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LMP91200

www.ti.com

SNAS571C –JANUARY 2012–REVISED MARCH 2013

LMP91200 Configurable AFE for Low-Power Chemical Sensing Applications

Check for Samples: LMP91200

FEATURES

DESCRIPTION

The LMP91200 is a configurable sensor AFE for use

• Programmable Output Current in Temperature

in low power analytical sensing applications. The

Measurement

LMP91200 is designed for 2-electrode sensors. This

• Programmable Output Common Mode Voltage

device provides all of the functionality needed to

• Active Guarding

detect changes based on a delta voltage at the

sensor. Optimized for low-power applications, the

• On Board Sensor Test

LMP91200 works over a voltage range of 1.8V to

• Supported by Webench Sensor AFE Designer

5.5V. With its extremely low input bias current it is

• Supported by Webench Sensor Designer Tools

optimized for use with pH sensors. Also in absence of

supply voltage the very low input bias current reduces

degradation of the pH probe when connected to the

APPLICATIONS

LMP91200. The Common Mode Output pin (VOCM)

• pH Sensor Platforms

provides a common mode offset, which can be

programmed to different values to accommodate pH

KEY SPECIFICATIONS

sensor output ranges. For applications requiring a

high impedance common mode this option is also

Unless otherwise noted, typical values at

available. Two guard pins provide support for high

= 25°C, V

=(VDD-GND) = 3.3V

parasitic impedance wiring. Support for an external

• pH Buffer Input bias current (0<V

INP

<3.3V)

Pt1000, Pt100, or similar temperature sensor is

integrated in the LMP91200. The control of this

– max @ 25°C: ±125 fA

feature is available through the SPI interface.

– max @ 85°C: ±445 fA

Additionally, a user controlled sensor diagnostic test

• pH Buffer Input bias current (-500mV<V

INP

-V

is available. This function tests the sensor for proper

<500mV), V

=(VDD-GND)=0V

connection and functionality. Depending on the

configuration, total current consumption for the device

– max @ 25°C: ±600 fA

is 50µA while measuring pH. Available in a 16-pin

– max @ 85°C: ±6.5 pA

TSSOP package, the LMP91200 operates from -40°C

• pH Buffer Input offset voltage: ±200 µV

to +125°C.

• pH Buffer Input offset voltage drift: ±2.5 μV/°C

• Supply current (pH mode): 50 μA

• Supply voltage: 1.8 V to 5.5 V

• Operating temperature range: -40°C to 125°C

• Package: 16-Pin TSSOP

Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of

Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.

2All trademarks are the property of their respective owners.

PRODUCTION DATA information is current as of publication date.

Products conform to specifications per the terms of the Texas

Instruments standard warranty. Production processing does not

necessarily include testing of all parameters.

Summary of content (31 pages)

