UCC256402: ucc256402

Pravin Khisti

Prodigy 100 points

Part Number: UCC256402
Other Parts Discussed in Thread: TIDA-010015, UCC256301

Hi I am using TIDA-010015. We are using UCC256402 for LLC (with relevant modifications) instead of UCC256301.

But I am observing 34 pulses at Gate of HO instead of 16 as mentioned in datasheet of .

Can you please help?

-Pravin

over 2 years ago

0 Manikanta Pallantla over 2 years ago

TI__Genius 13245 points

Hi Pravin,

Thanks for reaching out to us.

At what load power (percentage) you are seeing 34 pulses? Could you decrease the load power and count the number of pulses again?

Regards

Manikanta P

0 Pravin Khisti over 2 years ago in reply to Manikanta Pallantla

Prodigy 100 points

Hi Manikanta,

This is no load (0% power) condition. If load is applied (> approx. 2%) pulses are normal to 16 numbers,

Regards

Pravin Khisti

0 Manikanta Pallantla over 2 years ago in reply to Pravin Khisti

TI__Genius 13245 points

Hi Pravin,

Could you share the waveforms (Vout,Iout,Vin,LO,FB voltages) in both the cases? Also could you let me know the BMTH and BMTL values that you used?

Regards

Manikanta P

0 Pravin Khisti over 2 years ago in reply to Manikanta Pallantla

Prodigy 100 points

Hi Manikanta,

I will check and revert.

Regards

Pravin

0 Pravin Khisti over 2 years ago in reply to Pravin Khisti

Prodigy 100 points

Hi Manikanta,

First of all sorry for delayed response as board was unfunctional due to some damage and took time to get it back to the level.

Below are the wave forms. BMTH = 0.595V BMTL= 0.356V, RLL/SS Upper Res 390kohm and RLL/SS Lower resistor =190kohm

Regards

Pravin

0 Manikanta Pallantla over 2 years ago in reply to Pravin Khisti

TI__Genius 13245 points

Hi Pravin,

Thanks for sharing the waveforms.

The number of pulses in a burst packet depends on the FBreplica signal, BMTL threshold.

As you can see in above screenshot, it need not be exactly 16.

Please let me know if you have any further questions.

Regards

Manikanta P

0 Pravin Khisti over 2 years ago in reply to Manikanta Pallantla

Prodigy 100 points

Hi Manikanta,

Thanks for the support.

Regards

Pravin

0 Pravin Khisti over 2 years ago in reply to Pravin Khisti

Prodigy 100 points

Hi Manikanta,

We adjusted Upper and Lower RLL/SS and now we are getting 16 pulses.

But now we are facing issue, @100V AC input when we increase the load step by step, power supply gets Off @11ADC output.

Bulk voltage drops from 394V to 256V and SMPS goes in hiccup mode (keep trying to get ON).

But @ 230V AC input it works fine for full load (21ADC). Bulk Voltage sharply gets to lower value as PFC stops.

We tested LLC independently, it works fine with 390V DC and 21ADC load. We played with PFC inductor values (150 uH and 235 uH) but result is same.

Where things could be wrong?

- Regards

Pravin

0 Manikanta Pallantla over 2 years ago in reply to Pravin Khisti

TI__Genius 13245 points

Hi Pravin,

Was the converter working before at 100AC input before changing LL/SS resistors?

When the blk goes below BLK stop threshold, I would expect the converter to work in hiccup mode. So, it seems like the issue is with on PFC side.

I will add PFC expert to this thread once you respond to my question.

Regards

Manikanta P

+1 Pravin Khisti over 2 years ago in reply to Manikanta Pallantla

Prodigy 100 points

Hi Manikanta,

We resolved this issue. The AC source current limit was the cause. Now we are able to get 21A DC continuous when we set current limit of AC source

to maximum possible.

Regards

Pravin Khisti

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UCC256402: ucc256402