Fault-Protected, High-Voltage

Signal-Line Protectors

8

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Two clamp circuits limit the output voltage to within the

supply voltages. When the power supplies are off, any

input voltage applied at IN turns off both N1 and P1,

and OUT is clamped to 0V.

Normal Operation

When power is applied, each protector acts as a resis-

tor in series with the signal path. Any voltage source on

the “input” side of the switch will be conducted through

the protector to the output (Figure 2).

When the output load is resistive, it draws current

through the protector. The internal resistance is typically

less than 100

Ω. High-impedance loads are relatively

unaffected by the presence of the MAX4506/MAX4507.

The protector’s path resistance is a function of the supply

voltage and the signal voltage (see

Typical Operating

Characteristics).

Fault Protection, Power Off

When power is off (i.e., V+ = V- = 0), the protector is a

virtual open circuit. With up to ±40V applied to the input

pin, the output pin will be 0V.

Fault Protection, Power On

A fault condition exists when the voltage on the IN_

exceeds either supply rail. This definition is valid when

power is on or off, as well as during all states while

power ramps up or down.

Applications Information

Supplying Power Through External ICs

The MAX4506/MAX4507 have low supply currents

(<250µA), which allows the supply pins to be driven by

other active circuitry instead of connected directly to

the power sources. In this configuration, the parts can

be used as driven fault-protected switches with V+ or

V- used as the control pins. For example, with the V-

pin grounded, the output of a CMOS gate can drive the

V+ pin to turn the device on and off. This can effectively

connect and disconnect three (MAX4506) or eight

(MAX4507) separate signal lines at once. Ensure that

the driving source(s) does not drive the V+ pin more

negative than the V- pin.

Figure 3 shows a simple turn-on delay that takes

advantage of the MAX4506’s low power consumption.

The two RC networks cause gradual application of

power to the MAX4506, which in turn applies the input

signals smoothly after the amplifier has stabilized. The

two diodes discharge the two capacitors rapidly when

the power turns off. Note that the IC used to supply

power to the MAX4506/MAX4507 must be able to sup-

ply enough current to maintain the load voltage at the

supply rail in a fault condition.

MAX4506

IN1

V-

V-

V+

V+

1

4

7

8

OUT1

Figure 2. Application Circuit

MAX4506

IN3

V-

-15V

V+

+15V

3

4

5

10

µF

10

µF

OUT3

IN2

26

OUT2

IN1

17

OUT1

8

100k

100k

OP AMP

Figure 3. Turn-On Delay