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ADS8412: Conversions at half frequency

MH
Intellectual 300 points

Part Number: ADS8412

Hello,

We're seeing an odd behavior with ADS8412, here's the connections:

  • /CS and /CONVST connected together and pulsed low at 1MHz (50ns)
  • /RD connected to DGND

Instead of having a BUSY signal 1MHz, we are seeing a busy signal pulsing at 500kHz. Why are we having only every other conversion start detected?

Thank you.

  • 0
    Intellectual 300 points

    We also have the same behavior if all 3 pins (/CS, /CONVST & /RD) are pulsed low. These configurations should work as per the datasheet (tsu1=0), we would expect to have data out from previous conversion.

  • +1 in reply to MH
    TI__Genius 10797 points

    Hi Mehdi,

    Thanks for your post. I understand what you mean as tying CS and CONVST together should work due to tsu1=0. However, I believe this only takes care of the conversation phase, in which case both CS and CONVST need to be low to trigger a conversation/hold state. Referring to figure 2 in the datasheet, it looks like during the acquisition phase, the CONVST is held high and only the CS is brought low:

    As both the conversation and acquisition phase need to be completed to output a sample, I believe your ADC is not functioning as expected as it doesn't seem to be entering the acquisition phase. So, tying CS and CONVST together would not be a valid configuration. Could you try separating them?

    Here is an app note with additional details: https://www.ti.com/lit/an/slaa211/slaa211.pdf

    Best regards,

    Samiha