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OPA564: overcurrent flag (ILIM) asserts erratically , sensitive to slow ramping current

Vadim Bishtein
Prodigy 20 points

Part Number: OPA564

In our design OPA564 seems to go into/out of Overcurrent erratically while the op-amp is sinking about 250mA DC from external load. The amp is setup for 1.5A limit with ISET=4.7kOhm. Tried shorting ISET pin to GND to maximize current limit, but that didnt help. 

We observe that:

 -  ILIM triggers around -1.25A when current ramp is fast (3.5GA/sec slew rate)  - EXPECTED 

  - ILIM deasserts when current drops to -250mA (the 1A hysteresis seems rather large, but okay) - SOMEWHAT EXPECTED

 - ILIM asserts again if current crosses -250mA with a much slower slew rate (roughly 0.35GA/sec) .... so ILIM effectively keeps triggering for 250mA load  -- NOT NORMAL 

I'm attaching waveforms capturing this behaviour. Please comment if you have clue as to what might be going on. 

Thanks !

  • 0
    TI__Guru* 93105 points

    Hello Vadim,

    I haven't seen this particular IFLAG behavior before. It is odd that the low output di/dt is the condition that results in the flag indicating the amplifier is in current limiting. It does appear from the first DSO image that despite the current limit flag going to high state unexpectedly, that OPA564 is providing the -245 mA output current. 

    Would it be possible for you to provide your circuit schematic and information about the power supply levels, output load, input signal, how the IFLAG pin is configured, etc? I would like to see if there is something that may explain this behavior.

    Regards, Thomas

    Precision Amplifiers Applications Engineering

  • 0 in reply to Thomas Kuehl
    Prodigy 20 points

    Hi Thomas, Thanks for looking into this. Attaching schematic OPA564 in our design. I can provide more details about load via email, any way to contact you

    I can provide more details about load via email, possible to contact you directly?

  • 0 in reply to Vadim Bishtein
    TI__Guru* 93105 points

    Hello Vadim,

    Let's go ahead and take this off the E2E and communicate directly via email. That way we can keep the details of your circuit and application confidential.

    My email address is:

    Regards, Thomas

    Precision Amplifiers Applications Engineering