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TPS25947: Abnormal behavior on PG port (toggling

Gyeongseop Lee
Prodigy 50 points
Part Number: TPS25947


Tool/software:

Hello, 

I'm using TPS25944LRPW on board to switch for 12V power-rail.

I haven't applied any load yet so load is about 0 @ 12V, but I've found PG behave abnormal.

Design

Vin/out = 12.2V
PGTH : 43K / 5.6K (about 10.8V)
EN/UVLO : 3.3V logit Level High
UVLO : Pulled GND
Ctimer : 2.2nF
dvdt : 2.2nF
PG Pull up with 3.3V

And I've seen that PG output is toggling at about 380~420kHz but 12V Power out is OK (12.2V measured)
And i couldn't identity events to trigger PG other than pgth level 1.2V and the actual voltage of PTGH is about 1.4V so PG shouldn't triggered.

Do I missing any event of triggering PG, or any hint to debug that symptom?

  • 0
    Prodigy 50 points

    and this happens on not only one board

  • 0 in reply to Gyeongseop Lee
    TI__Mastermind 39295 points

    Hi Gyeongseop,

    Thank you for your patience. 

    Firstly can you check the pull up supply. It is possible that pull up itself is causing this.

    Secondly, you mentioned that there is no load at output so this is less likely but if device is going into RCB, then also PG will go down. How much capacitance are you using at input and output. If possible test with higher input capacitance and some resistive load (to check if device is turning off or not). Without any resistive load, Vout won't fall and you won't realize if RCB is triggered or not.

    Best Regards,
    Arush

  • 0 in reply to Arush Gupta
    Prodigy 50 points

    Thank you for reply,

    1) Pull up voltage stays normal while PG is toggling with 400Hz (no load)

    2) Input capacitance is about 400nF, and output capacitance is about 20uF.
    and I see there is PGTH path between output power-rail and ground(~50k in total) I thought I could have been checked if output is shutdown(no load)

    3) So I have attached FAN(12V 0.16A) and symptom disappeared. PG is not toggling anymore with the load.

    4) I still want IC not to toggle at no-load condition since it triggers interrupt of MCU forever...

    Then I summary the events that PG can toggle are:

    a) Vpgth is below 1.1xV
    b) Reverse Current Blocking (may C-L-C resonance on board???)

    could you suggest solution on this? will it be fine if i add greater input capacitance?

  • 0 in reply to Gyeongseop Lee
    Prodigy 50 points

    I control 3 branches with one switch. and i figured out that it is almost not possible to use this (with reverse current blocking of 0.03V)

    with no load condition, even with very small phase shift of resonance among CAPs of those branches, RCB is being invoked....