SLVS839F July 2008 – October 2014 TPS54331
Programming the slow-start time externally is highly recommended because no slow-start time is implemented internally. The TPS54331 device effectively uses the lower voltage of the internal voltage reference or the SS pin voltage as the reference voltage of the power supply that is fed into the error amplifier and regulates the output accordingly. A capacitor (CSS) on the SS pin to ground implements a slow-start time. The TPS54331 device has an internal pullup current-source of 2 μA that charges the external slow-start capacitor. Use Equation 3 to calculate the slow-start time (10% to 90%).
The slow-start time should be set between 1 ms to 10 ms to ensure good startup behavior. The value of the slow-start capacitor should not exceed 27 nF.
During normal operation, the TPS54331 device stops switching if the input voltage drops below the VIN UVLO threshold, the EN pin is pulled below 1.25 V, or a thermal shutdown event occurs.