Fault-Protected, High-Voltage

Single 8-to-1/Dual 4-to-1 Multiplexers

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-

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 SWITCH

A2

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

COMA

A0

EN

MAX4509 (Dual 4-to-1 Mux)

None

NO1B

NO2B

NO3B

NO4B

COMB

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