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TPS54336A: SS Pin Floating

Edward Perks
Prodigy 20 points
Part Number: TPS54336A

Hi, 

It is not clear from the datasheet if it is OK to leave the soft start (SS) pin floating on this device. We simply need the fastest output voltage rise time possible. 

Can you please confirm? 

Thanks. 

  • 0
    TI__Guru 56985 points

     

    Since the TPS54336A uses the longer of the externally programmed SS capacitor based soft-start time, or the internal 2ms soft-start time, selecting a soft-start capacitor for 2ms or less will provide the "fast output voltage rise-time possible.  Since the SS pin is used for Tracking and Hiccup timing, I would not recommend leaving the pin floating.

    Following the datasheet equation (Vref = 0.8V, Iss = 2.3μA) for a 1ms soft-start, I calculate a 2.8nF soft-start capacitor.  Selecting a  2.2nF soft-start capacitor will provide the fastest available start-up while maintaining a capacitor on the SS pin for noise immunity and hiccup restart timing.