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TPS40057 - driving SS/SD pin externally over 3.7V

TKO
Prodigy 225 points
Other Parts Discussed in Thread: TPS40057

Hello,

I'd like to know whether or not TPS40057 can tolerate higher than 3.7V on SS/SD pin as long as the voltage is lower than ABS max voltage?  

I have a design where TPS40057 Shut Down signal is controlled by an open collector transistor. However, the Shut Down signal trace may see leakage from other circuitry during normal operation when power supply is ON. This leakage will charge the capacitor on SS/SD pin to more than 3.7V. Basically this is a similar situation where external voltage is driving the SS/SD pin.

Since the SS/SD pin is connected to the error amplifier I'm wondering is it safe to use TPS40057 this way and will this have a negative effect on performance?

Thanks, Tuomas

  • 0
    TI__Expert 4455 points

    Hi TI DC/DC experts,

    Providing further details to Tuomas' inputs:
    We are thinking of using a ~5V...6V TVS/Zener to clamp the voltage below the 6V abs max spec listed in the datasheet if SS/SD pins sees leakage from an external >12V supply. This will add certain leakage current which might cause the voltage at SS/SD pin to drop below the typical 3.7V in normal operation and somewhere between 3.7V and 6V in case there's a weak connection and leakage to the external supply.

    a) Can you confirm that if the voltage at the SS/SD pin will “stuck” between 0.7V and 3.7V (internal Soft-start clamp voltage) no misbehavior will be observed?

    b)  Can you also confirm that if the voltage at the SS/SD pin will be held between 3.7V and 6.0V because of leakage current from a neighboring 15V signal and an attached TVS/Zener diode no misbehavior will be observed? Would you expect a degrade of reliability if SS/SD pin is exposed to eg a 5V for extended period of time?

    Thanks,
    KF