DG458 Datasheet, PDF (8/8 Pages) Vishay Siliconix – Fault-Protected Single 8-Ch/Differential 4-Ch Analog Multiplexers

DG458/459
Vishay Siliconix
TEST CIRCUITS
50 W
+15 V
EN
A₀
A₁
A₂
GND
V+
S₁
S₂ – S₈
DG458
D
V–
1 kW
–15 V
+5 V
V_O
35 pF
Enable
Input
Switch
Output
V_O
3V
0V
V_S
0V
t_ON(EN)
FIGURE 5. Enable Delay
50%
90%
t_OFF(EN
DETAILED DESCRIPTION
The Vishay Siliconix DG458 and DG459 multiplexers are fully
fault- and overvoltage-protected for continuous input voltages
up to "35 V whether or not voltage is applied to the power
supply pins (V+, V–). These multiplexers are built on a
high-voltage junction-isolated silicon-gate CMOS process.
Two n-channel and one p-channel MOSFETs are connected
in series to form each channel (Figure 1).
Within the normal analog signal range ("10 V), the r_DS(on)
variation as a function of analog signal voltage is comparable
to that of the classic parallel N-MOS and P-MOS switches.
–35 V
Overvoltage _S
Q₁ –35 V
DS
Q₂
DS
Q₃
+35 V
D ^Overvoltage
n-Channel
n-Channel
G
G
G
MOSFET
MOSFET
is Off
is On
p-Channel
MOSFET
is Off
(a) Overvoltage with Multiplexer Power Off
–15 V
+15 V
–15 V
When the analog signal approaches or exceeds either supply
rail, even for an on-channel, one of the three series MOSFETs
gets cut-off, providing inherent protection against
overvoltages even if the multiplexer power supply voltages are
lost. This protection is good up to the breakdown voltage of the
respective series MOSFETs. Under fault conditions only sub
microamp leakage currents can flow in or out of the multiplexer.
This not only provides protection for the multiplexer and
succeeding circuitry, but it allows normal, undisturbed
operation of all other channels. Additionally, in case of power
loss to the multiplexer, the loading caused on the transducers
and signal sources is insignificant, therefore redundant
multiplexers can be used on critical applications such as
telemetry and avionics.
www.vishay.com S FaxBack 408-970-5600
5-8
–35 V
Overvoltage
Q₁
Q₂
Q_{3 +35 V}
Overvoltage
n-Channel
MOSFET
is On
–15 V
p-Channel
MOSFET
is Off
+15 V
n-Channel
MOSFET
is Off
(b) Overvoltage with Multiplexer Power On
FIGURE 6. Overvoltage Protection
Document Number: 70064
S-52433—Rev. F, 06-Sep-99