LMP91200 Datasheet, PDF (1/25 Pages) Texas Instruments – Configurable AFE for Low-Power Chemical Sensing Applications

LMP91200
June 25, 2012
Configurable AFE for Low-Power Chemical Sensing
Applications
General Description
The LMP91200 is a configurable sensor AFE for use in low
power analytical sensing applications. The LMP91200 is de-
signed for 2-electrode sensors. This device provides all of the
functionality needed to detect changes based on a delta volt-
age at the sensor. Optimized for low-power applications, the
LMP91200 works over a voltage range of 1.8V to 5.5V. 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. The Common Mode Output pin
(VOCM) provides a common mode offset, which can be pro-
grammed to different values to accommodate pH sensor
output ranges. For applications requiring a high impedance
common mode this option is also available. Two guard pins
provide support for high parasitic impedance wiring. Support
for an external Pt1000, Pt100, or similar temperature sensor
is integrated in the LMP91200. The control of this feature is
available through the SPI interface. Additionally, a user con-
trolled sensor diagnostic test is available. This function tests
the sensor for proper connection and functionality. Depending
on the configuration, total current consumption for the device
is 50µA while measuring pH. Available in a 16-pin TSSOP
package, the LMP91200 operates from -40°C to +125°C.
Key Specifications
Unless otherwise noted, typical values at
T_A = 25°C, V_S=(VDD-GND) = 3.3V.
■ ^{pH Buffer Input bias current (0<V}_INP ^<3.3V)
— max @ 25°C
— max @ 85°C
±125 fA
±445 fA
■ ^{pH Buffer Input bias current (-500mV<V}_INP^-V_CM ^<500mV),
V_S=(VDD-GND)=0V
— max @ 25°C
±600 fA
— max @ 85°C
±6.5 pA
■ ^{pH Buffer Input offset voltage}
±200 µV
■ ^{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
Features
■ ^{Programmable output current in temperature measure-}
ment
■ ^{Programmable Output common mode voltage}
■ ^{Active guarding}
■ ^{On board sensor test}
■ ^{Supported by Webench Sensor AFE Designer}
■ ^{Supported by Webench Sensor Designer Tools}
Applications
■ ^{pH sensor platforms}
Typical Application
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