OP282/OP482

Data Sheet

Rev. I | Page 12 of 16

APPLICATIONS INFORMATION

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

are optimized for high speed at low power. This combination

makes these amplifiers excellent choices for battery-powered or

low power applications that require above average performance.

Applications benefiting from this performance combination

include telecommunications, geophysical exploration, portable

medical equipment, and navigational instrumentation.

HIGH-SIDE SIGNAL CONDITIONING

Many applications require the sensing of signals near the positive

rail. OP282 and OP482 were tested and are guaranteed over a

positive supply.

One application where such sensing is commonly used is in the

sensing of power supply currents. Therefore, the OP282/OP482

can be used in current sensing applications, such as the partial

circuit shown in Figure 45. 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 V. The output can then be used for current

limiting.

15V

100k

Ω

500k

Ω

0.1

Ω

500k

Ω

100k

Ω

1/2

OP282

Figure 45. High-Side Signal Conditioning

PHASE INVERSION

Most JFET input amplifiers invert the phase of the input signal

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

OP282/OP482, a negative signal in excess of 11 V causes phase

inversion. This is caused by saturation of the input stage, leading

to the forward-biasing of a gate-drain diode. Phase reversal in

the OP282/OP482 can be prevented by using Schottky diodes to

clamp the input terminals to each other and to the supplies. In

the simple buffer circuit shown in Figure 46, D1 protects the op

amp against phase reversal. R1, D2, and D3 limit the input

current when the input exceeds the supply rail. The resistor

should be selected to limit the amount of input current below

the absolute maximum rating.

D1

IN5711

V+

OP282/

OP482

V+

V–

V–

D2

IN5711

R1

10kΩ

D3

IN5711

Figure 46. Phase Reversal Solution Circuit

TIME (200µs/DIV)

2

Figure 47. No Phase Reversal

ACTIVE FILTERS

The wide bandwidth and high slew rates of the OP282/OP482

make either one an excellent choice for many filter applications.

There are many active filter configurations, but the four most

popular configurations are Butterworth, elliptic, Bessel, and

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

given characteristic, as shown in Table 4.

Table 4. Active Filter Configurations

Type

Selectivity

Overshoot

Phase

Amplitude (Pass Band)

Amplitude (Stop Band)

Butterworth

Moderate

Good

Maximum flat

Chebyshev

Good

Moderate

Nonlinear

Equal ripple

Elliptic

Best

Poor

Equal ripple

Equal ripple

Bessel (Thompson)

Poor

Best

Linear