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TMS570LS0714: ADC sampling time for one of the input signals

Filipe Madeira
Prodigy 20 points
Part Number: TMS570LS0714
Other Parts Discussed in Thread: HALCOGEN

Dear TI-Support,

The adc1 group1 trigger is synchronized with a specific PWM signal and the ADC is running at a cycle time of 62.5ns. There are more than 5 inputs signals in this ADC group. In short, I need to know exactly how much time the ADC will need to sample the input signal 3. 

I'm having doubts on how to compute the exact time for an input sample to be obtained. According to Halcogen, the following variables shall be taken into account: total scan (Tscan), time to discharge the capacitor (tDischarge), time to sample (tSample) and time to convert the signal (tConversion). I can't find any explanation or guide on how these variables intertwine with each other and what's their actual sequence.

Some questions I have regarding the sampling sequence:

  1. Are all input signals scanned first before anything else? 
  2. What is the scan period used for? 

Assuming that the continuous conversion is disabled and that there is no discharge time for the internal capacitor, how much time will it take for input signal 3 be sampled?  As I see it there are three options: 

  1. 3 * ( tScan + tSample ) 
  2. 3 * ( tScan + tSample ) + 2 * tConversion 
  3. total tScan + 3 * tSample 
  4. total tScan + 3 * tSample + 2 * tConversion 

Thanks for the support

  • +1
    TI__Mastermind 39215 points

    Hi,

    • Are all input signals scanned first before anything else? 

    Ans) No, the sequencer in ADC will select only one input at a time for the conversion and the second input will be selected only after completion of the conversion of the first input. 

    • What is the scan period used for? 

    Ans) Scan period is nothing but a switching period between one channel to another channel, it is the time taken by sequencer to switch from after completing one channel to pointing the next channel in sequence. Depends on number of channels in the group the scan time varies, if there is only a single channel in the group then scan period will be zero(because no switching required with in single iteration). 

    • Assuming that the continuous conversion is disabled and that there is no discharge time for the internal capacitor, how much time will it take for input signal 3 be sampled?

    Ans)  total tScan + 3 * tSample + 2 * tConversion 

    Note: 

    To complete 1 channel conversion

     total time = tSample + tConversio (Note here no switching required so tscan is zero here)

    To complete 2 channels conversion

     total time =tScan +  2*tSample + 2* tConversio (Note here tscan is nothing but one switching interval from channel-1 to channel-2)

    To complete 2 channels conversion and one channel sampling

    total time =tScan +  3*tSample + 2* tConversio (Note here tscan is nothing but two switching interval from channel-1 to channel-2 and channel-2 to channel-3)

    --

    Thanks,
    Jagadish.

  • 0 in reply to jagadish gundavarapu
    Prodigy 20 points

    Thanks for the reply. It's clear form me now.