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TPS54678: Vin UVLO

Given Ding
Genius 10315 points
Part Number: TPS54678
Other Parts Discussed in Thread: TPS62869

Hi Team, 

Here are two questions. 

1. Is there UVLO threshold for Vin pin?  In datasheet, UVLO is  only achieved through EN pin. 

2. in datasheet, recommended Vin range is 2.95V-6V in EC table, but there is also description " The TPS54678 has a typical default start-up voltage of 2.4 V " , so is there any risk that internal logic may have issue between 2.4V to 2.95V or below 2.4V to Vin pin UVLO threshold? 

Thanks. 

BRs

Given 

  • 0
    TI__Genius 14876 points

    Hello Given,

    1. UVLO is not only achieved by EN pin. If the voltage across the BOOT cap is lower than 2.2V, system goes in UVLO as well.

    2. You will be limited by the UVLO of the BOOT cap voltage when at 2,4V Vin. In order to avoid seeing any limitations in this 2.4V to 2.95V, I recommend you use a resistive bridge at the EN pin from VIN so you do not turn on the device when VIN is between 2.4V and 2.95V. 

    Are you willing to use this part and operate with a VIN between 2.4V and 2.95V ?

    If so, we have newer devices which have operating VIN going down to 2.4V. Have a look at the TPS62869.

    Thanks a lot!

    Regards,


    Dorian  

  • 0 in reply to Dorian Brillet de Cande
    TI__Genius 10315 points

    Hi Dorian,

    Thanks for your reply.

    #2  we will not use resistor divider from Vin to EN, we use IO port of MCU to enable/disable the part. And if the whole board is power off, then may be EN pin is still high ( floating )  but Vin drops faster . That's why we want to know if there will be logic issue when Vin is between 2.4V to 2.95V or even lower than 2.4V. We just want to confirm  if the part will not be damaged at such condition.

    Also as mentioned, datasheet seems not quite clear on the Vin working range, so we'd like to check on this.

    Thanks.

    BRs

    Given

  • 0 in reply to Given Ding
    TI__Genius 14876 points

    Hello Given,

    If VIN is above 2.4V then it will startup. You should not get the device damaged if the VIN is too low, normal operation of the device at VIN between 2.4V and 2.95V across different load is not tested in production.

    As I did mention, I would expect that the performance is limited by the UVLO of the BOOT cap voltage when at 2.4V Vin. I mean that the Voltage across the BOOT cap might not be sufficient to allow output voltage regulation at the target value or you would enter the BOOT PH UVLO.

    You can try those different cases on the TPS54678EVM at the customer's condition if necessary. 

    Let me know if you have other questions.

    Thanks a lot!

    Regards,
    Dorian 

  • 0 in reply to Dorian Brillet de Cande
    TI__Genius 14876 points

    Hello Given,

    I haven't heard back from you.

    Do you have any further questions here ?

    Thanks,

    Dorian