Datasheet

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      
SCDS140 − OCTOBER 2003
2
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
description/ordering information (continued)
The SN74CBT6845C is an 8-bit bus switch with a single output-enable (OE) input. When OE is low, the 8-bit
bus switch is ON, and the A port is connected to the B port, allowing bidirectional data flow between ports. When
OE
is high, the 8-bit bus switch is OFF, and a high-impedance state exists between the A and B ports. The B
port is precharged to BIASV through the equivalent of a 10-kΩ resistor when OE
is high, or if the device is
powered down (V
CC
= 0 V).
During insertion (or removal) of a card into (or from) an active bus, the card’s output voltage may be close to
GND. When the connector pins make contact, the card’s parasitic capacitance tries to force the bus signal to
GND, creating a possible glitch on the active bus. This glitching effect can be reduced by using a bus switch
with precharged bias voltage (BIASV) of the bus switch equal to the input threshold voltage level of the receivers
on the active bus. This method will ensure that any glitch produced by insertion (or removal) of the card will not
cross the input threshold region of the receivers on the active bus, minimizing the effects of live-insertion noise.
This device is fully specified for partial-power-down applications using I
off
. The I
off
feature ensures that
damaging current will not 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.
ORDERING INFORMATION
T
A
PACKAGE
†
ORDERABLE
PART NUMBER
TOP-SIDE
MARKING
QFN − RGY Tape and reel SN74CBT6845CRGYR CT6845C
SOIC − DW
Tube SN74CBT6845CDW
CBT6845C
SOIC − DW
Tape and reel SN74CBT6845CDWR
CBT6845C
SSOP − DB
Tube SN74CBT6845CDB
CT6845C
−40°C to 85°C
SSOP − DB
Tape and reel SN74CBT6845CDBR
CT6845C
−40 C to 85 C
SSOP (QSOP) − DBQ Tape and reel SN74CBT6845CDBQR CBT6845C
TSSOP − PW
Tube SN74CBT6845CPW
CT6845C
TSSOP − PW
Tape and reel SN74CBT6845CPWR
CT6845C
TVSOP − DGV Tape and reel SN74CBT6845CDGVR CT6845C
†
Package drawings, standard packing quantities, thermal data, symbolization, and PCB design guidelines are
available at www.ti.com/sc/package.
FUNCTION TABLE
INPUT
INPUT/OUTPUT
FUNCTION
INPUT
OE
INPUT/OUTPUT
A
FUNCTION
L B A port = B port
H Z
Disconnect
B port = BIASV