I2C INTERFACE
AND
CONTROL
REGISTERS
RE
VREF VDD
AGND
CE
WE VOUT
C1
SCL
TEMP
SENSOR
VREF
DIVIDER
C2
SDA
RLoad
VARIABLE
BIAS MENB
DGND
A1 +
-
TIA
+
-
RTIA
CE
WE
RE
3-Lead
Electrochemical
Cell CONTROLLER
LMP91000
Product
Folder
Sample &
Buy
Technical
Documents
Tools &
Software
Support &
Community
LMP91000
SNAS506I –JANUARY 2011–REVISED DECEMBER 2014
LMP91000 Sensor AFE System: Configurable AFE Potentiostat for Low-Power Chemical-
Sensing Applications
1 Features 3 Description
The LMP91000 is a programmable analog front-end
1• Typical Values, TA= 25°C (AFE) for use in micro-power electrochemical sensing
• Supply Voltage 2.7 V to 5.25 V applications. It provides a complete signal path
• Supply Current (Average Over Time) <10 µA solution between a sensor and a microcontroller that
generates an output voltage proportional to the cell
• Cell Conditioning Current Up to 10 mA current. The LMP91000’s programmability enables it
• Reference Electrode Bias Current (85°C) 900pA to support multiple electrochemical sensors such as
(max) 3-lead toxic gas sensors and 2-lead galvanic cell
• Output Drive Current 750 µA sensors with a single design as opposed to the
multiple discrete solutions. The LMP91000 supports
• Complete Potentiostat Circuit-to-Interface to Most gas sensitivities over a range of 0.5 nA/ppm to 9500
Chemical Cells nA/ppm. It also allows for an easy conversion of
• Programmable Cell Bias Voltage current ranges from 5 µA to 750 µA full scale.
• Low-Bias Voltage Drift The LMP91000’s adjustable cell bias and
• Programmable TIA gain 2.75 kΩto 350 kΩtransimpedance amplifier (TIA) gain are
• Sink and Source Capability programmable through the I2C interface. The I2C
interface can also be used for sensor diagnostics. An
• I2C Compatible Digital Interface integrated temperature sensor can be read by the
• Ambient Operating Temperature –40°C to 85°C user through the VOUT pin and used to provide
• Package 14-Pin WSON additional signal correction in the µC or monitored to
• Supported by WEBENCH®Sensor AFE Designer verify temperature conditions at the sensor.
The LMP91000 is optimized for micro-power
2 Applications applications and operates over a voltage range of 2.7
to 5.25 V. The total current consumption can be less
• Chemical Species Identification than 10 μA. Further power savings are possible by
• Amperometric Applications switching off the TIA amplifier and shorting the
• Electrochemical Blood Glucose Meter reference electrode to the working electrode with an
internal switch.
Device Information(1)
PART NUMBER PACKAGE BODY SIZE (NOM)
LMP91000 WSON (14) 4.00 mm × 4.00 mm
(1) For all available packages, see the orderable addendum at
the end of the datasheet.
Simplified Application Schematic
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.
LMP91000
SNAS506I –JANUARY 2011–REVISED DECEMBER 2014
www.ti.com
Table of Contents
7.3 Feature Description................................................. 13
1 Features.................................................................. 17.4 Device Functional Modes........................................ 19
2 Applications ........................................................... 17.5 Programming .......................................................... 20
3 Description............................................................. 17.6 Registers Maps ...................................................... 21
4 Revision History..................................................... 28 Application and Implementation ........................ 24
5 Pin Configuration and Functions......................... 38.1 Application Information............................................ 24
6 Specifications......................................................... 48.2 Typical Application ................................................. 26
6.1 Absolute Maximum Ratings ...................................... 49 Power Supply Recommendations...................... 28
6.2 ESD Ratings.............................................................. 49.1 Power Consumption................................................ 28
6.3 Recommended Operating Conditions....................... 410 Layout................................................................... 29
6.4 Thermal Information.................................................. 410.1 Layout Guidelines ................................................. 29
6.5 Electrical Characteristics .......................................... 510.2 Layout Example .................................................... 29
6.6 I2C Interface.............................................................. 711 Device and Documentation Support................. 30
6.7 Timing Requirements ............................................... 811.1 Trademarks........................................................... 30
6.8 Typical Characteristics.............................................. 911.2 Electrostatic Discharge Caution............................ 30
7 Detailed Description............................................ 13 11.3 Glossary................................................................ 30
7.1 Overview................................................................. 13 12 Mechanical, Packaging, and Orderable
7.2 Functional Block Diagram....................................... 13 Information........................................................... 30
4 Revision History
Changes from Revision H (March 2013) to Revision I Page
• Added ESD Ratings table, Feature Description section, Device Functional Modes, Application and Implementation
section, Power Supply Recommendations section, Layout section, Device and Documentation Support section, and
Mechanical, Packaging, and Orderable Information section ................................................................................................. 3
Changes from Revision G (March 2013) to Revision H Page
• Changed layout of National Data Sheet to TI format ........................................................................................................... 27
2Submit Documentation Feedback Copyright © 2011–2014, Texas Instruments Incorporated
Product Folder Links: LMP91000
DGND CE1 14
REMENB
SCL WE
VREF
SDA
NC C1
C2VDD
7 8AGND VOUT
DAP
LMP91000
www.ti.com
SNAS506I –JANUARY 2011–REVISED DECEMBER 2014
5 Pin Configuration and Functions
14-Pin WSON
Top View
Pin Functions
PIN I/O DESCRIPTION
NAME NO.
DGND 1 G Connect to ground
MENB 2 I Module Enable, Active-Low
SCL 3 I Clock signal for I2C compatible interface
SDA 4 I/O Data for I2C compatible interface
NC 5 N/A Not Internally Connected
VDD 6 P Supply Voltage
AGND 7 G Ground
VOUT 8 O Analog Output
C2 9 N/A External filter connector (Filter between C1 and C2)
C1 10 N/A External filter connector (Filter between C1 and C2)
VREF 11 I Voltage Reference input
WE 12 I Working Electrode. Output to drive the Working Electrode of the chemical sensor
RE 13 I Reference Electrode. Input to drive Counter Electrode of the chemical sensor
CE 14 I Counter Electrode. Output to drive Counter Electrode of the chemical sensor
DAP — N/C Connect to AGND
Copyright © 2011–2014, Texas Instruments Incorporated Submit Documentation Feedback 3
Product Folder Links: LMP91000
LMP91000
SNAS506I –JANUARY 2011–REVISED DECEMBER 2014
www.ti.com
6 Specifications
6.1 Absolute Maximum Ratings
over operating free-air temperature (unless otherwise noted) (1)
MIN MAX UNIT
Voltage between any two pins 6.0 V
Current through VDD or VSS 50 mA
Current sunk and sourced by CE pin 10 mA
Current out of other pins(2) 5 mA
Junction Temperature (3) 150 °C
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.
(2) All non-power pins of this device are protected against ESD by snapback devices. Voltage at such pins will rise beyond absmax if
current is forced into pin.
(3) The maximum power dissipation is a function of TJ(MAX), RθJA, and the ambient temperature, TA. The maximum allowable power
dissipation at any ambient temperature is PDMAX = (TJ(MAX) - TA)/ θJA All numbers apply for packages soldered directly onto a PCB.
6.2 ESD Ratings VALUE UNIT
Human-body model (HBM), per ANSI/ESDA/JEDEC JS-001(1) ±2000
V(ESD) Electrostatic discharge V
Charged-device model (CDM), per JEDEC specification JESD22- ±1000
C101(2)
(1) JEDEC document JEP155 states that 500-V HBM allows safe manufacturing with a standard ESD control process.
(2) JEDEC document JEP157 states that 250-V CDM allows safe manufacturing with a standard ESD control process.
6.3 Recommended Operating Conditions
MIX MAX UNIT
Supply Voltage VS= (VDD - AGND) 2.7 5.25 V
Temperature Range(1) –40 85 °C
(1) The maximum power dissipation is a function of TJ(MAX), RθJA, and the ambient temperature, TA. The maximum allowable power
dissipation at any ambient temperature is PDMAX = (TJ(MAX) - TA)/ θJA All numbers apply for packages soldered directly onto a PCB.
6.4 Thermal Information LMP91000
THERMAL METRIC(1) WSON UNIT
14 PINS
RθJA Package Thermal Resistance 44 °C/W
(1) For more information about traditional and new thermal metrics, see the IC Package Thermal Metrics application report, SPRA953.
