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LM3404 - LED Driver - Humming issue at LOW Duty Cycles

Atul Bhakay
Genius 3205 points
Other Parts Discussed in Thread: LM3404, LM3405A

6327.ILUMI_CONTROL_BOARD_SCH_V1 0.pdf

Hi,

Earlier in first prototype we had LM3404 LED drivers for driving RGBW LED's. As per design the RON pin was contiously kept high whereas the DIM pin was controlled by PWM o/p of MSP430. The typical DIM frequency was 5Khz - 10KHz and the duty cycle variation was from 10% - 100% for brightness control.

 

When duty duty cycle was 100% the circuit used to deliver good results but as soon as the duty cycle was reduced, humming sound was heard from the driver section. Possibly from the output inductors or output capacitors (read it somewhere on forums). The humming noise was dominant at lower duty cycles.

 

This time too, except for the LED driver part, we have everything else same. We are now using LM3405A driver and want to ensure if any design change is required to eliminate the humming noise, is done at this satge only. Is there anything you can suggest on eliminating the humming noise ?