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LMP91200 www.ti.com SNAS571C – JANUARY 2012 – REVISED MARCH 2013 LMP91200 Configurable AFE for Low-Power Chemical Sensing Applications Check for Samples: LMP91200 FEATURES DESCRIPTION • The LMP91200 is a configurable sensor AFE for use in low power analytical sensing applications. The LMP91200 is designed for 2-electrode sensors. This device provides all of the functionality needed to detect changes based on a delta voltage at the sensor.
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LMP91200 SNAS571C – JANUARY 2012 – REVISED MARCH 2013 www.ti.com Typical Application VDD LMP91200 pH Meter RANGE SETTING CSB SCLK SDI SPI PGA CONTROLLER CAL VOUT R_REF RTD VOUT MUX 2-wire RTD GUARD1 INP + pH BUFFER VOCM VCM MUX GUARD2 VREF VCM BUFFER VCM SDO_DIAG GND pH ELECTRODE VCMHI Connection Diagram 16-Pin TSSOP VDD 1 16 SDI SCLK CAL 2 15 RTD 3 14 CSB GUARD1 4 13 SDO_DIAG INP 5 12 VOUT GUARD2 6 11 VOCM VCMHI 7 10 GND VCM 8 9 LMP91200 VREF Figure 1.
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LMP91200 www.ti.
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LMP91200 SNAS571C – JANUARY 2012 – REVISED MARCH 2013 www.ti.com Electrical Characteristics (1) (2) (3) Unless otherwise specified, all limits specified for TA = 25°C. VS=(VDD-GND)=3.3V. VREF=3.3V. Boldface limits apply at the temperature extremes.
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LMP91200 www.ti.com SNAS571C – JANUARY 2012 – REVISED MARCH 2013 Electrical Characteristics(1)(2)(3) (continued) Unless otherwise specified, all limits specified for TA = 25°C. VS=(VDD-GND)=3.3V. VREF=3.3V. Boldface limits apply at the temperature extremes. Symbol Parameter Condition enpH Input referred noise (high frequency) (9) IscpH Output short circuit current (11) Min (4) f=1kHz Typ (5) Max (4) Units 90 nV/√Hz Sourcing, Vout to GND, INP=1.65V 10 13 mA Sinking, Vout to VDD, INP=1.
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LMP91200 SNAS571C – JANUARY 2012 – REVISED MARCH 2013 www.ti.com Electrical Characteristics(1)(2)(3) (continued) Unless otherwise specified, all limits specified for TA = 25°C. VS=(VDD-GND)=3.3V. VREF=3.3V. Boldface limits apply at the temperature extremes. Symbol Parameter Min (4) Condition Typ (5) Max (4) Units 275 480 µV 2.
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LMP91200 www.ti.com SNAS571C – JANUARY 2012 – REVISED MARCH 2013 Electrical Characteristics (Serial Interface)(1) (continued) Unless otherwise specified. All limits specified for TA=25°C, VS=(VDD-GND)=3.3V.
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LMP91200 SNAS571C – JANUARY 2012 – REVISED MARCH 2013 www.ti.com TEST CIRCUIT DIAGRAMS SCLK t9 t1 t2 t3 t7 CSB t4 t8 t5 D15 SDI D0 D14 t6 OLD D15 SDO_DIAG 90% OLD D1 10% 90% 10% tR OLD D0 tF Figure 2. SERIAL INTERFACE TIMING DIAGRAM DIAG_tSET CSB 50% DIAG_tON DIAG_tF 50% SDO_DIAG 50% 50% 90% 90% 10% 90% 10% 10% 90% 90% 10% VCMHI DIAG_tR 10% VCM_DIAG_tR VCM_DIAG_tF T1 T2 T3 Figure 3.
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LMP91200 www.ti.com SNAS571C – JANUARY 2012 – REVISED MARCH 2013 Typical Performance Characteristics Unless otherwise specified, TA=25°C, VS=(VDD-GND)=3.3V, VREF=3.3V. pH Buffer Input Bias Current vs. VINP - Device ON 100 500 Average Average -31 Average +31 60 300 40 200 20 0 -20 -40 -60 240 0.5 1.0 1.5 2.0 INP (V) 2.5 3.0 3.5 -0.50 pH Buffer Input Bias Current vs. VINP - Device OFF 5 Average Average -31 Average +31 3 INPUT BIAS (pA) INPUT BIAS (fA) 0.
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LMP91200 SNAS571C – JANUARY 2012 – REVISED MARCH 2013 www.ti.com Typical Performance Characteristics (continued) Unless otherwise specified, TA=25°C, VS=(VDD-GND)=3.3V, VREF=3.3V. pH Buffer Input Bias Current vs. Temp - Device ON 500 400 pH Buffer Input Bias Current vs. Temp - Device OFF 5 Average Average -31 Average +31 3 INPUT BIAS (pA) INPUT BIAS (fA) 300 200 100 0 -100 -200 -300 -400 2 1 -1 -4 INP=1.
