Electronic – Ceramic capacitor 4kHz sound

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I have an LDO (TPS7A4101) which has two 10 uF, 50 V ceramic capacitors on the input. The LDO is generating 3.3 V, which is used by MCU to drive the LEDs.

When the system goes into standby mode, the LEDs turn on for 1 sec and stay off for 8 sec. During that time, the capacitors make a buzzing sound which is at 4kHz. The LEDs are driven by the MCU using PWM signal, which is running at 4kHz.

I tried using film capacitors which are too big for the PCB, but that stops the sounds for sure. I also tried different values of capacitors such as 4.7 uF, 50 V and 35 V versions, but the noise remains the same.

Does anyone know how this can be fixed in hardware?

In software I know that if, instead of PWM signal, I use high and low signal then it works, but I am looking for a hardware solution.

Best Answer

  1. Check whether during "PWM on" condition and with sound emission the LDO is stable, i.e. it does not go oscillating at output. If it oscillates, that might be the root cause.
  2. Try to use another capacitors in similar packaging, for example tantalum ones. But first check whether your LDO allows that.
  3. Which dielectric your capacitors are made of? Probably swapping X5R to X7R, or going for other capacitor manufacturers might help. Also try to select capacitor series (at the specific manufacturer) that are less susceptible to electrostriction AKA microphone effect.
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