OP282/OP482

Rev. F | 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

There are many applications that require the sensing of signals

near the positive rail. OP282s and OP482s were tested and are

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 44.

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 44. 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, negative signals in excess of approximately 14 V

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 kΩ has been found to work;

however, this adds a significant amount of noise.

–15

–10

–5

5

10

15

15

10

5

0

0

Figure 45. OP282 Phase Reversal

ACTIVE FILTERS

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

make either an excellent choice for many filter applications.

There are many 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 4.

Table 4.

Type

Selectivity

Overshoot

Phase

Amplitude (Pass Band)

Amplitude (Stop Band)

Butterworth

Moderate

Good

Maximum Flat

Chebyshev

Good

Moderate

Nonlinear

Equal Ripple

Elliptical

Best

Poor

Equal Ripple

Equal Ripple

Bessel (Thompson)

Poor

Best

Linear