• State TI Thinks Resolved
  • Locked Locked
  • Replies 3 replies
  • Answers 1 answer
  • Subscribers 82 subscribers
  • Views 100 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

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.

TMS320F28P650DH: Is it possible to use the differential ADC in pseudo differential format?

Kappa
Prodigy 10 points
Part Number: TMS320F28P650DH

Tool/software:

Hi,

I want to measure couple of analog signals using ADC of TMS320F28P650DH in differential mode. However, my signals are not differential. They are pseudo differential bipolar. Signal on P pin of ADC will swing between 3 and zero while the N pin is connected to the reference voltage coming from sensor nominal 1.5V (with tolerance, etc). I read the TRM saw that there is limitation on how much common mode voltage of the inputs can be away from VREFHI + VREFLO)/2 (page 3195 of TRM), and I looked at datasheet, did not find any thing except a picture showing ±50mV.

My question is can I use differential ADC in the format I explained? and what is the limitation on CM voltage on inputs?

Thank you.

  • 0
    TI__Intellectual 860 points

    Hi,

    There is a limitaion on the CM for the ADC input while using in differential mode, as this ADC is pseudo Differential.

    Kappa said:
    I read the TRM saw that there is limitation on how much common mode voltage of the inputs can be away from VREFHI + VREFLO)/2 (page 3195 of TRM), and I looked at datasheet, did not find any thing except a picture showing ±50mV.

    This above statment is correct for CM to be (VREHI+VREFLO)/2. 

    Best way is to use a FDA to provide (VREHI+VREFLO)/2 to the CM terminal of AMP and provide the voltage as per you stated above. 

    Example of FDA amplifier

    Thanks,

    Niles

  • 0
    Prodigy 10 points

    Hi Nilesh,

    Thank you for the response. IN my opinion the circuit included in your response won't work. Whole purpose of using differential is taking tolerances and the noises on the sensor' reference voltage into account in A/D conversion. The circuit is just converting single-end to differential signal, however, using FDA as subtractor would work. It is simple change to the circuit you shared, but it adds to complexity, more stages more noises/tolerances/resistor noise...Even though I think the only way is this, if CM of the MCU is limited.

    Thank you

  • 0 in reply to Kappa
    TI__Intellectual 860 points

    Hi,

    Got it, undersood & agreed that FDA will make solution complex. 

    Thanks, 

    Nilesh