2001 Fairchild Semiconductor Corporation
DS011997
www.fairchildsemi.com
February 1994
Revised March 2001
7
4
LCX646
Low V
o
lt
age
Oct
a
l T
r
a
n
sceiv
e
r/
R
e
gist
er wit
h
5V T
o
ler
a
nt In
puts and O
u
t
put
s
74LCX646
Low Voltage Octal Transceiver/Register
with 5V Tolerant Inputs and Outputs
General Description
The LCX646 consists of registered bus transceiver circuits,
D-type flip-flops, and control circuitry providing multiplexed
transmission of data directly from the input bus or from the
internal storage registers. Data on the A or B bus will be
loaded into the respective registers on the LOW-to-HIGH
transition of the appropriate pin (CPAB or CPBA) (see
Functional Description).
The LCX646 is designed for low voltage (2.5V or 3.3V) V
CC
applications with capability of interfacing to a 5V signal
environment.
The LCX646 is fabricated with an advanced CMOS tech-
nology to achieve high speed operation while maintaining
CMOS low power dissipation.
Features
s
5V tolerant inputs and outputs
s
2.3V
-
3.6V V
CC
specifications provided
s
7.0 ns t
PD
max (V
CC
=
3.3V), 10
A I
CC
max
s
Power down high impedance inputs and outputs
s
Supports live insertion/withdrawal (Note 1)
s
24 mA output drive (V
CC
=
3.0V)
s
Implements patented noise/EMI reduction circuitry
s
Latch-up performance exceeds 500 mA
s
ESD performance:
Human body model
>
2000V
Machine model
>
200V
Note 1: To ensure the high-impedance state during power up or down, OE
should be tied to V
CC
through a pull-up resistor: the minimum value or the
resistor is determined by the current-sourcing capability of the driver.
Ordering Code:
Devices also available in Tape and Reel. Specify by appending the suffix letter "X" to the ordering code.
Connection Diagram
Pin Descriptions
Order Number
Package Number
Package Description
74LCX646WM
M24B
24-Lead Small Outline Integrated Circuit (SOIC), JEDEC MS-013, 0.300 Wide
74LCX646MSA
MSA24
24-Lead Shrink Small Outline Package (SSOP), EIAJ TYPE II, 5.3mm Wide
74LCX646MTC
MTC24
24-Lead Thin Shrink Small Outline Package (TSSOP), JEDEC MO-153, 4.4mm Wide
Pin Names
Description
A
0
A
7
Data Register A Inputs
Data Register A Outputs
B
0
B
7
Data Register B Inputs
Data Register B Outputs
CPAB, CPBA
Clock Pulse Inputs
SAB, SBA
Transmit/Receive Inputs
OE
Output Enable Input
DIR
Direction Control Input
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2
74LCX646
Logic Symbols
IEEE/IEC
Truth Table
(Note 2)
H
=
HIGH Voltage Level
L
=
LOW Voltage Level
X
=
Immaterial
=
LOW-to-HIGH Transition
Note 2: The data output functions may be enabled or disabled by various signals at the OE and DIR inputs. Data input functions are always enabled;
i.e., data at the bus pins will be stored on every LOW-to-HIGH transition of the appropriate clock inputs.
Inputs
Data I/O
Function
OE
DIR
CPAB CPBA
SAB
SBA
A
0
A
7
B
0
B
7
H
X
H or L H or L
X
X
Isolation
H
X
X
X
X
Input
Input
Clock A
n
Data into A Register
H
X
X
X
X
Clock B
n
Data into B Register
L
H
X
X
L
X
A
n
to B
n
--Real Time (Transparent Mode)
L
H
X
L
X
Input
Output
Clock A
n
Data into A Register
L
H
H or L
X
H
X
A Register to B
n
(Stored Mode)
L
H
X
H
X
Clock A
n
Data into A Register and Output to B
n
L
L
X
X
X
L
B
n
to A
n
--Real Time (Transparent Mode)
L
L
X
X
L
Output
Input
Clock B
n
Data into B Register
L
L
X
H or L
X
H
B Register to A
n
(Stored Mode)
L
L
X
X
H
Clock B
n
Data into B Register and Output to A
n
3
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7
4
LCX646
Functional Description
In the transceiver mode, data present at the HIGH imped-
ance port may be stored in either the A or B register or
both. The select (SAB, SBA) controls can multiplex stored
and real-time. The examples shown below demonstrate the
four fundamental bus-management functions that can be
performed.
