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TLV9002: Single-supply strain gauge bridge amplifier circuit

Part Number: TLV9002
Other Parts Discussed in Thread: INA350

Hi Team,
I want to design a circuit that measures the readings from a strain gauge.
The Bridge resistance is 350 Ohms.
The excitation voltage is 12V.
I am following this application note as my reference. (https://www.ti.com/lit/an/sboa247/sboa247.pdf?ts=1651680187339&ref_url=https%253A%252F%252Fwww.google.com%252).
The output of the bridge is 2mV/V.
 
My required output voltage is in the range of 0V - 5V
In the application note SBOA247, 
1). The Vcm (common-mode voltage) is taken as 2.15V. Why is that?.
2). How was the Vcm calculated?.

  • Hello Shibin,

    I believe you found an error in the VCM equation. The VCM should be approximately 2.39V when R10=120Ohm. 

    I I believe the error lies in how the author calculated the bridge resistance. 

    This is the document equation:

    However I calculate the VCM voltage to be: ((2.5V- (.9mA*120Ohm))= 2.39V 

    I will work to correct the equations for the next document revision. 

    You can calculate VCM for your specific bridge via subtracting the voltage drop across R5 from Vext.

    Please also consider using our new cost-sensitive selectable gain instrumentation amplifier- INA350 for similar performance with reduced system size. 

    I have included a TINA simulation using the INA350 in a similar bridge application here:

    INA350_Bridge.TSC.

    You can use the Analog Engineer's Calculator to calculate the expected INA output swing for your application.

    Here is an example G=50 VOUT vs. Vcm plot for the INA350CD.

    Please let me know if you have any questions.

    BR,

    Jacob