下载
1
09/16/99
123456789012345678901234567890121234567890123456789012345678901212345678901234567890123456789012123456789012345678901234567890121234567890123
123456789012345678901234567890121234567890123456789012345678901212345678901234567890123456789012123456789012345678901234567890121234567890123
Application Brief AB-32
12345678901234567890123456789012123456789012345678901234567890121234567890123456789012345678901212345678901234567890123456789012123456789012
12345678901234567890123456789012123456789012345678901234567890121234567890123456789012345678901212345678901234567890123456789012123456789012
3.3V Bus Switches for PC100
TM
/
PC133
TM
DIMM Switching
by Refugio Jones August 18, 1999
In high-end PC and server applications, the Pentium II
TM
processor
memory bus runs at bus speeds of 100 or 133 MHz. Here, bus
switches are used to switch 100/133 MHz SDRAM modules in den-
sities of 128 MBytes and higher.
Pericom’s 3.3V DIMM bus switch series is designed with near zero
delay, low ON Resistance (five ohms), low-capacitance, and ultra-
low quiescent power.
For reliability, the unused module data pins should be connected to
ground. Figure 1 shows the application of Pericom’s PI3B16226 bus
switches in a Intel Pentium II memory system with bus speeds of
133 MHz and 133 MHz SDRAM DIMMs.
Figure 1. Using Pericom’s 3.3V Bus Switch in DIMM Switching
Application Brief AB32
Highlights
To prevent overloading, a bus switch is required where more than
three SDRAM DIMMs are connected to the bus. The block
diagram shows that the DIMM modules are connected to the
B ports of the bus switch.
The PI3B16226 (see Figure 2), has weak pull-down resistors on
B ports connected to ground. The B port gets enabled when the
switch is disabled. This ensures non-floating connections and
reliable DIMM operation.
Furthermore, PC133 applications require low ON Capacitance to
reduce bus loading under 133 MHz tight timing requirements. The
PI3B16226 provides 9pF of ON Capacitance.
(B0)
133MHz
SDRAM Module
Intel
Pentium II
Processor
(B1)
133MHz
SDRAM Module
(B2)
133MHz
SDRAM Module
(B3)
133MHz
SDRAM Module
TM
RCC
Chipset
A Ports
(133MHz)
Address Line
Data Line, 72 bits
Control Signals
Control Signal
Data Line, 72 bits
Data Line, 72 bits
B Ports
Bus Switch
24:12 - PI3B16226
32:16 - PI3B16234
TM
