High-Speed, Low-Power, Single-Supply,

Multichannel, Video Multiplexer-Amplifiers

______________________________________________________________________________________

13

Low-Power Shutdown Mode

All parts feature a low-power shutdown mode that is

activated by driving the SHDN input low. Placing the

amplifier in shutdown mode reduces the quiescent sup-

ply current to 560µA and places the output into a high-

impedance state, typically 35k

Ω. By tying the outputs

of several devices together and disabling all but one of

the paralleled amplifiers’ outputs, multiple devices may

be paralleled to construct larger switch matrices.

For MAX4310/MAX4311/MAX4312 application circuits

operating with a closed-loop gain of +2V/V or greater,

consider the external-feedback network impedance of

all devices used in the mux application when calculat-

ing the total load on the output amplifier of the active

device. The MAX4313/MAX4314/MAX4315 have a fixed

gain of +2V/V that is internally set with two 500

Ω thin-

film resistors. The impedance of the internal feedback

resistors must be taken into account when operating

multiple MAX4313/MAX4314/MAX4315s in large multi-

plexer applications.

For normal operation, drive SHDN high. If the shutdown

Layout and Power-Supply Bypassing

The MAX4310–MAX4315 have very high bandwidths

and consequently require careful board layout, includ-

ing the possible use of constant-impedance microstrip

or stripline techniques.

To realize the full AC performance of these high-speed

amplifiers, pay careful attention to power-supply

bypassing and board layout. The PC board should

have at least two layers: a signal and power layer on

one side, and a large, low-impedance ground plane on

the other side. The ground plane should be as free of

voids as possible, with one exception: the feedback

(FB) should have as low a capacitance to ground as

possible. Therefore, layers that do not incorporate a

signal or power trace should not have a ground plane.

Whether or not a constant-impedance board is used, it

is best to observe the following guidelines when

designing the board:

1) Do not use wire-wrapped boards (they are too

inductive) or breadboards (they are too capacitive).

2) Do not use IC sockets; they increase parasitic

capacitance and inductance.

3) Keep signal lines as short and straight as possible.

Do not make 90° turns; round all corners.

4) Observe high-frequency bypassing techniques to

maintain the amplifier’s accuracy and stability.

5) Use surface-mount components. They generally

have shorter bodies and lower parasitic reactance,

yielding better high-frequency performance than

through-hole components.

OUT

IN-

SHDN, A0, A1, A2

IN+

10k

LOGIC INPUT

MAX431_

Figure 3. Circuit to Reduce Logic-Low Input Current

0

-10

0

50 100 150

300 350

500

-7

-8

-1

200 250

400 450

-3

-5

-9

-2

-4

-6

Resistor

20

-160

0

50 100 150

300 350

500

-100

-120

0

200 250

400 450

-60

-140

-20

-40

-80