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FST3244 — 8-Bit Bus Switch
March 2008
FST3244 — 8-Bit Bus Switch
Features
4Ω Switch Connection between Two Ports
Minimal Propagation Delay through the Switch
Low I
CC
Zero Bounce in Flow-through Mode
Control Inputs Compatible with TTL Level
Description
The FST3244 switch provides eight-bits of high-speed,
CMOS, TTL-compatible bus switching in a standard
’244 pin-out. The low on resistance allows inputs to be
connected to outputs without adding propagation delay
or generating additional ground bounce noise.
The device is organized as two four-bit switches with
separate /OE inputs. When /OE is LOW, the switch is
ON and port A is connected to port B. When /OE is
HIGH, the switch is OPEN and a high-impedance state
exists between the two ports.
Ordering Information
Operating
Part Number Temperature
Range
FST3244WMX
FST3244QSCX
FST3244MTCX
-40 to +85°C
-40 to +85°C
-40 to +85°C
Package
20-Lead, Small Outline Integrated Circuit (SOIC), JEDEC MS-013,
0.300-inch Wide
20-Lead Quarter Size Outline Package (QSOP), JEDEC MO-137,
0.150-inch Wide
Packing
Method
Tape and
Reel
Tape and
Reel
20-Lead Thin Shrink Small Outline Package (TSSOP), JEDEC MO-153, Tape and
4.4mm Wide
Reel
All packages are lead free per JEDEC: J-STD-020B standard.
The Fairchild switch family derives from and embodies Fairchild’s proven switch technology used for several years in its
74LVX3L384 (FST3384) bus switch product.
Logic Diagram
1A
0
2
18 1B
0
1A
3
8
12 1B
3
/OE
1
1
2A
0
11
9 2B
0
2A
3
17
3
2B
3
/OE
2
19
Figure 1. Logic Diagram
© 1997 Fairchild Semiconductor Corporation
FST3244 • Rev. 1.0.3
www.fairchildsemi.com
FST3244 — 8-Bit Bus Switch
Pin Configurations
/OE
1
1A
0
2B
3
1A
1
2B
2
1A
2
2B
1
1A
3
2B
0
GND
1
2
3
4
5
6
7
8
9
10
20
19
18
17
16
15
14
13
12
11
V
CC
/OE
2
1B
0
2A
3
1B
1
2A
2
1B
2
2A
1
1B
3
2A
0
Figure 2. Pin Configuration
Pin Descriptions
Pin #
1,19
2,4,6,8,11,13,15,17
3,5,7,9,12,14, 16,18
20
10
Pin Names
/OE
1
, /OE
2
1A, 2A
1B, 2B
V
CC
GND
Description
Bus Switch Enables
Bus A
Bus B
Supply Voltage
Ground
Truth Table
Inputs
/OE1
LOW
LOW
HIGH
HIGH
/OE
2
LOW
HIGH
LOW
HIGH
Inputs/Outputs
1A, 1B
1A = 1B
1A = 1B
High Impedance
High Impedance
2A, 2B
2A = 2B
High Impedance
2A = 2B
High Impedance
© 1997 Fairchild Semiconductor Corporation
FST3244 • Rev. 1.0.3
www.fairchildsemi.com
2
FST3244 — 8-Bit Bus Switch
Absolute Maximum Ratings
Stresses exceeding the absolute maximum ratings may damage the device. The device may not function or be
operable above the recommended operating conditions and stressing the parts to these levels is not recommended.
In addition, extended exposure to stresses above the recommended operating conditions may affect device
reliability. The absolute maximum ratings are stress ratings only.
Symbol
V
CC
V
S
V
IN
I
IK
I
OUT
I
CC
/ I
GND
T
STG
Supply Voltage
DC Switch Voltage
DC Input Voltage
(1)
Parameter
Min.
-0.5
-0.5
-0.5
Max.
7.0
7.0
7.0
-50
128
±100
Unit
V
V
V
mA
mA
mA
°C
DC Input Diode Current V
IN
<0V
DC Output Sink Current
DC V
CC
/ GND Current
Storage Temperature Range
-65
+150
Note:
1. The input and output negative voltage ratings may be exceeded if the input and output diode current ratings are
observed.