4Submit Documentation Feedback Copyright © 2011–2014, Texas Instruments Incorporated
Product Folder Links: LMP91000
LMP91000
www.ti.com
SNAS506I –JANUARY 2011–REVISED DECEMBER 2014
6.5 Electrical Characteristics
Unless otherwise specified, TA= 25°C, VS=(VDD – AGND), VS= 3.3 V and AGND = DGND = 0 V, VREF = 2.5 V, Internal
Zero = 20% VREF.(1)
PARAMETER TEST CONDITIONS MIN(2) TYP(3) MAX(2) UNIT
POWER SUPPLY SPECIFICATION
3-lead amperometric cell mode
MODECN = 0x03 10 13.5
–40 to 80°C (please verify that the degree is 15
correct)
Standby mode
MODECN = 0x02 6.5 8
–40 to 80°C 10
Temperature Measurement mode with TIA OFF
MODECN = 0x06 11.4 13.5
–40 to 80°C 15
ISSupply Current µA
Temperature Measurement mode with TIA ON
MODECN = 0x07 14.9 18
–40 to 80°C 20
2-lead ground-referred galvanic cell mode
VREF=1.5 V 6.2
MODECN = 0x01 8
–40 to 80°C 9
Deep Sleep mode
MODECN = 0x00 0.6 0.85
–40 to 80°C 1
POTENTIOSTAT
Bias Programming range Percentage of voltage referred to VREF or VDD
(differential voltage between RE ±24%
pin and WE pin)
Bias_RW First two smallest step ±1
Bias Programming Resolution All other steps ±2%
VDD = 2.7 V
Internal Zero 50% VDD –90 90
–40 to 80°C –800 800
IRE Input bias current at RE pin pA
VDD = 5.25 V
Internal Zero 50% VDD –90 90
–40 to 80°C –900 900
ICE Minimum operating current sink 750 µA
capability source 750
Minimum charging capability(4) sink 10 mA
source 10
AOL_A1 Open-loop voltage gain of control 300 mV ≤VCE ≤Vs-300 mV;
loop op amp (A1) –750 µA ≤ICE ≤750 µA dB
–40 to 80°C 104 120
(1) Electrical 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.
(2) Limits are 100% production tested at 25°C. Limits over the operating temperature range are specified through correlations using
statistical quality control (SQC) method.
(3) 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 specified on shipped
production material.
(4) At such currents no accuracy of the output voltage can be expected.
Copyright © 2011–2014, Texas Instruments Incorporated Submit Documentation Feedback 5
Product Folder Links: LMP91000
LMP91000
SNAS506I –JANUARY 2011–REVISED DECEMBER 2014
www.ti.com
Electrical Characteristics (continued)
Unless otherwise specified, TA= 25°C, VS=(VDD – AGND), VS= 3.3 V and AGND = DGND = 0 V, VREF = 2.5 V, Internal
Zero = 20% VREF.(1)
PARAMETER TEST CONDITIONS MIN(2) TYP(3) MAX(2) UNIT
en_RW Low Frequency integrated noise 0.1 Hz to 10 Hz, Zero Bias 3.4
between RE pin and WE pin (5) µVpp
0.1 Hz to 10 Hz, with Bias 5.1
(5) (6)
0% VREF
Internal Zero=20% VREF
0% VREF –550 550
Internal Zero=50% VREF
0% VREF
Internal Zero=67% VREF
±1% VREF –575 575
±2% VREF –610 610
±4% VREF –750 750
BIAS polarity ±6% VREF –840 840
VOS_RW WE Voltage Offset referred to RE (7) µV
±8% VREF –930 930
–40 to 80°C ±10% VREF –1090 1090
±12% VREF –1235 1235
±14% VREF –1430 1430
±16% VREF –1510 1510
±18% VREF –1575 1575
±20% VREF –1650 1650
±22% VREF –1700 1700
±24% VREF –1750 1750
0% VREF
Internal Zero=20% VREF
0% VREF –4 4
Internal Zero=50% VREF
0% VREF
Internal Zero=67% VREF
±1% VREF –4 4
±2% VREF –4 4
±4% VREF –5 5
WE Voltage Offset Drift referred ±6% VREF –5 5
BIAS polarity
TcVOS_RW to RE from –40°C to 85°C µV/°C
(7) ±8% VREF –5 5
(8)
±10% VREF –6 6
±12% VREF –6 6
±14% VREF –7 7
±16% VREF –7 7
±18% VREF –8 8
±20% VREF –8 8
±22% VREF –8 8
±24% VREF –8 8
(5) This parameter includes both A1 and TIA's noise contribution.
(6) In case of external reference connected, the noise of the reference has to be added.
(7) For negative bias polarity the Internal Zero is set at 67% VREF.
(8) Offset voltage temperature drift is determined by dividing the change in VOS at the temperature extremes by the total temperature
change. Starting from the measured voltage offset at temperature T1 (VOS_RW(T1)), the voltage offset at temperature T2 (VOS_RW(T2)) is
calculated according the following formula: VOS_RW(T2)=VOS_RW(T1)+ABS(T2–T1)* TcVOS_RW.
6Submit Documentation Feedback Copyright © 2011–2014, Texas Instruments Incorporated
Product Folder Links: LMP91000
LMP91000
www.ti.com
SNAS506I –JANUARY 2011–REVISED DECEMBER 2014
Electrical Characteristics (continued)
Unless otherwise specified, TA= 25°C, VS=(VDD – AGND), VS= 3.3 V and AGND = DGND = 0 V, VREF = 2.5 V, Internal
Zero = 20% VREF.(1)
PARAMETER TEST CONDITIONS MIN(2) TYP(3) MAX(2) UNIT
Transimpedance gain accuracy 5%
Linearity ±0.05%
7 programmable gain resistors 2.75
3.5
7
TIA_GAIN 14
Programmable TIA Gains kΩ
35
120
350
Maximum external gain resistor 350
Internal zero voltage 3 programmable percentages of VREF 20%
50%
67%
TIA_ZV 3 programmable percentages of VDD 20%
50%
67%
Internal zero voltage Accuracy ±0.04%
RL Programmable Load 4 programmable resistive loads 10
33 Ω
50
100
Load accuracy 5%
2.7 V ≤VDD≤5.25 Internal zero 20% VREF
Power Supply Rejection Ratio at V
PSRR Internal zero 50% VREF 80 110 dB
RE pin Internal zero 67% VREF
TEMPERATURE SENSOR SPECIFICATION (Refer to Table 1 in the Feature Description for details)
Temperature Error TA= –40˚C to 85˚C –3 3 °C
Sensitivity TA= –40˚C to 85˚C -8.2 mV/°C
Power on time 1.9 ms
EXTERNAL REFERENCE SPECIFICATION
VREF External Voltage reference range 1.5 VDD V
Input impedance 10 MΩ
6.6 I2C Interface
Unless otherwise specified, TA= 25°C, VS= (VDD – AGND), 2.7 V <VS< 5.25 V and AGND = DGND = 0 V, VREF = 2.5 V.(1)
PARAMETER TEST CONDITIONS MIN (2) TYP (3) MAX(2) UNIT
VIH Input High Voltage –40 to 80°C 0.7*VDD V
VIL Input Low Voltage –40 to 80°C 0.3*VDD V
VOL Output Low Voltage IOUT= 3 mA 0.4 V
Hysteresis (4) –40 to 80°C 0.1*VDD V
CIN Input Capacitance on all digital pins –40 to 80°C 0.5 pF
(1) Electrical 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.
(2) Limits are 100% production tested at 25°C. Limits over the operating temperature range are specified through correlations using
statistical quality control (SQC) method.
(3) 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 specified on shipped
production material.
(4) This parameter is specified by design or characterization.
