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ADS8866: Please help us solve ADS8866 DOUT PIN still output High level, can't recover normal work, thanks!

Jacking Jin
Expert 1145 points
Part Number: ADS8866

Dears,

 Could you please give me some suggestions how to processing ADS8866 Dout pin still keep high level? Project background: Set ADS8866 work on 3-wire module, when we do the aging test, some time power on cause ADS8866 Dout is keep high level output, and can't recover normal work , it's must restart system can working, it's happens occasionally. please refer design schematic diagram and test waveform, thanks!

Picture3 Dout Normal waveform

Picture DOUT abnormal waveform

  • 0
    Expert 1145 points

    Dear Team,

    Could you please help check this case? Customer will PP recently, now face this problem maybe cause production delay, please give great support it, thanks!

  • 0 in reply to Jacking Jin
    TI__Mastermind 39230 points

    Hello Jacking,

    Everything looks correct in the schematic.  I guess there is some kind of signal integrity or timing issue.

    Please provide scope waveforms showing all 3 IO signals; SCK (TP19), MSIO (TP18), and NSS1 (TP20).

    Question:

    1.  Does this problem occur on multiple boards, or only on 1 board?

    2.  Does the problem occur as soon as device is powered up, or does it operate correctly for some time and then stop working?

    Regards,
    Keith Nicholas
    Precision ADC Applications

  • 0 in reply to Keith Nicholas
    Expert 1145 points

    Dear Keith，

    Thanks for your quickly answer it. Please refer below timing PINS waveform, thanks so much.

    1.  Does this problem occur on multiple boards, or only on 1 board?

    Yes, It's appear on multiple boards.

    2.  Does the problem occur as soon as device is powered up, or does it operate correctly for some time and then stop working?

    This happens when the chip is powered up, if it does not appear when the power is on, it will always work, but it often happens when the power is on.

    Best regards

    Jacking

  • 0 in reply to Jacking Jin
    Expert 1145 points

    Dear Keith，

    I have another question also need you help advice it, thanks!

    When ADS8866 is already working, if can we change operation mode?

    Best regards

    Jacking

  • 0 in reply to Jacking Jin
    TI__Mastermind 39230 points

    Hello Jacking,

    The above waveforms show that MOSI is changing. 

    1. Is this connected to pin 9 (DIN) of the ADS8866?
    2. Or, is DIN always connected to DVDD (high) as shown in the schematic?

    The above waveforms show the device working correctly.  Can you ask your customer to provide the same waveforms for an ADS8866 NOT working.
    SCK (pin8, TP19), MISO (pin7, TP18), and NSS1 (pin6, TP20).  Also, if DIN (pin9) is connected to MOSI, then provide this as well.

    AVDD and DVDD are powered from ZD1 zener regulator circuit.  This will take some time to power-up.  The customer needs to make sure SCLK and CONVST pins are held low until AVDD and DVDD are powered up to 3.3V.  If these digital inputs are driven high (3.3V) before AVDD/DVDD reach 3.3V, this could cause the device to not operate correctly.

    When ADS8866 is already working, if can we change operation mode?

    Yes, you can change modes.  If DIN is high 7.5nS or longer before the rising edge of CONVST (pin 6), then the device will operate in Chip Select mode.  If DIN is low on the rising edge of CONVST, the ADS8866 will go into daisy-chain mode.  In this mode, DOUT (pin 7) is always driven high or low.

    Regards,
    Keith

  • 0 in reply to Keith Nicholas
    Expert 1145 points

    Dear Keith,

    By optimizing the power supply circuit of the system, the problem is solved, It's should be timing issue, thanks for your suggestion to help it, thanks so much!

    Best regards,

    Jacking