Single-supply operation also limits signal levels and

interferes with grounded signals. When V- = 0V, AC sig-

nals are limited to -0.3V. Voltages below -0.3V can be

clipped by the internal ESD-protection diodes, and the

parts can be damaged if excessive current flows.

Power Off

When power to the MAX4545/MAX4546/MAX4547 is off

(i.e., V+ = 0V and V- = 0V), the Absolute Maximum

Ratings still apply. This means that neither logic-level

inputs on IN_ nor signals on COM_, NO_, or NC_ can

exceed ±0.3V. Voltages beyond ±0.3V cause the inter-

nal ESD-protection diodes to conduct, and the parts

can be damaged if excessive current flows.

Grounding

DC Ground Considerations

Satisfactory high-frequency operation requires that

careful consideration be given to grounding. For most

applications, a ground plane is strongly recom-

mended, and all GND_ pins should be connected to

it with solid copper. While the V+ and V- power-supply

pins are common to all switches in a given package,

each switch has separate ground pins that are not

internally connected to each other. This contributes to

the overall high-frequency performance and provides

added flexibility in some applications, but it can cause

problems if it is overlooked. All the GND_ pins have

ESD diodes to V+ and V-.

In systems that have separate digital and analog (sig-

nal) grounds, connect these switch GND_ pins to ana-

log ground. Preserving a good signal ground is much

more important than preserving a digital ground.

Ground current is only a few nanoamps.

The logic-level inputs, IN_, have voltage thresholds

determined by V+ and GND_. (V- does not influence

the logic-level threshold.) With +5V and 0V applied to

V+ and GND_, the threshold is about 1.6V, ensuring

compatibility with TTL- and CMOS-logic drivers.

The various GND_ pins can be connected to separate

voltage potentials if any or all of the logic-level inputs is

not a normal logic signal. (The GND_ voltages cannot

exceed (V+ - 2V) or V-.) Elevating GND_ reduces off

isolation. For example, using the MAX4545, if GND2–

GND6 are connected to 0V and GND1 is connected to

V-, then switches 2, 3, and 4 would be TTL/CMOS com-

patible, but switch 1 (IN1) could be driven with the rail-

to-rail output of an op amp operating from V+ and V-.

Note, however, that IN_ can be driven more negative

than GND_, as far as V-. GND_ does not have to be

removed from 0V when IN_ is driven from bipolar

sources, but the voltage on IN_ should never exceed V-.

GND_ should be separated from 0V only if the logic-

level threshold has to be changed.

Any GND_ pin not connected to 0V should be

bypassed to the ground plane with a surface-mount

10nF capacitor to maintain good RF grounding. DC

current in the IN_ and GND_ pins is less than 1nA, but

increases with switching frequency.

On the MAX4545 only, two extra ground pins—GND5

and GND6—are provided to improve isolation and

crosstalk. They are not connected to the logic-level cir-

cuit. These pins should always be connected to the

ground plane with solid copper.

AC Ground and Bypassing

A ground plane is mandatory for satisfactory high-

frequency operation. (Prototyping using hand wiring or

wire-wrap boards is strongly discouraged.) Connect all

0V GND_ pins to the ground plane with solid copper.

(The GND_ pins extend the high-frequency ground

through the package wire-frame, into the silicon itself,

thus improving isolation.) The ground plane should be

solid metal underneath the device, without interruptions.

There should be no traces under the device itself. For

DIP packages, this applies to both sides of a two-sided

board. Failure to observe this will have a minimal effect

on the “on” characteristics of the switch at high frequen-

cies, but it will degrade the off isolation and crosstalk.

All V+ and V- pins should be bypassed to the ground

plane with surface-mount 10nF capacitors. For DIP

packages, they should be mounted as close as possi-

ble to the pins on the same side of the board as the

device. Do not use feedthroughs or vias for bypass

capacitors. For surface-mount packages, the pins are

so close to each other that the bypass capacitors

should be mounted on the opposite side of the board

from the device. In this case, use short feedthroughs or

vias, directly under the V+ and V- pins. Any GND_ pin

not connected to 0V should be similarly bypassed. If V-

is 0V, connect it directly to the ground plane with solid

copper. Keep all leads short.

The MAX4547 has two V+ and V- pins. Make DC con-

nections to only one of each to minimize crosstalk. Do

not route DC current into one of the V+ or V- pins and

out the other V+ or V- pin to other devices. The second

set of V+ and V- pins is for AC bypassing only.

For dual-supply operation, the MAX4547 should have

four 10nF bypass capacitors connected to each V+

and V- pin, as close to the package as possible. For

single-supply operation, the MAX4547 should have two

10nF bypass capacitors connected (one to each V+

pin), as close to the package as possible.

Quad/Dual, Low-Voltage,

Bidirectional RF/Video Switches

10

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