OPA241 Datasheet, PDF (9/10 Pages) Burr-Brown (TI) – Single-Supply, MicroPOWER OPERATIONAL AMPLIFIERS

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 0.01µF ceramic
capacitors.
OPERATING VOLTAGE
The OPA241 series is laser-trimmed for low offset voltage
and drift at low supply voltage (V_S = +5V). The OPA251
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.
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
most susceptible to the effects of capacitive load. With V_S =
+5V, G = +1, and I_OUT = 0, operation remains stable with
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-
ample, with V_S = ±1.35V and R_S = 5kΩ, the OPA241 series
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.
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.
100k
10k
V_S = +2.7V
V_S = +5V
Operation above
selected gain curve
not recommended
G = 10
1k
G = –1
Sinking
G = +1
100
–1
–0.1 –0.01
0
0.01
Output Current (mA)
Sourcing
0.1
1
V+
OPA241 and OPA251 (single op amps) only.
0.01µF
7
2
Use offset adjust pins only to null
offset voltage of op amp—see text.
6
3
OPA241
5
1
0.01µF ⁴ 100kΩ
Trim Range: ±2mV
FIGURE 2. Stability—Capacitive Load versus Output Cur-
rent for Low Supply Voltage.
100k
V_S = ±15V
10k
G = 10
Operation above
selected gain curve
not recommended
(V–) = 0V for single-supply operation.
V–
FIGURE 1. OPA241 and OPA251 Offset Voltage Trim
Circuit.
1k
G = +1
Sinking
G = –1
Sourcing
CAPACITIVE LOAD AND STABILITY
100
–1
–0.1 –0.01
0
0.01
0.1
1
The OPA241 series and OPA251 series can drive a wide
Output Current (mA)
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.
FIGURE 3. Stability—Capacitive Load versus Output Cur-
rent for ±15V Supplies.
OPA241, 2241, 4241
®
9
OPA251, 2251, 4251