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OPA1622: Enable function dead after power sequencing.

Andreas Broeckling
Prodigy 20 points
Part Number: OPA1622

Hello,
the enable function does'nt work on 8 x OPA1622 after power supply sequencing.
It is possible to turn the op amps correctly on if enable is high. If low, the OPA1622
pulls out a strong distorted 2Vrms signal.

This happens if the +/- 13V opa1622 supply rail is turned off and enable signal is still high.
We have in this state a  strong + 2V signal on the pos and + 0.7V on the neg supply line coming out of the Opa1622 supply lines through
the enable input pin  if set to high.

I assume enable should be set to logic low before turn off the rails.


TI please check this sequencing behavior and please give a guideline for the redesign.

Best regards
Andy

  • +1
    TI__Mastermind 18465 points

    Andy,

    Yeah, the enable pin should be set to logic low before turning off the supplies. You want to make sure that the enable pin is not more than the limits in the specification section, specifically no greater than the abs max:

    What is happening, is a forward biased diode to the positive rail and a reversed biased diode to the negative rail assuming that each supply is 0V and Enable is set high. The input current should also be no more than +/-10mA. Stresses beyond the limits may cause permanent damage to the device. 

  • 0
    Prodigy 20 points

    Hi Chris,
    i have overlooked the input schematic. Better having the problem on the prototype as in the production state.
    Thanks to clearify the problem. I have changed the supply sequence and will add a series resistor to protect the enable pin.
    The amp is not a cheap one. Just want to make sure that i am  right on this topic.

    Thanks Chris

    Andy