The IDT logo is a registered trademark of Integrated Device Technology, Inc.
FEATURES:
Bus switches provide zero delay paths
Extended commercial range of 40
C to +85
C
Low switch on-resistance:
FST3xxx 5
TTL-compatible input and output levels
ESD > 2000V per MIL-STD-883, Method 3015;
> 200V using machine model (C = 200pF, R = 0)
Available in QSOP and SOIC
COMMERCIAL TEMPERATURE RANGE
AUGUST 1996
1996 Integrated Device Technology, Inc.
DSC-4668/-
1
IDT74FST3125
4-BIT BUS SWITCH
capability. Thus they generate little or no noise of their own
while providing a low resistance path for an external driver.
These devices connect input and output ports through an n-
channel FET. When the gate-to-source junction of this FET is
adequately forward-biased the device conducts and the resis-
tance between input and output ports is small. Without
adequate bias on the gate-to-source junction of the FET, the
FET is turned off, therefore with no V
CC
applied, the device
has hot insertion capability.
The low on-resistance and simplicity of the connection
between input and output ports reduces the delay in this path
to close to zero.
The FST3125 is a 4-bit TTL-compatible bus switch. The
xOE pins provide individual enable control for each of the four
bits.
DESCRIPTION:
The FST3125 belong to IDT's family of Bus switches. Bus
switch devices perform the function of connecting or isolating
two ports without providing any inherent current sink or source
1A
1Y
2A
2Y
3Y
4Y
3A
4A
4OE
2OE
1OE
3OE
FUNCTIONAL BLOCK DIAGRAM
PIN CONFIGURATION
PIN DESCRIPTION
3471 drw 01
3471 drw 02
3471 tbl 01
Pin Names
I/O
Description
1A
-
4A
I/O
Bus A
1Y
-
4Y
I/O
Bus B
NC
--
No Connect
1
OE
, 4
OE
I
Bus Switch Enable (Active LOW)
Integrated Device Technology, Inc.
5
6
7
8
1
2
3
4
14
13
12
11
10
9
1A
1Y
NC
2A
2Y
GND
4A
4Y
3A
3Y
NC
Vcc
1OE
SO16-1
SO16-7
15
16
2OE
3OE
4OE
SOIC/QSOP
TOP VIEW
2
IDT74FST3125
4-BIT BUS SWITCH
COMMERCIAL TEMPERATURE RANGE
FUNCTION TABLE
OE
OE
Y
Description
H
Hi-Z
Disconnect
L
A
Connect
3471 tbl 03
DC ELECTRICAL CHARACTERISTICS OVER OPERATING RANGE
Following Conditions Apply Unless Otherwise Specified:
Commercial: T
A
= 40
C to +85
C, V
CC
= 5.0V
5%
ABSOLUTE MAXIMUM RATINGS
(1)
Symbol
Description
Max.
Unit
V
TERM(2)
Terminal Voltage with Respect
to GND
0.5 to +7.0
V
T
STG
Storage Temperature
65 to +150
C
I
OUT
Maximum Continuous Channel
Current
128
mA
NOTES:
1. Stresses greater than those listed under ABSOLUTE MAXIMUM RAT-
INGS may cause permanent damage to the device. This is a stress rating
only and functional operation of the device at these or any other conditions
above those indicated in the operational sections of this specification is not
implied. Exposure to absolute maximum rating condiitions for extended
periods may affect reliability.
2. V
CC
, Control and Switch terminals.
3471 tbl 02
Symbol
Parameter
Conditions
(2)
Typ. Unit
C
IN
Control Input Capacitance
4
pF
C
I/O
Switch Input/Output
Capacitance
Switch Off
pF
3471 tbl 04
CAPACITANCE
(1)
NOTES:
1. Capacitance is characterized but not tested
2. T
A
= 25
C, f = 1MHz, VI
N
= 0V, V
OUT
= 0V
Symbol
Parameter
Test Conditions
(1)
Min.
Typ.
(2)
Max.
