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Original question:

TPS54625: Component locked, VREG5 at GND

TPS54625: Component locked, VREG5 at GND

Thibaud Deffayet
Prodigy 45 points
Part Number: TPS54625


Hello,

Some time ago we had trouble using TPS54625. A problem occured when we plugged a battery on our system and creating a short circuit between GND and VREG5 or VIN or VOUT (and disabling the component). We fixed it by doubling the value of the input capacitors and it was fine for almost 70 of our systems (during 10 months).

But recently, the problem occured again. If we use a stabilized power supply the component works fine, but if we plug a 3S lipo battery on our system, three possible short circuits are created : VREG5 and GND; VREG5 and GND and VOUT; VREG and GND and VOUT and VIN (and sometimes the component bursts to flames).

Here are our schematic and layout.

  • 0
    Prodigy 45 points

    We captured the voltage rise of our system. 5V/div and 10µs/div. So it goes up to almost 25V at booting.

    It does this only on our new  batch of PCB. Which have the same schematic and layout than our previous one and are used with the same battery.

    Anyone has an idea of what could do that?

  • 0 in reply to Thibaud Deffayet
    TI__Genius 9550 points
    hi,
    Vout jumps to near 25V and atable at 12V (Equal Vin). I suppose it likes "FB open".
    Suggest:
    1. Measue the resistance between Vout and VFB pin; 2. check resistance between FB pin and GND; 3. also measue FB pin voltage when operating.
    (prefer select a good board to compare the resistance and voltage)
  • 0 in reply to Jason Wang (BSR-MV)
    Prodigy 45 points

    Hello Jason,

    Thank you for your answer!

    In fact the graph shows the Vin of our TPS54625, not the Vout. Vout is at 5.05V (the desired value) when the component works.

    The resistance between FB pin and GND is at 22k1.

    Vfb is at 0.764V

    We tested many things today and after desoldering and resoldering the TPS54625 and all the passive components related to it, it appears that if we plug the GND of the battery before the PWR, everything works fine. But if we plug the PWR before the GND, the TPS54625 bursts.

    Once again, if we use a stabilized power source it works fine every time. The problem appears only if we use a lipo battery.

  • 0 in reply to Thibaud Deffayet
    TI__Genius 9550 points

    Hi,

    Operations of "plug GND first then PWR" and "plug PWR first then GND" should be equivalent.

    1. try to increase c77 to 0.1uF (Connected to SS pin) which will solve the issue.

    2. for this application, root cause is: connect the EN pin to VCC_12V directl in schematic.

    suggestion: add resistor divider from VCC_12V->EN PIN->GND.

    for example, when VCC_12V ramps up to about 8V then EN Pin voltage is 1.6V.