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LM3478: Inquiry about POS Boost using LM3478 and 24V I/O board - Potential Issue and Possible Adjustments

Part Number: LM3478

Hi Team,

The POS boost uses the LM3478 in conjunction with the customer-supplied I/O board (24V). An abnormal sound is produced at 0A, which is currently believed to be caused by not entering CCM.


During customer recent experiments, it was found that by replacing L20 with 6.8uH (originally 3.3uH) and loading 0.1A, the abnormal sound has disappeared.


However, in actual tests, the phase at 0.1A will be at the DCM and CCM boundary and ringing is generated as shown in Figure A.



  1. Could you help us understand the reason for the ring formation and whether there are related compensations that need to be adjusted?
  2. This 24V Boost circuit will be paired with a thermal printer. If the printer is in standby mode (with a load of 0.1A), the situation will be as shown in Figure A (in the threshold area). Would there be any risk involved with this?


I appreciate your help in this matter. Thank you.


Case A: Iout = 0.1A


Case B: Iout = 0.5A