(ACTIVE) Integrated AFE for Low-Power pH Sensing Applications


Functional Diagram

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The LMP91200 device is a 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 1.8 V to 5.5 V. With its extremely low input bias current it is 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 LMP91200. Two guard pins provide support for high parasitic impedance wiring. Depending on the configuration, total current consumption for the device is 50 µA while measuring pH. Available in a 16-pin TSSOP package, the LMP91200 operates from –40°C to +125°C.


  • Active Guarding
  • Key Specifications
    Unless otherwise noted, typical values at
    TA = 25°C, VS = (VDD-GND) = 3.3 V
    • pH Buffer Input Bias Current (0 < VINP < 3.3 V)
      • Maximum at 25°C: ±125 fA
      • Maximum at 85°C: ±445 fA
    • pH Buffer Input Bias Current
      (–500 mV < VINP– VCM < 500 mV),
      VS = (VDD – GND) = 0 V
      • Maximum at 25°C: ±600 fA
      • Maximum at 85°C: ±6.5 pA
    • pH Buffer Input Offset Voltage: ±200 µV
    • pH Buffer Input Offset Voltage Drift: ±2.5 µV/°C
    • Supply Current: 50 µA
    • Supply Voltage: 1.8 V to 5.5 V
    • Operating Temperature Range: –40°C to 125°C
    • Package: 16-Pin TSSOP


Features Current Sources (iDACs)^PGA    
Operating Temperature Range (C) -40 to 125    
Package Group TSSOP|16    
Package Size: mm2:W x L (PKG) 16TSSOP: 22 mm2: 4.4 x 5 (TSSOP|16)    
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