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Pericom Semiconductor |
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Application Brief AB-32
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Application Brief AB321122334455667788990011223344556677889900112233445566778899001122112233445566778899001122334455667788990011223344556677889900112211223344556677889900112233445566778899001122334455667788990011221122334455667788990011223344556677889900112233445566778899001122112233445566778899001122
3.3V Bus Switches for PC100TM/PC133TM
DIMM Switching
by Refugio Jones August 18, 1999
Highlights
In high-end PC and server applications, the Pentium IITM 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.
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.
RCCTM
Chipset
Data Line, 72 bits
Control Signals
Control Signal
A Ports
Address Line
(133MHz)
Bus Switch
24:12 - PI3B16226
32:16 - PI3B16234
Intel
Pentium IITM
Processor
B Ports
Data Line, 72 bits
Data Line, 72 bits
(B0)
133MHz
SDRAM Module
(B1)
133MHz
SDRAM Module
(B2)
133MHz
SDRAM Module
(B3)
133MHz
SDRAM Module
Figure 1. Using Pericom’s 3.3V Bus Switch in DIMM Switching
1 09/16/99
Application Brief AB-32
12345678901234567890123456789012123456789012345678901234567890121234567890123456789012345678901212345678901234567890123456789012123456789012
1A 1B
1B
12A 12B
12B
SF
Figure 2. PI3B16226 Block Diagram
Pericom has recently introduced several bus switch products for low quiescent power (0.2µA typically) makes these products ide-
DIMM switching in computer, networking and multi-media applica- ally suited for notebook application. A detail of these products and
tions with configuration up to 32 bits. It should be noted that ultra- their compatibility to standard chipsets is shown in Figure 3.
Pericom
BusSwitch
PI3B16226
PI3B16234
PI5C16292
PI5C16225
PI5C16226
PI5C16234
Configuration
24:12 Mux/Demux
32:16 Mux/Demux
24:12 Mux/Demux
24:12 Mux/Demux
24:12 Mux/Demux
32:16 Mux/Demux
Generic Chipset
PC133 & RCC
PC133 & RCC
PC100TM & 440BXTM / 440GXTM
PC133 & RCC
PC133 & RCC
PC133 & RCC
Pin Count
40
56
56
56
40
56
Figure 3. Pericom’s DIMM Switching Bus Switch Selection Guide
Packages
BQSOP
TSSOP
TSSOP
TSSOP
BQSOP
TSSOP
2 09/16/99
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