Fault-Protected, High-Voltage Single 8-to-1/
Dual 4-to-1 Multiplexers with Output Clamps
MAX4508/MAX4509
Pin Descriptions
MAX4508 (Single 8-to-1 Mux)
PIN
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
NAME
A0
EN
V-
NO1
NO2
NO3
NO4
COM
NO8
NO7
NO6
NO5
V+
GND
A2
A1
Mux Enable
Negative Supply Voltage
Channel Input 1
Channel Input 2
Channel Input 3
Channel Input 4
Analog Output
Channel Input 8
Channel Input 7
Channel Input 6
Channel Input 5
Positive Supply Voltage
Ground
Address Bit 2
Address Bit 1
FUNCTION
Address Bit 0
MAX4509 (Dual 4-to-1 Mux)
PIN
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
NAME
A0
EN
V-
NO1A
NO2A
NO3A
NO4A
COMA
COMB
NO4B
NO3B
NO2B
NO1B
V+
GND
A1
Mux Enable
Negative Supply Voltage
Channel Input 1A
Channel Input 2A
Channel Input 3A
Channel Input 4A
Mux Output A
Mux Output B
Channel Input 4B
Channel Input 3B
Channel Input 2B
Channel Input 1B
Positive Supply Voltage
Ground
Address Bit 1
FUNCTION
Address Bit 0
Truth Tables
MAX4508 (Single 8-to-1 Mux)
A2
x
0
0
0
0
1
1
1
1
A1
x
0
0
1
1
0
0
1
1
A0
x
0
1
0
1
0
1
0
1
EN
0
1
1
1
1
1
1
1
1
ON SWITCH
None
NO1
NO2
NO3
NO4
NO5
NO6
NO7
NO8
Detailed Description
Traditional fault-protected multiplexers are constructed
with three series FET switches. This produces good off
protection, but limits the switches input voltage range
to as much as 3V below the supply rails, reducing its
usable dynamic range. As the voltage on one side of
the switch approaches within about 3V of either supply
rail (a fault condition), the switch impedance increases,
limiting the output signal range to approximately 3V
less than the appropriate polarity supply voltage.
The MAX4508/MAX4509 differ considerably from tradi-
tional fault-protected multiplexers, offering several
advantages. First, they are constructed with two paral-
lel FETs, allowing very low resistance when the switch
is on. Second, they allow signals on the NO_ pins that
are within or beyond the supply rails to be passed
through the switch to the COM terminal. This allows rail-
to-rail signal operation. Third, when a signal V
NO_
exceeds the supply rails (i.e., a fault condition), the
voltage on COM_ is limited to the supply rails.
Operation is identical for both fault polarities.
MAX4509 (Dual 4-to-1 Mux)
A1
x
0
0
1
1
A0
x
0
1
0
1
EN
0
1
1
1
1
COMA
None
NO1A
NO2A
NO3A
NO4A
COMB
None
NO1B
NO2B
NO3B
NO4B
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