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DAC7558 Output Issue

Derek Xie
Genius 12255 points
Other Parts Discussed in Thread: DAC7558, OP07

Hi Team:

My customer is using the DAC7558 in their application.

The DAC7558 have eight outputs from Vo1 to Vo8. They find Vo7 and Vo8 is always failure. The voltage is always 4.7V. The DAC is in one board, the output will connect to board 2 with JP1 and JP3. The Vo7 and Vo8 will be IC1 and ID1 in the board 2. The IC1 and ID1 will be connect the OP07 circuit. Could you help me to check whether it's possible will cause the Vo7 and Vo8 failure. Thanks.

  • 0
    TI__Genius 12255 points
    Hi Team:
    Any update?
  • 0 in reply to Derek Xie
    TI__Genius 11750 points
    Howdy Derek,

    I have a couple of questions that will be useful for our debug:

    - Can you ask the customer to measure VCC, VDD, and VREF?
    - Do they still see the issue when the 2nd board is not connected?
    - Do they see any oscillation on VREF or DAC output?
    - Can they verify the other VOUT voltages?

    Best Regards,
    Matt
  • 0 in reply to Matthew Sauceda
    TI__Genius 12255 points
    Matt:
    1. We have measure all voltage, it's all normal.
    2. Just power on DAC7588 board, the chip will be very hot.
    3. No.
    4. Vout at VOUTE-F-G-H is all 4.7V.
    It looks like out internal amplifier damaged.
    Could you tell me what situation will damaged internal ampifier?
  • 0 in reply to Derek Xie
    TI__Genius 11750 points
    Derek,

    I noticed that the customer wasn't consistent in the naming of their grounds. For instance the first board has 3 different net names for ground: SGND, AGND, and GND. From their schematic it looks like only SGND and AGND are connected, the "GND" net on pin 26 of the DAC is not connected and may be floating. The interesting part about this is that the op-amp supplies on board 2 are tied directly to bypass through the net "GND", which is not connected to SGND or AGND. This may create issues since all the ground planes are not tied together. These incorrect connections may have possibly damaged the outputs of the DAC.

    - Can the customer power up a new board 1? Please make sure that it is not connected to board2. If the DAC outputs correctly, then it may be a matter of the ground connections on both the first and second board. It is best to keep the name of "ground" consistent across all devices.

    Best Regards,
    Matt
  • 0 in reply to Matthew Sauceda
    TI__Genius 11750 points
    Derek,

    I've also noticed the GND symbol tied to the header does not have a net name. If this GND is not connected to any of the three grounds mentioned, then ground is not being applied to any of the devices, which may result in damage.

    Best Regards,
    Matt
  • 0 in reply to Matthew Sauceda
    TI__Genius 12255 points

    Matt:

    Great, I will double check the ground plane.

    BUt this issue is 10pcs when 198pcs is used. If the ground plane is not connect together, it should be high failure rate.

    Do you have any other idea about it? Thanks.