NC_) and COM_ so that signals pass equally well in

either direction.

Positive Fault Condition

When the signal on NO_ (or NC_) exceeds V+ by about

150mV, the high-fault comparator output is high, turn-

ing off FETs N1 and P1. This makes the NO_ (or NC_)

input high impedance regardless of the switch state. If

the switch state is “off”, all FETs are turned off and both

NO_ (or NC_) and COM_ are high impedance. If the

switch state is “on”, clamp FET P2 is turned on, sourc-

ing current from V+ to COM_.

Negative Fault Condition

When the signal on NO_ (or NC_) exceeds V- by about

150mV, the low-fault comparator output is high, turning

off FETs N1 and P1. This makes the NO_ (or NC_) input

high impedance regardless of the switch state. If the

switch state is “off”, all FETs are turned off and both

NO_ (or NC_) and COM_ are high impedance. If the

switch state is “on”, clamp FET N2 is turned on, sinking

current from COM_ to V-.

Transient Fault Response and Recovery

When a fast rise-time or fall-time transient on NC_ or

NO_ exceeds V+ or V-, the output (COM_) follows the

input to the supply rail with only a few nanoseconds

delay. This delay is due to the switch on-resistance and

circuit capacitance to ground. When the input transient

returns to within the supply rails, however, there is a

700ns output recovery delay time. These values

depend on the COM_ output resistance and capaci-

tance, and are not production tested or guaranteed.

The delays are not dependent on the fault amplitude.

Higher COM_ output resistance and capacitance

increase recovery times.

COM_ and IN_ Pins

FETs N2 and P2 can source about ±15mA from V+ or

V- to COM_ in the fault condition. Ensure that if the

COM_ pin is connected to a low-resistance load, the

absolute maximum current rating of 40mA is never

exceeded both in normal and fault conditions.

Fault-Protected, Low-Voltage,

Quad SPST Analog Switches

______________________________________________________________________________________

11

V+

NO_

(NC_)

IN_

GND

V-

HIGH

FAULT

LOW

FAULT

ON

N1

P1

P2

COM_

N2

NC SWITCH

-ESD DIODE

NORMALLY OPEN SWITCH CONSTRUCTION

Figure 1. Block Diagram