Precision, Dual-Supply, SPST

Analog Switches

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5

__________Applications Information

Logic Levels

Power-supply consumption is minimized when IN1 and

IN2 are driven with logic-high levels equal to V+ and logic-

and IN2 can be driven to V- without damage.

Analog Signal Levels

Analog signals that range over the entire supply voltage

(V- to V+) can be switched, with very little change in on-

resistance over the entire voltage range (see

Typical

Operating Characteristics). All switches are bidirec-

tional, so NO_, NC_, and COM_ pins can be used as

either inputs or outputs.

Power-Supply Sequencing

and Overvoltage Protection

Do not exceed the absolute maximum ratings, because

stresses beyond the listed ratings may cause perma-

nent damage to the devices.

Proper power-supply sequencing is recommended for

all CMOS devices. Always apply V+, followed by V-,

before applying analog signals or logic inputs, especial-

ly if the analog or logic signals are not current-limited. If

this sequencing is not possible, and if the analog or

logic inputs are not current-limited to <30mA, add two

small signal diodes (D1, D2) as shown in Figure 1.

Adding protection diodes reduces the analog signal

range to a diode drop (about 0.7V) below V+ for D1,

and a diode drop above V- for D2. Leakage is not

affected by adding the diodes. On-resistance increas-

es by a small amount at low supply voltages. Maximum

supply voltage (V- to V+) must not exceed 17V.

Adding protection diode D1 causes the logic thresh-

olds to be shifted relative to the positive power-supply

rail. This can be significant when low positive supply

voltages (+5V or less) are used. Driving IN1 and IN2 all

the way to the supply rails (i.e., to a diode drop higher

than the V+ pin or a diode drop lower than the V- pin) is

always acceptable.

The protection diodes D1 and D2 also protect against

some overvoltage situations. With the circuit of Figure 1,

if the supply voltage is below the absolute maximum

rating and if a fault voltage up to the absolute maximum

rating is applied to an analog signal pin, no damage

will result. For example, with ±5V supplies, analog sig-

nals up to ±8.5V will not damage the circuit of Figure 1.

If only a single fault signal is present, the fault voltage

can rise to +12V or to -12V without damage.

_____________________Pin Description

POSITIVE SUPPLY

COM

D1

D2

NO

V-

Vg

V+

NEGATIVE SUPPLY

MAX320

MAX321

MAX322

Figure 1. Overvoltage Protection Using Two External Blocking

Diodes

5

Normally Closed Analog

Switch Terminal

NC2

(MAX321/MAX322)

Normally Open Analog

Switch Terminal

NO2

(MAX320)

Negative Supply

V-

4

Logic Inputs

IN2, IN1

3, 7

PIN

Analog Switch Common

Terminals

COM1, COM2

2, 6

Normally Closed Analog

Switch Terminal

NC1

(MAX321)

Normally Open Analog

Switch Terminal

NO1

(MAX320/MAX322)

1

FUNCTION

NAME

Positive Supply

V+

8