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ADG431 Schematic ( PDF Datasheet ) - Analog Devices

Teilenummer ADG431
Beschreibung LC2MOS Precision Quad SPST Switches
Hersteller Analog Devices
Logo Analog Devices Logo 




Gesamt 8 Seiten
ADG431 Datasheet, Funktion
a
LC2MOS
Precision Quad SPST Switches
ADG431/ADG432/ADG433
FEATURES
44 V Supply Maximum Ratings
؎15 V Analog Signal Range
Low On Resistance (<24 )
Ultralow Power Dissipation (3.9 W)
Low Leakage (<0.25 nA)
Fast Switching Times
tON <165 ns
tOFF <130 ns
Break-Before-Make Switching Action
TTL/CMOS Compatible
Plug-in Replacement for DG411/DG412/DG413
APPLICATIONS
Audio and Video Switching
Automatic Test Equipment
Precision Data Acquisition
Battery Powered Systems
Sample Hold Systems
Communication Systems
GENERAL DESCRIPTION
The ADG431, ADG432 and ADG433 are monolithic CMOS
devices comprising four independently selectable switches. They
are designed on an enhanced LC2MOS process which provides
low power dissipation yet gives high switching speed and low on
resistance.
The on resistance profile is very flat over the full analog input
range ensuring excellent linearity and low distortion when
switching audio signals. Fast switching speed coupled with high
signal bandwidth also make the parts suitable for video signal
switching. CMOS construction ensures ultralow power dissipa-
tion making the parts ideally suited for portable and battery
powered instruments.
The ADG431, ADG432 and ADG433 contain four indepen-
dent SPST switches. The ADG431 and ADG432 differ only in
that the digital control logic is inverted. The ADG431 switches
are turned on with a logic low on the appropriate control input,
while a logic high is required for the ADG432. The ADG433
has two switches with digital control logic similar to that of the
ADG431 while the logic is inverted on the other two switches.
Each switch conducts equally well in both directions when ON
and has an input signal range which extends to the supplies. In
the OFF condition, signal levels up to the supplies are blocked.
All switches exhibit break before make switching action for use
in multiplexer applications. Inherent in the design is low charge
injection for minimum transients when switching the digital inputs.
FUNCTIONAL BLOCK DIAGRAMS
IN1
IN2
ADG431
IN3
IN4
S1
IN1
D1
S2
IN2
D2
S3 ADG432
IN3
D3
S4
IN4
D4
IN1
IN2
ADG433
IN3
IN4
S1
D1
S2
D2
S3
D3
S4
D4
SWITCHES SHOWN FOR A LOGIC "1" INPUT
S1
D1
S2
D2
S3
D3
S4
D4
PRODUCT HIGHLIGHTS
1. Extended Signal Range
The ADG431, ADG432 and ADG433 are fabricated on an
enhanced LC2MOS process giving an increased signal range
which extends fully to the supply rails.
2. Ultralow Power Dissipation
3. Low RON
4. Break-Before-Make Switching
This prevents channel shorting when the switches are config-
ured as a multiplexer.
5. Single Supply Operation
For applications where the analog signal is unipolar, the
ADG431, ADG432 and ADG433 can be operated from a
single rail power supply. The parts are fully specified with a
single +12 V power supply and will remain functional with
single supplies as low as +5 V.
REV. B
Information furnished by Analog Devices is believed to be accurate and
reliable. However, no responsibility is assumed by Analog Devices for its
use, nor for any infringements of patents or other rights of third parties
which may result from its use. No license is granted by implication or
otherwise under any patent or patent rights of Analog Devices.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781/329-4700 World Wide Web Site: http://www.analog.com
Fax: 781/326-8703
© Analog Devices, Inc., 1998






ADG431 Datasheet, Funktion
ADG431/ADG432/ADG433
120
VDD = +15V
VSS = –15V
VL = +5V
100
80
60
40
100
1k 10k 100k 1M 10M
FREQUENCY – Hz
Figure 7. Off Isolation vs. Frequency
110
VDD = +15V
VSS = –15V
100 VL = +5V
90
80
70
60
100
1k 10k 100k
FREQUENCY – Hz
1M
Figure 8. Crosstalk vs. Frequency
10M
TRENCH ISOLATION
In the ADG431A, ADG432A and ADG433A, an insulating
oxide layer (trench) is placed between the NMOS and PMOS
transistors of each CMOS switch. Parasitic junctions, which
occur between the transistors in junction isolated switches, are
eliminated, the result being a completely latch-up proof switch.
In junction isolation, the N and P wells of the PMOS and
NMOS transistors from a diode that is reverse-biased under
normal operation. However, during overvoltage conditions, this
diode becomes forward biased. A silicon-controlled rectifier
(SCR) type circuit is formed by the two transistors causing a
significant amplification of the current which, in turn, leads to
latch up. With trench isolation, this diode is removed, the result
being a latch-up proof switch.
VS VG VD
VS VG VD
T
R
P+ P-CHANNEL P+
T
R
N+ N-CHANNEL N+
T
R
EEE
NNN
C
H
N
C
H
P
C
H
BURIED OXIDE LAYER
SUBSTRATE (BACKGATE)
Figure 9. Trench Isolation
APPLICATION
Figure 10 illustrates a precise, fast sample-and-hold circuit. An
AD845 is used as the input buffer while the output operational
amplifier is an AD711. During the track mode, SW1 is closed
and the output VOUT follows the input signal VIN. In the hold
mode, SW1 is opened and the signal is held by the hold capaci-
tor CH.
Due to switch and capacitor leakage, the voltage on the hold
capacitor will decrease with time. The ADG431/ADG432/
ADG433 minimizes this droop due to its low leakage specifica-
tions. The droop rate is further minimized by the use of a poly-
styrene hold capacitor. The droop rate for the circuit shown is
typically 30 µV/µs.
A second switch SW2, which operates in parallel with SW1, is
included in this circuit to reduce pedestal error. Since both
switches will be at the same potential, they will have a differen-
tial effect on the op amp AD711 which will minimize charge
injection effects. Pedestal error is also reduced by the compensa-
tion network RC and CC. This compensation network also
reduces the hold time glitch while optimizing the acquisition
time. Using the illustrated op amps and component values, the
pedestal error has a maximum value of 5 mV over the ± 10 V
input range. Both the acquisition and settling times are 850 ns.
+15V
VIN
AD845
–15V
+15V +5V
SW2
S
SW1
S
D
D
ADG431
ADG432
ADG433
2200pF
+15V
RC
75
CC
1000pF
CH
2200pF
AD711
–15V
VOUT
–15V
Figure 10. Fast, Accurate Sample-and-Hold
–6– REV. B

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