Low-Voltage, Bidirectional

RF/Video Switch

_______________________________________________________________________________________

7

Pin Description

6

FUNCTION*

SOT23-6

NAME

Analog Switch Common** Terminal. Analog signal voltages should never exceed

V+ or V-.

—

7

Not Internally Connected

PIN

1

COM

Analog Switch Normally Closed** Terminal

2

Positive Supply-Voltage Input (analog and digital). The voltage difference between

V+ and V- should never exceed 12V.

5

RF and Logic Ground. Connect to ground plane.

3

-5V Supply Input. Connect to GND for single-supply operation.

DIP/SO/µMAX

1, 6

2

8

3

5

N.C.

NC

V+

GND

V-

*

All pins except N.C. have ESD diodes to V- and V+.

**

NC and COM pins are identical and interchangeable. Either may be considered as an input or output; signals pass equally well in

either direction.

Theory of Operation

Logic-Level Translators

The MAX4529 is constructed as a high-frequency “T”

switch, as shown in Figure 1. The logic-level input, IN,

is translated by amplifier A1 into a V+ to V- logic signal

that drives inverter A2. Amplifier A2 drives the gates of

N-channel MOSFETs N1 and N2 from V+ to V-, turning

them fully on or off. The same signal drives inverter A3

(which drives the P-channel MOSFETs P1 and P2) from

V+ to V-, turning them fully on or off, and drives the N-

channel MOSFET N3 off and on.

The logic-level threshold is determined by V+ and

GND. The voltage on GND is usually at ground poten-

tial, but it may be set to any voltage between

(V+ - 2V) and V-. When the voltage between V+ and

GND is less than 2V, the level translators become very

slow and unreliable. Normally, GND should be connect-

ed to the ground plane.

Switch On Condition

When the switch is on, MOSFETs N1, N2, P1, and P2

are on and MOSFET N3 is off. The signal path is COM to

NC, and because both N-channel and P-channel

MOSFETs act as pure resistances, it is symmetrical (i.e.,

signals may pass in either direction). The off MOSFET,

N3, has no DC conduction, but has a small amount of

capacitance to GND. The four on MOSFETs also have

capacitance to ground that, together with the series

resistance, forms a lowpass filter. All of these capaci-

tances are distributed evenly along the series resis-

tance, so they act as a transmission line rather than a

simple R-C filter. This helps to explain the exceptional

300MHz bandwidth when the switches are on.

Typical attenuation in 50

Ω systems is -2dB and is rea-

sonably flat up to 100MHz. Higher-impedance circuits

show even lower attenuation (and vice versa), but

slightly lower bandwidth due to the increased effect of

the internal and external capacitance and the switch’s

internal resistance.

A1

A2

A3

S

S

P1

N3

D

D

D

N1

V-

GND

IN

V+

V+

V-

COM

NC

S

D

N2

S

S

P2

D

NORMALLY CLOSED SWITCH CONSTRUCTION

COM - NC

IN

0

1

ON

OFF

ESD DIODES

ON GND, IN,

COM, AND NC

Figure 1. T-Switch Construction

4

Logic-Level Control Input. Logic-level voltages should never exceed V+ or V-.

4

IN