UCC256304: schematic review.

HI KIM Andy,

Thanks for your interest in UCC256304. I will review your schematic and get back to you. Also could you share waveforms of FB, HS, VCR and ISNS when the converter has a light load on it? Does the output voltage look ok when no load is present?

Best Regards,

Ben Lough

Hello
Thank you for your quick reply.
The voltage waveform at NO LOAD and LOAD ON (VOUT DROP) was measured for the requested waveform.
CH1: HS, CH2: ISNS, CH3: VCR, CH4: FB

NO LOAD

load on_vout drop

Please let me know what additional points you need to consider.

Hi KIM Andy,

The switching is ~1s apart which would indicate a fault has occured. Could you take a look at RVCC? If there is no fault, RVCC should be a stable 12V. If there is a fault, you will see RVCC get disabled by the controller and turn off.

The FB voltage looks irregular to me. If there is a constant load on the converter, I would expect the opto-coupler to demand a fairly constant current from the FB pin. Could you add a resistor and zener connected from RVCC to FB? In the EVM schematic, this is R21 and D10:www.ti.com/.../sluubq8b.pdf

I would also suggest populating a small capacitance at CA9.

Best Regards,
Ben Lough

Hello
Thank you for your quick reply.
I did all the review of what you said, but I did not find any improvements.
Are there any additional areas to consider?
Please confirm once more about the time constant of the circuit diagram.

2620.66W_AD(선행)_180320.pdf

Hi KIM Andy,

Thanks for the update. We need to identify which fault is occurring. Check ISNS and BW to make sure OCP1, OCP2, OCP3 or OVP are not being tripped.

Best Regards,
Ben Lough