Copyright © 2011–2014, Texas Instruments Incorporated Submit Documentation Feedback 7
Product Folder Links: LMP91000
SCL
SDA
tHD;STA
tLOW
tHD;DAT tHIGH tSU;DAT
tSU;STA tSU;STO
tf
START REPEATED
START STOP
tHD;STA
START
tSP
tBUF
1/fSCL
tVD;DAT
tVD;ACK
30%
70%
30%
70%
MENB 30%
70%
tEN;START tEN;STOP tEN;HIGH
LMP91000
SNAS506I –JANUARY 2011–REVISED DECEMBER 2014
www.ti.com
6.7 Timing Requirements
Unless otherwise specified, TA= 25°C, VS= (VDD – AGND), VS= 3.3 V and AGND = DGND = 0 V, VREF = 2.5 V, Internal
Zero= 20% VREF.(1)
MIN TYP MAX UNIT
fSCL Clock Frequency –40 to 80°C 10 100 kHz
tLOW Clock Low Time –40 to 80°C 4.7 µs
tHIGH Clock High Time –40 to 80°C 4.0 µs
After this period, the first clock
tHD;STA Data valid 4.0 µs
pulse is generated
tSU;STA Set-up time for a repeated START condition –40 to 80°C 4.7 µs
tHD;DAT Data hold time(2) –40 to 80°C 0 ns
tSU;DAT Data Set-up time –40 to 80°C 250 ns
IL ≤3 mA;
tfSDA fall time (3) CL ≤400 pF 250 ns
–40 to 80°C
tSU;STO Set-up time for STOP condition –40 to 80°C 4.0 µs
Bus free time between a STOP and START –40 to 80°C
tBUF 4.7 µs
condition
tVD;DAT Data valid time –40 to 80°C 3.45 µs
tVD;ACK Data valid acknowledge time –40 to 80°C 3.45 µs
tSP Pulse width of spikes that must be –40 to 80°C 50 ns
suppressed by the input filter(3)
t_timeout SCL and SDA Timeout –40 to 80°C 25 100 ms
tEN;START I2C Interface Enabling –40 to 80°C 600 ns
tEN;STOP I2C Interface Disabling –40 to 80°C 600 ns
tEN;HIGH Time between consecutive I2C interface –40 to 80°C 600 ns
enabling and disabling
(1) Electrical 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.
(2) LMP91000 provides an internal 300-ns minimum hold time to bridge the undefined region of the falling edge of SCL.
(3) This parameter is specified by design or characterization.
Figure 1. Timing Diagram
8Submit Documentation Feedback Copyright © 2011–2014, Texas Instruments Incorporated
Product Folder Links: LMP91000
10 100 1k 10k 100k
80
90
100
110
120
130
140
PSRR (dB)
FREQUENCY (Hz)
2.5 3.0 3.5 4.0 4.5 5.0 5.5
1310
1312
1314
1316
1318
1320
VOUT (mV)
SUPPLY VOLTAGE (V)
-50 -25 0 25 50 75 100
-300
-280
-260
-240
-220
-200
-180
-160
-140
-120
-100
VOS (V)
TEMPERATURE (°C)
VDD = 2.7V
VDD = 3.3V
VDD = 5V
2.5 3.0 3.5 4.0 4.5 5.0 5.5
-300
-280
-260
-240
-220
-200
-180
-160
-140
-120
-100
VOS (V)
SUPPLY VOLTAGE (V)
85°C
25°C
-40°C
LMP91000
www.ti.com
SNAS506I –JANUARY 2011–REVISED DECEMBER 2014
6.8 Typical Characteristics
Unless otherwise specified, TA= 25°C, VS= (VDD – AGND), 2.7V <VS< 5.25 V and AGND = DGND = 0 V, VREF = 2.5 V.
Figure 2. Input VOS_RW vs. Temperature (Vbias 0 mV) Figure 3. Input VOS_RW vs. VDD (Vbias 0 mV)
Figure 4. IWE Step Current Response (Rise) Figure 5. IWE Step Current Response (Fall)
Figure 6. AC PSRR vs. Frequency Figure 7. Temperature Sensor Output vs. VDD
(Temperature = 30°C)
Copyright © 2011–2014, Texas Instruments Incorporated Submit Documentation Feedback 9
Product Folder Links: LMP91000
-50 -25 0 25 50 75 100
9.0
9.2
9.4
9.6
9.8
10.0
10.2
10.4
10.6
10.8
11.0
SUPPLY CURRENT (A)
TEMPERATURE (°C)
VDD = 2.7V
VDD = 3.3V
VDD = 5V
2.5 3.0 3.5 4.0 4.5 5.0 5.5
9.0
9.2
9.4
9.6
9.8
10.0
10.2
10.4
10.6
10.8
11.0
SUPPLY CURRENT (A)
SUPPLY VOLTAGE (V)
85°C
25°C
-40°C
-50 -25 0 25 50 75 100
5.50
5.75
6.00
6.25
6.50
6.75
7.00
7.25
7.50
SUPPLY CURRENT (A)
TEMPERATURE (°C)
VDD = 2.7V
VDD = 3.3V
VDD = 5V
2.5 3.0 3.5 4.0 4.5 5.0 5.5
5.50
5.75
6.00
6.25
6.50
6.75
7.00
7.25
7.50
SUPPLY CURRENT (A)
SUPPLY VOLTAGE (V)
85°C
25°C
-40°C
-50 -25 0 25 50 75 100
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
SUPPLY CURRENT (A)
TEMPERATURE (°C)
VDD = 2.7V
VDD = 3.3V
VDD = 5V
2.5 3.0 3.5 4.0 4.5 5.0 5.5
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
SUPPLY CURRENT (A)
SUPPLY VOLTAGE (V)
85°C
25°C
-40°C
LMP91000
SNAS506I –JANUARY 2011–REVISED DECEMBER 2014
www.ti.com
Typical Characteristics (continued)
Unless otherwise specified, TA= 25°C, VS= (VDD – AGND), 2.7V <VS< 5.25 V and AGND = DGND = 0 V, VREF = 2.5 V.
Figure 8. Supply Current vs. Temperature Figure 9. Supply Current vs. VDD
(Deep Sleep Mode) (Deep Sleep Mode)
Figure 10. Supply Current vs. Temperature Figure 11. Supply Current vs. VDD
(Standby Mode) (Standby Mode)
Figure 12. Supply Current vs. Temperature Figure 13. Supply Current vs. VDD
(3-Lead Amperometric Mode) (3-Lead Amperometric Mode)
10 Submit Documentation Feedback Copyright © 2011–2014, Texas Instruments Incorporated
Product Folder Links: LMP91000
-50 -25 0 25 50 75 100
5.00
5.25
5.50
5.75
6.00
6.25
6.50
6.75
7.00
7.25
7.50
SUPPLY CURRENT (A)
TEMPERATURE (°C)
VDD = 2.7V
VDD = 3.3V
VDD = 5V
2.5 3.0 3.5 4.0 4.5 5.0 5.5
5.0
5.5
6.0
6.5
7.0
7.5
8.0
8.5
9.0
SUPPLY CURRENT (A)
SUPPLY VOLTAGE (V)
85°C
25°C
-40°C
-50 -25 0 25 50 75 100
9.0
9.5
10.0
10.5
11.0
11.5
12.0
12.5
13.0
SUPPLY CURRENT (A)
TEMPERATURE (°C)
VDD = 2.7V
VDD = 3.3V
VDD = 5V
2.5 3.0 3.5 4.0 4.5 5.0 5.5
10.0
10.5
11.0
11.5
12.0
12.5
13.0
SUPPLY CURRENT (A)
SUPPLY VOLTAGE (V)
85°C
25°C
-40°C
-50 -25 0 25 50 75 100
13.0
13.5
14.0
14.5
15.0
15.5
16.0
16.5
17.0
SUPPLY CURRENT (A)
TEMPERATURE (°C)
VDD = 2.7V
VDD = 3.3V
VDD = 5V
2.5 3.0 3.5 4.0 4.5 5.0 5.5
14.0
14.2
14.4
14.6
14.8
15.0
15.2
15.4
15.6
15.8
16.0
SUPPLY CURRENT (A)
SUPPLY VOLTAGE (V)
85°C
25°C
-40°C
LMP91000
www.ti.com
SNAS506I –JANUARY 2011–REVISED DECEMBER 2014
Typical Characteristics (continued)
Unless otherwise specified, TA= 25°C, VS= (VDD – AGND), 2.7V <VS< 5.25 V and AGND = DGND = 0 V, VREF = 2.5 V.
