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TPS63070: Power good in TPS63070

Yurii Zakharchenko
Prodigy 50 points
Part Number: TPS63070

Dear Sir or Madam,

I have a question about Power good input current.
I put 6000 uF according to the load power requirements (the load is always connected to DC-DC). As a result, tps63070 can`t rich the required output voltage, so I decided to disconnect +4V8 SS power line from the load using PG and VT4, VT5. BUT, I have found that the maximum sink current to PG is 1mA, so the question is - Is it possible to discharge energy from C6 to PG pin directly?
It works in real life but i don`t know how long PG pin will be alive.
P.S. If i put the resistor to C6 in series, i cann`t provide overcurrent protection (VT4 will be overheated), that`s why i put C6 to increase rise time(as a result - reduce switching frequency)

 

  • 0
    TI__Expert 7925 points

    Hi Yurii,

    Thanks for reaching out.

    If I understood correctly, you are turning on the +4V8 line with a delay, after the TPS63070 reaches the nominal voltage and PG output goes high?

    The maximum continuous sink current for the PG pin is 1 mA. In your case there is only a short pulse, however, we didn't characterize this so we cannot guarantee that there will be no long term effects. Could you try adding a ~4.7 kΩ resistor in series with the PG pin? This would limit the PG current to 1 mA. It will not affect the VT5 turn-on much, but will it slow down the turn-off a little, not sure if that is critical. Additionally, you can also try decreasing C6 to 100 nF, and increasing R? to 1 MΩ to reduce the influence of the added 4.7 kΩ resistor.

    Best regards,
    Milos

  • 0 in reply to Milos
    Prodigy 50 points

    Dear Milos,

    Thanks for reply.

    "If I understood correctly, you are turning on the +4V8 line with a delay, after the TPS63070 reaches the nominal voltage and PG output goes high?" - Yes.

    Is it possible to increase R? up to 2MOhm? I have put 4.7kOhm resistor to C6 (100nF) in series and my circuit can live without any damage during short circuit. 

  • 0 in reply to Yurii Zakharchenko
    TI__Expert 7925 points

    Hi Yurii,

    Check out this app note on how to select a pull-up/pull-down resistor for an open-drain output:

    http://www.ti.com/lit/an/slva485/slva485.pdf

    When choosing the maximum pull-up resistor value, consider the leakage current on the PG pin. According to the datasheet, the PG pin leakage current is 0.2 µA maximum. This will make a voltage drop of  up to 0.4 V on R?, if you chose 2 MΩ. This is a bit on a high side, but probably still fine to keep your VT5 on. 

    Best regards,
    Milos