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UCC256403: VCC at which switching starts and VCC at which switching stops

user6230314
Prodigy 220 points
Part Number: UCC256403



Could you tell me the variation of VCC at which switching starts and the variation of VCC at which switching stops?

  • 0
    TI__Expert 8210 points

    Hi

    UCC256403 starts switching when VCC exceeds VCCStartSwitching, which for UCC256403 is 10.9V and there are no active fault conditions (such as BLK pin below VBLKStart).  Switching stops when any fault condition is triggered.  If no fault is triggered, switching will stop when UVLO reduces below 8V (VCCUVLOrising - VCCUVLOHYS).

    Figure 48 (page 45) of the UCC256403 datasheet has a timing diagram for startup that illustrates this.  In it this diagram VCC comes up before the "PFC output voltage," which means PWM starts once VBLKStart threshold is exceeded.

    Please note that it's recommended to keep VCC between 13V-26V for operation.

    Best Regards,

    Eric

  • 0 in reply to Eric Faraci
    Prodigy 220 points

    Hi

    I have a few questions.

    ① I understand that the typical voltage of VCCStartSwitching is 10.9V.
    　Could you tell me the minimum and maximum values of VCCStartSwitching?

    ②When UVLO falls below 8V, switching stops.Can you tell me the minimum and maximum Vcc values at that time?

    Best Regards

  • 0 in reply to user6230314
    TI__Expert 8210 points

    Hi

    For UCC256403 we do not have data on guaranteed values for minimum and maximum VCCStartSwitching.

    Four UVLO turn off, the min and max voltage can be determined by subtracting VCCUVLOHYS from VCCUVLOrising.  With VCCUVLOrising abs min of 7.85V and VCCUVLOrising abs max 8.70V, and VCCUVLOHYS abs min 0.15V and abs max 0.35V this gives a UVLO turn off abs min of 7.5V and abs max of 8.55V

    Best Regards,

    Eric

  • 0 in reply to Eric Faraci
    Prodigy 220 points

    Hi,

    What determines the minimum and maximum VCCStartSwitching range?
    I would like it to stay within a variation of about ± 1V.

    I would like to know if you know.

    Best Regards

  • 0 in reply to user6230314
    TI__Expert 8210 points

    Hi

    Unfortunately at this time we do not have any guarantee on min and max values.  The only specification we can guarantee is the typical value of 10.9V.

    Best Regards,

    Eric