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LMP91200 www.ti.com SNAS571C – JANUARY 2012 – REVISED MARCH 2013 Typical Performance Characteristics (continued) Unless otherwise specified, TA=25°C, VS=(VDD-GND)=3.3V, VREF=3.3V. pH Buffer DC CMRR vs. Temperature 105 100 pH Buffer DC PSRR vs. Temperature 110 VDD=1.8V VDD=3.3V VDD=5V INP=7/8 VREF INP=1/8VREF PSRR (dB) 105 95 90 100 95 85 80 -50 -25 0 25 50 90 75 100 125 -50 -25 0 25 50 75 TEMPERATURE (°C) Figure 16. Figure 17.
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LMP91200 SNAS571C – JANUARY 2012 – REVISED MARCH 2013 www.ti.com Typical Performance Characteristics (continued) Unless otherwise specified, TA=25°C, VS=(VDD-GND)=3.3V, VREF=3.3V. pH Buffer CMRR vs. VINP - lower rail pH Buffer CMRR vs. VINP - upper rail 120 120 VDD=VREF=5V VDD=VREF=5V 110 CMRR (dB) CMRR (dB) 110 100 100 90 80 90 70 80 60 0.00 0.12 0.24 0.36 INP (V) 0.48 0.60 4.4 4.5 4.6 4.7 4.8 INP (V) Figure 22. Figure 23. pH Buffer CMRR vs. Frequency pH Buffer PSRR vs.
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LMP91200 www.ti.com SNAS571C – JANUARY 2012 – REVISED MARCH 2013 Typical Performance Characteristics (continued) Unless otherwise specified, TA=25°C, VS=(VDD-GND)=3.3V, VREF=3.3V. VCM Buffer TcVos VCM Buffer TcVos 40 35 UNITS TESTED >5000 VCMHI=1/8VREF 30 25 20 15 10 20 15 10 5 0 0 -2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 TCVOSVCM( V/°C) -2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 TCVOSVCM( V/°C) Figure 28. Figure 29. VCM Buffer DC CMRR vs. Temperature VCM Buffer DC PSRR vs.
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LMP91200 SNAS571C – JANUARY 2012 – REVISED MARCH 2013 www.ti.com Typical Performance Characteristics (continued) Unless otherwise specified, TA=25°C, VS=(VDD-GND)=3.3V, VREF=3.3V. VCMHI error vs. Temp 0.25 ERROR (%) 0.20 0.15 0.30 VCMHI=1/8VREF VCMHI=1/4VREF VCMHI=3/8VREF VCMHI=1/2VREF VCMHI=5/8VREF VCMHI=3/4VREF VCMHI=7/8VREF 0.20 0.10 0.05 0.15 0.10 0.05 0.00 0.00 -0.05 -0.05 -0.10 -50 VCMHI=1/8VREF VCMHI=1/4VREF VCMHI=3/8VREF VCMHI=1/2VREF VCMHI=5/8VREF VCMHI=3/4VREF VCMHI=7/8VREF 0.
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LMP91200 www.ti.com SNAS571C – JANUARY 2012 – REVISED MARCH 2013 Typical Performance Characteristics (continued) Unless otherwise specified, TA=25°C, VS=(VDD-GND)=3.3V, VREF=3.3V. PGA PSRR vs. Frequency PGA Time domain Voltage Noise 90 INTEGRATED NOISE (500nV/DIV) 80 +INPGA=100mV PSRR (dB) 70 60 50 40 30 20 10 0 10 TIME (1s/DIV) Figure 41.
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LMP91200 SNAS571C – JANUARY 2012 – REVISED MARCH 2013 www.ti.com Typical Performance Characteristics (continued) Unless otherwise specified, TA=25°C, VS=(VDD-GND)=3.3V, VREF=3.3V. Current Source (ICS=1000µA) Temperature coefficient Current Source (ICS=1000µA) 25 25 20 PERCENTAGE (%) 20 PERCENTAGE (%) UNITS TESTED >5000 IOUTCS=1000 A UNITS TESTED >5000 IOUTCS=1000 A 15 10 15 10 5 5 0 0 980 990 1000 1010 IOUTCS( A) 1020 -200 -150 -100 -50 0 50 100 150 200 IOUTCS(ppm/°C) Figure 46.
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LMP91200 www.ti.com SNAS571C – JANUARY 2012 – REVISED MARCH 2013 Typical Performance Characteristics (continued) Unless otherwise specified, TA=25°C, VS=(VDD-GND)=3.3V, VREF=3.3V. Supply current (pH Mode) vs. Temperature 50 Supply current (Temp Mode) vs.
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LMP91200 SNAS571C – JANUARY 2012 – REVISED MARCH 2013 www.ti.com FUNCTIONAL DESCRIPTION GENERAL INFORMATION The LMP91200 is a configurable sensor AFE for use in low power analytical sensing applications. The LMP91200 is designed for 2-electrode sensors. This device provides all of the functionality needed to detect changes based on a delta voltage at the sensor. Optimized for low-power applications, the LMP91200 works over a voltage range of 1.8V to 5.5V.
