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TLC5941-Q1: audible noise when using TLC5941

Frank(EP) Liu
Expert 3775 points
Part Number: TLC5941-Q1
Other Parts Discussed in Thread: TLC5941

Hi Sir.,

my customer uses 10 TLC5941 to drive 160 LEDs for backlight. They use PWM mode with 6MHz GSCLK. below is the waveform. it looks correct for me.

They drive all LED in the same PWM setting.

Ch1: one of out pin

ch2: BLANK

CH3: GSCLK(it should be 6MHz. due to scope resolution, the frequency in scope is wrong.)

They can hear the audible noise. 

Do you have any suggestion to reduce it?

BR,

frank

  • 0
    TI__Genius 15776 points

    The hawling may trigger by the output cap because the frequency of vout is with the human audible range, you can increase the frequency of vout to 20k to identify

  • 0 in reply to Frank Qiu
    TI__Expert 3775 points

    hi Frank Qiu,

    Change GSCLK to 24MHz and Blank to 20KHz. but the PWM step is only 1024. The audible noise becomes very small. 1024 steps seems the max steps for this asic to avoid the audible noise.

    Can I know if this is the only solution? 

    Audible noise issue should be very normal for this application. How does other customer fix this issue?

    BR,

    frank

  • 0 in reply to Frank(EP) Liu
    TI__Genius 15776 points

    From my opinion the source of noise is the output cap , could you help me to double confirm it?

    There are two ways to solve this issue:

    1) change the frequency of vout out of the range of human audio

    2) change the ceramic cap to electrolytic cap or tantalum capacitor