LMR16020: Output capacitor formula

Jenny Lu69

Part Number: LMR16020

Hi friends,

I have my doubt about the formula of output capacitor in the datasheet as attached.

If IOH=2A, IOL=0.2A, Vout=50v, Vos=250mV, L=9.55uH, the value that I calculated based on equation 12 is 108uF(fsw=200k),not 36uF, and the value that I calculated based on equation 13 is 1.5089uF, not 7.7uF, did I misunderstand? Please kindly explain the formula for me.

Best Regards,

Thanks

over 8 years ago

0 JohnTucker over 8 years ago

TI__Guru**** 191445 points

The equation is correct. You get that very low value because you are using the maximum output voltage of 50 V. EQ 12 will be a more stringent requirement in you case, requiring Cout > 36 uF.

0 Jenny Lu69 over 8 years ago in reply to JohnTucker

Expert 1810 points

Hi Tucker,

Thank you for your reply.

And I want to ask where the value of 36uF and 7.7uF come from, would you please tell me the exact parameters of EQ12 and EQ13?

0 JohnTucker over 8 years ago in reply to Jenny Lu69

TI__Guru**** 191445 points

I can't say. When i rub those equations I get 36 uF (correct) and 15.4 uF instead of 7.7 uF (off by a factor of 2). I did not write that datasheet, so it is impossible for me to say. I checked another datasheet using the same equations and it shows the correct answers, so we can assume that the 7.7 uF is off by a factor of 2 x.

0 Jenny Lu69 over 8 years ago in reply to JohnTucker

Expert 1810 points

Hi Tucker,

I appreciate your kind help.

Best Regards,

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LMR16020: Output capacitor formula