• State Resolved
  • Locked Locked
  • Replies 3 replies
  • Answers 1 answer
  • Subscribers 63 subscribers
  • Views 358 views
  • Users 0 members are here
Support feedback
Options
Options
Related

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.

UCD3138: Can I use EADC to instead of ADC ,if I need more ADC channels?

HAN LEE
Expert 1515 points
Part Number: UCD3138


 Hi Ereryone,

Can i use EADC to instead of ADC? Can you show me how to config the EADC , thanks.

  • 0
    TI__Genius 17090 points
    If you have a limited range of signals to measure, within the dynamic range of the EADC itself, it's pretty easy to use and fast. Just set the AFE Gain to cover the range you need, and put the EADCDAC in the middle of the range. Use the DPWM to trigger the sampling, just like you would for a compensating filter, but don't connect it to a filter. Just read the measured error. Of course, the total range is only around 0 to 1.6 volts or so, and the maximum dynamic range is +- 32 ADC steps. So if you go to the lowest resolution, 8 mV, you will get 8 * 64 or .512 volts of dynamic range.

    The SAR mode is is a bit more problematic. It's slower than the ADC, and if the signal is too dynamic, it may not converge. It doesn't have a sample and hold, so if things are changing rapidly, either to noise or real change, successive approximation doesn't work very well.

    If the variation isn't that great for short times, you could use a software method of successive approximation, and try to center the EADC DAC in the current range.
  • 0 in reply to Ian Bower
    Expert 1515 points
    Hi Ian,

    Can you tell me why "The SAR mode is slower than ADC"? I checked the reference manual that ADC & EADC are both sar mode ,thanks.
  • 0 in reply to HAN LEE
    TI__Genius 17090 points

    It's true that both are SAR.  In fact, the EADC is faster - 6 bits at 64 ns, which the ADC is much slower - 12 bits at 3.9 microseconds.

    But the EADCs 6 bits only cover a maximum of 512 millivolts range. 

    The SAR mode on the front end uses the EADC SAR and the EADCDAC, plus some logic, to make a SAR convertor which covers the full 1.6 volt range of the EADC DAC.  I have been told that it's actually faster than the ADC, taking about 2 microseconds to complete, typically.