OP282/OP482

REV. B

–4–

APPLICATIONS INFORMATION

The OP282 and OP482 are single and dual JFET op amps that

have been optimized for high speed at low power. This

combination makes these amplifiers excellent choices for battery

powered or low power applications requiring above average

performance. Applications benefiting from this performance

combination include telecom, geophysical exploration, portable

medical equipment and navigational instrumentation.

HIGH SIDE SIGNAL CONDITIONING

There are many applications that require the sensing of signals

near the positive rail. OP282s and OP482s have been tested and

guaranteed over a common-mode range (–11 V

≤ V

that includes the positive supply.

One application where this is commonly used is in the sensing of

power supply currents. This enables it to be used in current

sensing applications such as the partial circuit shown in Figure

1. In this circuit, the voltage drop across a low value resistor,

such as the 0.1

Ω shown here, is amplified and compared to 7.5

volts. The output can then be used for current limiting.

+15V

100k

100k

100k

500k

0.1

1/2

OP282

+

R

L

Ω

Figure 1. Phase Inversion

PHASE INVERSION

Most JFET-input amplifiers will invert the phase of the input

signal if either input exceeds the input common-mode range.

For the OP282 and OP482 negative signals in excess of approxi-

mately 14 volts will cause phase inversion. The cause of this

effect is saturation of the input stage leading to the forward-

biasing of a drain-gate diode. A simple fix for this in noninverting

applications is to place a resistor in series with the noninverting

input. This limits the amount of current through the forward-

biased diode and prevents the shutting down of the output

stage. For the OP282/OP482, a value of 200 k

Ω has been found

to work. However, this adds a significant amount of noise.

-15

15

10

5

0

-5

-10

-15

-10

-5

0

5

10

15

OUT

V

Figure 2. OP282 Phase Reversal

ACTIVE FILTERS

The OP282 and OP482’s wide bandwidth and high slew rates

make either an excellent choice for many filter applications.

There are many types of active filter configurations, but the four

most popular configurations are Butterworth, elliptical, Bessel,

and Chebyshev. Each type has a response that is optimized for a

given characteristic as shown in Table I.

PROGRAMMABLE STATE-VARIABLE FILTER

Table I.

Amplitude

Amplitude

Type

Selectivity

Overshoot

Phase

(Pass Band)

(Stop Band)

Butterworth

Moderate

Good

Max Flat

Chebyshev

Good

Moderate

Nonlinear

Equal Ripple

Elliptical

Best

Poor

Equal Ripple

Equal Ripple

Bessel (Thompson)

Poor

Best

Linear