This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

PGA302: Recommendation for low resistance bridge

Part Number: PGA302
Other Parts Discussed in Thread: ADS1235

Hello team, 

Customer is looking for an integrated solution for strain gauge measurement. The main goal is to measure strain on a flex cable that is suspected of causing problems in assembly. Hence, the resistance may be in the very low (20 ohm range). I see for PGA302 in the previous post it's stated that with 2.5V excitation min resistance would be 300 Ohm. 

Is there a way to use PGA302 for smaller resistance? Or maybe another part that we'd recommend instead of the PGA302?

I was looking at ADS1235 specs, not sure if that would work either. Appreciate your feedback.

Thanks!

  • Hello Sepeedah,

    Using a sensor with such a low resistance will require a large amount of current. The limiting factor is the current output capabilities of the PGA302's VBRG supply, which is 8.5mA. In order to drive the current needed for a 20ohm sensor at 2.5V you would need to have an external supply. You can use a simple buffer circuit with an inexpensive opamp and just use the accurate and stable VBRG output from the PGA302 as the input for the buffer. This will allow you to drive the current from a source other than the PGA302 itself.


    Regards,

  • Thank you Scott! Much appreciated.

    Also, how would PGA302 compare to ADS1235 for this use case? I understand these are very different options in terms of resolution and output format, but not sure how you'd go about picking one.

  • Hello Sepeedah,

    The biggest difference here is the internal temperature and linearity compensation engine in the PGA302. With some calibration the compensation engine will generate much more accurate results than a raw ADC output, and it does not require firmware development like what would be needed to do that compensation afterward in a system MCU. So if high accuracy is a concern (<0.5% FSO) I would recommend the PGA302.

    Because of the low impedance of the sensor, the benefits of having an integrated bridge excitation supply are a bit lessened, but that would normally be a selling point compared to a standard ADC. Additionally the PGA302 has a DAC for voltage output, which is a benefit if an analog output is needed.

    Regards,