LM61460-Q1: Calculate of snubber circuit

Shawn Li

Part Number: LM61460-Q1
Other Parts Discussed in Thread: LM61460

Tool/software:

Hi team,

There is a problem when my customer test LM61460, so I would like to seek your advice. First, please take a look at their schematics.

The working condition of the circuit is input voltage 12V, switching frequency 400kHz, output voltage 6.5V, output current 1A under light load, 4A under heavy load, and peak value 6A. Now they found that the SW node has a large voltage spike during the test, so please help calculate a suitable resistance and capacitance value of the snubber circuit so that the voltage of the SW node is within the range given in the datasheet, that is, -0.3V to Vin+0.3V.

For your information, the value of snubber circuit is 62R and 220pF, and the test waveforms are as below.

1.Heavy load:

2.Light load:

Thank you very much for your assistance!

Best regards,

Shawn Li

8 months ago

+1 Ryan 8 months ago

TI__Expert 3400 points

Hi Shawn,

You can find helpful insight on snubber calculations at the following link:

http://www.ti.com/general/docs/lit/getliterature.tsp?baseLiteratureNumber=slva255&keyMatch=snubber&tisearch=Search-EN-TechDocs

Despite this targeting a boost converter, the resolution is similar for buck converters.

Best,

Ryan

0 Shawn Li 8 months ago in reply to Ryan

TI__Prodigy 70 points

Hi Ryan

Thank you very much for your information and I should be most grateful if you would provide specific resistor and capacitor values to help customers reduce voltage spikes, pass their tests. They want the voltage of SW node to be strictly within the range provided on the datasheet.

Best regards,

Shawn

+1 Ryan 8 months ago in reply to Shawn Li

TI__Expert 3400 points

Hi Shawn,

Can you first confirm that the customer is using tip-and-barrel method to measure the switch node? Long test leads and large ground loops may affect the measurement.

Additionally, please help me by measuring the ringing frequency from the first peak and trough of the switch waveform to help begin the calculation.

Thank you,

Ryan

0 Shawn Li 8 months ago in reply to Ryan

TI__Prodigy 70 points

Hi Ryan

Thanks for reply. I have already solved their problem.

Best regards,

Shawn

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LM61460-Q1: Calculate of snubber circuit