LM2672: Abnormal output voltage of LM2672MX-3.3/NOPB

FRANK1

Part Number: LM2672

Hi sir,

Regarding this part, at the moment a higher voltage 6V are output from LM2672MX-3.3/NOPB when our production power on and repeating ON/OFF operation,

then the DP83822 in our production had a breakdown due to this reason.

Vin=24v DC

Please find the ripple below, yellow line is DC/DC converter output ripple, and aqua line is DC/DC converter input ripple.

Could you please help me to analysis why the output voltage is over 3.3V?

BOM:

L2：CLF10060NIT-470M (TDK)

　　　　Max Vin：DC26V

　　　　Max I：47μF/2A

　　　C52：GRM31CF10J107ZE01L (Murata)

　　　　Max Vout：3.3V

　　　　inductor: 100μF/6.3V

　　　D1：B240A-13-F (Diodes Incorporated)

　　　　2A/40V

　　　C63：C2012X5R1V226M125AC (TDK)

　　　　22μF/35V

　　　C51：GRM155B31H103KA88D (Murata)

　　　　0.01μF/50V

　　PCB layout design

　　　Vin：Red

　　　GND：Blue（Bottom to GND）

　　　Vout：Green

Best Regards,

over 4 years ago

0 Daniel Li14 over 4 years ago

TI__Mastermind 27030 points

the VIn slew rate is too quick ,and the dcdc loop response is slow which make the the duty can change by Vin change. so Vo=Vin*D, when D can't change, Vin raise, Vo will raise up by VIn until the loop reponise for the overshoot of Vo.

You can monitor the SW waveform especially the Vo jump from 3V to 6V.

can you try use slow VIn slew rate see any improvement?

Thanks

0 user1567465 over 4 years ago in reply to Daniel Li14

Prodigy 220 points

Hi sir,

Thank you for your reply.

Please tell me, how long should I lower the slew rate?

Best Regards,

0 Daniel Li14 over 4 years ago in reply to user1567465

TI__Mastermind 27030 points

Hi:

pls try to slow down the Vin slew rate to 5V/ms.

Thanks

Daniel Li

0 user1567465 over 4 years ago in reply to Daniel Li14

Prodigy 220 points

Hi sir,

Thank you for your reply.

I tried it.

This problem was solved.

Best Regards,

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LM2672: Abnormal output voltage of LM2672MX-3.3/NOPB