AN1849 Motorola / Freescale Semiconductor, AN1849 Datasheet - Page 22

• Manufacturer Part Number: AN1849
• Description: MPC107 Design Guide
• Manufacturer: Motorola / Freescale Semiconductor

While switching power supplies are more complicated and require more components than simple linear
regulators, modern switching components are fairly easy to design with if the recommendations in the
manufacturers data sheets are followed. In addition, efficiencies of 85-95% are possible, which translates
into very low heat dissipation.
1.7.1 PLL/DLL Filters
The MPC107 requires filters for the PLL power supply pins (AVDD and LAVDD) to insure that power
supply noise is not coupled into the voltage-controlled oscillator (VCO), which would cause clock jitter and
imprecise I/O timing (which can limit the maximum bus performance). The filter is a simple R-C network,
with values chosen to minimize noise in the resonant frequency band of the VCO (approximately 500 kHz
to 10 MHz). Note that these AVDD and LAVDD filters cannot be shared, there should be one filter per pin.
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+5V
3A
SWITCHES
3x
680uF
low-ESR
VID(4:0)
RC5051
GND
VCC
Figure 15. Shared MPC107 Power Supply
VFB
LO
IFB
HI
MPC107 Design Guide
4x
820uF
low-ESR
+2.5V
to MPC107
+2.5V
5A
to CPU