8.3.1.6 Spread-Spectrum Mode

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 LP8758's register selectable spread-spectrum mode minimizes the need for output filters, ferrite beads, or chokes. In spread spectrum mode, the switching frequency varies randomly by ±5% (depending on selected switching frequency) about the center frequency, reducing the EMI emissions radiated by the converter and associated passive components and PCB traces (see Figure 10). This feature is enabled with the CONFIG.EN_SPREAD_SPEC bit, and it affects all the buck cores.

Where a fixed frequency converter exhibits large amounts of spectral energy at the switching frequency, the spread spectrum architecture of the LP8758 spreads that energy over a large bandwidth.

Figure 10. Spread-Spectrum Modulation