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LDC0851
SNOSCZ7A – DECEMBER 2015 – REVISED JANUARY 2016
LDC0851 Differential Inductive Switch
1 Features
3 Description
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The LDC0851 is a close range inductive switch ideal
for contactless and robust applications such as
presence detection, event counting, and simple
buttons.
1
Threshold tolerance: LR)
LS
+
OUT
LCOM
Sensor
Cap
Approaching
Metal Target
LREF
Sense
Coil
dswitch
Reference
Coil
Inductance
Converter
LR
+
Output Low
(LS < LR)
±
dswitch
±
1.8 V
1.8 V
Offset Adjust
R1
ADJ
R2
4-bit ADC
VDD
Power
Management
EN
CBYP
GND
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.
LDC0851
SNOSCZ7A – DECEMBER 2015 – REVISED JANUARY 2016
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Table of Contents
1
2
3
4
5
6
7
8
Features ..................................................................
Applications ...........................................................
Description .............................................................
Simplified Schematic.............................................
Revision History.....................................................
Pin Configuration and Functions .........................
Specifications.........................................................
1
1
1
1
2
3
4
7.1
7.2
7.3
7.4
7.5
7.6
7.7
7.8
4
4
4
4
5
5
6
7
Absolute Maximum Ratings ......................................
ESD Ratings ............................................................
Recommended Operating Conditions.......................
Thermal Information ..................................................
Electrical Characteristics...........................................
Interface Voltage Levels ...........................................
Timing Requirements ................................................
Typical Characteristics ..............................................
Detailed Description ............................................ 10
8.1 Overview ................................................................. 10
8.2 Functional Block Diagram ....................................... 10
8.3 Feature Description................................................. 11
8.4 Device Functional Modes........................................ 18
9
Application and Implementation ........................ 19
9.1 Application Information............................................ 19
9.2 Typical Application ................................................. 21
10 Power Supply Recommendations ..................... 28
11 Layout................................................................... 29
11.1 Layout Guidelines ................................................. 29
11.2 Layout Example .................................................... 29
12 Device and Documentation Support ................. 31
12.1
12.2
12.3
12.4
12.5
Device Support......................................................
Community Resources..........................................
Trademarks ...........................................................
Electrostatic Discharge Caution ............................
Glossary ................................................................
31
31
31
31
31
13 Mechanical, Packaging, and Orderable
Information ........................................................... 31
5 Revision History
Changes from Original (December 2015) to Revision A
•
2
Page
Product Preview to Production Data Release ....................................................................................................................... 1
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6 Pin Configuration and Functions
DSG Package
8-Pin WSON with DAP
Top View
LCOM
1
LSENSE
2
8
VDD
7
GND
DAP
LREF
3
6
EN
ADJ
4
5
OUT
Pin Functions
PIN
TYPE
(1)
DESCRIPTION
NAME
NO.
LCOM
1
A
Common coil input
LSENSE
2
A
Sense coil input
LREF
3
A
Reference coil input
ADJ
4
A
Threshold adjust pin
OUT
5
O
Switch output
EN
6
I
Enable input
GND
7
G
Ground
VDD
8
P
Power Supply
DAP
DAP
G
Connect to Ground for improved thermal performance (2)
(1)
(2)
I = Input, O = Output, P = Power, A = Analog, G = Ground
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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7 Specifications
7.1 Absolute Maximum Ratings
over operating free-air temperature range (unless otherwise noted)
(1)
MIN
VDD
Supply Voltage Range
Vi
MAX
UNIT
3.6
V
V
Voltage on LSENSE, LREF, and EN
-0.3
3.6
Voltage on ADJ and LCOM
-0.3
2
V
5
mA
IA
Current LSENSE, LREF, and VOUT
TJ
Junction Temperature
-55
150
°C
Tstg
Storage Temperature
-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.
7.2 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 JESD22-C101 (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.
7.3 Recommended Operating Conditions
over operating free-air temperature range (unless otherwise noted)
MIN
NOM
MAX
UNIT
VDD
Supply Voltage
1.71
3.46
V
TA
Operating Temperature
-40
125
°C
7.4 Thermal Information
over operating free-air temperature range (unless otherwise noted)
LDC0851
THERMAL METRIC (1)
DSG (WSON)
UNIT
8 PINS
RθJA
Junction-to-ambient thermal resistance
67.4
°C/W
RθJC(top)
Junction-to-case (top) thermal resistance
89.3
°C/W
RθJB
Junction-to-board thermal resistance
37.3
°C/W
ψJT
Junction-to-top characterization parameter
2.4
°C/W
ψJB
Junction-to-board characterization parameter
37.7
°C/W
RθJC(bot)
Junction-to-case (bottom) thermal resistance
9.2
°C/W
(1)
4
For more information about traditional and new thermal metrics, see the Semiconductor and IC Package Thermal Metrics application
report (SPRA953).
