LMR14030: How is the spread spectrum function of the LMR14030SSQDDARQ1 used?

Spread spectrum is a factory option. The purpose of spread spectrum is to eliminate peak emissions at specific frequencies by spreading these peaks across a wider range of frequencies than a part with fixed frequency operation. Low frequency conducted emissions from the first few harmonics of the switching frequency can be easily filtered. A more difficult design criterion is reduction of emissions at higher harmonics which fall in the FM band. These harmonics often couple to the environment through electric fields around the switch node and inductor. Spread of frequencies which can spread energy smoothly across the FM and TV bands but is small enough to limit sub-harmonic emissions below the device switching frequency. Peak emissions at the part’s switching frequency are only reduced slightly, by less than 1 dB, while peaks in the FM band are typically reduced by more than 6 dB. Generally TI Part uses a cycle-to-cycle frequency hopping method based on a linear feedback shift register (LFSR). This intelligent pseudo-random generator limits cycle to cycle frequency changes to limit output ripple. The pseudo-random pattern repeats at less than 1 Hz, which is below the audio band.

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Ankit Gupta,

Application Engineer