Figure 14. Supply Current vs. Temperature Figure 15. Supply Current vs. VDD
(Temp Measurement TIA On) (Temp Measurement TIA On)
Figure 16. Supply Current vs. Temperature Figure 17. Supply Current vs. VDD
(Temp Measurement TIA Off) (Temp Measurement TIA Off)
Figure 18. Supply Current vs. Temperature Figure 19. Supply Current vs. VDD
(2-Lead Ground-Referred Amperometric Mode) (2-Lead Ground-Referred Amperometric Mode)
Copyright © 2011–2014, Texas Instruments Incorporated Submit Documentation Feedback 11
Product Folder Links: LMP91000
012345678910
-2.5
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
2.5
EN_RW (V)
TIME (s)
0 25 50 75 100 125 150
1.0
1.1
1.2
1.3
1.4
1.5
1.6
1.7
1.8
1.9
2.0
VOUT (V)
TIME (s)
RTIA=35k,
Rload=10,
VREF=5V
LMP91000
012345678910
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
EN_RW (V)
TIME (s)
012345678910
-2.5
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
2.5
EN_RW (V)
TIME (s)
LMP91000
SNAS506I –JANUARY 2011–REVISED DECEMBER 2014
www.ti.com
Typical Characteristics (continued)
Unless otherwise specified, TA= 25°C, VS= (VDD – AGND), 2.7V <VS< 5.25 V and AGND = DGND = 0 V, VREF = 2.5 V.
Figure 20. 0.1-Hz to 10-Hz Noise, 0-V Bias Figure 21. 0.1-Hz to 10-Hz Noise, 300-mV Bias
Figure 22. 0.1-Hz to 10-Hz Noise, 600-mV Bias Figure 23. A VOUT Step Response 100-PPM to 400-PPM CO
(CO Gas Sensor Connected to LMP91000)
12 Submit Documentation Feedback Copyright © 2011–2014, Texas Instruments Incorporated
Product Folder Links: LMP91000
I2C INTERFACE
AND
CONTROL
REGISTERS
RE
VREF VDD
AGND
CE
WE VOUT
C1
SCL
TEMP
SENSOR
VREF
DIVIDER
C2
SDA
RLoad
VARIABLE
BIAS MENB
DGND
A1 +
-
TIA
+
-
RTIA
CE
WE
RE
3-Lead
Electrochemical
Cell
LMP91000
LMP91000
www.ti.com
SNAS506I –JANUARY 2011–REVISED DECEMBER 2014
7 Detailed Description
7.1 Overview
The LMP91000 is a programmable AFE for use in micropower chemical sensing applications. The LMP91000 is
designed for 3-lead single gas sensors and for 2-lead galvanic cell sensors. This device provides all of the
functionality for detecting changes in gas concentration based on a delta current at the working electrode. The
LMP91000 generates an output voltage proportional to the cell current. Transimpedance gain is user
programmable through an I2C compatible interface from 2.75 kΩto 350 kΩmaking it easy to convert current
ranges from 5 µA to 750 µA full scale. Optimized for micro-power applications, the LMP91000 AFE works over a
voltage range of 2.7 V to 5.25 V. The cell voltage is user selectable using the on board programmability. In
addition, it is possible to connect an external transimpedance gain resistor. A temperature sensor is embedded
and it can be power cycled through the interface. The output of this temperature sensor can be read by the user
through the VOUT pin. It is also possible to have both temperature output and output of the TIA at the same
time; the pin C2 is internally connected to the output of the transimpedance (TIA), while the temperature is
available at the VOUT pin. Depending on the configuration, total current consumption for the device can be less
than 10 µA. For power savings, the transimpedance amplifier can be turned off and instead a load impedance
equivalent to the TIA’s inputs impedance is switched in.
7.2 Functional Block Diagram
7.3 Feature Description
7.3.1 Potentiostat Circuitry
The core of the LMP91000 is a potentiostat circuit. It consists of a differential input amplifier used to compare the
potential between the working and reference electrodes to a required working bias potential (set by the Variable
Bias circuitry). The error signal is amplified and applied to the counter electrode (through the Control Amplifier
-A1). Any changes in the impedance between the working and reference electrodes will cause a change in the
voltage applied to the counter electrode, in order to maintain the constant voltage between working and
reference electrodes. A Transimpedance Amplifier connected to the working electrode, is used to provide an
output voltage that is proportional to the cell current. The working electrode is held at virtual ground (Internal
ground) by the transimpedance amplifier. The potentiostat will compare the reference voltage to the desired bias
potential and adjust the voltage at the counter electrode to maintain the proper working-to-reference voltage.
Copyright © 2011–2014, Texas Instruments Incorporated Submit Documentation Feedback 13
Product Folder Links: LMP91000
LMP91000
SNAS506I –JANUARY 2011–REVISED DECEMBER 2014
www.ti.com
Feature Description (continued)
7.3.1.1 Transimpedance Amplifier
The transimpedance amplifier (TIA) has 7 programmable internal gain resistors. This accommodates the full
scale ranges of most existing sensors. Moreover an external gain resistor can be connected to the LMP91000
between C1 and C2 pins. The gain is set through the I2C interface.
7.3.1.2 Control Amplifier
The control amplifier (A1 op amp) has two tasks: a) providing initial charge to the sensor, b) providing a bias
voltage to the sensor. A1 has the capability to drive up to 10 mA into the sensor in order to to provide a fast initial
conditioning. A1 is able to sink and source current according to the connected gas sensor (reducing or oxidizing
gas sensor). It can be powered down to reduce system power consumption. However powering down A1 is not
recommended, as it may take a long time for the sensor to recover from this situation.
7.3.1.3 Variable Bias
The Variable Bias block circuitry provides the amount of bias voltage required by a biased gas sensor between
its reference and working electrodes. The bias voltage can be programmed to be 1% to 24% (14 steps in total) of
the supply, or of the external reference voltage. The 14 steps can be programmed through the I2C interface. The
polarity of the bias can be also programmed.
7.3.1.4 Internal Zero
The internal Zero is the voltage at the non-inverting pin of the TIA. The internal zero can be programmed to be
either 67%, 50% or 20%, of the supply, or the external reference voltage. This provides both sufficient headroom
for the counter electrode of the sensor to swing, in case of sudden changes in the gas concentration, and best
use of the ADC’s full scale input range.
The Internal zero is provided through an internal voltage divider. The divider is programmed through the I2C
interface.
7.3.1.5 Temperature Sensor
The embedded temperature sensor can be switched off during gas concentration measurement to save power.
The temperature measurement is triggered through the I2C interface. The temperature output is available at the
VOUT pin until the configuration bit is reset. The output signal of the temperature sensor is a voltage, referred to
the ground of the LMP91000 (AGND).
Table 1. Temperature Sensor Transfer
TEMPERATURE OUTPUT VOLTAGE TEMPERATURE OUTPUT VOLTAGE
(°C) (mV) (°C) (mV)
-40 1875 23 1375
-39 1867 24 1367
-38 1860 25 1359
-37 1852 26 1351
-36 1844 27 1342
-35 1836 28 1334
-34 1828 29 1326
-33 1821 30 1318
-32 1813 31 1310
-31 1805 32 1302
-30 1797 33 1293
-29 1789 34 1285
-28 1782 35 1277
-27 1774 36 1269
-26 1766 37 1261
-25 1758 38 1253
14 Submit Documentation Feedback Copyright © 2011–2014, Texas Instruments Incorporated
Product Folder Links: LMP91000
LMP91000
www.ti.com
SNAS506I –JANUARY 2011–REVISED DECEMBER 2014
Feature Description (continued)
Table 1. Temperature Sensor Transfer (continued)
TEMPERATURE OUTPUT VOLTAGE TEMPERATURE OUTPUT VOLTAGE
(°C) (mV) (°C) (mV)
-24 1750 39 1244
-23 1742 40 1236
-22 1734 41 1228
-21 1727 42 1220
-20 1719 43 1212
-19 1711 44 1203
-18 1703 45 1195
-17 1695 46 1187
-16 1687 47 1179
-15 1679 48 1170
-14 1671 49 1162
-13 1663 50 1154
-12 1656 51 1146
-11 1648 52 1137
-10 1640 53 1129
-9 1632 54 1121
-8 1624 55 1112
-7 1616 56 1104
-6 1608 57 1096
-5 1600 58 1087
-4 1592 59 1079
-3 1584 60 1071
-2 1576 61 1063
-1 1568 62 1054
0 1560 63 1046
1 1552 64 1038
2 1544 65 1029
3 1536 66 1021
4 1528 67 1012
5 1520 68 1004
6 1512 69 996
7 1504 70 987
8 1496 71 979
9 1488 72 971
10 1480 73 962
11 1472 74 954
12 1464 75 945
13 1456 76 937
14 1448 77 929
15 1440 78 920
16 1432 79 912
17 1424 80 903
18 1415 81 895
19 1407 82 886
20 1399 83 878
Copyright © 2011–2014, Texas Instruments Incorporated Submit Documentation Feedback 15
Product Folder Links: LMP91000
LMP91000
SNAS506I –JANUARY 2011–REVISED DECEMBER 2014
www.ti.com
Feature Description (continued)
Table 1. Temperature Sensor Transfer (continued)
TEMPERATURE OUTPUT VOLTAGE TEMPERATURE OUTPUT VOLTAGE
(°C) (mV) (°C) (mV)
21 1391 84 870
22 1383 85 861
Although the temperature sensor is very linear, its response does have a slight downward parabolic shape. This
shape is very accurately reflected in Table 1. For a linear approximation, a line can easily be calculated over the
desired temperature range from Table 1 using the two-point equation:
V-V1=((V2–V1)/(T2–T1))*(T-T1)
where
• V is in mV, T is in °C, T1and V1are the coordinates of the lowest temperature
• T2and V2are the coordinates of the highest temperature. (1)
For example, to determine the equation of a line over a temperature range of 20°C to 50°C, proceed as follows:
V-1399mV=((1154 mV - 1399 mV)/(50°C -20°C))*(T-20°C) (2)
V-1399mV= -8.16 mV/°C*(T-20°C) (3)
V=(-8.16 mV/°C)*T+1562.2 mV (4)
Using this method of linear approximation, the transfer function can be approximated for one or more
temperature ranges of interest.
