6

FN7492.0

February 14, 2005

Applications Information

Product Description

The EL5462 is a low power, current-feedback operational

amplifier that offers a wide -3dB bandwidth of 500MHz and a

low supply current of 1.5mA per amplifier. The EL5462

works with supply voltages ranging from a single 5V to 10V

and they are also capable of swinging to within 1V of either

supply on the output. Because of its current-feedback

topology, the EL5462 does not have the normal gain-

bandwidth product associated with voltage-feedback

operational amplifiers. Instead, its -3dB bandwidth to remain

relatively constant as closed-loop gain is increased. This

combination of high bandwidth and low power, together with

aggressive pricing makes the EL5462 the ideal choice for

many low-power/high-bandwidth applications such as

portable, handheld, or battery-powered equipment.

Power Supply Bypassing and Printed Circuit

Board Layout

As with any high frequency device, a good printed circuit

board layout is necessary for optimum performance. Low

impedance ground plane construction is essential. Surface

mount components are recommended, but if leaded

components are used, 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 0.01µF 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 Inverting Input section) Even when

ground plane construction is used, it should be removed

from the area near the inverting input to minimize 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 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 additional

peaking and overshoot.

Capacitance at the Inverting Input

Any manufacturer’s high-speed voltage or current-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 amplifier. 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 feedback and gain resistors exacerbates the problem

by further lowering the pole frequency (increasing the

possibility of oscillation.)

The EL5462 has been optimized with a 600

Ω feedback

resistor. With the high bandwidth of these amplifiers, these

resistor values might cause stability problems when

combined with parasitic capacitance, thus ground plane is

not recommended around the inverting input pin of the

amplifier.

Pin Descriptions

EL5462

PIN NAME

FUNCTION

EQUIVALENT CIRCUIT

2, 6, 9, 13

IN-

Inverting input

Circuit 1

3, 5, 10, 12

IN+

Non-inverting input

(See circuit 1)

11

VS-

Negative supply

1, 7, 8, 14

OUT

Output

Circuit 2

4

VS+

Positive supply

IN-

IN+

OUT

EL5462