• State TI Thinks Resolved
  • Locked Locked
  • Replies 4 replies
  • Answers 1 answer
  • Subscribers 63 subscribers
  • Views 95 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TPS51397A: VCC pin on TPS51397A: can it be an input ?

THomas Hermans
Prodigy 90 points
Part Number: TPS51397A

Hello all,

In table 5-1 of the TPS51397A datasheet, the VCC pin is clearly defined as the output of an internal LDO, with a recommended 1µF decoupling.

But, in chapters 6.1 and 6.3, VCC is listed among the inputs.

Is it possible to connect a 5.0V rail on VCC (ie use it as an input) ?

With many thanks in advance.

Thomas

  • 0
    TI__Genius 14857 points

    Hi Thomas,

    VCC-pin is an output pin.

    May I know why you need to connect an external 5V to VCC-pin?

  • 0 in reply to Miranda Gu
    Prodigy 90 points

    Hi Miranda,

    We based one of our design on VCC being an input and connected the board 5V rail to VCC. The rework is very tricky. Our last hope was that the TPS51397A could be able to use the external rail instead of its internal LDO, but as you said, it is not the case...

    Our problem now is to evaluate the risk associated with this mistake :

    - In steady mode, our 5V rail is in the range 4.965V-5.032V whereas the TPS51397A is in the range 4.85V-5.15V. So the difference between the setpoints could be 150mV + 32mV = 182mV worst case. And the question is : who wins ? Is there a risk of malfunction within either controller ?

    - Then at powerup, the TPS51397A is powered through Vin=12V before the board enables its 5V rail. So the TPS51397A is alone but it sees all the capacitors on board (many µF). Can it handle such a load ?

    If you could have any hint on the TPS51397A behavior (assumed or from experience) in such case, that would be a great help.

    Thomas

  • 0 in reply to THomas Hermans
    TI__Genius 14857 points

    Hi Thomas,

    Understood your requirement. Let me discuss with team then reply you.

  • 0 in reply to Miranda Gu
    TI__Genius 14857 points

    Hi Thomas,

    Like you said, our part doesn't support external VCC. If using the external VCC, our design team estimate that the power loss will increase, and there will be reverse current at input when VCC>VIN.

    We didn't validate on bench, don't know whether has other problems, suggest you to not take this risk.