUS bit only
changes from 0 to 1 after the first button assertion.
OUTn DQG ,17% DUH SURJUDPPHG WR ³$FWLYH /RZ´. Scan Rate: 40 SPS.
25 ms scan cycle
25 ms scan cycle
Sampling
Sampling
25 ms scan cycle
Sampling
OUT0
Pin
OUT1
Pin
INTB
Pin
STATUS
Register
Events
Button 0
pressed
OUT0 and
INTB asserted
Button 1 Button 0
pressed released
OUT0 de-asserted
OUT1 asserted
Button 1
released
OUT1 and INTB
de-asserted
Reading the Status Register
clears the OUT_STATUS bit.
Figure 30. Timing Diagram of Multiple Button Presses
The INTB pin also reports any error event. If an error occurs, the INTB pin is asserted and the error is reported in
the STATUS register (Address 0x00). Refer to Register STATUS (Address 0x00) for possible error events.
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8.1.12 Estimating Supply Current
When the LDC2112/LDC2114 is active (in either Normal Power Mode or Low Power Mode), its current can be
characterized by Equation 13:
12
IACTIVEn 1.6
0.011u fSENSORn
1 16 u RPn1.21
where
•
•
•
•
IACTIVEn is the supply current in mA during active sampling,
RPn is the sensor parallel resonant impedance in kΩ,
fSENSORn is the sensor frequency in MHz, and
n is the channel index, i.e. n = 0 or 1 for LDC2112; n = 0, 1, 2, or 3 for LDC2114.
(13)
The LDC2112/LDC2114 is only actively sampling the enabled channels during a fraction of the scan window. So
the average supply current is:
1
IDD
tSCAN
§
u¨
¨
©
·
¦IACTIVEn u tSAMPLEn ¸¸
n
0.005
¹
where
•
•
•
•
IDD is the average supply current in mA,
tSCAN is the scan window (set by the scan rate) in ms,
IACTIVEn is the supply current when the device is active as defined by Equation 13, and
tSAMPLE is the button sampling window in ms.
(14)
8.2 Typical Application
8.2.1 Touch Button Design
The low power architecture of LDC2112/LDC2114 makes them suitable for driving button sensors in consumer
electronics, such as mobile phones. Most mobile phones today have three buttons along the edges, namely the
power button, volume up, and volume down. The LDC2112 can support two buttons, and LDC2114 can support
four.
On a typical smartphone, the two volume buttons are next to each other, so they may be susceptible to false
detections such as simultaneous button presses. To prevent such mis-triggers, they can be grouped together to
take advantage of the various features that mitigate false detections as explained in Mitigating False Button
Detections. For example, if Max-win is applied to the two volume buttons, only the one with the greater force will
be triggered.
The inductive touch solution does not require any mechanical cutouts at the button locations. This can support
reduced manufacturing cost for the phone case and enhance the case’s resistance to moisture, dust, and dirt.
This is a great advantage compared to mechanical buttons in the market today.
8.2.1.1 Design Requirements
The sensor parameters, including frequency, RP, and Q factor have to be within the design space of the
LDC2112/LDC2114 as specified in Electrical Characteristics.
8.2.1.2 Detailed Design Procedure
The LDC2112/LDC2114 is a multi-channel device. The italic n in the parameters below refers to the channel
index, i.e., n = 0 or 1 for LDC2112, and n = 0, 1, 2, or 3 for LDC2114.
1. Select system-based options:
• Select Normal or Low Power Mode of operation by setting the LPWRB pin to VDD or Ground, respectively.
Configure the enable bits for all channels in Register EN (Address 0x0C).
• Select the polarities of OUTn and INTB pins by configuring Register OPOL_DPOL (Address 0x1C) and
Register INTPOL (Address 0x11).
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Typical Application (continued)
•
Configure the sensor frequency setting in Registers SENSORn_CONFIG (Addresses 0x20, 0x22, 0x24,
0x26).
2. Choose the sampling rate (80, 40, 20, 10, 5, 2.5, 1.25, or 0.625 SPS) based on system power consumption
requirement, and configure Register NP_SCAN_RATE (Address 0x0D) or Register LP_SCAN_RATE (Address
0x0F).
