The TPS552882-Q1 provides an optional switching frequency dithering that is enabled by connecting a capacitor from the DITH/SYNC pin to ground. Figure 7-4 illustrates the dithering circuit. By charging and discharging the capacitor, a triangular waveform centered at 1 V is generated at the DITH/SYNC pin. The triangular waveform modulates the oscillator frequency by ±7% of the nominal frequency set by the resistance at the FSW pin. The capacitance at the DITH/SYNC pin sets the modulation frequency. A small capacitance modulates the oscillator frequency at a fast rate than a large capacitance. For the dithering circuit to effectively reduce peak EMI, the modulation rate normally is below 1 kHz. Equation 4 calculates the capacitance required to set the modulation frequency, F_MOD.

Equation 4.

where

• R_FSW is the switching frequency setting resistance (Ω) at the FSW pin
• F_MOD is the modulation frequency (Hz) of the dithering

Connecting the DITH/SYNC pin below 0.4 V or above 1.2 V disables switching frequency dithering. The dithering function also is disabled when an external synchronous clock is used.

Figure 7-4 Switching Frequency Dithering