16 Submit Documentation Feedback Copyright © 2011–2014, Texas Instruments Incorporated
Product Folder Links: LMP91000
I2C INTERFACE
AND
CONTROL
REGISTERS
RE
VREF VDD
AGND
CE
WE VOUT
C1
SCL
TEMP
SENSOR
VREF
DIVIDER
C2
SDA
RLoad
VARIABLE
BIAS MENB
DGND
A1 +
-
TIA
+
-
RTIA
CE
WE
RE
3-Lead
Electrochemical
Cell
LMP91000
LMP91000
www.ti.com
SNAS506I –JANUARY 2011–REVISED DECEMBER 2014
7.3.1.6 Gas Sensor Interface
The LMP91000 supports both 3-lead and 2-lead gas sensors. Most of the toxic gas sensors are amperometric
cells with 3 leads (Counter, Worker and Reference). These leads should be connected to the LMP91000 in the
potentiostat topology. The 2-lead gas sensor (known as galvanic cell) should be connected as simple buffer
either referred to the ground of the system or referred to a reference voltage. The LMP91000 support both
connections for 2-lead gas sensor.
7.3.1.6.1 3-Lead Amperometric Cell in Potentiostat Configuration
Most of the amperometric cell have 3 leads (Counter, Reference and Working electrodes). The interface of the 3-
lead gas sensor to the LMP91000 is straightforward, the leads of the gas sensor need to be connected to the
namesake pins of the LMP91000.
The LMP91000 is then configured in 3-lead amperometric cell mode; in this configuration the Control Amplifier
(A1) is ON and provides the internal zero voltage and bias in case of biased gas sensor. The transimpedance
amplifier (TIA) is ON, it converts the current generated by the gas sensor in a voltage, according to the
transimpedance gain:
Gain=RTIA (5)
If different gains are required, an external resistor can be connected between the pins C1 and C2. In this case
the internal feedback resistor should be programmed to “external”. The RLoad together with the output
capacitance of the gas sensor acts as a low pass filter.
Figure 24. 3-Lead Amperometric Cell
Copyright © 2011–2014, Texas Instruments Incorporated Submit Documentation Feedback 17
Product Folder Links: LMP91000
I2C INTERFACE
AND
CONTROL
REGISTERS
RE
VREF VDD
AGND
CE
WE VOUT
C1
SCL
TEMP
SENSOR
VREF
DIVIDER
C2
SDA
RLoad
VARIABLE
BIAS
LMP91000
MENB
DGND
A1 +
-
TIA
+
-
RTIA
VE-
VE+
NC
2-wire
Sensor
such as
Oxygen
LMP91000
SNAS506I –JANUARY 2011–REVISED DECEMBER 2014
www.ti.com
7.3.1.6.2 2-Lead Galvanic Cell In Ground Referred Configuration
When the LMP91000 is interfaced to a galvanic cell (for instance to an Oxygen gas sensor) referred to the
ground of the system, an external resistor needs to be placed in parallel to the gas sensor; the negative
electrode of the gas sensor is connected to the ground of the system and the positive electrode to the Vref pin of
the LMP91000, the working pin of the LMP91000 is connected to the ground.
The LMP91000 is then configured in 2-lead galvanic cell mode and the Vref bypass feature needs to be enabled.
In this configuration the Control Amplifier (A1) is turned off, and the output of the gas sensor is amplified by the
Transimpedance Amplifier (TIA) which is configured as a simple non-inverting amplifier.
The gain of this non inverting amplifier is set according the following formula:
Gain= 1+(RTIA/RLoad) (6)
If different gains are required, an external resistor can be connected between the pins C1 and C2. In this case
the internal feedback resistor should be programmed to “external”.
Figure 25. 2-Lead Galvanic Cell Ground-Referred
18 Submit Documentation Feedback Copyright © 2011–2014, Texas Instruments Incorporated
Product Folder Links: LMP91000
I2C INTERFACE
AND
CONTROL
REGISTERS
RE
VREF VDD
AGND
CE
WE VOUT
C1
SCL
TEMP
SENSOR
VREF
DIVIDER
C2
SDA
RLoad
VARIABLE
BIAS MENB
DGND
A1 +
-
TIA
+
-
RTIA
VE-
VE+
NC
LMP91000
2-wire Sensor
such as Oxygen
LMP91000
www.ti.com
SNAS506I –JANUARY 2011–REVISED DECEMBER 2014
7.3.1.6.3 2-lead Galvanic Cell in Potentiostat Configuration
When the LMP91000 is interfaced to a galvanic cell (for instance to an Oxygen gas sensor) referred to a
reference, the Counter and the Reference pin of the LMP91000 are shorted together and connected to negative
electrode of the galvanic cell. The positive electrode of the galvanic cell is then connected to the Working pin of
the LMP91000.
The LMP91000 is then configured in 3-lead amperometric cell mode (as for amperometric cell). In this
configuration the Control Amplifier (A1) is ON and provides the internal zero voltage. The transimpedance
amplifier (TIA) is also ON, it converts the current generated by the gas sensor in a voltage, according to the
transimpedance gain:
Gain= RTIA (7)
If different gains are required, an external resistor can be connected between the pins C1 and C2. In this case
the internal feedback resistor should be programmed to “external”.
Figure 26. 2-Lead Galvanic Cell in Potentiostat Configuration
7.3.1.7 Timeout Feature
The timeout is a safety feature to avoid bus lockup situation. If SCL is stuck low for a time exceeding t_timeout,
the LMP91000 will automatically reset its I2C interface. Also, in the case the LMP91000 hangs the SDA for a time
exceeding t_timeout, the LMP91000’s I2C interface will be reset so that the SDA line will be released. Since the
SDA is an open-drain with an external resistor pull-up, this also avoids high power consumption when LMP91000
is driving the bus and the SCL is stopped.
7.4 Device Functional Modes
The LMP91000 has 6 operational modes to optimize the current consumption and meet the needs of the
applications. It is possible to select the operational mode through the I2C bus.
At the power on the LMP91000 is in deep sleep mode. In this mode the device accepts I2C commands and
burns the lowest supply current. In this mode the TIA, the A1 control amplifier and the temperature sensor are
OFF. This mode of operation is suggested when the gas detector is not used and a zero bias is required
between WE and RE electrodes of the gas sensor. The zero bias between the WE and RE electrodes is kept by
enabling the internal FET feature.
In the standby mode, the TIA is OFF, while the A1 control amplifier is ON. This mode of operation is suggested
when the gas detector is not used for short amount of time and a faster warm-up of the gas detector is required.
