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TPS54335A: 100pF capacitor on EN pin

Danilo A.
Mastermind 28590 points
Part Number: TPS54335A

Hi Team,

A customer wants to delay the the output of TPS54335A. He removed the R1 and R2 resistors (refer to Figure 15 of the datasheet) on the EN pin since there is an internal weak pull up current then he added a 100pF capacitor to delay the voltage at the EN pin before reaching the Enable threshold voltage of 1.21V (typical). Will there be any issue with this configuration?

Regards,

Danilo

  • 0
    TI__Genius 15135 points

    Hi, Danilo 

    No issue for this configuration. 

  • 0
    TI__Genius 15135 points

    Hi, Danilo

    I gave a second thought about your question, this configuration will have issue when do high frequency Vin power cycle test. 

    See below, due to there is no pull down current/resistor for EN pin, when the interval time is small than 100mS, the EN voltage will not fall down to 0V during interval time. 

    If EN voltage keeps above enable threshold, when the second power on, the Vout will rise up at once when Vin > UVLO, then there will be no EN delay time. 

  • 0 in reply to Zhao Ma
    TI__Mastermind 28590 points

    Hi Zhao,

    Thank you for this insight on the function of the EN pin and the effect of time interval on power cycling to the ON delay time of the device.

    The background of this inquiry is that when the customer hot plugged their modules containing TPS54335A, the VIN of TPS54335A directly connects and disconnects from the power source and the internal MOSFET shorts. He tried to delay the output of TPS54335A for a few milliseconds by removing the voltage divider to EN and replacing with a 100pF capacitor. The capacitor at EN pin solves the issue but he wants to confirm if there will be any unforeseen issue with this configuration. 

    Although 100ms is very short in terms of manually plugging and unplugging the module, does a resistor from EN pin to ground helps to discharge the capacitor and ensure the voltage is below the threshold voltage of EN pin every time the module is disconnected from the power source? If yes, can you suggest a value of resistor he can connect in parallel with the capacitor at EN pin to ground?

    Regards,

    Danilo

     

     

  • 0 in reply to Danilo A.
    TI__Genius 15135 points

    Hi, Danilo

    Suggest to add a 3Megohm resistor paralleled with 100pF.