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  • LMP91000 Sensor AFE System: Configurable AFE Potentiostat for Low-Power Chemical-Sensing Applications

    • SNAS506I January   2011  – December 2014 LMP91000

      PRODUCTION DATA.  

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  • LMP91000 Sensor AFE System: Configurable AFE Potentiostat for Low-Power Chemical-Sensing Applications
  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Pin Configuration and Functions
  6. 6 Specifications
    1. 6.1 Absolute Maximum Ratings
    2. 6.2 ESD Ratings
    3. 6.3 Recommended Operating Conditions
    4. 6.4 Thermal Information
    5. 6.5 Electrical Characteristics
    6. 6.6 I2C Interface
    7. 6.7 Timing Requirements
    8. 6.8 Typical Characteristics
  7. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 Potentiostat Circuitry
        1. 7.3.1.1 Transimpedance Amplifier
        2. 7.3.1.2 Control Amplifier
        3. 7.3.1.3 Variable Bias
        4. 7.3.1.4 Internal Zero
        5. 7.3.1.5 Temperature Sensor
        6. 7.3.1.6 Gas Sensor Interface
          1. 7.3.1.6.1 3-Lead Amperometric Cell in Potentiostat Configuration
          2. 7.3.1.6.2 2-Lead Galvanic Cell In Ground Referred Configuration
          3. 7.3.1.6.3 2-lead Galvanic Cell in Potentiostat Configuration
        7. 7.3.1.7 Timeout Feature
    4. 7.4 Device Functional Modes
    5. 7.5 Programming
      1. 7.5.1 I2C Interface
      2. 7.5.2 Write and Read Operation
    6. 7.6 Registers Maps
      1. 7.6.1 STATUS -- Status Register (Address 0x00)
      2. 7.6.2 LOCK -- Protection Register (Address 0x01)
      3. 7.6.3 TIACN -- TIA Control Register (Address 0x10)
      4. 7.6.4 REFCN -- Reference Control Register (Address 0x11)
      5. 7.6.5 MODECN -- Mode Control Register (Address 0x12)
  8. 8 Application and Implementation
    1. 8.1 Application Information
      1. 8.1.1 Connection of More Than One LMP91000 to the I2C BUS
      2. 8.1.2 Smart Gas Sensor Analog Front-End
      3. 8.1.3 Smart Gas Sensor AFES on I2C BUS
    2. 8.2 Typical Application
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedure
        1. 8.2.2.1 Sensor Test Procedure
      3. 8.2.3 Application Curve
  9. 9 Power Supply Recommendations
    1. 9.1 Power Consumption
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
  11. 11Device and Documentation Support
    1. 11.1 Trademarks
    2. 11.2 Electrostatic Discharge Caution
    3. 11.3 Glossary
  12. 12Mechanical, Packaging, and Orderable Information
  13. IMPORTANT NOTICE

Package Options

Mechanical Data (Package|Pins)
  • NHL|14
    • MPDS421
Thermal pad, mechanical data (Package|Pins)
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DATA SHEET

LMP91000 Sensor AFE System: Configurable AFE Potentiostat for Low-Power Chemical-Sensing Applications

1 Features

  • Typical Values, TA = 25°C
  • Supply Voltage 2.7 V to 5.25 V
  • Supply Current (Average Over Time) <10 µA
  • Cell Conditioning Current Up to 10 mA
  • Reference Electrode Bias Current (85°C) 900pA (max)
  • Output Drive Current 750 µA
  • Complete Potentiostat Circuit-to-Interface to Most Chemical Cells
  • Programmable Cell Bias Voltage
  • Low-Bias Voltage Drift
  • Programmable TIA gain 2.75 kΩ to 350 kΩ
  • Sink and Source Capability
  • I2C Compatible Digital Interface
  • Ambient Operating Temperature –40°C to 85°C
  • Package 14-Pin WSON
  • Supported by WEBENCH® Sensor AFE Designer

2 Applications

  • Chemical Species Identification
  • Amperometric Applications
  • Electrochemical Blood Glucose Meter

3 Description

The LMP91000 is a programmable analog front-end (AFE) for use in micro-power electrochemical sensing applications. It provides a complete signal path solution between a sensor and a microcontroller that generates an output voltage proportional to the cell current. The LMP91000’s programmability enables it to support multiple electrochemical sensors such as 3-lead toxic gas sensors and 2-lead galvanic cell sensors with a single design as opposed to the multiple discrete solutions. The LMP91000 supports gas sensitivities over a range of 0.5 nA/ppm to 9500 nA/ppm. It also allows for an easy conversion of current ranges from 5 µA to 750 µA full scale.

