LM5118 quick start calculation spreadsheet - capacitor values

John Vranes

Hello,

In the quick start calculations spreadsheet, there are some capacitor values where it is unclear if it's talking about a catalog value or an actual capacitance (after tolerance, temperature, applied voltage, etc.). The two capacitor values specifically in question are "Minimum Bootstrap Capacitor Chb (µF)" and "Initial Input Capacitor Value(μF)". Are these recommended minimum catalog values or actual capacitance minimum values?

Thanks.

over 9 years ago

0 Garrett Roecker over 9 years ago

TI__Mastermind 21720 points

John,

These are recommend values. The calculation does not include any type of capacitor de-rating values.

-Garrett

0 John Vranes over 9 years ago in reply to Garrett Roecker

Intellectual 590 points

Thanks, Garrett. I have a couple follow-up questions.

1) To clarify, since the calculation doesn't include de-rating/margin, that would mean it's intended that the circuit designer account for any derating in obtaining the recommended minimum capacitance value, correct?

2) What are the consequences of not meeting the minimum Chb capacitance value provided in the spreadsheet?

Thanks,

John

0 Garrett Roecker over 9 years ago in reply to John Vranes

TI__Mastermind 21720 points

John,

1). The values don't account for and de-rating. That is left up to the designer to select the correct capacitor type of the the correct function.
2). The Chb (bootstrap) capacitor is undersized there will can be issues with turning on the highside MOSFET.

Thanks,

Garrett

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LM5118 quick start calculation spreadsheet - capacitor values