UCC256404: UCC256404

Adhithiyan Perumal

Prodigy 35 points

Part Number: UCC256404

In one of our application, we are using UCC256404 for the LLC design. Design details are as follows

Input Voltage - 300V DC

Output Watts - 200W

Output Voltage - 28V

Output Curretnt - 7.2A

Resonant capacitor - 22nF

Resonant Inductor - 28uH

Primary inductance - 120uH

BW Upper resistor - 20k, BW lower resistor - 3k (To disable the burst mode )

RLL Upper - 750k, RLL Lower - 75k

CLL - 100nF

VCR Upper Cap - 47pF/1kV, VCR Lower Cap - 5.6nF

In no load, the LLC output voltage remians constant at 30V. When we tried to load the system with minimum load of 10W, the output voltage controls at 28.7V.

In light load, the system is operating in burst mode as mentioned in the datasheet.

When we tried to increase the system load upto 200W, the system stills operates in burst mode and the output voltage regulation is not good.

How to bring the system out of burst mode when load is increased ?

over 2 years ago

0 Harish Ramakrishnan5 over 2 years ago

TI__Mastermind 24375 points

Hi,

This has been assigned to a product expert. Please wait two business days for a reply.

Thank you

Regards,

0 Manikanta Pallantla over 2 years ago in reply to Harish Ramakrishnan5

TI__Genius 16155 points

Hi Adhithiyan,

Please remove the upper resistor at the LL/SS pin for debugging purpose. The lower resistor of the LL/SS pin can be of any value. As a result, the BMTH and BMTL values will be the lowest (0.2).

Also, Could you share the design calculator (https://www.ti.com/lit/zip/sluc675 ) with your schematic values. I will verify and recommend the values needs to be used for final prototype.

Regards

Manikanta P

0 Adhithiyan Perumal over 2 years ago in reply to Manikanta Pallantla

Prodigy 35 points

4064.UCC25640x Design Calculator Rev4.0.xlsx

Hi Manikanta,

I have removed the upper resistor of LL pin. Lower resistor value = 402k.

Even though the system runs only is burst mode. Attached the design sheet with the existing values for your reference.

Kindly go through it and let us know for the solution

0 Manikanta Pallantla over 2 years ago in reply to Adhithiyan Perumal

TI__Genius 16155 points

Hi,

Could you share the waveforms?

1)Switch node voltage, VCR pin voltage, output current, output voltage

2)RVCC, VCC, FB pin, LL/SS pin voltage

Regards

Manikanta P

0 Adhithiyan Perumal over 2 years ago in reply to Manikanta Pallantla

Prodigy 35 points

Ti-Support.xlsx 1033.UCC25640x Design Calculator Rev4.0.xlsx

Hi Manikanta,

I have shared the waveforms requested by you.

Also find the updated design sheet.

Considering the primary leakage inductance resonant inductance was taken as 29.6uH.

Resonant Inductance - 24uH

Primary leakage inductance - 5.6uH

0 Manikanta Pallantla over 2 years ago in reply to Adhithiyan Perumal

TI__Genius 16155 points

Hi Adhithiyan,

Thanks for sharing the waveforms. The converter is operating in the burst mode. Also, Some times, converter is hitting the ZCS region (That is when LL/SS pin voltage is ramping up).

I would like to have a look at the compensator. So, Could you share whole schematics with me.

Regards

Manikanta P

0 Adhithiyan Perumal over 2 years ago in reply to Manikanta Pallantla

Prodigy 35 points

Hi Manikanta,

I would like to send the schematic in mail as we have some restrictions in sharing it here. Please check your mail for the schematic. Go through it and let us know if you have found any issues with that.

0 Manikanta Pallantla over 2 years ago in reply to Adhithiyan Perumal

TI__Genius 16155 points

I got your email, Adithiyan.

I will have a look at it and get back to you. Since we will be discussing through email, I will close this thread.

Regards

Manikanta P

Power management

Power management forum

UCC256404: UCC256404

Please remove the upper resistor at the LL/SS pin for debugging purpose. The lower resistor of the LL/SS pin can be of any value. As a result, the BMTH and BMTL values will be the lowest (0.2).