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OPA860: Effect of loosing RQ connection to Pin 1 IQ Adjust (FMEA related)

Andy Hammond
Prodigy 10 points
Part Number: OPA860

Hi. We want to use OPA860 as a current feedback amplifier in one of our designs. As such, we need to prepare an FMEA. I have one failure that I am struggling with. "What will be the effect on the signal path if the current setting resistor RQ at pin 1 fails and becomes open circuit".

It is used in part of a signal chain carrying small, fast pulses. The macro transistor is configured as common emitter. The current setting resistor RQ is 1KOhm, connected between pin 1 and the -5V rail.

The datasheet on page 14 states RQ is required for proper operation, but what will actually happen to our pulses in the event that RQ fails? 

Kind regards,

Andy Hammond

  • 0
    TI__Genius 16491 points

    Hello Andy,

    This is a very good question; I will take a look at datasheets and figure out a good way to explain what would happen to the IC.  

    In the meantime, the old Burr Brown datasheets for similar OTA parts, the OPA660 and OPA2662c, do explain the function of RQ in slightly greater detail.

    Please see the two attachments for that helpful information, located on page 9 (OPA660) and page 13 (OPA2662) respectively.

    I will ask my team as well and see if we can get a solid answer to this.  Is there a certain level of detail needed to satisfy the FMEA question?  Depending on the needed specificity of your answer, these datasheets might give you enough context.

    7752.OPA660.pdf

    opa2662.pdf

    Best,

    Alec