I'm using two daisy chained TLC5940PWP chips to control 32 LEDs from an ATmega32U4 MCU. When PWM'ing the LEDs in software from 0-4095, I hear high pitched sounds/beeps/buzzes, but I would like the board to be silent...
The beep is gone from 0 till around 200, and from 3900 till 4095. Between 200 and 3900 the sound is present. I tried to locate the sound but it looks like it is coming from the TLC chips. I tried pushing on the chips with a small wooden/plastic stick to see if the pitch changes. This does not seem to be the case. Also tried this on the 100 nF capacitors but that also does not seem to change the pitch. Then I desoldered both the capacitors but without luck, the sound remains. Lastly I tried to change the PWM frequency.
This site has some formulas on how to change the PWM frequency. In software I can adjust the TLC_PWM_PERIOD and the TLC_GSCLK_PERIOD. I've tried different values, from 4096:1, 8192:3, 16384:7 till 32768:15 respectively. But every setting results in different pitched beeps/buzzes and the sound does not go away.
Here is the schematic, which is really standard. The 5 signal lines go to the MCU and the SOUT of LED_DRIVER1 goes to SIN of LED_DRIVER2. (This is not shown.) Would the sound come from the way I designed the board from the schematic? Do you need this design in order to help me out?