The direction control (DIR) determines which bus will
receive data when OE is LOW. In the isolation mode (OE
HIGH), A data may be stored in one register and/or B data
may be stored in the other register. When an output func-
tion is disabled, the input function is still enabled and may
be used to store and transmit data. Only one of the two
busses, A or B, may be driven at a time.
Real-Time Transfer
Bus B to Bus A
Real-Time Transfer
Bus A to Bus B
Transfer Storage
Data to A or B
Storage
OE DIR CPAB CPBA SAB SBA
L
L
X
X
X
L
OE
DIR
CPAB CPBA
SAB
SBA
L
H
X
X
L
X
OE
DIR
CPAB CPBA
SAB
SBA
L
L
X
H or L
X
H
L
H
H or L
X
H
X
OE
DIR
CPAB CPBA
SAB
SBA
L
H
X
L
X
L
L
X
X
L
H
X
X
X
X
H
X
X
X
X
5
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7
4
LCX646
Absolute Maximum Ratings
(Note 3)
Recommended Operating Conditions
(Note 5)
Note 3: The Absolute Maximum Ratings are those values beyond which the safety of the device cannot be guaranteed. The device should not be operated
at these limits. The parametric values defined in the Electrical Characteristics tables are not guaranteed at the Absolute Maximum Ratings. The "Recom-
mended Operating Conditions" table will define the conditions for actual device operation.
Note 4: I
O
Absolute Maximum Rating must be observed.
Note 5: Unused inputs or I/Os must be held HIGH or LOW. They may not float.
DC Electrical Characteristics
Symbol
Parameter
Value
Conditions
Units
V
CC
Supply Voltage
-
0.5 to
+
7.0
V
V
I
DC Input Voltage
-
0.5 to
+
7.0
V
V
O
DC Output Voltage
-
0.5 to
+
7.0
Output in 3-STATE
V
-
0.5 to V
CC
+
0.5
Output in HIGH or LOW State (Note 4)
I
IK
DC Input Diode Current
-
50
V
I
<
GND
mA
I
OK
DC Output Diode Current
-
50
V
O
<
GND
mA
+
50
V
O
>
V
CC
I
O
DC Output Source/Sink Current
50
mA
I
CC
DC Supply Current per Supply Pin
100
mA
I
GND
DC Ground Current per Ground Pin
100
mA
T
STG
Storage Temperature
-
65 to
+
150
C
Symbol
Parameter
Min
Max
Units
V
CC
Supply Voltage
Operating
2.0
3.6
V
Data Retention
1.5
3.6
V
I
Input Voltage
0
5.5
V
V
O
Output Voltage
HIGH or LOW State
0
V
CC
V
3-STATE
0
5.5
I
OH
/I
OL
Output Current
V
CC
=
3.0V
-
3.6V
24
mA
V
CC
=
2.7V
-
3.0V
12
V
CC
=
2.3V
-
2.7V
8
T
A
Free-Air Operating Temperature
-
40
85
C
t/
V
Input Edge Rate, V
IN
=
0.8V
-
2.0V, V
CC
=
3.0V
0
10
ns/V
Symbol
Parameter
Conditions
V
CC
T
A
=
-
40
C to
+
85
C
Units
(V)
Min
Max
V
IH
HIGH Level Input Voltage
2.3
-
2.7
1.7
V
2.7
-
3.6
2.0
V
IL
LOW Level Input Voltage
2.3
-
2.7
0.7
V
2.7
-
3.6
0.8
V
OH
HIGH Level Output Voltage
I
OH
=
-
100
A
2.3
-
3.6
V
CC
-
0.2
V
I
OH
=
-
8 mA
2.3
1.8
I
OH
=
-
12 mA
2.7
2.2
I
OH
=
-
18 mA
3.0
2.4
I
OH
=
-
24 mA
3.0
2.2
V
OL
LOW Level Output Voltage
I
OL
=
100
A
2.3
-
3.6
0.2
V
I
OL
=
8 mA
2.3
0.6
I
OL
=
12 mA
2.7
0.4
I
OL
=
16 mA
3.0
0.4
I
OL
=
24 mA
3.0
0.55
I
I
Input Leakage Current
0
V
I
5.5V
2.3
-
3.6
5.0
A
I
OZ
3-STATE I/O Leakage
0
V
O
5.5V
2.3
-
3.6
5.0
A
V
I
=
V
IH
or V
IL
I
OFF
Power-Off Leakage Current
V
I
or V
O
=
5.5V
0
10
A
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