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TPS54202H: EN pin capacitance

Carl Audet
Prodigy 10 points
Part Number: TPS54202H
Other Parts Discussed in Thread: TPS54202

I am using the TPS54202HDDCR for a 24V to 5V (0.5A) regulator. The 24V comes from an isolated regulator and it has a difficult time coming up if the 5V comes up before it so we have added a 1uF capacitor to the EN of the TPS54202. We have seen field failures where the EN pin becomes only about 0.8V over time and it looks to be due to mechanical stress on the cap but I want to make sure that this isn't something to do with the TPS54202 current source or something else internal not being able to handle that much capacitance on the enable. I attached our regulator circuit. Thank you in advance for the support. 

  • 0
    TI__Genius 9280 points

    Hi Carl,

    The EN pin has an internal pull down resistance Rpd (typical 1 MΩ) which allows the user to float the EN pin to disable the device, a Zener diode (typical break down voltage 6.9 V) is used to clamp the EN input voltage. 

    And i'm not clear the reason why you add 1uF cap here, while this 1UF cap should be oaky here to filter some noise and stable voltage. 

    regarding the sch, the inductor Isat is too small for application. Suggest to change it to larger , as the inductor would shrink much at larger loading and current would change rapidly.

    About the failure cases, could you help share us more details ? like when it happed and any observation ?  It would be great if you have any waveform for analysis.

    BRs,

    YZ

  • 0 in reply to Young Zhao
    Prodigy 10 points

    Hi Young, 

    I added the cap to EN because I needed to delay the startup of the regulator, which works. But we have  field failures that are coming back with the EN pin voltage at about 0.7V - 0.8V. I just want to rule out the possibility of the EN pin being damaged by the 1uF capacitance. Thank you,

    Carl 

  • 0 in reply to Carl Audet
    Prodigy 10 points

    Another note, when we remove the 1uF capacitor the EN voltage goes back to ~6.9V and the part appears to be fine. We can put a new cap on and it is still okay. I guess if the 54202 was damaged, the EN voltage probably wouldn't come back to 6.9V if the cap was reinstalled and that was the issue. Do you see any reason to be concerned with this 1uF cap on the EN pin? Thanks

  • 0 in reply to Carl Audet
    TI__Genius 9280 points

    Hi Carl,

    Sounds like that there is somthing wrong with the C220cap, as the part appears to be fine after removing this cap, right ?

    Could you help check if this cap is damaged , then make EN pin short to GND ?

    and not sure if adjusting under voltage lockout meets your requirement for the delay . You can set the start working voltage as you needed to delay .