MAX4222EEE Просмотр технического описания (PDF) - Maxim Integrated

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MAX4222EEE

High-Speed, Single-Supply, Gain of 2, Closed-Loop, Rail-to-Rail Buffers with Enable

Maxim Integrated 

High-Speed, Single-Supply, Gain of 2,

Closed-Loop, Rail-to-Rail Buffers with Enable

________________Detailed Description

The MAX4214/MAX4215/MAX4217/MAX4219/MAX4222

are single-supply, rail-to-rail output, voltage-feedback,

closed-loop buffers that employ current-feedback tech-

niques to achieve 600V/µs slew rates and 230MHz

bandwidths. These buffers use internal 500Ω resistors

to provide a preset closed-loop gain of 2V/V in the non-

inverting configuration or -1V/V in the inverting configu-

ration. Excellent harmonic distortion and differential

gain/phase performance make them an ideal choice for

a wide variety of video and RF signal-processing appli-

cations.

Local feedback around the buffer’s output stage

ensures low output impedance, which reduces gain

sensitivity to load variations. This feedback also pro-

duces demand-driven current bias to the output tran-

sistors for ±120mA drive capability, while constraining

total supply current to less than 7mA.

___________Applications Information

Power Supplies

These devices operate from a single 3.15V to 11V

power supply or from dual supplies of ±1.575V to

±5.5V. For single-supply operation, bypass the VCC pin

to ground with a 0.1µF capacitor as close to the pin as

possible. If operating with dual supplies, bypass each

supply with a 0.1µF capacitor.

Selecting Gain Configuration

Each buffer in the MAX4214 family can be configured

for a voltage gain of 2V/V or -1V/V. For a gain of 2V/V,

ground the inverting terminal. Use the noninverting ter-

minal as the signal input of the buffer (Figure 1a).

Grounding the noninverting terminal and using the

inverting terminal as the signal input configures the

buffer for a gain of -1V/V (Figure 1b).

Since the inverting input exhibits a 500Ω input imped-

ance, terminate the input with a 56Ω resistor when con-

figured for an inverting gain in 50Ω applications

(terminate with 88Ω in 75Ω applications). Terminate the

input with a 49.9Ω resistor in the noninverting case.

Output terminating resistors should directly match

cable impedances in either configuration.

Layout Techniques

Maxim recommends using microstrip and stripline tech-

niques to obtain full bandwidth. To ensure the PC

board does not degrade the buffer’s performance,

design it for a frequency greater than 1GHz. Pay care-

ful attention to inputs and outputs to avoid large para-

sitic capacitance. Whether or not you use a constant-

impedance board, observe the following guidelines

when designing the board:

• Don’t use wire-wrapped boards. They are too induc-

tive.

• Don’t use IC sockets. They increase parasitic capac-

itance and inductance.

• Use surface-mount instead of through-hole compo-

nents for better high-frequency performance.

• Use a PC board with at least two layers; it should be

as free from voids as possible.

• Keep signal lines as short and as straight as possi-

ble. Do not make 90° turns; round all corners.

Input Voltage Range and Output Swing

The MAX4214 family’s input range extends from

(VEE - 100mV) to (VCC - 2.25V). Input ground sensing

increases the dynamic range for single-supply applica-

tions. The outputs drive a 2kΩ load to within 60mV of

the power-supply rails. With smaller resistive loads, the

output swing is reduced as shown in the Electrical

Characteristics and Typical Operating Characteristics.

IN+

IN

RTIN

OUT RTO

500Ω

500Ω

IN-

MAX42_ _

OUT

RO

IN+

RS

OUT

RTO

500Ω

IN

IN-

RTIN

500Ω

MAX42_ _

OUT

RO

Figure 1a. Noninverting Gain Configuration (AV = +2V/V)

Figure 1b. Inverting Gain Configuration (AV = -1V/V)

_______________________________________________________________________________________ 9

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