1 Features
1• 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

2 Applications
• pH Sensor Platforms

3 Description
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.