Copyright © 2011–2014, Texas Instruments Incorporated Submit Documentation Feedback 19
Product Folder Links: LMP91000
D7 D6 D5 D4 D3 D2 D1 D0
1 9 1 9
Ack
by
LMP91000
Start by
Master
R/W Ack
by
LMP91000
Frame 1
Serial Bus Address Byte
from Master
Frame 2
Internal Address Register
Byte from Master
1 9
Ack
by
LMP91000
Frame 3
Data Byte
D3 D1D2
D4D5D6D7
A2 A0A1A3A4A5A6
SCL
SDA
SCL
(continued)
SDA
(continued) Stop by
Master
D0
MENB
MENB
(continued)
LMP91000
SNAS506I –JANUARY 2011–REVISED DECEMBER 2014
www.ti.com
Device Functional Modes (continued)
In the 3-lead amperometric cell, the LMP91000 is configured as a standard potentiostat with A1, TIA and bias
circuitry completely ON.
In the Temperature measurement (TIA OFF) the LMP91000 is in Standby mode with the Temperature sensor
ON, at theVOUT pin of the LMP91000 it s possible to read the temperature sensor's output.
In the Temperature measurement (TIA ON) the LMP91000 is 3-lead amperometric cell mode with the
Temperature sensor ON, at theVOUT pin of the LMP91000 it s possible to read the temperature sensor's output.
In 2-lead ground referred galvanic cell the A1 control amplifer is OFF and the Internal zero circuitry is bypassed.
In this mode it is possible to connect 2-lead sensors like the O2 sensor to the LMP91000.
7.5 Programming
7.5.1 I2C Interface
The I2C compatible interface operates in Standard mode (100kHz). Pull-up resistors or current sources are
required on the SCL and SDA pins to pull them high when they are not being driven low. A logic zero is
transmitted by driving the output low. A logic high is transmitted by releasing the output and allowing it to be
pulled-up externally. The appropriate pull-up resistor values will depend upon the total bus capacitance and
operating speed. The LMP91000 comes with a 7 bit bus fixed address: 1001 000.
7.5.2 Write and Read Operation
In order to start any read or write operation with the LMP91000, MENB needs to be set low during the whole
communication. Then the master generates a start condition by driving SDA from high to low while SCL is high.
The start condition is always followed by a 7-bit slave address and a Read/Write bit. After these 8 bits have been
transmitted by the master, SDA is released by the master and the LMP91000 either ACKs or NACKs the
address. If the slave address matches, the LMP91000 ACKs the master. If the address doesn't match, the
LMP91000 NACKs the master. For a write operation, the master follows the ACK by sending the 8-bit register
address pointer. Then the LMP91000 ACKs the transfer by driving SDA low. Next, the master sends the 8-bit
data to the LMP91000. Then the LMP91000 ACKs the transfer by driving SDA low. At this point the master
should generate a stop condition and optionally set the MENB at logic high level (refer to Figure 27,Figure 28,
and Figure 29).
A read operation requires the LMP91000 address pointer to be set first, also in this case the master needs
setting at low logic level the MENB, then the master needs to write to the device and set the address pointer
before reading from the desired register. This type of read requires a start, the slave address, a write bit, the
address pointer, a Repeated Start (if appropriate), the slave address, and a read bit (refer to Figure 27,
Figure 28, and Figure 29). Following this sequence, the LMP91000 sends out the 8-bit data of the register.
When just one LMP91000 is present on the I2C bus the MENB can be tied to ground (low logic level).
Figure 27. Register Write Transaction
20 Submit Documentation Feedback Copyright © 2011–2014, Texas Instruments Incorporated
Product Folder Links: LMP91000
D7 D6 D5 D4 D3 D2 D1 D0
1 9
Ack
by
LMP91000
Start by
Master No Ack
by
Master
SCL
SDA
Stop
by
Master
1 9
Frame 1
Serial Bus Address Byte
from Master
Frame 2
Data Byte from
Slave
R/W
A2 A0A1
A3A4A5A6
MENB
D7 D6 D5 D4 D3 D2 D1 D0
1 9 1 9
Ack
by
LMP91000
Start by
Master
R/W Ack
by
LMP91000
Frame 1
Serial Bus Address Byte
from Master
Frame 2
Internal Address Register
Byte from Master
A2 A0A1
A3A4A5A6
SCL
SDA Stop by
Master
MENB
LMP91000
www.ti.com
SNAS506I –JANUARY 2011–REVISED DECEMBER 2014
Programming (continued)
Figure 28. Pointer Set Transaction
Figure 29. Register Read Transaction
7.6 Registers Maps
The registers are used to configure the LMP91000.
If writing to a reserved bit, user must write only 0. Readback value is unspecified and should be discarded.
Table 2. Register Map
Address Name Power on default Access Lockable?
0x00 STATUS 0x00 Read only No
0x01 LOCK 0x01 R/W No
0x02 through 0x09 RESERVED — — —
0x10 TIACN 0x03 R/W Yes
0x11 REFCN 0x20 R/W Yes
0x12 MODECN 0x00 R/W No
0x13 through 0xFF RESERVED — — —
7.6.1 STATUS -- Status Register (Address 0x00)
The status bit is an indication of the LMP91000's power-on status. If its readback is “0”, the LMP91000 is not
ready to accept other I2C commands.
Bit Name Function
[7:1] RESERVED Status of Device
0 STATUS 0 Not Ready (default)
1 Ready
7.6.2 LOCK -- Protection Register (Address 0x01)
The lock bit enables and disables the writing of the TIACN and the REFCN registers. In order to change the
content of the TIACN and the REFCN registers the lock bit needs to be set to “0”.
Copyright © 2011–2014, Texas Instruments Incorporated Submit Documentation Feedback 21
Product Folder Links: LMP91000
LMP91000
SNAS506I –JANUARY 2011–REVISED DECEMBER 2014
www.ti.com
Bit Name Function
[7:1] RESERVED Write protection
0 LOCK 0 Registers 0x10, 0x11 in write mode
1 Registers 0x10, 0x11 in read only mode (default)
7.6.3 TIACN -- TIA Control Register (Address 0x10)
The parameters in the TIA control register allow the configuration of the transimpedance gain (RTIA) and the load
resistance (RLoad).
Bit Name Function
[7:5] RESERVED RESERVED
TIA feedback resistance selection
000 External resistance (default)
001 2.75kΩ
010 3.5kΩ
[4:2] TIA_GAIN 011 7kΩ
100 14kΩ
101 35kΩ
110 120kΩ
111 350kΩ
RLoad selection
00 10Ω
[1:0] RLOAD 01 33Ω
10 50Ω
11 100Ω(default)
7.6.4 REFCN -- Reference Control Register (Address 0x11)
The parameters in the Reference control register allow the configuration of the Internal zero, Bias and Reference
source. When the Reference source is external, the reference is provided by a reference voltage connected to
the VREF pin. In this condition the Internal Zero and the Bias voltage are defined as a percentage of VREF
voltage instead of the supply voltage.
Bit Name Function
Reference voltage source selection
7 REF_SOURCE 0 Internal (default)
1 external
Internal zero selection (Percentage of the source reference)
00 20%
[6:5] INT_Z 01 50% (default)
10 67%
11 Internal zero circuitry bypassed (only in O2ground referred measurement)
Selection of the Bias polarity
4 BIAS_SIGN 0 Negative (VWE – VRE)<0V (default)
1 Positive (VWE –VRE)>0V
BIAS selection (Percentage of the source reference)
0000 0% (default)
0001 1%
0010 2%
0011 4%
0100 6%
0101 8%
[3:0] BIAS 0110 10%
0111 12%
1000 14%
1001 16%
1010 18%
1011 20%
1100 22%
1101 24%
22 Submit Documentation Feedback Copyright © 2011–2014, Texas Instruments Incorporated
Product Folder Links: LMP91000
LMP91000
www.ti.com
SNAS506I –JANUARY 2011–REVISED DECEMBER 2014
7.6.5 MODECN -- Mode Control Register (Address 0x12)
The Parameters in the Mode register allow the configuration of the Operation Mode of the LMP91000.
Bit Name Function
Shorting FET feature
7 FET_SHORT 0 Disabled (default)
1 Enabled
[6:3] RESERVED Mode of Operation selection
000 Deep Sleep (default)
001 2-lead ground referred galvanic cell
[2:0] OP_MODE 010 Standby
011 3-lead amperometric cell
110 Temperature measurement (TIA OFF)
111 Temperature measurement (TIA ON)
When the LMP91000 is in Temperature measurement (TIA ON) mode, the output of the temperature sensor is
present at the VOUT pin, while the output of the potentiostat circuit is available at pin C2.
