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BQ24780S: protection feature when SYS is suddenly shorted to GND

K.Yaita
Guru 29710 points
Part Number: BQ24780S

Hi Team,

I would like to ask a protection feature when SYS is suddenly shorted to GND.

My customer is evaluating BQ24780S in his system and saw ~60A adapter current flow instantanously when SYS is suddenly shorted to GND.
I believe the instantanous large current (~60A) can't be prevent because the current flow is occured simultanously with SYS is shorted, then Q1 and Q2 could be damaged.
How does BQ24780S protect Q1 and Q2 when SYS is suddenly shorted to GND?
Could sense register (following red part) protect Q1 and Q2 in this case?



Best Regards,
Yaita / Japan disty

  • 0
    TI__Guru 56650 points
    The sense resistor is only 10mohm. It is just a sensing resistor. When system short, bq24780S has ACOC function to turn off the Q1.
  • 0 in reply to Wang5577
    Guru 29710 points

    Hi Wang-san,

    Thank you for your reply.

    I confirmed the datasheet and the deglitch time of ACOC is 12ms(typ).



    However my customer saw ~60A adapter current flow shortly after SYS was shorted to GND so I believe ACOC function can't protect Q1 and Q2 in this case.
    note) duration of ~60A adapter current flow is about 250us.

    Is there any solution to protect Q1 and Q2 in this case?

    Best Regards,
    Yaita

  • 0 in reply to K.Yaita
    TI__Guru 56650 points
    When that 60A was happened, did the ACDET is lower than 2.4V? If the ACDET is lower than 2.4V, the ACFET is turned off immediately.
  • 0 in reply to Wang5577
    Guru 29710 points

    Wang-san,

    >When that 60A was happened, did the ACDET is lower than 2.4V?
    ~60A adapter current flows shortly after SYS is shorted to GND, and then ACDET goes lower than 2.4V.
    My customer wants to prevent this ~60A instantanous current to protect Q1 and Q2.
    He said that the instantanous adapter current is also occured at the moment when connecting AC adapter under the condition that SYS is already shorted to GND.

    I would like to send waveform that shows above.
    Could you send e-mail to the following address?
    yaita-k@clv.macnica.co.jp

    Best Regards,
    Yaita

  • 0 in reply to K.Yaita
    TI__Guru 56650 points
    OK. I will send an email to you and discuss it.