This report describes how the frequency modulation reduces electromagnetic interference on an SMPS using Viper53 as primary PWM-switch. For your reference, comparison of EMI measurement data will be presented.
The document details how frequency modulation (FM) reduces electromagnetic interference when using the VIPer53 as a primary PWM switch. It presents test results comparing original fixed-frequency operation against two FM configurations, demonstrating significant improvements in average noise levels below 10MHz.
The note provides specific circuit descriptions and resistor calculations for implementing Configuration "A" (50Hz cycle) and Configuration "B" (700Hz cycle). It also analyzes the difference between peak and average EMI measurements and offers optimization guidelines for the external oscillator to balance noise reduction with audible noise concerns.
The target FM percentage is +/-10%.
The frequency modulation technique reduces electromagnetic interference on a switched-mode power supply using the VIPer53 as the primary PWM-switch.
Using configuration "A" or "B" results in a 5 dBuV/m drop for frequencies lower than 200kHz.
The maximum value of the switching frequency is 77 kHz.