Copyright © 2011–2014, Texas Instruments Incorporated Submit Documentation Feedback 23
Product Folder Links: LMP91000
LMP91000
µC
SCL
SDA
GPIO 1 GPIO 2 GPIO 3 GPIO N
SDA
SCL
MENB
LMP91000
SDA
SCL
MENB
LMP91000
SDA
SCL
MENB
LMP91000
SDA
SCL
MENB
LMP91000
SNAS506I –JANUARY 2011–REVISED DECEMBER 2014
www.ti.com
8 Application and Implementation
NOTE
Information in the following applications sections is not part of the TI component
specification, and TI does not warrant its accuracy or completeness. TI’s customers are
responsible for determining suitability of components for their purposes. Customers should
validate and test their design implementation to confirm system functionality.
8.1 Application Information
8.1.1 Connection of More Than One LMP91000 to the I2C BUS
The LMP91000 comes out with a unique and fixed I2C slave address. It is still possible to connect more than one
LMP91000 to an I2C bus and select each device using the MENB pin. The MENB simply enables/disables the
I2C communication of the LMP91000. When the MENB is at logic level low all the I2C communication is enabled,
it is disabled when MENB is at high logic level.
In a system based on a μcontroller and more than one LMP91000 connected to the I2C bus, the I2C lines (SDA
and SCL) are shared, while the MENB of each LMP91000 is connected to a dedicate GPIO port of the
μcontroller.
The μcontroller starts communication asserting one out of N MENB signals where N is the total number of
LMP91000s connected to the I2C bus. Only the enabled device will acknowledge the I2C commands. After
finishing communicating with this particular LMP91000, the microcontroller de-asserts the corresponding MENB
and repeats the procedure for other LMP91000s. Figure 30 shows the typical connection when more than one
LMP91000 is connected to the I2C bus.
Figure 30. More Than One LMP91000 on I2C Bus
8.1.2 Smart Gas Sensor Analog Front-End
The LMP91000 together with an external EEPROM represents the core of a SMART GAS SENSOR AFE. In the
EEPROM it is possible to store the information related to the GAS sensor type, calibration and LMP91000's
configuration (content of registers 10h, 11h, 12h). At startup the microcontroller reads the EEPROM's content
and configures the LMP91000. A typical smart gas sensor AFE is shown in Figure 31. The connection of MENB
to the hardware address pin A0 of the EEPROM allows the microcontroller to select the LMP91000 and its
corresponding EEPROM when more than one smart gas sensor AFE is present on the I2C bus. Note: only
EEPROM I2C addresses with A0=0 should be used in this configuration.
24 Submit Documentation Feedback Copyright © 2011–2014, Texas Instruments Incorporated
Product Folder Links: LMP91000
µC
SCL
SDA
GPIO 1 GPIO 2 GPIO N
SMART SENSOR AFE
LMP91000
SDA
SCL
I2C EEPROM
SDA
SCL
A0
MENB
LMP91000
SDA
SCL
I2C EEPROM
SDA
SCL
A0
MENB
SMART SENSOR AFE SMART SENSOR AFE
LMP91000
SDA
SCL
I2C EEPROM
SDA
SCL
A0
MENB
SCL SDA
LMP91000
SDA
SCL
I2C EEPROM
SDA
SCL
A0
MENB
MENB
LMP91000
www.ti.com
SNAS506I –JANUARY 2011–REVISED DECEMBER 2014
Application Information (continued)
Figure 31. Smart Gas Sensor AFE
8.1.3 Smart Gas Sensor AFES on I2C BUS
The connection of Smart gas sensor AFEs on the I2C bus is the natural extension of the previous concepts. Also
in this case the microcontroller starts communication asserting 1 out of N MENB signals where N is the total
number of smart gas sensor AFE connected to the I2C bus. Only one of the devices (either LMP91000 or its
corresponding EEPROM) in the smart gas sensor AFE enabled will acknowledge the I2C commands. When the
communication with this particular module ends, the microcontroller de-asserts the corresponding MENB and
repeats the procedure for other modules. Figure 32 shows the typical connection when several smart gas sensor
AFEs are connected to the I2C bus.
Figure 32. I2C Bus
Copyright © 2011–2014, Texas Instruments Incorporated Submit Documentation Feedback 25
Product Folder Links: LMP91000
Temp 29°C
CO 0PPM
TIME xx:xx
Date xx/xx/xxxx
DISPLAY
Button
ButtonButton
Button
KEYBOARD
GAS
SENSOR
D0
D1
TPL5000
D2
VDD
PGOOD
RSTn
WAKE
TCAL
GND DONE
VIN
POWER MANAGEMENT
VOUT VBAT_OK
GND
Rp
100k
RST
µC
GPIO
GPIO
VDD
GPIO GND
SCL
LMP91000
SDA
VOUT
VREF
GND
SDA
SCL
ADC
CE
RE
WE
MENB
CE
RE
WE
VDD
VOLTAGE
REFERENCE
GND
VOUTVIN
Rp
100k Rp
100k
Lithium
ion battery
-
+
GPIO
GPIO
GPIO
GPIO
LMP91000
SNAS506I –JANUARY 2011–REVISED DECEMBER 2014
www.ti.com
8.2 Typical Application
The LMP91000 can be used in conjunction with environment sensors to build a battery power environment
monitors such as an air quality data-loggers, or wirless sensors. In this application due to the monitored
phenomena the micro-controller and the LMP9100 spend most of the time in idle state. In order to save power
and enlarge the battery life, the LMP91000 can be put in deep sleep mode with Internal FET feature enabled. To
optimize the current consumption of the entire system, the acquisitions and in general the activities of the micro
can operate at set intervals with the TPL5000. The TPL5000 is a programmable timer with watch-dog feature.
Figure 33. Data-Logger
8.2.1 Design Requirements
The Design is driven by the low-current consumption constraint. The data are usually acquired on a rate that
ranges between 1s to 10s. The highest necessity it the maximization of the battery life. The TPL5000 helps
achieving that goal because it allows putting the micro-controller in its lowest power mode. Moreover the deep
slep mode of the LMP91000 allows burning only some hundreds of nA.
8.2.2 Detailed Design Procedure
When the focal constraint is the battery, the selection of a low power voltage reference, a micro-controller and
display is mandatory. The first step in the design is the calculation of the power consumption of each device in
the different mode of operations. An example is the LMP91000; the device has gas measurement mode, sleep
mode and micro-controller in low power mode which is normal operation. The different modes offer the possibility
to select the appropriate timer interval which respect the application constraint and maximize the life of the
battery.
8.2.2.1 Sensor Test Procedure
The LMP91000 has all the hardware and programmability features to implement some test procedures. The
purpose of the test procedure is to:
a. test proper function of the sensor (status of health)
b. test proper connection of the sensor to the LMP91000
The test procedure is very easy. The variable bias block is user programmable through the digital interface. A
step voltage can be applied by the end user to the positive input of A1. As a consequence a transient current will
start flowing into the sensor (to charge its internal capacitance) and it will be detected by the TIA. If the current
transient is not detected, either a sensor fault or a connection problem is present. The slope and the aspect of
the transient response can also be used to detect sensor aging (for example, a cell that is drying and no longer
26 Submit Documentation Feedback Copyright © 2011–2014, Texas Instruments Incorporated
Product Folder Links: LMP91000
OUTPUTT VOLTTAGE (1V/DIV)
TIME (25ms/DIV)
INPUT PULSE (100mV/DIV)
LMP91000 OUTPUT
TEST PULSE
LMP91000
www.ti.com
SNAS506I –JANUARY 2011–REVISED DECEMBER 2014
Typical Application (continued)
efficiently conducts the current). After it is verified that the sensor is working properly, the LMP91000 needs to be
reset to its original configuration. It is not required to observe the full transient in order to contain the testing time.
All the needed information are included in the transient slopes (both edges). Figure 34 shows an example of the
test procedure, a Carbon Monoxide sensor is connected to the LMP91000, two pulses are then sequentially
applied to the bias voltage:
1. from 0 mV to 40 mV
2. from 40 mV to –40 mV
and finally the bias is set again at 0mV since this is the normal operation condition for this sensor.
