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TPS23731: Way to add power good function: with react immediately

Satoshi
Guru 19645 points
Part Number: TPS23731
Other Parts Discussed in Thread: TPS2372, TPS2373,

Before I resolved below thread, and this time additional question for power good function.

https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/1112847/tps23731-way-to-add-power-good-function

For above answer, VB pin can use power good function.

But in this case become timing delay on power down, VB pin output change to low in the middle of secondary Vout decrease. 

I guess that between switching stop to decrease VB voltage need a little take time.

My ideal is power good function react immediately on switching stopped (= timing for decrease primary VDD-VSS voltage), and react before decrease secondary Vout.

If there any idea for above function, please let me know.

Best regards,

Satoshi

  • 0
    TI__Mastermind 37121 points

    Hi Satoshi,

    You are correct. VB is good for power on, and when power off VB response is later than the primary gate voltage response. TPS23731 does not have a dedicated PG pin since this IC integrates the PMW controller. For PDs without PWM controller (like TPS2373 or TPS2372), they have the PG pin for the external gate drive IC.

    To sense the gate voltages at turn off, you could consider the test point (V_reg) at the auxiliary winding side. And the test waveforms are shown below. 

    While, the V_reg will also get a delay (> 10 ms) with V_out during power off, since there is a soft-stop function which will cause reduced V_out before stopping Vgs. Removing the soft-stop function could reduce the delay time but not too much. 

    If the desired PG is referred on Vout side (or using Vreg on PRI side), maybe a voltage divider and a comparator at the Vout could set PG high or low when Vout is higher or lower than a value.

    Best regards,

    Diang

  • 0 in reply to Diang Xing
    TI__Mastermind 37121 points

    Hi Satoshi,

    Since your question has been answered, I will close this question for now. If you have any further questions, please open a new thread and we will be glad help you!

    Best regards,

    Diang