HD74ALVCHR162269A
12-bit to 24-bit Registered Bus Exchanger with 3-state Outputs
ADE-205-125 (Z)
Preliminary
1st. Edition
January 1998
Description
The HD74ALVCHR162269A is a 12-bit to 24-bit registered bus exchanger, which is intended for
applications where two separate ports must be multiplexed onto, or de-multiplexed from, a single port. It is
particularly suitable as an interface between synchronous DRAMs and high speed microprocessors. The
HD74ALVCHR162269A is designed specifically for low voltage (from 2.5 V to 3.3 V) V
CC
operation.
Data is stored in the internal B-port registers on the low to high transition of the CLK input, provided that
the appropriate
CLKENA
inputs are low. Proper control of these inputs allows two sequential 12-bit words
to be presented as a 24-bit word on the B-port. For data transfer in the B to A direction, a single storage
register is provided. The
SEL
line selects 1B or 2B data for the A outputs.
The register on the A output permits the fastest possible data transfer, thus extending the period that the
data will be valid on the bus. The control pins are registered so that all transactions are synchronous with
the clock. Data flows is controlled by the active low output enables (OEA,
OEB1, OEB2).
Active bus-hold circuitry is provided to hold unused or floating data inputs at a valid logic level.
All outputs, which are designed to sink up to 12 mA, include 26
Ω
resistors to reduce overshoot and
undershoot.
Features
•
All outputs have equivalent 26
Ω
series resistors, so no external resistors are required.
•
Bus hold on data inputs eliminates the need for external pullup / pulldown resistors.
HD74ALVCHR162269A
Absolute Maximum Ratings
Item
Supply voltage range
Input voltage range
*1, 2
Symbol
V
CC
V
I
Ratings
–0.5 to 4.6
–0.5 to 4.6
–0.5 to V
CC
+0.5
Unit
V
V
Conditions
Except I/O ports
I/O ports
Output voltage range
*1, 2
Input clamp current
Output clamp current
Continuous output current
Continuous current through
Maximum power dissipation
at Ta = 55°C (in still air)
*3
Storage temperature range
Notes:
V
O
I
IK
I
OK
I
O
I
CC
/ I
GND
P
T
Tstg
–0.5 to V
CC
+0.5
–50
±50
±50
±100
1
–65 to 150
V
mA
mA
mA
mA
W
°C
TSSOP
V
I
< 0
V
O
< 0 or V
O
> V
CC
V
O
= 0 to V
CC
Stresses beyond those listed under “absolute maximum ratings” may cause permanent damage
to the device. These are stress ratings only, and functional operation of the device at these or
any other conditions beyond those indicated under “recommended operating conditions” is not
implied. Exposure to absolute-maximum-rated conditions for extended periods may affect
device reliability.
1. The input and output negative-voltage ratings may be exceeded if the input and output clamp
current ratings are observed.
2. This value is limited to 4.6 V maximum.
3. The maximum power dissipation is calculated using a junction temperature of 150°C and board
trace length of 750 mils.
Recommended Operating Conditions
Item
Supply voltage
Input voltage
Output voltage
High-level output current
Symbol
V
CC
V
I
V
O
I
OH
Min
2.3
0
0
—
—
—
Low-level output current
I
OL
—
—
—
Input transition rise or fall rate
Operating free-air temperature
∆t
/
∆v
Ta
0
–40
Max
3.6
V
CC
V
CC
–6
–8
–12
6
8
12
10
85
ns / V
°C
mA
Unit
V
V
V
mA
V
CC
= 2.3 V
V
CC
= 2.7 V
V
CC
= 3.0 V
V
CC
= 2.3 V
V
CC
= 2.7 V
V
CC
= 3.0 V
Conditions
Note: Unused or floating control pins must be held high or low.
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