MAX477EPA Просмотр технического описания (PDF) - Maxim Integrated

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MAX477EPA

300MHz High-Speed Op Amp

Maxim Integrated 

300MHz High-Speed Op Amp

_____________________Pin Description

PIN

SO/µMAX/DIP

1, 5, 8

2

3

4

6

7

SOT23 NAME

—

N.C.

4

IN-

3

IN+

2

VEE

1

OUT

5

VCC

FUNCTION

No Connect. Not inter-

nally connected.

Inverting Input

Noninverting Input

Negative Power

Supply

Amplifier Output

Positive Power

Supply

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 capaci-

tance 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.

Setting Gain

The MAX477 can be configured as an inverting or non-

inverting gain block in the same manner as any other

voltage-feedback op amp. The gain is determined by

the ratio of two resistors and does not affect amplifier

frequency compensation. This is unlike CMF op amps,

which have a limited range of feedback resistors, typi-

cally one resistor value for each gain and load setting.

This is because the -3dB bandwidth of a CMF op amp

is set by the feedback and load resistors. Figure 1a

shows the inverting gain configuration and its gain

RG

RF

VIN

MAX477

VOUT

VOUT = -(RF/RG) VIN

Figure 1a. Inverting Gain Configuration

_______________________________________________________________________________________ 7

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