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7.5 Electrical Characteristics (1)
Over recommended operating conditions unless otherwise noted. VDD= 3.3 V, EN tied to 3.3 V, TA=25 °C, ADJ tied to GND.
PARAMETER
TEST CONDITIONS
MIN (2)
TYP (3)
MAX (2)
UNIT
POWER
VDD
Supply Voltage
ISTATIC
Static Supply Current
1.71
IDYN
Dynamic Supply Current (not including
sensor current) (4)
ISD
Shutdown Mode Supply Current
(4)
ƒSENSOR = 15 MHz
CPARASITIC = 22 pF
3.46
V
0.70
mA
0.66
mA
0.14
1
µA
SENSOR
ISENSOR_MAX
Maximum sensor current (4)
VDD = 1.71 V
4.35
mA
VDD = 3.3 V
6
mA
CTOTAL = 33 pF
LSENSOR_MIN
Sensor Minimum Inductance
2.5
VDD = 1.71 V
(5)
CTOTAL = 33 pF
1.8
µH
19
MHz
Includes parasitic pin capacitance and
PCB parasitic capacitance
33
pF
Pin parasitic capacitance on LCOM
12
pF
Pin parasitic capacitance on LREF and
LSENSE
8
pF
VDD = 3.3 V
ƒSENSOR_MAX
Sensor inductance = 2 µH
Max Sensor Resonant Frequency (5)
CTOTAL = 33 pF
Minimum total capacitance on LCOM (5)
CTOTAL
CIN
DETECTION
dHYST
Switching distance hysteresis (6)
2.5 %
dTOL
Switching threshold tolerance (6)
0.1 %
THRESHOLD ADJUST
VADJ
Adjust input range
VADJ_TOL
Adjust threshold tolerance
(1)
(2)
(3)
(4)
(5)
(6)
0
VDD/2
±6
V
mV
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.
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.
Refer to section Active Mode for a description and calculation of the various supply currents.
See Sensor Design for sensor guidance.
Two matched 10 mm diameter sensors were used with a switching distance of 3 mm. See Hysteresis for more information.
7.6 Interface Voltage Levels
PARAMETER
MIN
VIH
Input High Voltage
VIL
Input Low Voltage
VOH
Output High Voltage(1mA source current)
VOL
Output Low Voltage (1mA sink current)
TYP
MAX
0.8ˣVDD
V
0.2ˣVDD
VDD-0.4
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V
V
0.4
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UNIT
V
5
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7.7 Timing Requirements
Over recommended operating conditions unless otherwise noted. VDD= 3.3 V, EN tied to 3.3 V, TA=25 °C, ADJ tied to GND.
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
VOLTAGE LEVELS
tCONVERSION
Conversion time
ƒSENSOR = 15 MHz
290
µs
tDELAY
Output delay time (Response time)
ƒSENSOR = 15 MHz
580
µs
tSTART
Start-up time
450
µs
tAMT
Shutdown-to-active mode transition time
450
µs
tSMT
Active-to-shutdown mode transition time
fref
Metal
Present
fsense > fref
tD
Power-on Start State
OUT
ttSTARTt
1st Sample Output
2nd Sample Output
tCONVERSION
t(2nd Sample)t
tCONVERSION
t(1st Sample)t
tD
tCONVERSION
t(3rd Sample)t
ttDELAYt
Figure 1. Start-up and Delay Time Diagram
Refer to Power-Up Conditions for more information on the Power-On Start State.
