I have the TPS92691EVM-752 evaluation kit setup to run a string of 16 LEDs. There is a very noticeable audible frequency generated from the board and I am wondering what I can do to significantly reduce this noise.
Setup:
- Input Voltage 12V from bench power supply connected to POS and NEG on J2
- LED String connected to LED+ and LED- on J3
- J4 Jumper position moved to pins 1 and 2 for external IADJ
- 0.45V from bench power supply feeding IADJ TP4 input for 200mA drive current (negative terminal of power supply connected to NEG on J2)
- PWM connected to function generator (negative terminal of power supply connected to NEG on J2)
Function Generator PWM:
- 200 Hertz square wave
- 100 uS pulse width
- 3.3 V amplitude
LEDs:
- V_f 2.3V at 200mA
Scope Trace:
Channel 1 Yellow - PWM Input - TP8
Channel 2 Light Blue - Voltage on LED+ on J3
Channel 3 Purple - IMON - TP2
Channel 4 Blue - Current Clamp on LED String