Normally, the IC switches in fixed frequency which can be adjusted through FSW_SYNC pin. The charger also supports frequency dithering to improve EMI performance and help pass the IEC-CISPR 32 specification. Dithering is disabled by default as EN_DITHER=00b at startup. It can be enabled by setting EN_DITHER=01/10/11b. The switching frequency is not fixed when dithering is enabled and varies within determined range by setting EN_DITHER to 01/10/11b, which corresponds to ±2%/4%/6% switching frequency variation. A larger dithering range results in a smaller EMI noise peak, but a larger dithering range also causes slightly more output voltage ripple. Therefore, the dithering frequency range selection is a trade-off between EMI noise peak and output voltage ripple and we recommend you to choose the lowest dithering range which can pass IEC-CISPR 32 specification. The patented dithering pattern can improve EMI performance in the switching frequency up to 30-MHz range which covers the entire conductive EMI noise range.

It should be noted that the Dithering feature will not work if an external clock is provided.