EL2157 datasheet(13/19 Pages) INTERSIL

13 / 19 page

Simplified Schematic

Applications Information

Product Description

The EL2150 and EL2157 are the industry's fastest single

supply operational amplifiers. Connected in voltage follower

mode, their -3dB bandwidth is 125MHz while maintaining a

275V/µs slew rate. With an input and output common mode

range that includes ground, these amplifiers were optimized

for single supply operation, but will also accept dual

supplies. They operate on a total supply voltage range as

low as +2.7V or up to +12V. This makes them ideal for +3V

applications, especially portable computers.

While many amplifiers claim to operate on a single supply,

and some can sense ground at their inputs, most fail to truly

drive their outputs to ground. If they do succeed in driving to

ground, the amplifier often saturates, causing distortion and

recovery delays. However, special circuitry built into the

EL2150 and EL2157 allows the output to follow the input

signal to ground without recovery delays.

Power Supply Bypassing And Printed Circuit

Board Layout

As with any high-frequency device, good printed circuit

board layout is necessary for optimum performance. Ground

plane construction is highly recommended. Lead lengths

should be as short as possible. The power supply pins must

be well bypassed to reduce the risk of oscillation. The

combination of a 4.7µF tantalum capacitor in parallel with a

0.1µF ceramic capacitor has been shown to work well when

placed at each supply pin. For single supply operation,

where pin 4 (VS-) is connected to the ground plane, a single

4.7µF tantalum capacitor in parallel with a 0.1µF ceramic

capacitor across pins 7 and 4 will suffice.

For good AC performance, parasitic capacitance should be

kept to a minimum. Ground plane construction should be

used. Carbon or Metal-Film resistors are acceptable with the

Metal-Film resistors giving slightly less peaking and

bandwidth because of their additional series inductance.

Use of sockets, particularly for the SO package should be

avoided if possible. Sockets add parasitic inductance and

capacitance which will result in some additional peaking and

overshoot.

Supply Voltage Range and Single-Supply

Operation

The EL2150 and EL2157 have been designed to operate

with supply voltages having a span of greater than 2.7V, and

less than 12V. In practical terms, this means that the EL2150

and EL2157 will operate on dual supplies ranging from

±1.35V to ±6V. With a single-supply, the EL2150 and

EL2157 will operate from +2.7V to +12V. Performance has

been optimized for a single +5V supply.

Pins 7 and 4 are the power supply pins. The positive power

supply is connected to pin 7. When used in single supply

mode, pin 4 is connected to ground. When used in dual

supply mode, the negative power supply is connected to

pin 4.

As supply voltages continue to decrease, it becomes

necessary to provide input and output voltage ranges that

can get as close as possible to the supply voltages. The

EL2150 and EL2157 have an input voltage range that

includes the negative supply and extends to within 1.2V of

the positive supply. So, for example, on a single +5V supply,

the EL2150 and EL2157 have an input range which spans

from 0V to 3.8V.

The output range of the EL2150 and EL2157 is also quite

large. It includes the negative rail, and extends to within 1V

of the top supply rail. On a +5V supply, the output is

therefore capable of swinging from 0V to +4V. On split

supplies, the output will swing ±4V. If the load resistor is tied

EL2150, EL2157

EL2157 Datasheet(PDF) 13 Page - Intersil Corporation

EL2157 Datasheet(HTML) 13 Page - Intersil Corporation

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