300MHz High-Speed Op Amp

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7

_______________Detailed Description

The MAX477 allows the flexibility and ease of a classic

voltage-feedback architecture while maintaining the

high-speed benefits of current-mode feedback (CMF)

amplifiers. Although the MAX477 is a voltage-feedback

op amp, its internal architecture provides an 1100V/µs

slew rate and a low 8mA supply current. CMF ampli-

fiers offer high slew rates while maintaining low supply

current, but use the feedback and load resistors as part

of the amplifier’s frequency compensation network. In

addition, they have only one input with high imped-

ance.

The MAX477 has speed and power specifications like

those of current-feedback amplifiers, but has high input

impedance at both input terminals. Like other voltage-

feedback op amps, its frequency compensation is

independent of the feedback and load resistors, and it

exhibits a constant gain-bandwidth product. However,

unlike standard voltage-feedback amplifiers, its large-

signal slew rate is not limited by an internal current

source, so the MAX477 exhibits a very high full-power

bandwidth.

Output Short-Circuit Protection

Under short-circuit conditions, the output current is typi-

cally limited to 150mA. This is low enough that a short to

ground of any duration will not cause permanent dam-

age to the chip. However, a short to either supply will

significantly increase the power dissipation and may

cause permanent damage. The high output-

current capability is an advantage in systems that trans-

mit a signal to several loads. See

High-Performance

Video Distribution Amplifier in the Applications

Information section.

__________Applications Information

Grounding, Bypassing,

and PC Board Layout

To obtain the MAX477’s full 300MHz bandwidth, Micro-

strip and Stripline techniques are recommended in

most cases. To ensure the PC board does not degrade

the amplifier’s performance, design the board for a fre-

quency greater than 1GHz. Even with very short traces,

use these techniques at critical points, such as inputs

and outputs. Whether you use a constant-impedance

board or not, observe the following guidelines when

designing the board:

• Do not use wire-wrap boards. They are too inductive.

• Do not use IC sockets. They increase parasitic

capacitance and inductance.

• In general, surface-mount components have shorter

leads and lower parasitic reactance, giving better

high-frequency performance than through-hole com-

ponents.

• The PC board should have at least two layers, with

one side a signal layer and the other a ground plane.

• Keep signal lines as short and straight as possible.

Do not make 90° turns; round all corners.

• The ground plane should be as free from voids as

possible.

_____________________Pin Description

MAX477

Figure 1a. Inverting Gain Configuration

MAX477

Figure 1b. Noninverting Gain Configuration

Amplifier Output

1

6

Positive Power

Supply

5

7

Negative Power

Supply

2

4

Noninverting Input

3

3

PIN

SO/µMAX/DIP

Inverting Input

4

2

No Connect. Not inter-

nally connected.

—

1, 5, 8

FUNCTION

SOT23

OUT

IN+

IN-

N.C.

NAME