11.1.1.2 Low-Crosstalk Supplies

These supplies include Vcc1_VCO, Vcc5_DIG, and Vcc6_PLL1.

Each of these pins has internal bypass capacitance. Ferrite beads should not be needed between these pins and the power supply. A ferrite bead can optionally before the common point connecting these supplies, in which case a large decoupling capacitance (1 µF or more) should be used for voltage stability after the ferrite bead. The typical application diagram in Figure 41 shows all these supply pins connected together to the power supply with an optional ferrite bead and decoupling capacitance.

These supplies are considered low-crosstalk supplies because they do not generate much noise. Vcc1_VCO noise is effectively captured by the on-chip bypass capacitance, since noise from this pin is typically very high frequency. This pin also uses a high-quality integrated LDO to minimize noise below 30 MHz. Vcc5_DIG is only active at startup and during GPIO events, so after startup there is no continuous noise contribution from this pin. Vcc6_PLL1 is usually low-noise as well, due to the low frequency of the PLL1 phase detector. An on-chip LDO regulates this supply and prevents most PLL1 charge pump noise from escaping. If the PLL1 phase detector is set to a high frequency, a ferrite bead may optionally be used on this supply. If a ferrite bead is used with this supply, the DC resistance of this ferrite bead should be minimized to avoid voltage fluctuation at the PLL1 supply/PLL1 charge pump, and a 0.1-µF decoupling capacitor should be placed after the ferrite bead close to the supply pin.