UCC256302: UCC25630X : startup sequence

Hi Masazumi-san,

Thanks for your interest in UCC256302.
1. VCC capacitance is charged through current source from HV pin.
2. When VCC voltage exceeds VCCStartSelf (~26V), RVCC is enabled. When BLK voltage exceeds 3V, switching begins
3. You should see a high side pulse, a long low side pulse (to charge the boot cap) and then normal switching. SS pin capacitance is charged during the startup cycles.

Do you see any switching? Are you getting RVCC = 12V? Are you able to share a schematic and any waveforms you have?

Best Regards,
Ben Lough

Hello.

Well, the waveform at the start of UCC25630X was set.(Attachment)

RVCC is 12V. LL / SS pin voltage appears to be low.

LO pin is not high.

If there is a cause and measures, please comment.

thank you.

UCC25630X2.pdf

Hi Masazumi-san,

Could you share a schematic of your evaluation board? You can email it to me directly if you do not want to post it publicly: ben.lough@ti.com

Best Regards,
Ben Lough

Hi Masazumi-san,

As a followup, it looks like the controller is hitting VCC UVLO. I would take a look at the bias winding voltage set point and also make sure there is enough capacitance on the VCC node. I will be able to provide more suggestions once I can see the schematic.

Best Regards,
Ben Lough