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TPS4813-Q1: TPS4813-Q1 — will G2→G1 handover occur early if V_G2_GOOD is reached before precharge finishes?

Michelle Mathew
Prodigy 190 points
Part Number: TPS4813-Q1


Tool/software:

Hello — question about the TPS4813-Q1 precharge/LWU behavior (ref: Fig. 7-13 in the datasheet).

If the bypass FETs’ VGS (G2) reaches V_G2_GOOD while the precharge of the load capacitor is still ongoing, and the load current exceeds I_LWU, will the device switch to MAIN FET (G1) conduction immediately — potentially before precharge is complete — causing a large inrush? Or does the TPS4813 have an internal sequencing/lock that prevents handover until the precharge sequence is finished regardless of V_G2_GOOD/I_LWU?

If it can hand over early, what’s the recommended way to guarantee switching to G1 only after precharge is complete (internal setting, layout change, external comparator, timing, use of ILWU hysteresis, etc.)?

  • +1
    TI__Genius 10031 points

    Hi Michelle,

    Yes, the device will switch to the main FET if the load wakeup threshold has been crossed after VGS_GOOD has already been reached, which can possibly cause large inrush if pre-charge is not complete. The device system needs to be designed such that the load current during pre-charge does not exceed the load wakeup threshold until pre-charge of the output has been complete. I_INRUSH can exceed I_LWU if the VGS_GOOD threshold has not been reached. 

    Thanks,

    Rishika Patel