PMC-Sierra, Inc.
STANDARD PRODUCT
PM5945 -UTP5
PMC-940202 ISSUE 2. APRIL 7, 1995
APP_SAPI_UTP5
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0.01 uF
0.01 uF
Vcc
0.1 uF
0.1 uF
0.1 uF
= Via connected
to Vcc
Power Plane and Decoupling of CY7B951
Pin 6 of the CY7B951 provides current for all output pins and is internally connected
to pin 17 and 19. Its voltage fluctuates as the outputs switch. When the voltage
difference between pin 6 and pins 17 and 19 will be amplified, causing the voltage
fluctuation on pin 6 to increase. When the voltage at pin 6 fluctuates, the outputs it
drives will start to draw more current which causes the voltage on pin 6 to fluctuate
further. Testing has shown this fluctuation can reach 2 V p-p.
The low impedance power plane puts pin 6, 17, and 19 at the same voltage level so
that if pin 6 fluctuates due to outputs switching, pin 17 and 19 will follow, preventing
any voltage difference between them.
Mounting Hole Clearance Requirements
The following clearances are required in order for the board to be mounted onto the
Vicksburg Motherboard:
• On the component side, each mounting hole should have 0.25"x0.25" square
clearance centered at the center of the mounting hole.
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57
PMC [ PMC-SIERRA, INC ]