3. Choose the button sampling window based on power consumption and noise requirements (recommended: 1
ms to 8 ms). While a longer button sampling window provides better noise performance, 1 ms is typically
sufficient for most applications. Set SENCYCn and LCDIV in Registers SENSORn_CONFIG (Addresses 0x20,
0x22, 0x24, 0x26) and Register LC_DIVIDER (Address 0x17) in the following steps:
• Calculate LCDIV = ceiling (log2 (fSENSORn × tSAMPLEn) – 12), where fSENSORn is the sensor frequency in MHz,
tSAMPLEn is the button sampling window in µs
• If LCDIV < 0, set it to 0
• Adjust SENCYCn to get desired tSAMPLEn according to tSAMPLEn = 128 × (SENCYCn + 1) × 2LCDIV / fSENSORn
4. Calibrate gain in the appropriate Registers GAINn (Addresses 0x0E, 0x10, 0x12, 0x14). The gain setting can
be used to tune the sensitivity of the touch button. GAINn is a 6-bit field with 64 different gain levels
corresponding to normalized gains between 1 and 232. A good mechanical and sensor design typically requires
a gain level of around 32 to 50, corresponding to relative gains of 16 to 76 (normalized to gain level of 0). Use
the following sequence to determine the appropriate gain for each button:
• Apply minimum desired force to the button.
• Read initial DATAn value after the button press. Note that the baseline tracking will affect this value.
• Calculate gain factor needed to increase DATAn to the programmed threshold (default is 160).
• Look up the Gain Table to find the required gain setting.
5. Enable special features to mitigate button interference if there is any. Registers BTPAUSE_MAXWIN, TWIST,
COMMON_DEFORM (Addresses 0x16, 0x19, 0x1A).
For more information on inductive touch system design, including mechanical design and sensor electrical
design, refer to Inductive Touch System Design Guide.
8.2.1.3 Application Curves
Figure 31 shows a sequence of button presses of 150 grams force, two presses to Channel 0, then two presses
to Channel 1. Each button press response is greater than the threshold.
400
Channel 0
Channel 1
Threshold
350
Conversion DATA
300
250
200
150
100
50
0
-50
0
2
4
Time (s)
6
8
D009
Figure 31. Conversion DATA vs Time for Channels 0 and 1
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9 Power Supply Recommendations
The LDC2112/LDC2114 power supply should be bypassed with a 1 µF and a 0.1 µF pair of capacitors in parallel
to ground. The capacitors should be placed as close to the LDC as possible. The smaller value 0.1 µF capacitor
should be placed closer to the VDD pin than the 1 µF capacitor. The capacitors should be a low ESL, low ESR
type. To enable close positioning of the capacitors, use of 0201 footprint devices for the bypass capacitors is
recommended for the DSBGA package.
Refer to Recommended Operating Conditions for more details.
10 Layout
10.1 Layout Guidelines
The COM pin must be bypassed to ground with an appropriate value capacitor. For details of how to choose the
capacitor value, refer to Setting COM Pin Capacitor. CCOM should be placed as close as possible to the COM
pin. The COM signal should be tied to a small copper fill placed underneath the INn signals. The INn signals
should stay clear of other high frequency traces.
Each active channel needs to have an LC resonator connected to the corresponding INn pins. The sensor
capacitor should be placed within 10 mm of the corresponding INn pin, and the inductor (NOT shown in
Figure 32) should be placed at the appropriate location next to (but not touching) the metal target. The INn traces
should be at least 6 mil (0.15 mm) wide to minimize parasitic inductances.
For the DSBGA package, the inner four device pads (INTB, OUT3, LPWRB, and SDA) should be routed out on
an inner layer through vias, with the traces offset to reduce coupling with other signals. These four vias may
need to use blind vias or microvias to bring the signals out. The PCB layer stack should use a thinner (4 mil or
0.1 mm thickness) dielectric between the top copper and next copper layer so that microvias can be used.
