Switching regulators are large contributors to PoC noise. To reduce their effect, TI recommends using low-dropout regulators (LDOs) wherever possible because an LDO does not generate any noise from switching. In the case where an LDO cannot be used and a switching regulator is required, switching noise introduced into the system must be taken into account. To reduce the switching noise, TI recommends using a high PoC voltage. As the PoC voltage rises, current consumption by the switching regulator is reduced, therefore reducing the noise introduced from switching.

Another way to reduce the effect of noise is to use a switching regulator with a higher switching frequency. A higher switching frequency increases the effectiveness of the decoupling capacitors because their impedance is lowered as frequency increases. Figure 5-1 shows decoupling capacitors C1 and C2; with higher switching frequency these capacitors become more effective. Finally, increasing the decoupling capacitance at V_PoC can help to better filter any high frequency noise introduced by the regulator. Equation 2 shows the impedance of a capacitor as a function of frequency where Z is the impedance in Ohms, f is the frequency in Hertz, and C is the capacitance in Farads. The capacitance and frequency are in the denominator, which means increasing either value decreases the impedance and therefore shorts high frequencies to ground. When choosing decoupling capacitors, select high quality capacitors rated for the voltage and temperature range required. Some capacitors can significantly degrade when operated near their rated voltage. Sometimes the capacity can drop as low as 20 – 40% of the nominal rating. For this reason, TI recommends selecting capacitors with a voltage rating 2x or 3x the voltage being used to avoid any unexpected drop in capacitance.