Fault-Protected, High-Voltage

Signal-Line Protectors

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9

Protectors as Circuit Elements

Each of the protectors in a MAX4506/MAX4507 may be

used as a switched resistor, independent of the func-

tions of other elements in the same package. For exam-

ple, Figure 4 shows a MAX4506 with two of the

protectors used to protect the input of an op amp, and

the third element used to sequence a power supply.

Combining the circuits of Figures 3 and 4 produces a

delayed action on the switched +15V, as well as

smooth application of signals to the amplifier input.

Figure 5 shows MAX4506 used in front of a MAX338

unprotected 1-to-8 multiplexer. With supplies at ±15V,

0V while the inputs remain at ±25V.

Use the MAX4506 with a MAX338 to enhance voltage

handling capability (Figure 6). The MAX4506 and

MAX338 share almost equal voltage drops in this con-

figuration. For example, applying ±40V on pins 1 and 2

of the MAX4506 causes a voltage drop of about 26V

across pin 1 of the MAX4506 to pin 4 of the MAX338,

and a voltage drop of about 28V across pin 4 of the

MAX4506 to pin 8 of the MAX338. Similarly, there is a

26V drop from pin 2 of the MAX4506 to pin 5 of the

MAX338. The system’s performance exceeds each

individual part’s specification because of shared volt-

age drops.

Multiplexer and Demultiplexer

As shown in Figure 7, the MAX4506 can be used in

series with the output of a MAX4508 (1-to-8 multiplexer)

to act as multiplexer or demultiplexer. The MAX4508 is a

fault-protected multiplexer whose inputs are designed to

interface with harsh environments; however, its common

output is not fault protected if connected to outside sig-

nals (i.e., demultiplexer use). If the common output can

see fault signals, then it needs to be protected, and the

MAX4506 can be added to provide complete protection.

SWITCHED +15V

MAX4506

IN3

V-

-15V

V+

+15V

3

4

5

OUT3

IN2

26

OUT2

IN1

17

OUT1

8

P

100k

OP AMP

16

15

14

13

12

11

10

9

1

2

3

4

5

6

7

8

MAX338

-15V

1

2

8

7

+15V

-25V

+25V

3

4

6

5

MAX4506

A1

A2

GND

V+

NO5

NO6

NO7

NO9

EN

V-

OV

+5V

+3V

+15V

-5V

NO3

NO1

NO2

NO4

Figure 4. Power-Supply Sequencing

16

15

14

13

12

11

10

9

1

2

3

4

5

6

7

8

MAX4508

-15V

1

2

8

7

+15V

NEW COM

3

4

6

5

MAX4506

A1

A2

GND

V+

NO5

NO6

NO7

NO9

EN

V-

O

+5V

+3V

+15V

-15V

NO3

NO1

NO2

NO4

COM

Figure 7. Multiplexer and Demultiplexer Application Using

MAX4506 (or MAX4507) with MAX4508

+40V

-40V

10k

6

4

7

1

5

2

8

MAX338

MAX4506

Figure 6. SPDT Switch Application

Figure 5. Protecting a MAX338 with a MAX4506