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LTM4625 ringing output voltage

Category: Hardware
Product Number: LTM4625


I use 4 LTM4625 ICs for 2board. the first board is ok. but with the second board, the outputs have big ripple, although the rms value is true.

for more details, the input voltage is 12V, the feedback Res is 8.25k, so the output is 5V. but in the 2nd board, the outputs change from 4.5 to 6.5, the rms is 5.0V. the current is 0.15-0.2A (with no load). Initially, I have the Freq pin open, the output ripple is so big, the input is ringing ,too. The input voltage go upto 14V. then I put 20kOhm resistor to Freq pin. the ripple is reduced, but it's still high as mentioned above.

Besides, I hear the sound that maybe the inductors inside the module is ringing.

please help.

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