VDD
t
LCOM
t
EN
t
OUT
Metal
Detected
(LOW)
Power Down State (HIGH)
1st sample in progress
(HIGH)
1st Sample Output
Metal Detected (LOW)
t
ttAMTt
ttSMTt
tCONVERSION
t(1st Sample)t
Figure 2. Shutdown and Resume Active Mode Timing Diagram
6
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7.8 Typical Characteristics
Common test conditions (unless specified otherwise): VDD = 3.3 V, Sense coil diameter = reference coil diameter, Target:
Aluminum, 1.5 mm thickness, Target area / Coil area > 100%
12
4
Switch ON
Switch OFF
Switch ON
Switch OFF
3.5
Switching Distance (mm)
Switching Distance (mm)
10
8
6
4
2
3
2.5
2
1.5
1
0.5
0
1
2
3
4
5
6
Target Distance to LREF Coil (mm)
Basic Operation Mode
Coil diameter = 10 mm
7
0
15 14 13 12 11 10
8
D001
ADJ Code = 0
Figure 3. Switching Distance vs. LREF Target Distance
5
4
3
2
1
D002
No reference target
Figure 4. Switching Distance vs. ADJ code
80
Switch ON (dcoil = 6 mm)
Switch ON (dcoil = 15 mm)
Switch ON (dcoil = 29 mm)
Switch OFF (dcoil = 6 mm)
Switch OFF (dcoil = 15 mm)
Switch OFF (dcoil = 29 mm)
100
80
Switching Distance (% of coil diameter)
Switching Distance (% of coil diameter)
6
Threshold Adjust Mode
Coil diameter = 10 mm
120
60
40
20
0
0
20
40
60
Target Distance to LREF Coil (% of coil diameter)
Basic Operation Mode
Coil diameter = 6 mm, 15 mm, 29 mm
Switch ON (dcoil = 6 mm)
Switch ON (dcoil = 15 mm)
Switch ON (dcoil = 29 mm)
Switch OFF (dcoil = 6 mm)
Switch OFF (dcoil = 15 mm)
Switch OFF (dcoil = 29 mm)
70
60
50
40
30
20
10
0
15 14 13 12 11 10
80
D003
ADJ Code = 0
9 8 7
ADJ Code
Threshold Adjust Mode
Coil diameter = 6 mm, 15 mm, 29 mm
Figure 5. Normalized Switching Distance vs. LREF Target
Distance
6
5
4
3
2
1
D004
No reference target
Figure 6. Normalized Switching Distance vs. ADJ Code
100
240
dcoil = 29 mm
dcoil = 15 mm
dcoil = 6 mm
90
Sensor Inductance (Ls / Lr%)
220
Sensor Frequency (fs / fr%)
9 8 7
ADJ Code
200
180
160
140
120
80
70
60
50
40
30
20
dcoil = 29 mm
dcoil = 15 mm
dcoil = 6 mm
10
100
0
0
20
40
60
80
Target Distance to LSENSE Coil (% of coil diameter)
LSENSE frequency (fs) varied
100
D005
LREF frequency (fr) fixed
0
20
40
60
80
Target Distance to LSENSE Coil (% of coil diameter)
LSENSE inductance (Ls) varied
Figure 7. Frequency vs. Distance
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D006
LREF inductance (Lr) fixed
Figure 8. Inductance vs. Distance
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Typical Characteristics (continued)
Common test conditions (unless specified otherwise): VDD = 3.3 V, Sense coil diameter = reference coil diameter, Target:
Aluminum, 1.5 mm thickness, Target area / Coil area > 100%
20
20
CTOTAL < 33 pF
16
16
14
14
12
10
Valid Region
8
6
12
10
Valid Region
8
6
4
4
2
2
ISENSOR > 4.35 mA
0
0
5
ISENSOR > 6 mA
0
10
15
0
20
Sensor Frequency (MHz)
5
10
15
20
Sensor Frequency (MHz)
D007
ISENSOR_MAX = 4.35 mA
Specified for closest target proximity or minimum inductance in the
application.
D008
ISENSOR_MAX = 6 mA
Specified for closest target proximity or minimum inductance in the
application.
