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UCC256301: Operation at light load

Guru 11170 points
Part Number: UCC256301
Other Parts Discussed in Thread: UCC256404

Hello E2E,

Please see the attached file.
At light load, the switching timing is not constant. Is it normal operation?
Individuals that behave in this way often appear. This operation increases standby power consumption and we cannot ship the system. It works normally when the IC is replaced.
Please tell me the cause.

Regards,
ACGUY

UCC256301.pdf

  • Hello,

    Your thread has been assigned. You should receive a response shortly.

  • Hi ACGuy,

    You are seeing skinny high side pulses because the controller is not reliably detecting the switch node has finished "slewing" up to Vin. Here are some ways to help improve the reliability of the slew rate detection:

    1. decrease your turn off resistance more to speed up the turn off of the MOSFETs.

    2. Use a larger burst mode setting to limit how high the switching frequency goes at light load. This would help maintain the magnetizing current above a certain threshold which would help increase the slew rate of the switch node.

    3. use MOSFETs with smaller Coss

    4. Decrease your magnetizing inductance to increase the magnetizing current

    5. swap to UCC256404 which has a lower slew rate detection threshold of 0.1V/ns (UCC256301 min slew rate detection threshold is 1V/ns).

    Best Regards,

    Ben Lough