9

®

OPA241, 2241, 4241

OPA251, 2251, 4251

APPLICATIONS INFORMATION

The OPA241 and OPA251 series are unity-gain stable and

suitable for a wide range of general purpose applications.

Power supply pins should be bypassed with 0.01

µF ceramic

capacitors.

OPERATING VOLTAGE

The OPA241 series is laser-trimmed for low offset voltage

series is trimmed for

±15V operation. Both products operate

over the full voltage range (+2.7V to +36V or

±1.35V to

±18V) with some compromises in offset voltage and drift

performance. However, all other parameters have similar

performance. Key parameters are guaranteed over the speci-

fied temperature range, –40

°C to +85°C. Most behavior

remains unchanged throughout the full operating voltage

range. Parameters which vary significantly with operating

voltage or temperature are shown in typical performance

curves.

OFFSET VOLTAGE TRIM

As mentioned previously, offset voltage of the OPA241

series is laser-trimmed at +5V. The OPA251 series is trimmed

at

±15V. Because the initial offset is so low, user adjustment

is usually not required. However, the OPA241 and OPA251

(single op amp versions) provide offset voltage trim connec-

tions on pins 1 and 5. Offset voltage can be adjusted by

connecting a potentiometer as shown in Figure 1. This

adjustment should be used only to null the offset of the op

amp, not to adjust system offset or offset produced by the

signal source. Nulling offset could degrade the offset drift

behavior of the op amp. While it is not possible to predict the

exact change in drift, the effect is usually small.

Figures 2 and 3 show the regions where the OPA241 series

and OPA251 series have the potential for instability. As

shown, the unity gain configuration with low supplies is the

load capacitance up to approximately 200pF. Increasing

supply voltage, output current, and/or gain significantly

improves capacitive load drive. For example, increasing the

supplies to

±15V and gain to 10 allows approximately

2700pF to be driven.

One method of improving capacitive load drive in the unity

gain configuration is to insert a resistor inside the feedback

loop as shown in Figure 4. This reduces ringing with large

capacitive loads while maintaining dc accuracy. For ex-

and OPA251 series perform well with capacitive loads in

excess of 1000pF. Without the series resistor, capacitive

load drive is typically 200pF for these conditions. However,

this method will result in a slight reduction of output voltage

swing.

CAPACITIVE LOAD AND STABILITY

The OPA241 series and OPA251 series can drive a wide

range of capacitive loads. However, all op amps under

certain conditions may be unstable. Op amp configuration,

gain, and load value are just a few of the factors to consider

when determining stability.

V+

V–

100k

Ω

Use offset adjust pins only to null

offset voltage of op amp—see text.

Trim Range:

±2mV

(V–) = 0V for single-supply operation.

OPA241

6

7

5

4

3

2

1

0.01

µF

0.01

µF

OPA241 and OPA251 (single op amps) only.

FIGURE 1. OPA241 and OPA251 Offset Voltage Trim

Circuit.

100k

10k

1k

100

Output Current (mA)

–1

–0.1

–0.01

0

0.01

0.1

1

Operation above

selected gain curve

not recommended

G = 10

G = –1

G = +1

Sinking

Sourcing

V

V

FIGURE 2. Stability—Capacitive Load versus Output Cur-

rent for Low Supply Voltage.

FIGURE 3. Stability—Capacitive Load versus Output Cur-

rent for

±15V Supplies.

100k

10k

1k

100

Output Current (mA)

–1

–0.1

–0.01

0

0.01

0.1

1

Operation above

selected gain curve

not recommended

G = 10

G = –1

G = +1

V

Sinking

Sourcing