EL2276CS datasheet(10/20 Pages) ELANTEC

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EL2176CEL2276C

70 MHz1 mA Current Mode Feedback Amp wDisable

Applications Information

Product Description

The EL2176CEL2276C are current-feedback op-

erational amplifiers that offer a wide b3dB

bandwidth of 70 MHz a low supply current of

1 mA per amplifier and the ability to disable to

0 mA Both products also feature high output

current drive The EL2176C can output 100 mA

while the EL2276C can output 55 mA per ampli-

fier The EL2176CEL2276C work with supply

voltages ranging from a single 3V to g6V and

they are also capable of swinging to with in 1V of

either supply on the input and the output Be-

cause of their current-feedback topology

the

EL2176CEL2276C do not have the normal gain-

bandwidth product associated with voltage-feed-

back operational amplifiers

This allows their

3 dB bandwidth to remain relatively constant

as closed-loop gain is increased This combina-

tion of high bandwidth and low power together

with aggressive pricing make the EL2176C

EL2276C the ideal choice for many low-power

high-bandwidth applications such as portable

computing HDSL and video processing

For Single Dual and Quad applications without

disable

consider the EL2170C (8-Pin Single)

EL2270C (8-Pin Dual) and EL2470C (14-Pin

Quad) If more AC performance is required refer

to the EL2180CEL2186C family which provides

Singles

Duals

and Quads with 250 MHz of

bandwidth while consuming 3 mA of supply cur-

rent 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

DisablePower-Down

The EL2176CEL2276C amplifiers can be dis-

abled placing their output in a high-impedance

state When disabled each amplifier’s supply cur-

rent is reduced to 0 mA

Each EL2176C

EL2276C

amplifier

disabled

when

its

ENABLE pin is floating or pulled up to within

05V of the positive supply Similarly each am-

plifier is enabled by pulling its ENABLE pin at

least 3V below the positive supply For g5V sup-

plies this means that an EL2176CEL2276C am-

plifier will be enabled when ENABLE is at 2V or

less and disabled when ENABLE is above 45V

Although the logic levels are not standard TTL

this choice of logic voltages allows the EL2176C

EL2276C to be enabled by tying ENABLE to

ground even in a3V single-supply applications

The ENABLE pin can be driven from CMOS

outputs or open-collector TTL

When enabled supply current does vary some-

what with the voltage applied at ENABLE For

example

with

the

supply

voltages

the

EL2176C at g5V if ENABLE is tied to b5V

(rather than ground) the supply current will in-

crease about 15% to 115 mA

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-

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