8.2.3 Application Curve
Figure 34. Test Procedure Example
Copyright © 2011–2014, Texas Instruments Incorporated Submit Documentation Feedback 27
Product Folder Links: LMP91000
LMP91000
SNAS506I –JANUARY 2011–REVISED DECEMBER 2014
www.ti.com
9 Power Supply Recommendations
9.1 Power Consumption
The LMP91000 is intended for use in portable devices, so the power consumption is as low as possible in order
to ensure a long battery life. The total power consumption for the LMP91000 is below 10 µA at 3.3 v average
over time, (this excludes any current drawn from any pin). A typical usage of the LMP91000 is in a portable gas
detector and its power consumption is summarized in Table 3. This has the following assumptions:
• Power On only happens a few times over life, so its power consumption can be ignored.
• Deep Sleep mode is not used.
• The system is used about 8 hours a day, and 16 hours a day it is in Standby mode.
• Temperature Measurement is done about once per minute.
This results in an average power consumption of approximately 7.95 µA. This can potentially be further reduced,
by using the Standby mode between gas measurements. It may even be possible, depending on the sensor
used, to go into deep sleep for some time between measurements, further reducing the average power
consumption.
Table 3. Power Consumption Scenario
3-Lead Temperature Temperature
Deep Sleep StandBy Amperometric Measurement Measurement Total
Cell TIA OFF TIA ON
Current consumption
(µA)
typical value 0.6 6.5 10 11.4 14.9
Time ON
(%) 0 60 39 0 1
Average
(µA) 0 3.9 3.9 0 0.15 7.95
Notes
A1 OFF ON ON ON ON
TIA OFF OFF ON OFF ON
TEMP SENSOR OFF OFF OFF ON ON
I2C interface ON ON ON ON ON
28 Submit Documentation Feedback Copyright © 2011–2014, Texas Instruments Incorporated
Product Folder Links: LMP91000
TOP LAYER BOTTOM LAYER
LMP91000
www.ti.com
SNAS506I –JANUARY 2011–REVISED DECEMBER 2014
10 Layout
10.1 Layout Guidelines
The most critical point when designing with electrocemical gas sensors and the LMP91000 is the connection of
the sensor to the LMP91000. Particular attention is required in the layout of the RE, CE and WE traces which
connect the sensor to the front-end. The traces needs to be short and far from hifh freqency signals, such as
clock. A way to reduce the lenght of the traces is positioning the LMP91000 below the gas sensor, this is
possible with cyclindrical electrochemical gas sensor or on the oppoite layer in case of solid gas sensor or low
profile gas sensor. In case of uasge of external transimpeance gain resistance it needs to be placed close to the
LMP91000, the terminal of the resistance conencted to C1 needs to be far from high frequency signals.
10.2 Layout Example
Figure 35. Layout
Copyright © 2011–2014, Texas Instruments Incorporated Submit Documentation Feedback 29
Product Folder Links: LMP91000
LMP91000
SNAS506I –JANUARY 2011–REVISED DECEMBER 2014
www.ti.com
11 Device and Documentation Support
11.1 Trademarks
WEBENCH is a registered trademark of Texas Instruments.
All other trademarks are the property of their respective owners.
11.2 Electrostatic Discharge Caution
These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam
during storage or handling to prevent electrostatic damage to the MOS gates.
11.3 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.
30 Submit Documentation Feedback Copyright © 2011–2014, Texas Instruments Incorporated
Product Folder Links: LMP91000
PACKAGE OPTION ADDENDUM
www.ti.com 10-Dec-2020
Addendum-Page 1
PACKAGING INFORMATION
Orderable Device Status
(1)
Package Type Package
Drawing Pins Package
Qty Eco Plan
(2)
Lead finish/
Ball material
(6)
MSL Peak Temp
(3)
Op Temp (°C) Device Marking
(4/5)
Samples
LMP91000SD/NOPB ACTIVE WSON NHL 14 1000 RoHS & Green SN Level-3-260C-168 HR -40 to 85 L91000
LMP91000SDE/NOPB ACTIVE WSON NHL 14 250 RoHS & Green SN Level-3-260C-168 HR -40 to 85 L91000
LMP91000SDX/NOPB ACTIVE WSON NHL 14 4500 RoHS & Green SN Level-3-260C-168 HR -40 to 85 L91000
(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 <=1000ppm threshold. Antimony trioxide based
flame retardants must also meet the <=1000ppm threshold requirement.
(3) MSL, Peak Temp. - The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature.
(4) There may be additional marking, which relates to the logo, the lot trace code information, or the environmental category on the device.
(5) Multiple Device Markings will be inside parentheses. Only one Device Marking contained in parentheses and separated by a "~" will appear on a device. If a line is indented then it is a continuation
of the previous line and the two combined represent the entire Device Marking for that device.
(6) Lead finish/Ball material - Orderable Devices may have multiple material finish options. Finish options are separated by a vertical ruled line. Lead finish/Ball material values may wrap to two
lines if the finish value exceeds the maximum column width.
Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on information
provided by third parties, and makes no representation or warranty as to the accuracy of such information. Efforts are underway to better integrate information from third parties. TI has taken and
continues to take reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on incoming materials and chemicals.
TI and TI suppliers consider certain information to be proprietary, and thus CAS numbers and other limited information may not be available for release.
PACKAGE OPTION ADDENDUM
www.ti.com 10-Dec-2020
Addendum-Page 2
In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI to Customer on an annual basis.
TAPE AND REEL INFORMATION
*All dimensions are nominal
Device Package
Type Package
Drawing Pins SPQ Reel
Diameter
(mm)
Reel
Width
W1 (mm)
A0
(mm) B0
(mm) K0
(mm) P1
(mm) W
(mm) Pin1
Quadrant
LMP91000SD/NOPB WSON NHL 14 1000 178.0 12.4 4.3 4.3 1.3 8.0 12.0 Q1
LMP91000SDE/NOPB WSON NHL 14 250 178.0 12.4 4.3 4.3 1.3 8.0 12.0 Q1
LMP91000SDX/NOPB WSON NHL 14 4500 330.0 12.4 4.3 4.3 1.3 8.0 12.0 Q1
PACKAGE MATERIALS INFORMATION
www.ti.com 20-Sep-2016
Pack Materials-Page 1
*All dimensions are nominal
Device Package Type Package Drawing Pins SPQ Length (mm) Width (mm) Height (mm)
LMP91000SD/NOPB WSON NHL 14 1000 210.0 185.0 35.0
LMP91000SDE/NOPB WSON NHL 14 250 210.0 185.0 35.0
LMP91000SDX/NOPB WSON NHL 14 4500 367.0 367.0 35.0
PACKAGE MATERIALS INFORMATION
www.ti.com 20-Sep-2016
Pack Materials-Page 2
MECHANICAL DATA
NHL0014B
www.ti.com
SDA14B (Rev A)
IMPORTANT NOTICE AND DISCLAIMER
TI PROVIDES TECHNICAL AND RELIABILITY DATA (INCLUDING DATASHEETS), DESIGN RESOURCES (INCLUDING REFERENCE
DESIGNS), APPLICATION OR OTHER DESIGN ADVICE, WEB TOOLS, SAFETY INFORMATION, AND OTHER RESOURCES “AS IS”
AND WITH ALL FAULTS, AND DISCLAIMS ALL WARRANTIES, EXPRESS AND IMPLIED, INCLUDING WITHOUT LIMITATION ANY
IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE OR NON-INFRINGEMENT OF THIRD
PARTY INTELLECTUAL PROPERTY RIGHTS.
These resources are intended for skilled developers designing with TI products. You are solely responsible for (1) selecting the appropriate
TI products for your application, (2) designing, validating and testing your application, and (3) ensuring your application meets applicable
standards, and any other safety, security, or other requirements. These resources are subject to change without notice. TI grants you
permission to use these resources only for development of an application that uses the TI products described in the resource. Other
reproduction and display of these resources is prohibited. No license is granted to any other TI intellectual property right or to any third
party intellectual property right. TI disclaims responsibility for, and you will fully indemnify TI and its representatives against, any claims,
damages, costs, losses, and liabilities arising out of your use of these resources.
TI’s products are provided subject to TI’s Terms of Sale (www.ti.com/legal/termsofsale.html) or other applicable terms available either on
ti.com or provided in conjunction with such TI products. TI’s provision of these resources does not expand or otherwise alter TI’s applicable
warranties or warranty disclaimers for TI products.
Mailing Address: Texas Instruments, Post Office Box 655303, Dallas, Texas 75265
Copyright © 2020, Texas Instruments Incorporated