__________Applications Information

Power-Supply Considerations

Overview

The MAX4530/MAX4531/MAX4532 construction is typi-

cal of most CMOS analog switches. They have three

supply pins: V+, V-, and GND. V+ and V- drive the

internal CMOS switches and set the limits of the analog

voltage on any switch. Reverse ESD-protection diodes

are internally connected between each analog-signal

pin and both V+ and V-. One of these diodes conducts

if any analog signal exceeds V+ or V-. During normal

operation, these and other reverse-biased ESD diodes

leak, forming the only current drawn from V+ or V-.

Virtually all of the analog leakage current comes from

the ESD diodes. Although the ESD diodes on a given

signal pin are identical and therefore fairly well bal-

anced, they are reverse biased differently. Each is

biased by either V+ or V- and the analog signal. This

means their leakages vary as the signal varies. The

difference in the two diode leakages to the V+ and V-

pins constitutes the analog-signal-path leakage current.

All analog leakage current flows between each pin and

one of the supply terminals, not to the other switch ter-

minal. For this reason, both sides of a given switch can

show leakage currents of either the same or opposite

polarity.

The analog-signal paths and GND are not connected.

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

translators, and set both the input and output logic lim-

its. The logic-level translators convert the logic levels

into switched V+ and V- signals to drive the analog sig-

nals’ gates. This drive signal is the only connection

between the logic supplies and signals and the analog

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

GND.

The logic-level thresholds are TTL/CMOS compatible

when V+ = +5V. As V+ rises, the threshold increases

slightly, so when V+ reaches +12V, the threshold is

about 3.1V—above the TTL guaranteed, high-level min-

imum of 2.8V, but still compatible with CMOS outputs.

Bipolar Supplies

The MAX4530/MAX4531/MAX4532 operate with bipolar

supplies between ±2.0V and ±6V. The V+ and V- sup-

plies need not be symmetrical, but their sum cannot

exceed the +13V absolute maximum rating.

Single Supply

The MAX4530/MAX4531/MAX4532 operate from a sin-

gle supply between +2V and +12V when V- is connect-

ed to GND. All of the bipolar precautions must be

observed. At room temperature, they actually work with

a single supply at, near, or below +1.7V, although as

supply voltage decreases, switch on-resistance and

switching times become very high.

High-Frequency Performance

In 50

Ωsystems, signal response is reasonably flat up to

50MHz (see

Typical Operating Characteristics). Above

20MHz, the on response has several minor peaks that

are highly layout dependent. The problem is not in turn-

ing the switch on, but in turning it off. The off-state

switch acts like a capacitor and passes higher frequen-

cies with less attenuation. At 10MHz, off isolation is

about -65dB in 50

Ωsystems, becoming worse (approxi-

mately 20dB per decade) as frequency increases.

Higher circuit impedances also make off isolation

worse. Adjacent channel attenuation is about 3dB

above that of a bare IC socket, and is due entirely to

capacitive coupling.

Low-Voltage, CMOS Analog Multiplexers/Switches

with Enable Inputs and Address Latching

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