NO_ Input Voltage

The maximum allowable input voltage for safe opera-

tion depends on whether supplies are on or off and on

the load configuration at the COM output. If COM is

referred to a voltage other than ground, but within the

supplies, VNO_ may range higher or lower than the

supplies, provided the absolute value of VNO_ -

VCOM_ is less than 40V. For example, if the load is

referred to +10V at COM_, then the NO_ voltage range

can be from +50V to -30V. As another example, if the

load is connected to -10V at COM_, the NO_ voltage

range is limited to -50V to +30V.

If the supplies are ±15V and COM is referenced to

ground through a load, the maximum NO_ voltage is

±36V. If the supplies are off and the COM output is ref-

erenced to ground, the maximum NO_ voltage is ±40V.

Normal Operation

Two comparators continuously compare the voltage on

the NO_ pin with V+ and V- supply voltages. When the

signal on NO_ is between V+ and V-, the multiplexer

behaves normally, with FETs N1 and P1 turning on and

off in response to A_ signals (Figure 1). The parallel

combination of N1 and P1 forms a low-value resistor

between NO_ and COM_ so that signals pass equally

well in either direction.

Positive Fault Condition

When the signal on NO_ exceeds V+ by about 150mV,

the positive fault comparator output goes high, turning

off FETs N1 and P1 (Figure 1). This makes the NO_ pin

high impedance regardless of the switch state. If the

switch state is “off,” all FETs turn off, and both NO_ and

COM_ are high impedance. If the switch state is “on,”

FET P2 turns on, clamping COM_ to V+.

Negative Fault Condition

When the signal on NO_ goes about 150mV below V-,

the negative fault comparator output goes high, turning

off FETs N1 and P1 (Figure 1). This makes the NO pin

high impedance regardless of the switch state. If the

switch state is “off,” all FETs turn off, and both NO_ and

COM_ are high impedance. If the switch state is “on,”

FET N2 turns on, clamping COM_ to V-.

Fault-Protected, High-Voltage,

Single 4-to-1/Dual 2-to-1 Multiplexers

10

______________________________________________________________________________________

NORMALLY OPEN SWITCH CONSTRUCTION

COM_

P2

MAX4534

MAX4535

P1

N1

ON

LOW

FAULT

HIGH

FAULT

V+

NO_

A_

GND

ESD DIODE

V-

N2

Figure 1. Functional Diagram