Figure 10. Sensor Design Space for VDD = 3.3 V
Figure 9. Sensor Design Space for VDD = 1.8 V
1.5
10
Dynamic Supply Current (mA)
2 µH
20 µH
200 µH
Sensor Current (mA)
CTOTAL < 33 pF
18
Inductance (µH)
Inductance (µH)
18
1
0.1
1.7
2.2
2.7
VDD (V)
3.2
1.4
1.3
1.2
-40°C
-25°C
0°C
25°C
1.1
1
1.7
3.7
2.2
2.7
VDD (V)
D009
CTOTAL = 100 pF
50°C
75°C
100°C
125°C
3.2
3.7
D010
CBOARD = 12 pF
ƒSENSOR = 30 MHz
Figure 11. ISENSOR vs. VDD
Figure 12. IDYN vs. VDD
0.65
10
-40°C
-25°C
0°C
25°C
50°C
75°C
100°C
125°C
d 25°C
25 - 50°C
50 - 75°C
Shutdown Current (µA)
Static Supply Current (mA)
0.7
0.6
0.55
0.5
75 - 100°C
100 - 125°C
1
0.1
0.01
0.45
0.4
1.7
2.2
2.7
VDD (V)
3.2
3.7
0.001
1.7
D011
Figure 13. ISTATIC vs. VDD
8
2.1
2.5
2.9
VDD (V)
3.3
3.7
D012
Figure 14. ISD vs. VDD
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Typical Characteristics (continued)
Common test conditions (unless specified otherwise): VDD = 3.3 V, Sense coil diameter = reference coil diameter, Target:
Aluminum, 1.5 mm thickness, Target area / Coil area > 100%
100
0
Sensor Frequency Shift (%)
Sensor Current (µA)
2 µH
5 µH
10 µH
20 µH
10
1
0.1
0
5
10
15
Sensor Frequency (MHz)
See Equation 4
20
-2
-4
-6
-8
-10
1.7
D013
fSENSOR = 0.5 MHz
fSENSOR = 4 MHz
fSENSOR = 12 MHz
2.2
2.7
VDD (V)
3.2
3.7
D014
Normalized to frequency at VDD = 3.6 V
Figure 15. ISENSOR vs. ƒSENSOR
Figure 16. ƒSENSOR Shift vs. VDD
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8 Detailed Description
8.1 Overview
The LDC0851 is an inductance comparator with push/pull output. It utilizes a sensing coil and a reference coil to
determine the relative inductance in a system. The push/pull output (OUT) switches low when the sense
inductance drops below the reference and returns high when the reference inductance is higher than the sense
inductance. Matching the sense and reference coils is important to maintain a consistent switching distance over
temperature and to compensate for other environmental factors. The LDC0851 features internal hysteresis to
prevent false switching due to noise or mechanical vibration at the switching threshold. The switching threshold is
set by the sensor characteristics and proximity to conductive objects, which is considered Basic Operation Mode
described further in section Basic Operation Mode. The LDC0851 also features a Threshold Adjust Mode where
an offset is subtracted from the reference inductance to change the effective switching point as described in
section Threshold Adjust Mode.
The sensing coil is connected across the LSENSE and LCOM pins and the reference coil is connected across
the LREF and LCOM pins. A sensor capacitor is connected from LCOM to GND to set the sensor oscillation
frequency. The sensor capacitor is common to both LSENSE and LREF making the inductance measurement
differential.
8.2 Functional Block Diagram
LDC0851
Differential
LDC Core
Sense
Coil
Output High
(LS > Adjusted LR)
LSENSE
Inductance
Converter
LS
+
OUT
LCOM
Sensor
Cap
Adjusted LR
+
Inductance
Converter
LREF
±
Output Low
(LS < Adjusted LR)
±
Reference
Coil
Switch
Mode Select
0: Basic Operation
1 ± 15: Threshold Adjust
VDD
VDD
VDD
R1
ADJ
4-bit ADC
R2
Offset
Power
Management
EN
CBYP
GND
10
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8.3 Feature Description
8.3.1 Basic Operation Mode
The LDC0851 is configured for Basic Operation mode when the ADJ pin is tied to ground. Two identical coils
should be used for LSENSE and LREF. The switching point occurs when the inductances of both coils are equal.
Basic Operation mode can be used for a wide variety of applications including event counting or proximity
sensing. An example showing gear tooth counting can be found in section Event Counting.
For proximity sensing the switching point can be set by placing a conductive target at a fixed distance from the
reference coil as shown in Figure 17. The output will switch when a conductive target approaches LSENSE and
reaches the same distance set by the fixed reference target. For reliable and repeatable switching it is
recommended to place the reference target at a distance less than 40% of the coil diameter from the reference
coil.
Output High
(LS > LR)
LS (Inductance)
LR (Inductance)
Output Low
(LS < LR)
Target Distance
0
’
dswitch = d
Movable
Metal Target
LDC0851
Differential
LDC Core
Sense
Coil
LSENSE
Inductance
Converter
LS
+
OUTPUT
LCOM
Sensor
Cap
Fixed
Reference
LREF
±
±
Reference
Coil
Switching distance set
by Reference Target
LR
+
Inductance
Converter
Mode Select
0: Basic Operation
1 ± 15: Threshold Adjust
ADJ
4-bit ADC
Offset
VDD
VDD
Power
Management
EN
CBYP
GND
Figure 17. Basic Operation Mode Diagram for Distance Sensing With Reference Target
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Feature Description (continued)
In some systems adding a reference target at a fixed height to set the switching distance is not feasible.
Therefore to set the switching distance a small amount of mismatch between the sense and reference coils can
be introduced. To achieve the maximum switching distance the reference inductance should be approximately
0.4% less than the sense inductance as shown in Figure 18 below. The 0.4% mismatch will ensure that the
output will switch off when the target is removed.
