LM5122: Synchronous SEPIC on AC coupling

user6281095

Part Number: LM5122
Other Parts Discussed in Thread: PMP30491

Hi there,

https://www.ti.com/tool/PMP10886

I am using this part LM5122 for my synchronous SEPIC converter. I looked through your example (link on above) on this kind of setup. One thing I don't understand is the AC coupling of high side MOSFET gate drive. How would you calculate these parameters? An explanation will be really helpful. or is there other application notes I can read?

Thank you very much!

Best regards,

Mike

over 4 years ago

0 Bernd Geck over 4 years ago

TI__Intellectual 2770 points

Hello Mike,

for the coupling capacitance typically ten times input capacitance and Miller capacitance of sync FET
is sufficient; we don't care too much here, just taking 1uF that is good...
If you look at my smaller PMP30491 you'll find 1uF there as well and it works.
So no sophisticated maths here - just by experience and an electronics thumb.

Best regards, Bernd