OPA37 datasheet(10/24 Pages) TI2

10 / 24 page

OPA27, OPA37

SBOS135C

www.ti.com

COMPENSATION

Although internally compensated for unity-gain stability, the

OPA27 may require a small capacitor in parallel with a

feedback resistor (RF) which is greater than 2kΩ. This ca-

pacitor will compensate the pole generated by RF and CIN

and eliminate peaking or oscillation.

INPUT PROTECTION

Back-to-back diodes are used for input protection on the

OPA27 and OPA37. Exceeding a few hundred millivolts differ-

ential input signal will cause current to flow, and without

external current limiting resistors, the input will be destroyed.

Accidental static discharge, as well as high current, can dam-

age the amplifier’s input circuit. Although the unit may still be

functional, important parameters such as input offset voltage,

drift, and noise may be permanently damaged, as will any

precision operational amplifier subjected to this abuse.

Transient conditions can cause feedthrough due to the amplifier’s

finite slew rate. When using the OPA27 as a unity-gain buffer

(follower) a feedback resistor of 1k

Ω is recommended, as

shown in Figure 6.

NOISE: BIPOLAR VERSUS FET

Low-noise circuit design requires careful analysis of all noise

sources. External noise sources can dominate in many

cases, so consider the effect of source resistance on overall

operational amplifier noise performance. At low source im-

pedances, the lower voltage noise of a bipolar operational

amplifier is superior, but at higher impedances the high

current noise of a bipolar amplifier becomes a serious liabil-

ity. Above about 15k

Ω, the OPA111 low-noise FET opera-

tional amplifier is recommended for lower total noise than the

OPA27, as shown in Figure 5.

FIGURE 3. Offset Voltage Trim.

FIGURE 5. Voltage Noise Spectral Density Versus Source

Resistance.

FIGURE 6. Pulsed Operation.

FIGURE 8. Unity-Gain Inverting Amplifier.

FIGURE 7. Low-Noise RIAA Preamplifier.

FIGURE 4. High Resolution Offset Voltage Trim.

±4mV Typical Trim Range

NOTE: (1) 10k

Ω to 1MΩ

Trim Potentiometer

(10k

Ω Recommended).

–V

OPA27/37

(1)

±280µV Typical Trim Range

NOTE: (1) 1k

Ω Trim Potentiometer.

–V

OPA27/37

4.7k

Ω

4.7k

Ω

(1)

100

10k

100k

10M

100

OPA111 + Resistor

OPA27 + Resistor

Source Resistance, R

S (Ω)

O = √en

2 + (i

nRS)

2 + 4kTR

O = 1kHz

Resistor Noise Only

OPA27 + Resistor

OPA111 + Resistor

Resistor Noise Only

OPA27

Output

1.9V/

µs

≈ 1kΩ

Input

–

OPA37

Output

97.6k

Ω

≈ 40dB at 1kHz.

Metal film resistors.

Film capacitors.

L and CL per cartridge

manufacturer’s

recommendations.

100

Ω

0.03

µF

0.01

µF

7.87k

Ω

µF

20k

Ω

Moving

Magnet

Cartridge

OPA27

Output

Input

Ω

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