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TPS7B69-Q1: Input short circuit test ,IC is broken,no output 5V

Part Number: TPS7B69-Q1

HI,

TPS7B6950QDBVRQ1, Input short circuit test (Vin&GND),IC is broken,no output 5V,What is the reason? What are the good improvement measures

The IC was tested many times and broke every time.

 Input capacitor is 10uF, Output capacitor is 20uF,

When the output capacitor is changed to 4.7+ 4.7uF, the IC will not be damaged in the input short circuit test,

The actual test found that, when the input short circuit, the output current backflow to the input,such as FIG2,CHI1 .

Thanks!

  • Hi Neal, 

    I suspect it is the reverse recovery time of the diode being used. For example, a typical 1N4007's reverse recovery time could be as much as 30us whereas something like the 1N4148 is only around 8ns.

    Can you share which diode is being used to confirm this?

    Regards,

  • Hi John,

      It's schottky,not diode.

    Thanks!

  • Hi Neal,

    With the schottky diode shorted to RTN, the anode is tied to RTN and the cathode is tied to Vin of the LDO.

    So the schottky is reverse biased and there is no longer reverse protection of the input to the LDO.
    In this case the output capacitor, which is 2x greater in value than the input capacitor, acts as a large charge reservoir.

    Current flows from the output capacitor, through the internal body diode across the pass MOSFET, into the input capacitor.
    This is not an operating mode that the linear regulator was designed to withstand.
    So with enough current (charge) flowing from the output to the input, the internal MOSFET likely breaks.

    By reducing the output capacitor you have reduced the amount of charge that flows from the output to the input.
    My opinion is that this is not a very robust design solution, as it may risk a latent failure.

    I would recommend placing a parallel schottky diode from the output to the input of the LDO.
    As long as this new schottky diode has a lower ON threshold than the internal body diode, current will flow through it instead.
    That should protect the MOSFET from damage.

    Thanks,

    - Stephen