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TMS570LS1114: ADC sample issue

Strong ZHANG
Expert 4500 points
Part Number: TMS570LS1114


Hi Team,

my Customer configure two ADC channel Ib_C350 and UDC as ADC1 Group1 sample, they found that the voltage change on UDC will impact the AD value of Ib_C350 even when the voltage on Ib_C350 remain the same.

 

  0x00000001U |               //Group1  bit 0//   Ib_C350

 0x00000002U |               //Group1  bit 1//   UDC , the last channel

 

For example,  if UDC is 0V, Ib_C350 AD value is 1724 when input voltage is 1.397V.

                         But if UDC is 3.3V, Ib_C350 AD value is 1742 when input voltage remain 1.397V.

 

but if customer change the configuration as below, adding one ADC sample which is always stable like 3.3V. then the voltage change on UDC would not impact the ADC sample of Ib_C350.

 

     0x00000001U |            //Group1  bit 0//   Ib_C350

    0x00000002U |            //Group1  bit 1//   UDC

     0x00000003U |            // 3.3 reference stable voltage , the last channel

 

That means the voltage on the last sample channel change will impact the first sample channel AD result value.

 

Could you help to do the analysis and findthe reason why would have this issue? Thanks a lot.

  • 0
    Genius 4130 points

    Hi Strong,

    A while back I identified an issue with sharded ADC channel sampling which resulted in silicon errata ADC#1 being raised. I've just checked and this errata does apply to the TMS570LS1114 as described in SPNZ218C at link:

    .

    Perhaps this relates to the issue you describe.

    Regards, Tony.

  • 0 in reply to Tony Morrell
    TI__Expert 4500 points
    Tony,

    Thanks for your reply. I see the errata talking ADC issue caused by below condition:

    This issue occurs if:
    1. Input voltage on a shared input channel being sampled by one ADC is (VCCAD -
    0.3V) or higher, and
    2. The second ADC samples another channel such that there is some overlap between
    the sampling windows of the two ADCs

    but actually, if the voltage on UDC is below 3 Volt, there still have this issue, although is not as bad as that when UDC is 3.3V
    For example, if UDC is 0V, Ib_C350 AD value is 1724 when input voltage is 1.397V.
    if UDC is 1.23 V, Ib_C350 AD value is 1730 when input voltage is still 1.397V.
  • 0 in reply to Strong ZHANG
    TI__Mastermind 21425 points
    Hello,
    Please take look at this file: www.ti.com/.../spna118b.pdf

    Best regards,
    Miro