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Original question:

TPS54821: Is TPS54821 broken if it is used under no input voltage but output 5V applied

TPS54821:Is TPS54821 broken if frequently power on/off?

Shun Yshizawa
Prodigy 10 points
Part Number: TPS54821

Hello,

We are thinking to use relay for TPS54821’s Vin on/off.

Is TPS54821 broken if frequently power on/off?

We are need to “Slow-start” function, so for that frequently

Vin on/off Is required.

I will show you a reference circuit diagram,

It would be helpful if you could give me some advice.

よろしくお願いいたします。

吉澤 駿

  • 0
    TI__Mastermind 49470 points

    Hi Shun,

    1. TPS54821 won't break if power on/off frequently. However, your circuit may have issue and you could not use TPS54821 device for this application.

    2. From your schematic, the output voltage is 14.8V. The input voltage is 16V, it is around 90% duty cycle. There is a risk to violate BOOT_PH UVLO threshold voltage which is typical 2.1V. Please refer to section 7.4.7 in the datasheet. If you split input voltage, you must supply Vin >16+4=20V. thus, you will likely damageTPS54821 since the absolute max rating of Vin pin is 20V. 

    3. Please find another device for your application.

    Hope this helps,

    Thanks,

    Nancy

  • 0 in reply to Nancy Zhang
    Prodigy 10 points

    Hello Nancy-san

    Thank you for answering my question.

    our application is I will use output voltage under 12V
    because I will adjust of VR1.
    so I think that I'm not violate to
    "BOOT_PH UVLO threshold voltage which is typical 2.1V"

    But there are other pssible causes,
    From our application is using load of is it capacitor like
    If that case, TPS54821 that will be damaged if I power/off?

    Best regards.

    Shun Yoshizawa

  • +1 in reply to Shun Yshizawa
    TI__Mastermind 49470 points

    Hi Shun,

    1. If your output voltage is below 12V, R6 should be 10ohm (not 2.2k) for bodeplot  measurement.  

    2. PWRGD absolute max voltage is 6V, R4 should pull up to 5V or below voltage. Not 16V

    3. If you use relay to control input power on/off, must ensure PVIN pin voltage under 17V as max recommended operating voltage in section 6.3 of datasheet. Ensure no voltage spike >17V or 20V at any conditions during power on/off since 20V is the absolute max voltage for this device. Otherwise, the device would damage. 

    4. I would recommend control EN pin instead of PVIN for power on/off.  EN pin absolute max voltage is 6V. So 3.3V or 5V is good control signal. Relay is large, you may consider use optocoupler instead of relay to control EN pin.

    Hope this helps,

    Thanks,

    Nancy

  • 0 in reply to Nancy Zhang
    Prodigy 10 points

    hello Nancy-san

    I would change the control to use the EN pin for power on/off
    I will follow your advice and re-design the circuit.

    I wanted to thank you for the great advice.