Fault-Protected, High-Voltage,

Dual Analog Switches

10

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Transient Fault Response and Recovery

When a fast rising and falling transient on NO_ (or NC_)

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

(IN_) to the supply rail with only a few nanoseconds of

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

circuit capacitance to ground. However, when the input

transient returns to within the supply rails, there is a

longer output recovery time delay. For positive and

negative faults, the recovery time is typically 2.5µs.

These values depend on the COM_ output resistance

and capacitance, and are not production tested or

guaranteed. The delays are not dependent on the fault

amplitude. Higher COM_ output resistance and capaci-

tance increase recovery times.

Fault-Protection Voltage and Power Off

The maximum fault voltage on the NO_ (or NC_) pins is

±40V when the power is off. For the MAX4631/

MAX4633, with ±15V supplies, the highest voltage on

NO_ (or NC_) can be +36V, and the lowest voltage on

NO (or NC_) can be -36V. For the MAX4632, with ±15V

supplies, the highest voltage on NO_ (or NC_) can be

+25V, and the lowest voltage on NO_ (or NC_) can be

-25V. Exceeding these limits can damage the device.

IN_ Logic-Level Thresholds

The logic-level thresholds are TTL/CMOS compatible

when V+ is +15V. Raising V+ increases the threshold

slightly; when V+ reaches +25V, the level threshold is

about 2.8V—higher than the TTL output high-level mini-

mum of 2.4V, but still compatible with CMOS outputs

(see

Typical Operating Characteristics).

Increasing V- has no effect on the logic-level thresh-

olds, but it does increase the gate-drive voltage to the

signal FETs, reducing their on-resistance.

Failure Modes

The MAX4631/MAX4632/MAX4633 are not lightning

arrestors or surge protectors. Exceeding the fault-pro-

tection voltage limits on NO_ or NC_, even for very short

periods, can cause the device to fail. The failure modes

may not be obvious, and failure in one switch may or

may not affect other switches in the same package.

__________Applications Information

Ground

There is no connection between the analog signal

paths and GND. The analog signal paths consist of an

N-channel and a P-channel MOSFET with their sources

and drains paralleled and their gates driven out of

phase to V+ and V- by the logic-level translators.

V+ and GND power the internal logic and logic-level

translators and set the input logic thresholds. The logic-

level translators convert the logic levels to switched V+

and V- signals to drive the analog switch gates. This

drive signal is the only connection between the power

supplies and the analog signals. GND, IN_, and COM_

have ESD-protection diodes to V+ and V-.

Supply-Current Reduction

When the logic signals are driven rail-to-rail from 0 to

+12V or -15V to +15V, the supply current reduces to

approximately half of the supply current when the logic

input levels are at 0 to +5V.

Power Supplies

The MAX4631/MAX4632/MAX4633 operate with bipolar

supplies between ±4.5V and ±18V. The V+ and V- sup-

plies need not be symmetrical, but their difference can

not exceed the absolute maximum rating of +44V.

These devices operate from a single supply between

+9V and +36V when V- is connected to GND.

INPUT

RANGE

On

Between Rails

POWER

SUPPLIES

(V+, V-)

NC_

On

NO_

Off

OUTPUT

NC_

On

Between Rails

Off

On

NO_

On

Between V+ and (+40V - V+)

On

Off

V+

On

Between V+ and (+40V - V+)

Off

On

V+

On

Between V- and (-40V - V-)

On

Off

V-

On

Between V+ and (-40V - V-)

Off

On

V-

Off

Between Rails

Off

Off

Follows the load

terminal voltage

Table 1. Switch States in Normal and Fault Conditions