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LMP91200 www.ti.
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LMP91200 SNAS571C – JANUARY 2012 – REVISED MARCH 2013 www.ti.com Application Information Theory of pH measurement pH electrode measurements are made by comparing the readings in a sample with the readings in standards whose pH has been defined (buffers). When a pH sensing electrode comes in contact with a sample, a potential develops across the sensing membrane surface and that membrane potential varies with pH.
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LMP91200 www.ti.com SNAS571C – JANUARY 2012 – REVISED MARCH 2013 The pH measurement with the LMP91200 is straightforward, the pH electrode needs to be connected between VCM pin and INP pin. The voltage at VCM pin represent the internal zero of the system, so the potential of the electrode (voltage at INP pin) will be refered to VCM voltage.
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LMP91200 SNAS571C – JANUARY 2012 – REVISED MARCH 2013 www.ti.com Table 2. Configuration register: 1-step measurement Bit Name Description D15 MEAS_MODE 1 Temp measurement D14 I_MUX 0 RTD [D13:D12] I_VALUE 00 10 D11 PGA 1 [D10 :D8] VCM Leave these bits as they have been configured for the pH measurement.
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LMP91200 www.ti.com SNAS571C – JANUARY 2012 – REVISED MARCH 2013 Table 3. Bit Name Description D15 MEAS_MODE 1 Temp measurement D14 I_MUX 1 RCAL [D13:D12] I_VALUE 00 10 D11 PGA 1 [D10 :D8] VCM Leave these bits as they have been configured for the pH measurement. D7 VOCM 1 GND D6 DIAG_EN 0 DIAGNOSTIC disabled [D5 :D0] RESERVED RESERVED 100µA (Pt1000) 1 mA (Pt100) 10 V/V Table 4.
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LMP91200 SNAS571C – JANUARY 2012 – REVISED MARCH 2013 www.ti.
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LMP91200 www.ti.com SNAS571C – JANUARY 2012 – REVISED MARCH 2013 The 3-step temperature measurement can reach a precision as high as ±0.1°C (with RREF @ 0.01% of tolerance) when the analog signal is acquired by at least 16 bit ADC. With lower number of bit ADC this method gives the same result of the 2-step measurement due to the low voltage offset of the signal path. As rule of thumb, the 3step temperature measurement gives good result if he the LSB of the ADC is less than the input offset of the PGA.
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LMP91200 SNAS571C – JANUARY 2012 – REVISED MARCH 2013 www.ti.com REVISION HISTORY Changes from Revision B (March 2013) to Revision C • 26 Page Changed layout of National Data Sheet to TI format ..........................................................................................................
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PACKAGE OPTION ADDENDUM www.ti.
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PACKAGE MATERIALS INFORMATION www.ti.com 26-Mar-2013 TAPE AND REEL INFORMATION *All dimensions are nominal Device LMP91200MTX/NOPB Package Package Pins Type Drawing TSSOP PW 16 SPQ Reel Reel A0 Diameter Width (mm) (mm) W1 (mm) 2500 330.0 12.4 Pack Materials-Page 1 6.95 B0 (mm) K0 (mm) P1 (mm) 8.3 1.6 8.0 W Pin1 (mm) Quadrant 12.
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PACKAGE MATERIALS INFORMATION www.ti.com 26-Mar-2013 *All dimensions are nominal Device Package Type Package Drawing Pins SPQ Length (mm) Width (mm) Height (mm) LMP91200MTX/NOPB TSSOP PW 16 2500 367.0 367.0 35.
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