PMP4397: What is the function of C11 and R6 ?

Went Cao

Part Number: PMP4397
Other Parts Discussed in Thread: BQ24133

Dear all

What is the function of C11 and R6 ? Does it reduce EMI ?

I had used the C11 and R6, but find the C11 would be smoking, then BQ24133's SW pins will be breakdown, I don't know what's wrong with these C11 and C6.

over 5 years ago

0 Ryan Manack over 5 years ago

TI__Intellectual 2610 points

Hello,

C11 and R6 form a RC snubber to damp to voltage spike on the switch node. They should be the appropriate package size for the application. This white paper describes the RC snubber in more detail http://www.ti.com/lit/slup100

Regards,
Ryan

0 Went Cao over 5 years ago in reply to Ryan Manack

Genius 5550 points

Yes，I use 0603 package cap and 0805 package res.but it also was burning

0 Ryan Manack over 5 years ago in reply to Went Cao

TI__Intellectual 2610 points

What is the input voltage, output voltage and switching frequency of your circuit?

0 Went Cao over 5 years ago in reply to Ryan Manack

Genius 5550 points

Dear Ryan

The input voltage is 12V, output voltage is 7.4V, and the switching frequency is 1.6MHz, like below

0 Ryan Manack over 5 years ago in reply to Went Cao

TI__Intellectual 2610 points

Hi,

The calculation for snubber loss is P = C * V^2 * F. A 10nF capacitor at 12Vin and 1.6MHz yields 2.3W. All of the power is being dissipated in the 10ohm resistor. My guess is the 10ohm is heating up the capacitor.

I recommend reducing the snubber capacitor by an order of magnitude to reduce the losses. See the attached snubber design method for redesigning.

I will investigate this reference design to understand why 10nF is recommended. At 1.6MHz and 12Vin this is way too high.

Thanks,

RyanSnubbers - Betten.pptx

Regards,
Ryan

0 Went Cao over 5 years ago in reply to Ryan Manack

Genius 5550 points

Dear Ryan

could you give me with values of cap and res？so that I can try it . thank you

0 Ryan Manack over 5 years ago in reply to Went Cao

TI__Intellectual 2610 points

I would reduce to 1nF capacitor and use a 0.25W 100ohm resistor. The snubber design procedure that I sent is the best way to design the snubber.

Thanks,
Ryan

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PMP4397: What is the function of C11 and R6 ?