SNVSAL1C December 2017 – June 2021 LP87702-Q1
Systems with periodic switching signals may generate a large amount of switching noise in a set of narrowband frequencies (the switching frequency and its harmonics). The usual solution to reduce noise coupling is to add EMI-filters and shields to the boards. The LP87702-Q1 device supports the spread-spectrum switching frequency modulation mode that is register controlled. This mode minimizes the need for output filters, ferrite beads, or chokes. The switching frequency varies between 0.85 × fSW and fSW in spread spectrum mode, where fSW is switching the frequency selected in the OTP. Figure 8-2 shows how the spread spectrum modulation reduces conducted and radiated emissions by the converter and associated passive components and PCB traces. This feature is available only when internal RC oscillator is used (EN_PLL is 0 in PLL_CTRL register) and it is enabled with the EN_SPREAD_SPEC bit in CONFIG register, and it affects both buck converters and the boost converter.