Recommended Operating Conditions
The Recommended Operating Conditions table defines the conditions for actual device operation. Recommended
operating conditions are specified to ensure optimal performance to the datasheet specifications. Fairchild does not
recommend exceeding them or designing to Absolute Maximum Ratings.
Symbol
V
CC
V
IN
V
OUT
t
r
, t
f
T
A
Input Voltage
Output Voltage
Parameter
Power Supply Operating
Min.
4.0
0
0
Max.
5.5
5.5
5.5
5
DC
+85
Unit
V
V
V
ns/V
°C
Input Rise and Fall Time
Switch Control Input
Switch I/O
(2)
0
0
-40
Operating Temperature, Free Air
Note:
2. Unused control inputs must be held HIGH or LOW. They may not float.
© 1997 Fairchild Semiconductor Corporation
FST3244 • Rev. 1.0.3
www.fairchildsemi.com
3
FST3244 — 8-Bit Bus Switch
DC Electrical Characteristics
Typical values are at V
CC
= 5.0V and T
A
= 25°C.
Symbol
V
IK
V
IH
V
IL
I
IN
I
OZ
Parameter
Clamp Diode Voltage
High-Level Input Voltage
Low-Level Input Voltage
Input Leakage Current
Off-state Leakage
Current
Conditions
I
IN
= -18mA
V
CC
(V)
4.5
4.0 to 5.5
4.0 to 5.5
T
A
=-40 to +85°C
Min.
2.0
0.8
±1.0
±1.0
4
4
8
11
7
7
15
20
3
2.5
Units
V
V
V
µA
µA
Typ.
Max.
-1.2
0
≤
V
IN
≤
5.5V
0
≤
A, B
≤
V
CC
V
IN
= 0V, I
IN
= 64mA
5.5
5.5
4.5
4.5
4.5
4.0
5.5
5.5
R
ON
Switch On Resistance
(3)
V
IN
= 0V, I
IN
= 30mA
V
IN
= 2.4V, I
IN
= 15mA
V
IN
= 2.4V, I
IN
= 15mA
V
IN
= V
CC
or GND,
I
OUT
= 0
One Input at 3.4V, Other
Inputs at V
CC
or GND
Ω
I
CC
ΔI
CC
Quiescent Supply Current
Increase in I
CC
per Input
µA
mA
Note:
3. Measured by the voltage drop between the A and B pins at the indicated current through the switch. On
resistance is determined by the lower of the voltages on the A or B pins.
AC Electrical Characteristics
T
A
= -40 to +85°C, C
L
= 50pF, and R
U
= R
D
= 500Ω.
Symbol
t
PHL
, t
PLH
Parameter
Propagation Delay
(4)
Bus-to Bus
Output Enable Time
Conditions
V
IN
= Open
V
IN
= 7V for t
PZL
V
IN
= Open for
t
PZH
V
IN
= 7V for t
PLZ
V
IN
= Open for
t
PHZ
V
CC
= 4.5 – 5.5V
Min.
Max.
0.25
V
CC
= 4.0V
Min.
Max.
0.25
Units
ns
Figure
Figure 3
Figure 4
Figure 3
Figure 4
Figure 3
Figure 4
t
PZH
,t
PZL
1.0
5.6
6.1
ns
t
PHZ
, t
PLZ
Output Disable Time
1.0
6.2
5.6
ns
Note:
4. This parameter is guaranteed by design, but is not tested. The bus switch contributes no propagation delay
other than the RC delay of the typical on resistance of the switch and the 50pF load capacitance when driven by
an ideal voltage source (zero output impedance).
Capacitance
T
A
= +25°C, f = 1MHz. Capacitance is characterized, but not tested.
Symbol
C
IN
C
I/O
Parameter
Control Pin Input Capacitance
Input/Output Capacitance
Conditions
V
CC
= 5.0V
V
CC
, /OE = 5.0V
Typ.
3
5
Units
pF
pF
© 1997 Fairchild Semiconductor Corporation
FST3244 • Rev. 1.0.3
www.fairchildsemi.com
4
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