EL2170CS datasheet(10/16 Pages) ELANTEC

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EL2170CEL2270CEL2470C

70 MHz1 mA Current Mode Feedback Amplifiers

Applications Information

Product Description

The EL2170CEL2270CEL2470C are current-

feedback operational amplifiers that offer a wide

3 dB bandwidth of 70 MHz and a low supply

current of 1 mA per amplifier All of these prod-

ucts also feature high output current drive The

EL2170C can output 100 mA while the EL2270C

and the EL2470C can output 55 mA per amplifi-

er The EL2170CEL2270CEL2470C work with

supply voltages ranging from a single 3V to

6V and they are also capable of swinging to

within 1V of either supply on the input and the

output Because of their current-feedback topolo-

the EL2170CEL2270CEL2470C do not

have the normal gain-bandwidth product associ-

ated with voltage-feedback operational amplifi-

ers This allows their b3 dB bandwidth to re-

main relatively constant as closed-loop gain is in-

creased This combination of high bandwidth and

low power together with aggressive pricing make

the

EL2170CEL2270CEL2470C

the

ideal

choice for many low-powerhigh-bandwidth ap-

plications such as portable computing HDSL

and video processing

For applications where board space is extremely

critical the EL2170C is available in the tiny 5-

Lead SOT23 package which has a footprint 28%

the size of an 8-Lead SOIC

The EL2170C

EL2270CEL2470C are each also available in in-

dustry standard pinouts in PDIP and SOIC pack-

ages

For Single and Dual applications with disable

consider

the

EL2176C

(8-Pin

Single)

and

EL2276C (14-Pin Dual) If higher speed is re-

quired refer to the EL2180CEL2186C family

which provides Singles

Duals

Triples

and

Quads with 250 MHz of bandwidth while con-

suming 3 mA of supply current per amplifier

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 high-

ly 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 47

mF tantalum capacitor in

parallel with a 01

mF capacitor has been shown

to work well when placed at each supply pin

For good AC performance parasitic capacitance

should be kept to a minimum especially at the

inverting input (see the Capacitance at the In-

verting Input section) Ground plane construc-

tion should be used but it should be removed

from the area near the inverting input to mini-

mize any stray capacitance at that node 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 Sock-

ets add parasitic inductance and capacitance

which will result in some additional peaking and

overshoot

Capacitance at the Inverting Input

Any manufacturer’s high-speed voltage- or cur-

rent-feedback amplifier can be affected by stray

capacitance at the inverting input For inverting

gains this parasitic capacitance has little effect

because the inverting input is a virtual ground

but for non-inverting gains this capacitance (in

conjunction with the feedback and gain resistors)

creates a pole in the feedback path of the amplifi-

er This pole if low enough in frequency has the

same destabilizing effect as a zero in the forward

open-loop response The use of large value feed-

back and gain resistors further exacerbates the

problem by further lowering the pole frequency

EL2170CS Datasheet(PDF) 10 Page - Elantec Semiconductor

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