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BQ76952: Preventing discharge MOS from turn off oscillation circuit.

jmyang
Expert 1186 points
Part Number: BQ76952


Masters of TI,

To avoid further oscillation of the discharge MOS turn off.

So we plan to add the following circuit (Red).

Do you think it's okay?

Will there be any side effects?

    

  

  • 0
    TI__Expert 4085 points

    Dear jmyang,

    Before preceding with adding the circuit, I have a quick question. What sort of oscilliation are you seeing? While turning the DSG pin off, there is designed oscillations as described in section 16.5 of the datasheet due to the DSG pin being discharged based on LD instead of VSS. I would suggest reading over this if you want more information.  I've attached screenshots of what a typical waveform looks like for turning DSG off.

    The one on the left is the non zoomed in view while the right one is zoomed in. However, if this is not what you are seeing, please let me know and I will review the circuit addition further.

    Best,

    Asher Nederveld

  • 0 in reply to Asher Nederveld
    Expert 1186 points

    Hi Asher,

    During the Short-circuit test, we found that the voltage of G (MOSFET) rebounded after being pulled down, and the current output was restored. After repeated shocks, the MOSFET burned out.

    It seems that our layout's GND circuit has not been properly handled.

    Then we added the red part of the circuit and solved the problem.

  • 0 in reply to jmyang
    TI__Expert 4085 points

    Dear jmyang,

    I don't see anything in the additional circuit that should cause an issue with the device's normal operations. Since it resolves your issues with oscillations in transient conditions, it looks like it should not create a problem. Is there a name for the subcircuit you added or was it developed in house? I would like to be able to read up more on it.

    On a different note, this FAQ is a pretty good resource for future use when shorts are damaging MOSFETs while using the BQ76952.

    Best,

    Asher Nederveld