SNVSB29C October 2018 – June 2021 LM5143-Q1
The LM5143-Q1 provides a frequency dithering option that is enabled by connecting a capacitor from DITH to AGND. This generates a triangular voltage centered at 1.2 V at DITH. See Figure 8-2. The triangular waveform modulates the oscillator frequency by ±5% of the nominal frequency set by the RT resistance. Use Equation 3 to calculate the required DITH capacitance to set the modulating frequency, FMOD. For the dithering circuit to effectively attenuate the peak EMI, the modulation rate must be less than 20 kHz for proper operation of the clock circuit.
If DITH is connected to VDDA during power up, the dither feature is disabled and cannot be enabled unless VCC is recycled below the VCC UVLO threshold. If DITH is connected to AGND on power up, CDITH is prevented from charging, disabling dither. Also, dither is disabled when the LM5143-Q1 is synchronized to an external clock.