UCC25600: UCC25660 Boost Mode Operation

Mustafa Yildiz

Part Number: UCC25600
Other Parts Discussed in Thread: UCC25660

Tool/software:

Hi,

I am trying to design an LLC converter by using UCC25660 IC. In the LLC operation, if input voltage is lower than output voltage, i.e. boost operation, then LLC goes into capacitive region and ZVS is disrupted, isn't it?

In the IC's datasheet, it says that it includes ZCS protection property. What happens if I want to force IC to work as a boost converter in some input voltage intervals? Does it just face with the efficiency drop, or will there be an operational problem?

29 days ago

0 Mike O' 29 days ago

TI__Guru 70115 points

Hello,

The ZCS protection will not allow the LLC to operate in the capacitive region. It controller will force the design to operate at a frequency just above the capacitor region. This is to prevent feedback control latch up that older LLC controller would face.

It is not recommend to design LLC converters for more than a 2 to 1 input range. What is your input voltage range intervals?

Regards,

0 Mustafa Yildiz 28 days ago in reply to Mike O'

Prodigy 50 points

Hi,

Our input voltage range is 20-36V and output voltage is 28V. Will it create a problem? If there will be a problem, then adjusting input voltage to 28-36V and output still stands at 28V solve this case?

+1 Mike O' 28 days ago in reply to Mustafa Yildiz

TI__Guru 70115 points

Hello,

Your inquiry is under review and I will get back to you shortly.

Regards,

0 Mike O' 28 days ago in reply to Mike O'

TI__Guru 70115 points

Hello,

That should not be a problem. You just need to design the transformer of the minimum input.

Regards,

0 Mustafa Yildiz 21 days ago in reply to Mike O'

Prodigy 50 points

Hi,

I have one more question related to this issue. In the Texas Instruments UCC2566x Design Calculator Tool, turns ratio is calculated based on nominal input voltage not the minimum input voltage. How should we proceed in this case?

0 Mike O' 21 days ago in reply to Mustafa Yildiz

TI__Guru 70115 points

Hello,

I am reviewing your inquiry and will get back to you shortly.

Regards,

+1 Mike O' 21 days ago in reply to Mike O'

TI__Guru 70115 points

Hello,

I would calculate the transformer turns ratio by hand and enter it in the tool. I am not sure why the author chose to use nominal.

The option would be to fake out the tool by make the min and maximum the minimum voltage. This way the tool will calculate the transformer turns ratio to the minimum. After you get the correct turns ratio then return the input to your real input range and hand enter the turns ratio into the tool.

Regards,

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UCC25600: UCC25660 Boost Mode Operation