The LMP91000’s adjustable cell bias and transimpedance amplifier (TIA) gain are programmable through the I2C interface. The I2C interface can also be used for sensor diagnostics. An integrated temperature sensor can be read by the user through the VOUT pin and used to provide additional signal correction in the µC or monitored to verify temperature conditions at the sensor.

The LMP91000 is optimized for micro-power applications and operates over a voltage range of 2.7 to 5.25 V. The total current consumption can be less than 10 μA. Further power savings are possible by switching off the TIA amplifier and shorting the 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

30132505.gif

4 Revision History

Changes from H Revision (March 2013) to I Revision

  • 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 Go

Changes from G Revision (March 2013) to H Revision

  • Changed layout of National Data Sheet to TI formatGo

5 Pin Configuration and Functions

14-Pin WSON
Top View
30132502.gif

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

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
V(ESD) Electrostatic discharge Human-body model (HBM), per ANSI/ESDA/JEDEC JS-001(1) ±2000 V
Charged-device model (CDM), per JEDEC specification JESD22-C101(2) ±1000
(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

THERMAL METRIC(1) LMP91000 UNIT
WSON
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.

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(3) TYP(2) MAX(3) UNIT
POWER SUPPLY SPECIFICATION
IS Supply Current 3-lead amperometric cell mode µA
MODECN = 0x03 10 13.5
–40 to 80°C (please verify that the degree is correct) 15
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
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_RW Bias Programming range (differential voltage between RE pin and WE pin) Percentage of voltage referred to VREF or VDD ±24%
Bias Programming Resolution First two smallest step ±1
All other steps ±2%
IRE Input bias current at RE pin VDD = 2.7 V pA
Internal Zero 50% VDD –90 90
–40 to 80°C –800 800
VDD = 5.25 V
Internal Zero 50% VDD –90 90
–40 to 80°C –900 900
ICE Minimum operating current capability sink 750 µA
source 750
Minimum charging capability(5) sink 10 mA
source 10
AOL_A1 Open-loop voltage gain of control loop op amp (A1) 300 mV ≤ VCE ≤ Vs-300 mV; dB
–750 µA ≤ICE ≤ 750 µA
–40 to 80°C 104 120
en_RW Low Frequency integrated noise between RE pin and WE pin 0.1 Hz to 10 Hz, Zero Bias
(6)		 3.4 µVpp
0.1 Hz to 10 Hz, with Bias
(6)(7)		 5.1
VOS_RW WE Voltage Offset referred to RE BIAS polarity
(8)
–40 to 80°C		 0% VREF
Internal Zero=20% VREF		 –550 550 µV
0% VREF
Internal Zero=50% VREF
0% VREF
Internal Zero=67% VREF
±1% VREF –575 575
±2% VREF –610 610
±4% VREF –750 750
±6% VREF –840 840
±8% VREF –930 930
±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
TcVOS_RW WE Voltage Offset Drift referred to RE from –40°C to 85°C
(4)		 BIAS polarity
(8)		 0% VREF
Internal Zero=20% VREF		 –4 4 µV/°C
0% VREF
Internal Zero=50% VREF
0% VREF
Internal Zero=67% VREF
±1% VREF –4 4
±2% VREF –4 4
±4% VREF –5 5
±6% VREF –5 5
±8% VREF –5 5
±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
TIA_GAIN Transimpedance gain accuracy 5%
Linearity ±0.05%
Programmable TIA Gains 7 programmable gain resistors 2.75
3.5
7
14
35
120
350		 kΩ
Maximum external gain resistor 350
TIA_ZV Internal zero voltage 3 programmable percentages of VREF 20%
50%
67%
3 programmable percentages of VDD 20%
50%
67%
Internal zero voltage Accuracy ±0.04%
RL Programmable Load 4 programmable resistive loads 10
33
50
100		 Ω
Load accuracy 5%
PSRR Power Supply Rejection Ratio at RE pin 2.7 V ≤ VDD≤ 5.25 V Internal zero 20% VREF 80 110 dB
Internal zero 50% VREF
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
(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) 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.
(3) Limits are 100% production tested at 25°C. Limits over the operating temperature range are specified through correlations using statistical quality control (SQC) method.
(4) 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.
(5) At such currents no accuracy of the output voltage can be expected.
(6) This parameter includes both A1 and TIA's noise contribution.
(7) In case of external reference connected, the noise of the reference has to be added.
(8) For negative bias polarity the Internal Zero is set at 67% VREF.

