• State Resolved
  • Locked Locked
  • Replies 3 replies
  • Subscribers 63 subscribers
  • Views 363 views
  • Users 0 members are here
Support feedback
Options
Options
Related

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.

UCC256403: External Shutdown function

Andar Sundar nagaraj
Prodigy 70 points
Part Number: UCC256403
Other Parts Discussed in Thread: UCC256303, , TL431

Hi,

I would like to know if the external shutdown function is carried over from UCC256303? What happens when The Controller remains in the burst off mode for considerably long period of time and then there is a load transient?

  • 0
    TI__Expert 8210 points

    Andar

    To externally shut down UCC256403 you can use the same technique that we recommended with UCC256303, where you pull BLK to GND to disable operation.

    The output voltage is directly measured thru the opto/TL431 feedback, so if there is a load transient during burst UCC256403 will respond quickly to the transient event.

    Best Regards,

    Eric

  • 0 in reply to Eric Faraci
    Prodigy 70 points

    Hi Eric,

    External shutdown can be implemented in UCC256303 by pulling feedback pin to ground. 

    Let me rephrase my question.

    In UCC256303, when FBReplica is lower than BMT  (n FBLessThanBMT) for more than 200ms, the Controller goes to startup state. Does this happen in UCC256403 too? I am asking from perspective of CC application in Battery chargers.

    Regards,

    A S Nagaraj

  • 0 in reply to Andar Sundar nagaraj
    TI__Expert 8210 points

    A S Nagaraj

    "FBReplica is lower than BMT  (n FBLessThanBMT) for more than 200ms, the Controller goes to startup state" was a typo in UCC256303 datasheet.  This did not actually happen in UCC256303, and it does not happen in UCC256403 either.

    To insure that you have proper operation in burst mode, we recommend that you insure that the optocoupler you use does not enter saturation and that your VCC capacitor is sized large enough where it does not discharge down to UVLO turn off.

    We do not recommend disabling UCC256403 by pulling FB to GND, since when you re-enable operation UCC256403 will not start up in soft start mode.  This will probably cause over current fault protection to trigger, which will cause the converter to enter a fault shutdown protection.

    Best Regards,

    Eric