Datasheet

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DESCRIPTION/ORDERING INFORMATION (CONTINUED)
SN74CB3Q3257
4-BIT 1-OF-2 FET MULTIPLEXER/DEMULTIPLEXER
2.5-V/3.3-V LOW-VOLTAGE HIGH-BANDWIDTH BUS SWITCH
SCDS135A – SEPTEMBER 2003 – REVISED MARCH 2005
The SN74CB3Q3257 is a high-bandwidth FET bus switch utilizing a charge pump to elevate the gate voltage of
the pass transistor, providing a low and flat ON-state resistance (r
on
). The low and flat ON-state resistance allows
for minimal propagation delay and supports rail-to-rail switching on the data input/output (I/O) ports. The device
also features low data I/O capacitance to minimize capacitive loading and signal distortion on the data bus.
Specifically designed to support high-bandwidth applications, the SN74CB3Q3257 provides an optimized
interface solution ideally suited for broadband communications, networking, and data-intensive computing
systems.
The SN74CB3Q3257 is a 4-bit 1-of-2 high-speed FET multiplexer/demultiplexer with a single output-enable ( OE)
input. The select (S) input controls the data path of the multiplexer/demultiplexer. When OE is low, the
multiplexer/demultiplexer is enabled and the A port is connected to the B port, allowing bidirectional data flow
between ports. When OE is high, the multiplexer/demultiplexer is disabled and a high-impedance state exists
between the A and B ports.
This device is fully specified for partial-power-down applications using I
off
. The I
off
circuitry prevents damaging
current backflow through the device when it is powered down. The device has isolation during power off.
To ensure the high-impedance state during power up or power down, OE should be tied to V
CC
through a pullup
resistor; the minimum value of the resistor is determined by the current-sinking capability of the driver.
FUNCTION TABLE
INPUTS
INPUT/OUTPUT
FUNCTION
A
OE S
L L B1 A port = B1 port
L H B2 A port = B2 port
H X Z Disconnect
2