Unit
V
IH
Input HIGH Voltage
Guaranteed Logic HIGH for Control Inputs
2.0
--
--
V
V
IL
Input LOW Voltage
Guaranteed Logic LOW for Control Inputs
--
--
0.8
V
I
I H
Input HIGH Current
V
CC
= Max.
V
I
= V
CC
--
--
1
A
I
I L
Input LOW Voltage
V
I
= GND
--
--
1
I
OZH
High Impedance Output Current
V
CC
= Max.
V
O
= V
CC
--
--
1
A
I
OZL
(3-State Output pins)
V
O
= GND
--
--
1
I
OS
Short Circuit Current
V
CC
= Max., V
O
= GND
(3)
--
300
--
mA
V
IK
Clamp Diode Voltage
V
CC
= Min., I
IN
= 18mA
--
0.7
1.2
V
R
ON
Switch On Resistance
(4)
V
CC
= Min. V
IN
= 0.0V
--
5
7
I
ON
= 30mA
V
CC
= Min. V
IN
= 2.4V
--
10
15
I
ON
= 15mA
I
OFF
Input/Output Power Off Leakage
V
CC
= 0V, V
IN
or V
O
4.5V
--
--
1
A
I
CC
Quiescent Power Supply Current
V
CC
= Max., V
IN
= GND or V
CC
--
0.1
3
A
NOTES:
1. For conditions shown as Max. or Min., use appropriate value specified under Electrical Characteristics for the applicable device type.
2. Typical values are at VCC = 5.0V, +25
C ambient.
3. Not more than one output should be tested at one time. Duration of the test should not exceed one second.
4. Measured by voltage drop between ports at indicated current through the switch.
3471 tbl 05
IDT74FST3125
4-BIT BUS SWITCH
COMMERCIAL TEMPERATURE RANGE
3
POWER SUPPLY CHARACTERISTICS
Symbol
Parameter
Test Conditions
(1)
Min.
Typ.
(2)
Max.
Unit
I
CC
Quiescent Power Supply Current
TTL Inputs HIGH
V
CC
= Max.
V
IN
= 3.4V
(3)
--
0.5
1.5
mA
I
CCD
Dynamic Power Supply
Current
(4)
V
CC
= Max.
Outputs Open
V
IN
= V
CC
V
IN
= GND
--
30
40
A/
MHz/
Enable Pin Toggling
50% Duty Cycle
Switch
I
C
Total Power Supply Current
(6)
V
CC
= Max.
Outputs Open
Enable Pin Toggling
V
IN
= V
CC
V
IN
= GND
--
1.2
1.6
mA
(4 Switches Toggling)
fi = 10MHz
50% Duty Cycle
V
IN
= 3.4
V
IN
= GND
--
1.5
2.4
NOTES:
1. For conditions shown as Max. or Min., use appropriate value specified under Electrical Characteristics for the applicable device type.
2. Typical values are at V
CC
= 5.0V, +25
C ambient.
3. Per TTL driven input (V
IN
= 3.4V). All other inputs at V
CC
or GND.
4. This parameter is not directly testable, but is derived for use in Total Power Supply Calculations.
5. Values for these conditions are examples of the I
CC
formula. These limits are guaranteed but not tested.
6. I
C
= I
QUIESCENT
+ I
INPUTS
+ I
DYNAMIC
I
C
= I
CC
+
I
CC
D
H
N
T
+ I
CCD
(f
i
N)
I
CC
= Quiescent Current
I
CC
= Power Supply Current for a TTL High Input (V
IN
= 3.4V)
D
H
= Duty Cycle for TTL Inputs High
N
T
= Number of TTL Inputs at D
H
I
CCD
= Dynamic Current Caused by an Input Transition Pair (HLH or LHL)
f
i
= Input Frequency
N = Number of Switches Toggling at fi
All currents are in milliamps and all frequencies are in megahertz.
SWITCHING CHARACTERISTICS OVER OPERATING RANGE
Following Conditions Apply Unless Otherwise Specified:
Commercial: T
A
= 40
C to +85
C, V
CC
= 5.0V
5%
3471 tbl 06
Symbol
Description
Condition
(1)
Min.
(2)
Typ.
