MAX4508/MAX4509
Fault-Protected, High-Voltage Single 8-to-1/
Dual 4-to-1 Multiplexers with Output Clamps
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.
Pin Descriptions
Truth Tables
NAME FUNCTION
1 A0 Address Bit 0
2 EN Mux Enable
PIN
3 V- Negative Supply Voltage
4 NO1 Channel Input 1
8 COM Analog Output
7 NO4 Channel Input 4
6 NO3 Channel Input 3
5 NO2 Channel Input 2
12 NO5 Channel Input 5
11 NO6 Channel Input 6
10 NO7 Channel Input 7
9 NO8 Channel Input 8
13 V+ Positive Supply Voltage
14 GND Ground
15 A2 Address Bit 2
16 A1 Address Bit 1
MAX4508 (Single 8-to-1 Mux)
MAX4509 (Dual 4-to-1 Mux)
NAME FUNCTION
1 A0 Address Bit 0
2 EN Mux Enable
PIN
3 V- Negative Supply Voltage
4 NO1A Channel Input 1A
8 COMA Mux Output A
7 NO4A Channel Input 4A
6 NO3A Channel Input 3A
5 NO2A Channel Input 2A
13 NO1B Channel Input 1B
12 NO2B Channel Input 2B
11 NO3B Channel Input 3B
10 NO4B Channel Input 4B
9 COMB Mux Output B
14 V+ Positive Supply Voltage
15 GND Ground
16 A1 Address Bit 1
x x None
0 0 NO1
0 0 NO2
0 1 NO3
1 1 NO7
1 0 NO6
1 0 NO5
0 1 NO4
1 1 NO8
x
0
1
0
0
1
0
1
1
0
1
1
1
1
1
1
1
1
A1 ON SWITCHA2 A0 EN
MAX4508 (Single 8-to-1 Mux)
x None
0 NO1A
0 NO2A
1 NO3A
1 NO4A
x
0
1
0
1
0
1
1
1
1
A1 COMAA0 EN
MAX4509 (Dual 4-to-1 Mux)
None
NO1B
NO2B
NO3B
NO4B
COMB
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