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DAC8728 Offset DAC registers have 0x8000 in them instead of trimmed value after power-on

Jeff Robins
Prodigy 10 points
Other Parts Discussed in Thread: DAC8728

Hello,

We are currently using multiple DAC8728's in a design, where the power-up sequence does not always match the datasheet's sequence.  Specifically when power is quickly cycled and some of the rails still have voltage stored in bulk capacitors.

What we are seeing is that we sometimes have a problem where the Offset DAC registers are filled with 0x8000 and not 0x199A +/- 10LSB (RSTSEL and USB#/BTC are both tied high). We can change the values in the Offset DAC registers to 0x199d (power-on value for this chip, when the device works correctly) and receive normal output from the device.

However, resetting the device and/or changing the values of the GAIN-A and GAIN-B bits from 0->1->0 places 0x8000 back in the registers. 

Is there a way to correct this short of redesigning the board?

Thank you,

Jeff

  • 0
    TI__Mastermind 46290 points

    Hi Jeff,

    Sorry for my delays, I've been traveling and working towards catching up on forum activity...

    I've seen issues with violating the power supply sequence before related to the values read into the offset DAC registers. Essentially when the power up sequence is violated the OTP memory isn't read correctly and the device will load unipolar or incorrect values to the offset DAC register.

    Resets do not rectify the issue, and it's normal functionality for a write to the GAIN-A or GAIN-B bits to rest the offset DAC values.

    Can you try an experiment and remove these bulk capacitors and see if the problem persists?