LMP91000SD/NOPB - Texas Instruments

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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

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

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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

Product Folder Links: LMP91000

DGND CE1 14

REMENB

SCL WE

VREF

SDA

NC C1

C2VDD

7 8AGND VOUT

DAP

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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

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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.

Product Folder Links: LMP91000

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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.

Product Folder Links: LMP91000

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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.

Product Folder Links: LMP91000

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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

TIA_GAIN 14

Programmable TIA Gains kΩ

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

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.

Product Folder Links: LMP91000

SCL

SDA

tHD;STA

tLOW

tHD;DAT tHIGH tSU;DAT

tSU;STA tSU;STO

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

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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

Product Folder Links: LMP91000

10 100 1k 10k 100k

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)

NORMALIZED OUTPUT (200mV/DIV)

TIME (200s/DIV)

IWE(50A/DIV)

IWE

2.75k

3.5k

7k

14k

35k

120k

350k

NORMALIZED OUTPUT TIA (200mV/DIV)

TIME (200s/DIV)

IWE(50A/DIV)

IWE

2.75k

3.5k

7k

14k

35k

120k

350k

-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

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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)

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

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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)

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

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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)

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)

Product Folder Links: LMP91000

I2C INTERFACE

AND

CONTROL

REGISTERS

VREF VDD

AGND

WE VOUT

SCL

TEMP

SENSOR

VREF

DIVIDER

SDA

RLoad

VARIABLE

BIAS MENB

DGND

A1 +

TIA

RTIA

3-Lead

Electrochemical

Cell

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.

Product Folder Links: LMP91000

LMP91000

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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

Product Folder Links: LMP91000

LMP91000

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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

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LMP91000

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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.

Product Folder Links: LMP91000

I2C INTERFACE

AND

CONTROL

REGISTERS

VREF VDD

AGND

WE VOUT

SCL

TEMP

SENSOR

VREF

DIVIDER

SDA

RLoad

VARIABLE

BIAS MENB

DGND

A1 +

TIA

RTIA

3-Lead

Electrochemical

Cell

LMP91000

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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

Product Folder Links: LMP91000

I2C INTERFACE

AND

CONTROL

REGISTERS

VREF VDD

AGND

WE VOUT

SCL

TEMP

SENSOR

VREF

DIVIDER

SDA

RLoad

VARIABLE

BIAS

LMP91000

MENB

DGND

A1 +

TIA

RTIA

VE-

VE+

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

Product Folder Links: LMP91000

I2C INTERFACE

AND

CONTROL

REGISTERS

VREF VDD

AGND

WE VOUT

SCL

TEMP

SENSOR

VREF

DIVIDER

SDA

RLoad

VARIABLE

BIAS MENB

DGND

A1 +

TIA

RTIA

VE-

VE+

LMP91000

2-wire Sensor

such as Oxygen

LMP91000

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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.

Product Folder Links: LMP91000

D7 D6 D5 D4 D3 D2 D1 D0

1 9 1 9

Ack

LMP91000

Start by

Master

R/W Ack

LMP91000

Frame 1

Serial Bus Address Byte

from Master

Frame 2

Internal Address Register

Byte from Master

1 9

Ack

LMP91000

Frame 3

Data Byte

D3 D1D2

D4D5D6D7

A2 A0A1A3A4A5A6

SCL

SDA

SCL

(continued)

SDA

(continued) Stop by

Master

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

Product Folder Links: LMP91000

D7 D6 D5 D4 D3 D2 D1 D0

1 9

Ack

LMP91000

Start by

Master No Ack

Master

SCL

SDA

Stop

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

LMP91000

Start by

Master

R/W Ack

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

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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”.

Product Folder Links: LMP91000

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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%

Product Folder Links: LMP91000

LMP91000

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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.

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

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8 Application and Implementation

NOTE

Information in the following applications sections is not part of the TI component

specification, and TI does not warrant its accuracy or completeness. TI’s customers are

responsible for determining suitability of components for their purposes. Customers should

validate and test their design implementation to confirm system functionality.

8.1 Application Information

8.1.1 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.

Product Folder Links: LMP91000

µC

SCL

SDA

GPIO 1 GPIO 2 GPIO N

SMART SENSOR AFE

LMP91000

SDA

SCL

I2C EEPROM

SDA

SCL

MENB

LMP91000

SDA

SCL

I2C EEPROM

SDA

SCL

MENB

SMART SENSOR AFE SMART SENSOR AFE

LMP91000

SDA

SCL

I2C EEPROM

SDA

SCL

MENB

SCL SDA

LMP91000

SDA

SCL

I2C EEPROM

SDA

SCL

MENB

LMP91000

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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

Product Folder Links: LMP91000

Temp 29°C

CO 0PPM

TIME xx:xx

Date xx/xx/xxxx

DISPLAY

Button

ButtonButton

Button

KEYBOARD

GAS

SENSOR

TPL5000

VDD

PGOOD

RSTn

WAKE

TCAL

GND DONE

VIN

POWER MANAGEMENT

VOUT VBAT_OK

GND

100k

RST

µC

GPIO

VDD

GPIO GND

SCL

LMP91000

SDA

VOUT

VREF

GND

SDA

SCL

ADC

MENB

VDD

VOLTAGE

REFERENCE

GND

VOUTVIN

100k Rp

100k

Lithium

ion battery

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

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

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

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

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.

Product Folder Links: LMP91000

PACKAGE OPTION ADDENDUM

www.ti.com 3-Sep-2014

Addendum-Page 1

PACKAGING INFORMATION

Orderable Device Status

(1)

Package Type Package

Drawing Pins Package

Qty Eco Plan

(2)

Lead/Ball Finish

(6)

MSL Peak Temp

(3)

Op Temp (°C) Device Marking

(4/5)

Samples

LMP91000SD/NOPB ACTIVE WSON NHL 14 1000 Green (RoHS

& no Sb/Br) CU SN Level-3-260C-168 HR -40 to 85 L91000

LMP91000SDE/NOPB ACTIVE WSON NHL 14 250 Green (RoHS

& no Sb/Br) CU SN Level-3-260C-168 HR -40 to 85 L91000

LMP91000SDX/NOPB ACTIVE WSON NHL 14 4500 Green (RoHS

& no Sb/Br) CU 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) Eco Plan - The planned eco-friendly classification: Pb-Free (RoHS), Pb-Free (RoHS Exempt), or Green (RoHS & no Sb/Br) - please check http://www.ti.com/productcontent for the latest availability

information and additional product content details.

TBD: The Pb-Free/Green conversion plan has not been defined.

Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements for all 6 substances, including the requirement that

lead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes.

Pb-Free (RoHS Exempt): This component has a RoHS exemption for either 1) lead-based flip-chip solder bumps used between the die and package, or 2) lead-based die adhesive used between

the die and leadframe. The component is otherwise considered Pb-Free (RoHS compatible) as defined above.

Green (RoHS & no Sb/Br): TI defines "Green" to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and Antimony (Sb) based flame retardants (Br or Sb do not exceed 0.1% by weight

in homogeneous material)

(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/Ball Finish - Orderable Devices may have multiple material finish options. Finish options are separated by a vertical ruled line. Lead/Ball Finish 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

PACKAGE OPTION ADDENDUM

www.ti.com 3-Sep-2014

Addendum-Page 2

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.

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)

(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)

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