10.2 Layout Example
Figure 32. Layout of LDC2114 (DSBGA-16) With Decoupling Capacitors and Sensor Capacitors
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Layout Example (continued)
Figure 33. Layout of LDC2114 (TSSOP-16) With Decoupling Capacitors and Sensor Capacitors
10.3 DSBGA Light Sensitivity
Exposing the DSBGA device to direct light may cause incorrect operation of the device. Light sources such as
halogen lamps can affect electrical performance if they are situated in proximity to the device. Light with
wavelengths in the red and infrared part of the spectrum have the most detrimental effect.
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11 Device and Documentation Support
11.1 Documentation Support
11.1.1 Related Documentation
For related documentation see the following:
• LDC Calculations Tool
• Inductive Touch System Design Guide
11.2 Related Links
The table below lists quick access links. Categories include technical documents, support and community
resources, tools and software, and quick access to order now.
Table 44. Related Links
PARTS
PRODUCT FOLDER
ORDER NOW
TECHNICAL
DOCUMENTS
TOOLS &
SOFTWARE
SUPPORT &
COMMUNITY
LDC2112
Click here
Click here
Click here
Click here
Click here
LDC2114
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11.3 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.
11.4 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.
11.5 Trademarks
E2E is a trademark of Texas Instruments.
All other trademarks are the property of their respective owners.
11.6 Electrostatic Discharge Caution
This integrated circuit can be damaged by ESD. Texas Instruments recommends that all integrated circuits be handled with
appropriate precautions. Failure to observe proper handling and installation procedures can cause damage.
ESD damage can range from subtle performance degradation to complete device failure. Precision integrated circuits may be more
susceptible to damage because very small parametric changes could cause the device not to meet its published specifications.
11.7 Export Control Notice
Recipient agrees to not knowingly export or re-export, directly or indirectly, any product or technical data (as
defined by the U.S., EU, and other Export Administration Regulations) including software, or any controlled
product restricted by other applicable national regulations, received from Disclosing party under this Agreement,
or any direct product of such technology, to any destination to which such export or re-export is restricted or
prohibited by U.S. or other applicable laws, without obtaining prior authorization from U.S. Department of
Commerce and other competent Government authorities to the extent required by those laws.
42
Submit Documentation Feedback
Copyright © 2016–2017, Texas Instruments Incorporated
Product Folder Links: LDC2112 LDC2114
LDC2112, LDC2114
www.ti.com
SNOSD15B – DECEMBER 2016 – REVISED APRIL 2017
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.
Copyright © 2016–2017, Texas Instruments Incorporated
Product Folder Links: LDC2112 LDC2114
Submit Documentation Feedback
43
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)
LDC2112PWR
ACTIVE
TSSOP
PW
16
2000
RoHS & Green
NIPDAU
Level-2-260C-1 YEAR
-40 to 85
LDC2112
LDC2112PWT
ACTIVE
TSSOP
PW
16
250
RoHS & Green
NIPDAU
Level-2-260C-1 YEAR
-40 to 85
LDC2112
LDC2112YFDR
ACTIVE
DSBGA
YFD
16
3000
RoHS & Green
SNAGCU
Level-1-260C-UNLIM
-40 to 85
17M
LDC2112YFDT
ACTIVE
DSBGA
YFD
16
250
RoHS & Green
SNAGCU
Level-1-260C-UNLIM
-40 to 85
17M
LDC2114PWR
ACTIVE
TSSOP
PW
16
2000
RoHS & Green
NIPDAU
Level-2-260C-1 YEAR
-40 to 85
LDC2114
LDC2114PWT
ACTIVE
TSSOP
PW
16
250
RoHS & Green
NIPDAU
Level-2-260C-1 YEAR
-40 to 85
LDC2114
LDC2114YFDR
ACTIVE
DSBGA
YFD
16
3000
RoHS & Green
SNAGCU
Level-1-260C-UNLIM
-40 to 85
14G
LDC2114YFDT
ACTIVE
DSBGA
YFD
16
250
RoHS & Green
SNAGCU
Level-1-260C-UNLIM
-40 to 85
14G
(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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