LM2840 CBoot capacitor

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#1
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Searching the data sheet, I don't find anything about the voltage needed for the CBoot capacitor.

 

 

I design train related things for 10 to 30 volt input. 

 

* Thread title fixed. Ross

274,207,281-1 The largest known Mersenne Prime

Measure twice, cry, go back to the hardware store

Last Edited: Sat. Nov 11, 2017 - 01:13 AM
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Strange they would omit that.  FWIW, for the example circuit in the LM5010 data sheet they call out a 16v rating for the bootstrap capacitor.  In this example the input voltage range was up to 75v for a 10 volt output.

 

Tom Pappano
Tulsa, Oklahoma

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Which part number Torby?  The title and the one in the picture are different surprise

 

Jim

If you want a career with a known path - become an undertaker. Dead people don't sue! - Kartman

Please Read: Code-of-Conduct

Atmel Studio6.2/AS7, DipTrace, Quartus, MPLAB user

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Torby wrote:
I don't find anything about the voltage needed for the CBoot capacitor.

tpappano wrote:
Strange they would omit that.

 

Page 3 of the Datasheet reads:

 

I am thinking that based on a 7v limit over SW a 16v cap would suffiece?  But .15uF/16v caps are rare a .15uF/50v will do nicely

 

Jim

If you want a career with a known path - become an undertaker. Dead people don't sue! - Kartman

Please Read: Code-of-Conduct

Atmel Studio6.2/AS7, DipTrace, Quartus, MPLAB user

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I measured the actual DC across my LM5010 caps and they ran about 6.8v

 

Tom Pappano
Tulsa, Oklahoma

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Eye sea eye spelt itt rong.

274,207,281-1 The largest known Mersenne Prime

Measure twice, cry, go back to the hardware store

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So fix dear Henry, dear Henry fix it......

John Samperi

Ampertronics Pty. Ltd.

www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

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But there's a hole in the bucket!

 

It was about 1965 when I heard that for the first (and only) time, and I was permanently affected by it.

 

 

 

 

Tom Pappano
Tulsa, Oklahoma

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Note - if you’re using ceramic caps with a hi-k dielectric, that the actual capacitance is based on the applied voltage. So for a 50V part, you may only be getting about a tenth of the capacitance. Murata have some great docs that explain this.