SNVSB97A December 2018 – September 2021 LM34936-Q1
The LM34936-Q1 provides an optional frequency dithering function that is enabled by connecting a capacitor from DITH to AGND. Figure 7-4 illustrates the dithering circuit. A triangular waveform centered at 1.22 V is generated across the CDITH capacitor. This triangular waveform modulates the oscillator frequency by 10% of the nominal frequency set by the RT resistor. The CDITH capacitance value sets the rate of the low frequency modulation. A lower CDITH capacitance will modulate the oscillator frequency at a faster rate than a higher capacitance. For the dithering circuit to effectively reduce peak EMI, the modulation rate must be much less than the oscillator frequency (Fsw). Equation 6 calculates the DITH pin capacitance required to set the modulation frequency, FMOD. Connecting the DITH pin directly to AGND disables frequency dithering, and the internal oscillator operates at a fixed frequency set by the RT resistor. Dither is disabled when external SYNC is used.