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FSTU3125 4-Bit Bus Switch with
−2V
Undershoot Protection
June 2001
Revised August 2001
FSTU3125
4-Bit Bus Switch with
−
2V Undershoot Protection
General Description
The Fairchild Switch FSTU3125 provides four high-speed
CMOS TTL-compatible bus switches. The low On Resis-
tance of the switch allows inputs to be connected to out-
puts without adding propagation delay or generating
additional ground bounce noise. The A and B Ports are
protected against undershoot to support an extended
range to 2.0V below ground. Fairchild’s integrated Under-
shoot Hardened Circuit (UHC
) senses undershoot at the
I/O and responds by preventing voltage differentials from
developing and turning the switch on.
The device is organized as four 1-bit switches with sepa-
rate 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.
Features
s
Undershoot hardened to
−
2V (A and B Ports)
s
4
Ω
switch connection between two ports
s
Minimal propagation delay through the switch
s
Low l
CC
s
Zero bounce in flow-through mode
s
Control inputs compatible with TTL level
s
See application notes AN-5008 and AN-5021 for details
on undershoot
Ordering Code:
Order Number
FSTU3125M
FSTU3125QSC
FSTU3125MTC
Package Number
M14A
MQA16
MTC14
Package Description
14-Lead Small Outline Integrated Circuit (SOIC), JEDEC MS-012, 0.150" Narrow
16-Lead Quarter Size Outline Package (QSOP), JEDEC MO-137, 0.150" Wide
14-Lead Thin Shrink Small Outline Package (TSSOP), JEDEC MO-153, 4.4mm Wide
Devices also available in Tape and Reel. Specify by appending the suffix letter “X” to the ordering code.
Connection Diagrams
Pin Assignment for SOIC and TSSOP
Pin Descriptions
Pin Name
OE
1
, OE
2
, OE
3
, OE
4
1A, 2A, 3A, 4A
1B, 2B, 3B, 4B
NC
Description
Bus Switch Enables
Bus A
Bus B
Not Connected
Truth Table
Inputs
OE
Pin Assignment for QSOP
L
H
Inputs/Outputs
A,B
A
=
B
Z
© 2001 Fairchild Semiconductor Corporation
DS500449
www.fairchildsemi.com
FSTU3125
Logic Diagram
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2
FSTU3125
Absolute Maximum Ratings
(Note 1)
Supply Voltage (V
CC
)
DC Switch Voltage (V
S
)
DC Input Voltage (V
IN
)(Note 2)
DC Input Diode Current (l
IK
) V
IN
<
0V
DC Output (I
OUT
) Sink Current
DC V
CC
/GND Current (I
CC
/I
GND
)
Storage Temperature Range (T
STG
)
−
0.5V to
+
7.0V
−
2.0V to
+
7.0V
−
0.5V to
+
7.0V
−
50 mA
128 mA
Recommended Operating
Conditions
(Note 3)
Power Supply Operating (V
CC
)
Input Voltage (V
IN
)
Output Voltage (V
OUT
)
Input Rise and Fall Time (t
r
, t
f
)
Switch Control Input
Switch I/O
Free Air Operating Temperature (T
A
)
0 ns/V to 5 ns/V
0 ns/V to DC
4.0V to 5.5V
0V to 5.5V
0V to 5.5V
+
/
−
100 mA
−
65
°
C to
+
150
°
C
−
40
°
C to
+
85
°
C
Note 1:
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 rating.
The “Recommended Operating Conditions” table will define the conditions
for actual device operation.
Note 2:
The input and output negative voltage ratings may be exceeded if
the input and output diode current ratings are observed.
Note 3:
Unused control inputs must be held HIGH or LOW. They may not
float.
DC Electrical Characteristics
Symbol
Parameter
V
CC
(V)
4.5
4.0–5.5
4.0–5.5
5.5
0
I
OZ
R
ON
OFF-STATE Leakage Current
Switch On Resistance
(Note 5)
5.5
4.5
4.5
4.5
4.0
I
CC
∆I
CC
V
IKU
Quiescent Supply Current
Increase in I
CC
per Input
Voltage Undershoot
5.5
5.5
5.5
4
4
8
11
2.0
0.8
±1.0
10
±1.0
7
7
15
20
3
2.5
−2.0
T
A
= −40 °C
to
+85 °C
Min
Typ
(Note 4)
Max
−1.2
Units
Conditions
V
IK
V
IH
V
IL
I
I
Clamp Diode Voltage
HIGH Level Input Voltage
LOW Level Input Voltage
Input Leakage Current
V
V
V
µA
µA
Ω
Ω
Ω
Ω
µA
mA
V
I
IN
= −18
mA
0
≤
V
IN
≤
5.5V
V
IN
=
5.5V
0
≤
A, B
≤
V
CC
V
IN
=
0V, I
IN
=
64 mA
V
IN
=
0V, I
IN
=
30 mA
V
IN
=
2.4V, I
IN
=
15 mA
V
IN
=
2.4V, I
IN
=
15 mA
V
IN
=
V
CC
or GND,
I
OUT
=
0
One input at 3.4V.
Other inputs at V
CC
or GND
0.0 mA
≥
I
IN
≥ −50
mA
OE
=
5.5V
Note 4:
Typical values are at V
CC
=
5.0V and T
A
= +25°C
Note 5:
Measured by the voltage drop between A and B pins at the indicated current through the switch. On Resistance is determined by the lower of the
voltages on the two (A or B) pins.
3
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FSTU3125
AC Electrical Characteristics
T
A
= −40 °C
to
+85 °C,
C
L
=
50pF, RU
=
RD
=
500Ω
Symbol
Parameter
V
CC
=
4.5 – 5.5V
Min
t
PHL
, t
PLH
t
PZH
, t
PZL
t
PHZ
, t
PLZ
Propagation Delay Bus to Bus (Note 6)
Output Enable Time
Output Disable Time
1.0
1.5
Max
0.25
6.1
6.4
V
CC
=
4.0V
Min
Max
0.25
6.0
6.6
ns
ns
ns
V
I
=
OPEN
V
I
=
7V for t
PZL
V
I
=
OPEN for t
PZH
V
I
=
7V for t
PLZ
V
I
=
OPEN for t
PHZ
Figures
2, 3
Figures
2, 3
Figures
2, 3
Units
Conditions
Figure
Number
Note 6:
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
Symbol
C
IN
C
I/O
(Note 7)
Parameter
Typ
3
5
Max
Units
pF
pF
Conditions
V
CC
=
5.0V
V
CC
, OE
=
5.0V
Control Pin Input Capacitance
Input/Output Capacitance
Note 7:
T
A
= +25°C,
f
=
1 MHz, Capacitance is characterized but not tested.
Undershoot Characteristic
(Note 8)
Symbol
V
OUTU
Parameter
Output Voltage During Undershoot
Min
2.5
Typ
V
OH
−
0.3
Max
Units
V
Figure 1
Conditions
Note 8:
This test is intended to characterize the device’s protective capabilities by maintaining output signal integrity during an input transient voltage
undershoot event.
FIGURE 1.
Device Test Conditions
Parameter
V
IN
R
1
- R
2
V
TRI
V
CC
Value
See Waveform
100K
11.0
5.5
Units
V
Ω
V
V
Transient
Input Voltage (V
IN
) Waveform
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4
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