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AD5412/AD5422 - loss of independent digital supply

Question asked by J-B on Jul 13, 2017
Latest reply on Jul 17, 2017 by J-B

Hello,

 

In my case, I plan to use the AD5412 with two independent power supplies : 

 - A +3,3V digital supply coming from one source (source #1)

 - A +/-15V dual supplies coming from another source (source #2)

 

Both sources are independent. Here after the identified board states according to sources behaviour:

  • State #1: source #1 OFF, source #2 OFF:
  • State #2 : source #1 OFF, source #2 ON
  • State #3 : source #1 ON, source #2 OFF
  • State #4: source #1 ON, source #2 ON

 

At board power up (State #1 -> State #4), state #2 or state #3 can be a transitional state during unknown duration. To prevent any wrong DAC powering-up, the master will set the CLEAR pin to high level as the board goes to state #4. This preconisation is well explained in the datasheet.

 

My question is about the power-down event. Indeed, a external event can force the board to go from state #4 to state #2 or #3 for an unknown duration. In any case, the DAC output shall be deactivate (Unipolar Vout = 0V, Iout left open).

Could you confirm that loss of one supply would force the DAC output in this safe state ? I’m pretty sure that loss of Analog supply would force the DAC in safe state. However, I have few doubt about the DAC behaviour if only digital supply would go down: since the master could force a high level to CLEAR pin nor drive SPI, DAC output could be frozen in its previous configuration output (Vout > 0V or Iout > 0 mA depending on the DAC configuration) ?

Thank you in advance for your feedback, I hope I would have been clear enough to describe my issue.

 

Best regards,

Jean-Baptiste Osmont

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