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UCC27714EVM-551: how to test cycle-by-cycle current limit

Jose Maria Rey
Prodigy 60 points
Part Number: UCC27714EVM-551
Other Parts Discussed in Thread: UCC28950,

Hello,

I've been working with the UCC27714EVM-551 under overload condition to test the cycle-by-cycle current limit and see how the UCC28950 manages this.

I've tried to apply a non-inductive overload (from 40A to 60A) at the output and a capacitive charge to the output, but somehow the CS signal increases slowly, and it doesn't surpass the 2V level.

Why the CS pin is increasing slowly with a step-load that puts the converter clearly in overload condition, and why it doesn't surpass the 2V level? (even applying a capacitive load)

With a step load of 20A or more I expected the CS level to increase instantly, but it is like it is clamped to a level under 2V.

On the other hand, how could I test the cycle-by-cycle current limit?

Thank you.

  • 0
    TI__Mastermind 23215 points

    Hello Jose,

    Applying a step load to the output with the output filter in place including output capacitance will result in a delay of the output voltage response and the controller responding to this change. Also there is the control loop response to correct the output droop so you will not see an immediate step response to the load.

    I am not the controller expert, but I would suggest looking at the UCC28950 datasheet and possibly trying powering up only the UCC28950 with the bias and injecting a signal into the CS pin with an external generator. The timing of this CS signal should align with the expected signal from a power train.

    You might try posting this question under a UCC28950 thread to get advice from a controller expert.

    Regards,