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TPS7A85: It has voltage drop problem at some condition.

Chris kang
Prodigy 40 points
Part Number: TPS7A85

HI TI team.

I have problem using TPS7A85 below condition.

Condition

 - input voltage : 5.8V

- output voltage : 5V

- soft start C value : 100nf.

If i change the operating temperature rapidly(using freezer spray, -30 degree Celsius), there is output voltage drop (300mV) shortly.

but i change the soft start C value  from 100nf to 10nf , there is no output voltage drop at same conditon.

TI recommend the ss value 10nf ~ 100nf. 

However, this TPS7A85 is not reliable at 100nf under -30 degree Celsius operating temperature.

so please let me know the relation between ss value and operating temperature. or What is check point?

thanks.

  • 0
    TI__Mastermind 29140 points

    Hi Chris,

    Freezer spray can be slightly conductive, and the soft start capacitor can be a sensitive node.
    If you are cooling down the circuitry with freezer spray, it is possible that there is a leakage path being developed from the spray on the soft start pin to ground.
    This leakage path can act as a voltage divider from the internal reference and the internal 250 k-ohm resistor, which will then result in a lower output voltage.

    Can you retry the test in a temperature chamber instead of using a cold spray?

    Thanks,

    - Stephen

  • 0 in reply to Stephen Ziel
    Prodigy 40 points

    Thanks for your reply. 

    Okay. I Will test in a temperature chamber. and I will tell you the result.

    Please think about why it is working good at 10nf ss value.

    If leakage path can make voltage drop, It will also happen even if i use 10nf for ss.

    Thanks,

    - Chris