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UCC256304: Ucc256304 external control shut down mode

andy zhou
Prodigy 20 points
Part Number: UCC256304
Other Parts Discussed in Thread: UCC25630-1EVM-291, UCC256301

In the figure below, can SW1 enable UCC256304 to enter shut down mode?

  • 0
    TI__Expert 8210 points
    Andy

    Yes. For external disable of UCC256304 we recommend that you pull FB pin low as the schematic you show has.

    Section 7.3.5 (page 21) of the datasheet goes into more details and provides an example schematic of how to implement such a shutdown circuit. This circuit is on our EVM UCC25630-1EVM-291. While this EVM comes populated with UCC256301 on it, it can be modified to work with UCC256304 by following the changes that section 2.5 (page 6) of the EVM user guide.

    Best Regards,
    Eric
  • 0 in reply to Eric Faraci
    Prodigy 20 points

    The anode of the optocoupler sensor (U306) is connected to Vout, Is there a problem?

    Must be connected to an external control voltage?

  • 0 in reply to andy zhou
    TI__Expert 8210 points
    Andy

    I missed that in my original reply. The way you have it connected from Vout may cause issues. When you shut down UCC256304 it will stop supplying power. If Vout is only generated by this UCC256304 power stage, then once the disable command is sent it will cause Vout to decrease to 0V. This will turn off U306, preventing UCC256304 from receiving the signal to stay in shutdown mode. This will cause UCC256304 to attempt to startup again. If the external disable signal is still on this will cause UCC256304 to turn off again, so it will cause UCC256304 to power cycle.

    To resolve this it is recommended to have the anode of U306 powered by a voltage source that does not turn off when UCC256304 is disabled.

    Best Regards,
    Eric