UCC25630-1EVM-291: Lr, Cr value

K. Sasaki14

UCC256301EVM has 50uH L1 and 0.022uF C8.

I think these are Lr and Cr of the datasheet or Excel Calculator.

When we input design requirements value of datasheet into excel design calculator, excel tool result match with datasheet contents.

However we cannot design with excel tool when 50uH Lr and 0.022uF Cr are used like EVM.

How did you decide EVM components value? Is there any other calculation method?

Best Regards,
Kohei Sasaki

over 5 years ago

0 Hong Huang over 5 years ago

TI__Mastermind 47325 points

Can you explain why you cannot design with excel tool?

Can you design based on the datasheet for Cr and Lr, on equation (13) to (17)? These equations are to determine the value of each component.

If your question is actually to want to know how to design LLC resonant half-bridge power converter, you may read this article: "Designing an LLC Resonant Half-Bridge Power Converter" which provides design guidelines to help, the line is www.google.com/url

0 K. Sasaki14 over 5 years ago in reply to Hong Huang

Guru 10200 points

Hong-san,

According to datasheet equation and excel tool, recommended Cr and Lr are 0.043uF and 58.9uH.

However 0.022uF and 50uH are used on EVM.

When we use 0.022uF for Cr, I think recommended Lr becomes 115.14uH.

How did you decide these components value?

Best Regards,
Kohei Sasaki

0 Hong Huang over 5 years ago in reply to K. Sasaki14

TI__Mastermind 47325 points

Hi Sasaki-san,

I am forwarding this thread to Ben who designed this EVM so he can help to answer your question better.

Best Regards,

Hong Huang

0 Benjamin Lough over 5 years ago in reply to Hong Huang

TI__Mastermind 26215 points

Hi Kohei,

The UCC25630-1EVM uses a split resonant capacitor structure so the total resonant capacitance is C7 + C8 = 44nF.

Best Regards,
Ben Lough

0 K. Sasaki14 over 5 years ago in reply to Benjamin Lough

Guru 10200 points

Ben-san,

Thank you for your reply.
What level leakage inductance did you consider about T1?

Best Regards,
Kohei Sasaki

0 Benjamin Lough over 5 years ago in reply to K. Sasaki14

TI__Mastermind 26215 points

Hi Kohei,

The transformer leakage is around 1.5% nominal in this design. Generally speaking, LLC tends to be a bit more forgiving when it comes to leakage inductance as it will simply add onto your resonant inductance. There are some LLC designs that actually use the leakage as their resonant inductance and get rid of the external resonant inductor.

Best Regards,
Ben Lough

Power management

Power management forum

UCC25630-1EVM-291: Lr, Cr value