Detailed Description

The MAX4655–MAX4658 are single SPST CMOS ana-

log switches. The CMOS switch construction provides

rail-to-rail signal handling while consuming very little

power. The switch is controlled by a TTL/CMOS level

compatible digital input. The MAX4655/MAX4657 are

normally closed switches, and the MAX4656/MAX4658

are normally open switches.

These devices can be operated with either single

power supplies or dual power supplies. Operation at up

to ±20V supplies allows users a wide switching dynamic

range. Additionally, asymmetrical operation is possible

to tailor performance to a particular application.

These switches have been specifically designed to

handle high switch currents, up to 400mA peak current

and 300mA continuous currents. In order to do this, a

new technique is used to drive the body of the output

N-channel device. (Note: the basic switch between the

input NC/NO terminal, and the output common terminal

consists of an N-channel MOSFET and a P-channel

MOSFET in parallel.) The standard method limits opera-

tion to approximately a 600mV drop across the switch.

current (due to the turn-on of on-chip parasitic diodes)

and an increase in V+ supply current. With the new

sensing method, there is no limitation to the voltage

drop across the switch. Current and voltage are limited

only by the power dissipation rating of the package and

the absolute maximum ratings of the switch.

When the analog input to output voltage drop is

approximately 7mV there is an increase in power sup-

ply current from typically 90µA to 2mA within a 1mV to

7mV range, caused by the new sensing/driving circuitry.

Applications Information

Overvoltage Protection

Proper power-supply sequencing is recommended for

all CMOS devices. Do not exceed the absolute maxi-

mum ratings, because stresses beyond the listed rat-

ings can cause permanent damage to the devices.

First, connect GND, followed by V+, V-, and the remain-

ing pins. If power-supply sequencing is not possible,

add two small signal diodes (D1, D2) in series with sup-

ply pins (Figure 1). Adding diodes reduces the analog

signal range to one diode drop below V+ and one

diode drop above V-, but does not affect the devices’

low switch resistance and low leakage characteristics.

Device operation is unchanged, and the difference

between V+ and V- should not exceed 44V. The protec-

tion diode for the negative supply is not required when

V- is connected to GND.

Off-Isolation at High Frequencies

In 50

Ω systems, the high-frequency on-response of

these parts extends from DC to above 100MHz, with a

typical loss of -2dB. When the switch is turned off, how-

ever, it behaves like a capacitor, and off-isolation

decreases with increasing frequency. This effect is

more pronounced with higher source and load imped-

ances. Above 5MHz, circuit board layout becomes

critical. The graphs shown in the Typical Operating

Characteristics were taken using a 50

Ω source and

load connected with BNC connectors.

High-Current, 10

Analog Switches

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7

V+

COM_

V-

NO_

Vg

V+

V-

Figure 1. Overvoltage Protection Using Blocking Diodes