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Original question:

TPS25830-Q1: Current limit

TPS25830-Q1: VBUS voltage drop but without over-current FAULT assertion after output current is greater than current limit

Nan Su
Prodigy 10 points
Part Number: TPS25830-Q1
Other Parts Discussed in Thread: TPS25830A-Q1

Tool/software:

Hi,

According to Chapter 10.3.10.5 Cycle-by-Cycle Buck Current Limit. “If VCSN/OUT < 2-V typical due to a short circuit for 128 consecutive cycles, hiccup current protection mode will be activated”

That means VBUS voltage drops to <2V when short circuit happens and fault flag assets, which is what we noticed.

But if the current is only 10% higher (2,4A) than current limit set by Imon resistors (2,1A), VBUS/VCSN dropped to ~2.3V but without assertion of FAULT pin.

The question is if we want to monitor the over-current status more preciously by sensing voltage of VBUS, what is the relationship with VBUS and current?

  • 0
    TI__Mastermind 43205 points

    Hi Nan Su,

    Quick question: Are you using the TPS25830A-Q1? Or TPS25830-Q1? You wrote TPS25830-Q1 in the title of this thread, but the Cycle-by-Cycle Buck Current Limit section in the TPS25830-Q1 datasheet is Section 10.3.10.4. And it is in "Section 10.3.10.5" of the TPS25830A-Q1 datasheet.

    So it is a matter of a minor overcurrent vs a short circuit scenario. Overcurrent meaning that the load is pulling current higher than the programmed current limit, but is not a short. As the output current increases, VBUS will decrease as you've observed. 

    In terms of the relationship or characterization data how the output current affects VBUS voltage level, I do not have this data.

    BR,

    Seong