SNAS879 December 2024 LMR60420
PRODMIX
The purpose of the spread spectrum is to reduce peak emissions at specific frequencies by spreading emissions across a wider range of frequencies than a part with fixed frequency operation. In most systems containing the LMR60420 device, low frequency conducted emissions from the first few harmonics of the switching frequency can be easily filtered. The LMR60420 spreads the switching frequency 16% above of the set point switching frequency established by the RT resistor. This means that the set point switching frequency established by the RT resistor represents the lower bound of the switching frequency while the device is operating with spread spectrum.
The following conditions overrides spread spectrum, turning spread spectrum off: