I’ve seen that you implemented Spread Spectrum on the EVQ4430-L-00A using a 555 timer. I would like to do the same for the MP4575. However, I don’t know how to select the coupling between the output of the timer and the FREQ pin (C8, R9, R11 on the EVQ4430-L-00A). Unfortunately, there is no information about the Spread Spectrum and the component values on the EVQ4430-L-00A either.
Can you provide some information on the internals of the FREQ-Pin and/or reccomendations on how to design the coupling?
Hi mumplitz2,
The decoupling is used to create a sawtooth from the pulsing of the 555 timer. The combination of the C8 and R9 creates the time constant of the sawtooth. The sawtooth slightly adjusts the reference of the Rfreq, slightly modulating the frequency creating spread spectrum.
R11 is just used to connect to the circuit. R9 is initially 0 to connect the Rfreq to ground.
Regards,
Vinh Tran