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DAC8718 Power Up Problem

David Levi
Prodigy 30 points
Other Parts Discussed in Thread: DAC8718

Hello

I have DAC8718 on my pcb supplied with +/-16V

RSTSEL,USB/BTC connected to VIO (3.3V)

VIO,VDD are connected together

i expect the output to be 0V on start up (Table 7 on Datasheet)

instead of 0V i got 7.8V (middle scale)

looks like the chip ignores the negative power supply...

what can be the problem?

(my schematic is attached below)

thanks,

david

  • 0
    TI__Genius 10615 points

    Hello David,

    Thank you for sharing your schematic. I think that you need to connect /WAKEUP to GND. You can read the details on page 45 of the DAC8718 datasheet. As it is connected right now, the data will never be stored in the DACs register, any data on SDI will be directly sent to SDO. However, I don't think that this should affect your power-on state.

    If grounding the /WAKEUP pin does not solve the problem, it may be the result of a few different things. I am going to ask you some questions in order to be able to debug this issue.

    1. Where are you connecting the digital and analog grounds?
      1. Since you gave me a partial schematic, I assume you connected it somewhere else, but I wanted to make sure.
    2. Are you following the power-on sequence specified on page 44 of the DAC8718 datasheet?
      1. This would be my biggest suspect. The power-on sequence is very important. If it is not employed, the internal registers of the device will not power-on correctly and can cause the device to behave abnormally.
    3. Are you using the package with the thermal pad? What voltage do you have the thermal pad connected to?
      1. This can sometimes cause strange behaviors if not connected correctly.