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Charge pump circuit capacitor selection VNF1048F

srnath
Associate

Hello,

I was checking the evaluvation board of VNF1048F for a efuse application to control motor drive. I wish to know how the capcitors for the charge pump selected in the evaluvation board. I am able to see 470nF in the evaluvation board schematics.

Thank you,

1 ACCEPTED SOLUTION

Accepted Solutions
Peter BENSCH
ST Employee

There are too many unknown parameters to create a simple formula. However, practical tests can help to find the right value by looking at the slope of the gate voltage with an oscilloscope and using twice the capacitance value to be on the safe side.

In order to give better visibility on the answered topics, please click on Accept as Solution on the reply which solved your issue or answered your question.

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3 REPLIES 3
Peter BENSCH
ST Employee

Welcome @srnath, to the community!

Well, the capacitors must be able to supply the driver for the high-side MOSFET. The capacitance value therefore depends on the switching frequency of the charge pump (400kHz), the maximum switching frequency of the MOSFET, its gate charge and its gate resistance (internal + external), whereby 470nF is a good practicable value in each case.

Hope that helps?

Regards
/Peter

In order to give better visibility on the answered topics, please click on Accept as Solution on the reply which solved your issue or answered your question.
srnath
Associate

Hello @Peter BENSCH ,

Thank you for answering.

Is there any equations that will ease the calculation of the charge pump capacitor?

Peter BENSCH
ST Employee

There are too many unknown parameters to create a simple formula. However, practical tests can help to find the right value by looking at the slope of the gate voltage with an oscilloscope and using twice the capacitance value to be on the safe side.

In order to give better visibility on the answered topics, please click on Accept as Solution on the reply which solved your issue or answered your question.