R4400 Microprocessor User's Manual

E PLL Passive Components

The Phase Locked Loop circuit requires several passive components for proper operation, which are connected to PLLCap0, PLLCap1, VccP, and VssP, as illustrated in Figure E-1.

In addition, the capacitors for PLLCap0 (Cp) and PLLCap1 (Cp) can be connected to either VssP (as shown), VccP, or one to VssP and one to VccP. Note that C2 and the Cp capacitors are incorporated into both the 179PGA and 447PGA package designs as surface-mounted chip capacitors.

Figure E-1 PLL Passive Components

Figure E-2 shows a top view of the 179-pin package with capacitors.

Figure E-2 179-Pin Package

Figure E-3 shows a top view of the 447-pin package with chip capacitors.

Figure E-3 447-Pin Package

It is essential to isolate the analog power and ground for the PLL circuit (VccP/VssP) from the regular power and ground (Vcc/Vss). Initial evaluations have yielded good results with the following values:

R = 5 ohms C1 = 1 nF C2 = 82 nF

C3 = 10 mF Cp = 470 pF

Since the optimum values for the filter components depend upon the application and the system noise environment, these values should be considered as starting points for further experimentation within your specific application. In addition, the chokes (inductors: L) can be considered for use as an alternative to the resistors (R) for use in filtering the power supply.

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