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OPA521: IFLAG behavior during thermal shutdown

Oba
Genius 17315 points
Part Number: OPA521

Tool/software:

Hello,

My customer is evaluating OPA521 EVM now and have a question.

When thermal shutdown happens, both TFLAG and IFLAG are simultaneously set and off even though the currenct doesn't hit the limit value like the below figure.
I just wonder why IFLAG is set although the current is less than the limit setting. Is it expected behaviour?

CH4: Output current
CH1: VOUT
CH2: TFLAG
CH3: IFLAG

Regards,
Oba

  • 0
    TI__Genius 16505 points

    Hi Oba,

    It is hard to see the output current being measured, could you share this value as well as the limit being set with the external resistor. Do you see this behavior when no current limit is set (ILIM pin grounded)?

    Best Regards,

    Ignacio

  • 0 in reply to Ignacio Vazquez Lam1
    TI__Genius 17315 points

    Hello Ignacio,

    ILIM is grounded. So curremt limit should not happen with this level of current, around 300mA.
    Thermal shutdown happned with this level of current because VIN is 24V and VOUT is about 12~13V.
    I confirmed that when VIN voltage is lower than it, TFLAG(also IFLAG) was not set even with 1A.
    So I can understand why TFAG is set, but IFLGA should be set with this condition.

    Regtards,
    Oba

  • 0 in reply to Oba
    TI__Genius 16505 points

    Hi Oba,

    Thank you for clarifying this. I was able to speak with the team that originally worked on this device, and they confirmed this circuitry is independent, meaning they were not meant to trigger each other. However, they were not meant to be relied on as very precise flags, specifically the current flag as depending on the internal bias could result in a high state even when the output current is hundreds of milli-amps away from the limit. I would also like to add that the IFLAG specifically is considered a true state when this flag is high for longer than 100ms. It seems like the scope shots show a duration much less than this.

    Best Regards,

    Ignacio

  • 0 in reply to Ignacio Vazquez Lam1
    TI__Genius 17315 points

    Hello,

    So in this case, this IFLAG set is a kind of errata(unexpected behavior) of this device?

    Regards,
    Oba

  • +1 in reply to Oba
    TI__Genius 16505 points

    Hi Oba,

    Speaking with the team familiar with this device, this is something that could happen however they are independent. If the flag is high for 100ms or longer, we can assume the device has hit a current limit. If under, the flag could be falsely triggered as it can experience transient pulses.

    Best Regards,

    Ignacio