Output High
(LS > LR)
LR (Inductance)
LS (Inductance)
Output Low
(LS < LR)
Target Distance
0
’
dswitch § 0.8 x dcoil
Movable
Metal Target
LDC0851
Differential
LDC Core
Sense
Coil
LSENSE
Inductance
Converter
LS
+
OUTPUT
LCOM
Sensor
Cap
LREF
±
±
Reference
Coil
Switching distance set by
mismatch of Sense and
Reference Coils
LR
+
Inductance
Converter
Mode Select
0: Basic Operation
1 ± 15: Threshold Adjust
ADJ
4-bit ADC
Offset
VDD
VDD
Power
Management
EN
CBYP
GND
Figure 18. Basic Operation Mode Diagram for Distance Sensing With Mismatched Coils
12
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Feature Description (continued)
8.3.2 Threshold Adjust Mode
In Threshold Adjust mode, an offset inductance is subtracted from LREF to alter the switching threshold without
the use of a reference target. In order to configure the LDC0851 for Threshold Adjust mode, place a resistor
divider between VDD and GND as shown in Figure 19. The threshold adjust values can then be easily changed
as described in section Setting the Threshold Adjust Values. Threshold adjust mode can be used in a variety of
applications including coarse proximity sensing and simple button applications as shown in Coarse Position
Sensing. Two example coil configurations for proximity sensing are shown below for side by side coil orientation
in Figure 19 as well as stacked configuration in Figure 20.
Output High
(LS > Adjusted LR)
...
LSENSE
Adjusted LR
(ADJ = 1)
Adjusted LR
(ADJ = 15)
Output Low
(LS < Adjusted LR)
Target Distance
’
dswitch § 0.4x(dcoil)
(ADJ = 1)
0
dswitch
(ADJ = 15)
...
Movable
Metal Target
LDC0851
Differential
LDC Core
Sense
Coil
LSENSE
Inductance
Converter
LS
+
OUTPUT
LCOM
Switching distance set
by ADJ Value
Sensor
Cap
LREF
No Target on
Reference Reference
Adjusted LR
+
Inductance
Converter
±
±
Coil
Mode Select
VDD
VDD
0: Basic Operation
1 ± 15: Threshold Adjust
VDD
R1
ADJ
4-bit ADC
Offset
R2
EN
Power
Management
CBYP
GND
Figure 19. Threshold Adjust Mode for Distance Sensing Using Side by Side Coils
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Feature Description (continued)
Stacked coils can be utilized in designs where PCB space is a concern or if the user only wants to detect
proximity to metal from one side of the PCB such as a button application. The sensing range is slightly reduced
due to the fact that both the sense and the reference coil are affected by same conductive target, however since
the sense coil is closer to the target its respective inductance decreases more than the reference inductance
allowing the output to switch as shown in Figure 20.
Output High
(LS > Adjusted LR)
...
LS
Adjusted LR
(ADJ = 1)
Adjusted LR
(ADJ = 15)
Output Low
(LS < Adjusted LR)
Target Distance
’
dswitch § 0.3x(dcoil)
(ADJ = 1)
0
dswitch
(ADJ = 15)
...
LDC0851
Differential
LDC Core
LSENSE
Movable
Metal Target
Inductance
Converter
LS
+
LCOM
Ref
Coil
Sense
Coil
Sensor
Cap
LREF
Switching distance set by ADJ
Value and separation between
Sense and Ref coils
Inductance
Converter
Adjusted LR
+
OUTPUT
±
±
Mode Select
VDD
R1
VDD
0: Basic Operation
1 ± 15: Threshold Adjust
ADJ
4-bit ADC
Offset
R2
VDD
EN
Power
Management
CBYP
GND
Figure 20. Threshold Adjust Mode for Distance Sensing Using Stacked Coils
To get the most sensing range with stacked coils the spacing between the sensing coil and reference coil (height
= h) should be maximized as shown in Figure 21. See section Stacked Coils for more information on the layout
of stacked coils.
Layers 1, 2
Sense Coil
h
Layers 3, 4
Reference Coil
Figure 21. Stacked Coil Separation (PCB Side View)
14
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Product Folder Links: LDC0851
LDC0851
www.ti.com
SNOSCZ7A – DECEMBER 2015 – REVISED JANUARY 2016
Feature Description (continued)
8.3.3 Setting the Threshold Adjust Values
To configure a threshold setting, connect a 49.9 kΩ resistor (R1) between VDD and the ADJ pin as shown in
Figure 20. The threshold is determined by the value of R2 as shown in the Table 1 below. R1 and R2 should be
1% or tighter tolerance resistors with a temperature coefficient of
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