| 摘要 |
<p>A switch mode power supply has pulse width modulation (PWM) frequency dithering of a PWM clock frequency. The PWM frequency dithering circuit may change the frequency of the PWM clock based upon each of a plurality of frequencies. A PWM time base circuit may comprise a period register containing a PWM period value, a comparator, and a PWM counter, wherein a PWM count value may be incremented in the PWM counter by the variable frequency PWM clock, the comparator may compare the PWM period value with the PWM count value and when the PWM period value and the PWM count value are substantially equal the PWM count value may be reset. The PWM frequency dithering circuit may comprise a roll counter, wherein the roll counter changes a roll count value each time the comparator resets the PWM count value in the PWM counter; a multiplexer having a plurality of inputs and an output, wherein the output is coupled to each one of the plurality of inputs of the multiplexer based upon the roll counter count value; and a plurality of frequency registers, each one of the plurality of frequency registers may be coupled to a respective one of the plurality of inputs of the multiplexer; wherein the output of the multiplexer may be coupled to a frequency control input of the variable frequency PWM clock such that frequency values stored in the plurality of frequency registers may be used in determining the variable frequency PWM clock frequency.</p> |
