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LP5860: Audible Noise Issue with LP5860 on our PCB

Harry Berchtold
Prodigy 10 points
Part Number: LP5860

Tool/software:

Dear Support Team,

We are using the LP5860 component in our current project and have assembled a PCB accordingly. Unfortunately, we are experiencing an issue where the PCB produces an audible noise, and we are unable to identify the source.

We have already taken the following measures:
Replaced all ceramic capacitors with tantalum capacitors.
Increased the internal frequency from 62.5 kHz to 125 kHz, which shifted the audible noise to a higher frequency.
The PCB is powered using a lab power supply.

Despite these changes, the issue persists. Could you please assist us in identifying and resolving the cause of this audible noise?

We would greatly appreciate your support in this matter.

  • 0
    TI__Mastermind 20515 points

    Hi Harry,

    Can you make sure the source of this noise is from LP5860? Or can you please help to show me your schematic?

    BR, Jared

  • 0 in reply to Jared Zhou
    Prodigy 10 points

    Hi Jared,

    thank you for your feedback. We can confirm that the audible noise is coming from the Frontpanel Board. Our process is as follows:

        We program the chip.
        We then disconnect the Frontpanel Board from the Processor Board.
        The audible noise remains on the Frontpanel Board even after disconnection.

    However, the audible occurs only at certain brightness levels, not all.

    BR, Harry

  • 0 in reply to Harry Berchtold
    TI__Mastermind 20515 points

    Hi Harry,

    Can you please tell me the current register configuration of LP5860, such as the scan line number, PWM duty cycle?

    BR, Jared

  • 0 in reply to Jared Zhou
    Prodigy 10 points

    Hi Jared,

    Registers Configuration:

    Dev_initial: 0x5B // Max_Line_Num (1011), Data_Ref_Mode = Mode2 (01), PWM_Fre = 62.5kHz (1)
    Dev_config1: 0x07 // SW_BLK (0), PWM_Scale_Mode (1), PWM_Phase_Shift (1), CS_ON_Shift (1)
    Dev_config2: 0xFE // Comp_Group3 (11), Comp_Group2 (11), Comp_Group1 (11), LOD rem (1), LSD rem (0)
    Dev_config3: 0xFF // Down_Deghost (11), Up_Deghost (11), Maximum_Current = 50mA (111), Up_Deghost_enable (1)

    Color current = 100%
    Dot current = 100%

    PWM global = 100%
    PWM individual = 100%
    PWM group = 2 groups are defined. The maximum audible noise seems to be when one group is set to maximum (100%) and the other group to a value different than 100% (about 70%). If both groups have the same value, there is no noise.

    BR, Harry

  • 0 in reply to Harry Berchtold
    TI__Mastermind 20515 points

    Hi Harry,

    Thanks for providing this configuration, please give me some time and I will test in on EVM to see if I can hear this noise on EVM. I will reply to you ASAP.

    BR, Jared

  • 0 in reply to Jared Zhou
    TI__Mastermind 20515 points

    Hi Harry,

    Sorry for delay and thanks for your patience, I am OoO in a few days and will return back to office tomorrow. I will test on EVM tomorrow and reply to you.

    BR, Jared

  • 0 in reply to Jared Zhou
    TI__Mastermind 20515 points

    Hi Harry,

    Please refer the register configuration on my EVM board below:

    And I attached the EVM video, I didn't hear any noise from EVM board. I suspect the reason why you hear the noise from your board is the layout problem.

    BR, Jared