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TPS74801: TPS74801 SS pin Leakage current

Zhizhao Niu
Intellectual 2315 points
Part Number: TPS74801

Hi team,

I have two questions need your help. Thanks !

1. Is there any spec requirement for the leakage current on SS pin. I found in datasheet, there only recommend to use low leakage cap. Do we have a max or min value for leakage current spec?

2. From my understanding, the soft-start only enabled at start up stage. If there have a large leakage current on SS pin after start up, does it have any influence to whole system? such as will influence the output voltage.

B.R.

Zhizhao

  • 0
    TI__Mastermind 29040 points

    Hi Zhizhao,

    The soft start charging current is 440 nA typical, as listed in the datasheet.  A low leakage capacitor is needed to here to prevent startup from taking longer than expected.  If the capacitor has high leakage then it may take a very long time to turn on as much of the 440 nA will leak through the SS capacitor and directly into ground.  We recommend ceramic capacitors for low leakage capacitors on the soft start pin, such as X7R or X5R dielectric ceramic capacitors.

    See section 7.5.2 for some sequencing requirements on this device to make certain that the soft start operation behaves as expected.

    I tested an EVM to confirm the operation of Vout when the soft start pin is shorted after the output reaches steady state.  In this case, once enough leakage on the SS pin shorts it to ground, the output also collapses to ground.  So leakage current on the SS pin will affect Vout even after it has reached steady state.

    Thanks,

    - Stephen