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 (3) TYP (2) MAX(3) 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) 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.
(3) Limits are 100% production tested at 25°C. Limits over the operating temperature range are specified through correlations using statistical quality control (SQC) method.
(4) This parameter is specified by design or characterization.

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
tHD;STA Data valid After this period, the first clock pulse is generated 4.0 µs
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
tf SDA fall time (3) IL ≤ 3 mA;
CL ≤ 400 pF
–40 to 80°C		 250 ns
tSU;STO Set-up time for STOP condition –40 to 80°C 4.0 µs
tBUF Bus free time between a STOP and START condition –40 to 80°C 4.7 µs
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 suppressed by the input filter(3) –40 to 80°C 50 ns
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 enabling and disabling –40 to 80°C 600 ns
(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.
30132541.gif
Figure 1. Timing Diagram

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.
30132563.gif
Figure 2. Input VOS_RW vs. Temperature (Vbias 0 mV)
30132564.gif
Figure 4. IWE Step Current Response (Rise)
30132560.gif
Figure 6. AC PSRR vs. Frequency
30132591.gif
Figure 8. Supply Current vs. Temperature
(Deep Sleep Mode)
30132587.gif
Figure 10. Supply Current vs. Temperature
(Standby Mode)
30132586.gif
Figure 12. Supply Current vs. Temperature
(3-Lead Amperometric Mode)
30132588.gif
Figure 14. Supply Current vs. Temperature
(Temp Measurement TIA On)
30132589.gif
Figure 16. Supply Current vs. Temperature
(Temp Measurement TIA Off)
30132590.gif
Figure 18. Supply Current vs. Temperature
(2-Lead Ground-Referred Amperometric Mode)
30132598.gif
Figure 20. 0.1-Hz to 10-Hz Noise, 0-V Bias
301325100.gif
Figure 22. 0.1-Hz to 10-Hz Noise, 600-mV Bias
30132562.gif
Figure 3. Input VOS_RW vs. VDD (Vbias 0 mV)
30132566.gif
Figure 5. IWE Step Current Response (Fall)
30132569.gif
Figure 7. Temperature Sensor Output vs. VDD
(Temperature = 30°C)
30132597.gif
Figure 9. Supply Current vs. VDD
(Deep Sleep Mode)
30132592.gif
Figure 11. Supply Current vs. VDD
(Standby Mode)
30132593.gif
Figure 13. Supply Current vs. VDD
(3-Lead Amperometric Mode)
30132594.gif
Figure 15. Supply Current vs. VDD
(Temp Measurement TIA On)
30132595.gif
Figure 17. Supply Current vs. VDD
(Temp Measurement TIA Off)
30132596.gif
Figure 19. Supply Current vs. VDD
(2-Lead Ground-Referred Amperometric Mode)
30132599.gif
Figure 21. 0.1-Hz to 10-Hz Noise, 300-mV Bias
30132568.gif
Figure 23. A VOUT Step Response 100-PPM to 400-PPM CO
(CO Gas Sensor Connected to LMP91000)

 
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