Detailed Description

The MAX4450/MAX4451 are single-supply, rail-to-rail,

voltage-feedback amplifiers that employ current-feed-

back techniques to achieve 485V/µs slew rates and

210MHz bandwidths. Excellent harmonic distortion and

differential gain/phase performance make these ampli-

fiers an ideal choice for a wide variety of video and RF

signal-processing applications.

The output voltage swings to within 55mV of each sup-

ply rail. Local feedback around the output stage

ensures low open-loop output impedance to reduce

gain sensitivity to load variations. The input stage per-

mits common-mode voltages beyond the negative sup-

ply and to within 2.25V of the positive supply rail.

Applications Information

Choosing Resistor Values

Unity-Gain Configuration

The MAX4450/MAX4451 are internally compensated for

unity gain. When configured for unity gain, the devices

require a 24

path. This resistor improves AC response by reducing

the Q of the parallel LC circuit formed by the parasitic

feedback capacitance and inductance.

Inverting and Noninverting Configurations

resistor values to fit your application. Large resistor val-

ues increase voltage noise and interact with the amplifi-

er’s input and PC board capacitance. This can

generate undesirable poles and zeros and decrease

bandwidth or cause oscillations. For example, a nonin-

Ω

resistors, combined with 1pF of amplifier input capaci-

tance and 1pF of PC board capacitance, causes a pole

at 159MHz. Since this pole is within the amplifier band-

width, it jeopardizes stability. Reducing the 1k

Ω resis-

tors to 100

Ω extends the pole frequency to 1.59GHz,

but could limit output swing by adding 200

Ω in parallel

with the amplifier’s load resistor. Table 1 lists suggest-

ed feedback and gain resistors, and bandwidths for

several gain values in the configurations shown in

Figures 1a and 1b.

Layout and Power-Supply Bypassing

These amplifiers operate from a single +4.5V to +11V

power supply or from dual ±2.25V to ±5.5V supplies. For

Ultra-Small, Low-Cost, 210MHz, Single-Supply

Op Amps with Rail-to-Rail Outputs

_______________________________________________________________________________________

7

Pin Description

PIN

OUT

IN+

INA-

OUTA

IN-

INB+

INB-

OUTB

INA+

—

4

—

2

1

8

—

5

6

7

3

1

Amplifier Output

2

Negative Power Supply

or Ground (in single-

supply operation)

3

Noninverting Input

—

Amplifier A Inverting

Input

—

Amplifier A Output

5

Positive Power Supply

4

Inverting Input

—

Amplifier B Noninverting

Input

—

Amplifier B Inverting

Input

—

Amplifier B Output

—

Amplifier A Noninverting

Input

IN

MAX445 _

Figure 1a. Noninverting Gain Configuration

IN

MAX445 _

Figure 1b. Inverting Gain Configuration

FUNCTION

MAX4450

NAME

MAX4451