LM5156HEVM-FLY: LM5156HEVM-FLY Test & Guideline

Leo Kim

Part Number: LM5156HEVM-FLY
Other Parts Discussed in Thread: LM5156H-Q1

While I test LM5156HEVM-FLY, I have a question about that.

1.I checked and tested EVM, but it has a difference from what I think. Originally, Vsw is Vin + Vor(Reflected output voltage) + V leakage. Calculated value is 24(Vin) + 5(Vor) + Vleackage. But testing value is too high. Such as, Voltage of FET shows Vsw,max = 74V. It is correct? or Why is this value shown?

2. LM5156H-Q1's datasheet has less information for Flyback topology (I understand it is for boost mainly. For flyback design, Can I apply same equation in datasheet to Flyback? (such as Duty ratio, Vout… May be it is different equation that I knew)

Please let me know guideline to design.

over 2 years ago

0 EM over 2 years ago

TI__Genius 11215 points

Hello,

Thanks for reaching out. Do you have a scope shot of the switch node to share with us? For your flyback design, you might consider following this app note ( https://www.ti.com/lit/an/snva866/snva866.pdf ) as these 2 devices are pin2pin compatible (with the only difference of the spread spectrum pin). In addition you can also use the Excel QuickStart calculator at this link: https://www.ti.com/lit/zip/snvc240

Please let me know in case you have further questions.

Kind regards,