9.2 Typical Applications

9.2.1 Resistive-Bridge Pressure Sensor

The INA351 is an integrated instrumentation amplifier that measures small differential voltages while

simultaneously rejecting larger common-mode voltages. The device offers a low power consumption of 110

µA (typical) and has a smaller form factor.

The device is designed for portable applications where sensors measure physical parameters, such as changes

in fluid, pressure, temperature, or humidity. An example of a pressure sensor used in the medical sector is in

portable infusion pumps or dialysis machines.

The pressure sensor is made of a piezo-resistive element that can be derived as a classical 4-resistor

Wheatstone bridge.

Occlusion (infusion of fluids, medication, or nutrients) happens only in one direction, and therefore can only

cause the resistive element (R) to expand. This expansion causes a change in voltage on one leg of the

Wheatstone bridge, which induces a differential voltage VDIFF.

Figure 9-4 showcases an example circuit for an occlusion pressure sensor application, as required in infusion

pumps. When blockage (occlusion) occurs against a set-point value, the tubing depresses, thus causing the

piezo-resistive element to expand (Node AD: R + ΔR). The signal chain connected to the bridge downstream

processes the pressure change and can trigger an alarm.

GND

+

–

INA351

VOUT

VEXT = 5 V

0.1 F

VDIFF

ADC

Pressure

Occlusion

Sensor

µC

A

B

C

D

REF

1 F

VS = 5.5 V

1 F

R1

Figure 9-4. Resistive-Bridge Pressure Sensor

Low-tolerance bridge resistors must be used to minimize the offset and gain errors.

Given that there is only a positive differential voltage applied, this circuit is laid out in single-ended supply mode.

The excitation voltage, VEXT, to the bridge must be precise and stable; otherwise, measurement errors can be

introduced.

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INA351

SBOSAD5 – DECEMBER 2022

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