TPS55340: TPS55340 - slva559.pdf Clause 2.8 Input Capacitor typo?

John Duquette

Part Number: TPS55340

I'm reviewing an existing TPS55340 design against the calculations in slva559.pdf. It's a great app note, thanks!

I'm wondering if there is a typo on Equation 24. The text states that the equation is for 10% ripple (0.1) but the denominator of the equation uses (0.01) that appears to be for 1% ripple. Is that a typo or am I missing something?

For reference, my existing design that works well has a 10 uF input capacitor and the result of Equation 24 shows the minimum input capacitance is 67 uF. 6.7 uF would make a lot more sense so that's why I'm asking.

Thanks,

John D

over 8 years ago

0 Anthony F over 8 years ago

TI__Mastermind 35185 points

Hi John,

Good find. Yes this is supposed to be 10%. I also doubled checked that using 10% results in 15.4 µF result I had given.

Best Regards,
Anthony

0 John Duquette over 8 years ago in reply to Anthony F

Intellectual 710 points

I'm glad I could help. Thanks for a great app note!

0 John Duquette over 8 years ago in reply to Anthony F

Intellectual 710 points

Anthony,

One more question. In slva599.pdf on p. 5 you mention "ILIMmin" in Equation 8 for IOUTmax. I don't see this parameter referenced anywhere else. What is that referring to?

Thanks,

0 Anthony F over 8 years ago in reply to John Duquette

TI__Mastermind 35185 points

"ILIMmin" is referring to the minimum peak current limit of the TPS55340 and can be found on the datasheet of the TPS55340. I see now it's not very clear since there is no text on it so I'll add some explanation when we fix the typo in the equation.

0 John Duquette over 8 years ago in reply to Anthony F

Intellectual 710 points

Thanks. That makes sense.

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TPS55340: TPS55340 - slva559.pdf Clause 2.8 Input Capacitor typo?