Max.
Unit
t
PLH
t
PHL
Data Propagation Delay
A to Y, Y to A
(3,4)
C
L
= 50pF
R
L
= 500
--
--
0.25
ns
t
PZH
t
PZL
Switch Turn on Delay
OE
to A, Y
1.5
--
6.5
ns
t
PHZ
t
PLZ
Switch Turn off Delay
OE
to A, Y
(3)
1.5
--
5.5
ns
|Q
CI
|
Charge Injection
(5,6)
--
1.5
--
pC
NOTES:
1. See test circuit and waveforms.
2. Minimum limits guaranteed but not tested.
3. This parameter is guaranteed by design but not tested.
4. The bus switch contributes no propagation delay other than the RC delay of the on resistance of the switch and the load capacitance. The time constant
for the switch alone is of the order of 2.5ns for 50pF load. Since this time is constant and much smaller than the rise/fall times of typical driving signals,
it adds very little propagation delay to the system. Propagation delay on the bus switch when used in a system is determined by the driving circuit on the
driving side of the switch and its interaction with the load on the driven side.
5. Measured at switch turn off, load = 50 pF in parallel with 10M
scope probe, V
IN
= 0.0 volts.
6. Characterized parameter. Not 100% tested.
3471 tbl 07
4
IDT74FST3125
4-BIT BUS SWITCH
COMMERCIAL TEMPERATURE RANGE
TEST CIRCUITS AND WAVEFORMS
TEST CIRCUITS FOR ALL OUTPUTS
SWITCH POSITION
Pulse
Generator
R
T
D.U.T.
V
CC
V
IN
C
L
V
OUT
50pF
500
500
7.0V
3V
1.5V
0V
3V
1.5V
0V
3V
1.5V
0V
3V
1.5V
0V
DATA
INPUT
TIMING
INPUT
ASYNCHRONOUS CONTROL
PRESET
CLEAR
ETC.
SYNCHRONOUS CONTROL
t
SU
t
H
t
REM
t
SU
t
H
HIGH-LOW-HIGH
PULSE
LOW-HIGH-LOW
PULSE
t
W
1.5V
1.5V
SAME PHASE
INPUT TRANSITION
3V
1.5V
0V
1.5V
V
OH
t
PLH
OUTPUT
OPPOSITE PHASE
INPUT TRANSITION
3V
1.5V
0V
t
PLH
t
PHL
t
PHL
V
OL
CONTROL
INPUT
3V
1.5V
0V
3.5V
0V
OUTPUT
NORMALLY
LOW
OUTPUT
NORMALLY
HIGH
SWITCH
CLOSED
SWITCH
OPEN
V
OL
0.3V
0.3V
t
PLZ
t
PZL
t
PZH
t
PHZ
3.5V
0V
1.5V
1.5V
ENABLE
DISABLE
V
OH
PRESET
CLEAR
CLOCK ENABLE
ETC.
ENABLE AND DISABLE TIMES
PROPAGATION DELAY
PULSE WIDTH
SET-UP, HOLD AND RELEASE TIMES
Test
Switch
Disable Low
Enable Low
Closed
All Other Tests
Open
Open Drain
DEFINITIONS:
C
L
=
Load capacitance: includes jig and probe capacitance.
R
T
=
Termination resistance: should be equal to Z
OUT
of the Pulse
Generator.
NOTES:
1. Diagram shown for input Control Enable-LOW and input Control Disable-
HIGH
2. Pulse Generator for All Pulses: Rate
1.0MHz; t
F
2.5ns; t
R
2.5ns
3471 drw 03
3471 drw 04
3471 drw 05
3471 drw 06
3471 drw 07
3471 lnk 08
IDT74FST3125
4-BIT BUS SWITCH
COMMERCIAL TEMPERATURE RANGE
5
ORDERING INFORMATION
3471 drw 08
IDT XX
Temp. Range
XX
Device Type
X
Package
74
40
C to +85
C
SO
Q
3125
Small Outline IC (SO16-1)
Quarter-size Small Outline Package (SO16-7)
4-Bit Bus Switch
FST
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