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.

CCS/TMS320F28054F: ADC PGA disable

Part Number: TMS320F28054F

Tool/software: Code Composer Studio

Hi,

I'm using 3 of the ADC pins (A1, A3, B1) with programmable gain of 3, 6, or 11, but I want to disable the PGA (use gain of 1). Should this produce a gain of 1? Right now I'm reading values in the register much lower than expected (values should be ~1.6 V, seeing 0-0.3 V).

Also, is there any danger in applying too much gain and saturating the ADC pin?

Thanks

  • Braden,

    There is no mechanism on F2805x to sample a PGA input pin without using one of the supported gain settings (3, 6, 11).  Disabling the PGA will have the effect of powering down the amplifier and isolating the input from the ADC converter.

    The PGA is powered by the VDDA + VSSA analog supplies so its output will saturate at VDDA, which can be safely tolerated by the ADC module.

    Have you considered the F28004x device family?  It has a newer PGA design and more flexibility for the ADC mapping such that some PGA inputs can also be sampled without amplification.

    -Tommy

  • Thanks, we were able to modify the board such that the incoming voltage is reduced by a factor of 3, allowing us to use the PGA of 3 effectively