OPA380AID Datasheet, PDF (10/22 Pages) Texas Instruments – Precision, High-Speed Transimpedance Amplifier

OPA380
OPA2380
SBOS291G − NOVEMBER 2003 − REVISED SEPTEMBER 2007
OUTPUT RANGE
The OPA380 is specified to swing within at least 600mV
of the positive rail and 100mV of the negative rail with
a 2kΩ load with excellent linearity. Swing to the negative
rail while maintaining good linearity can be extended to
0V—see the section, Achieving Output Swing to
Ground. See the Typical Characteristic curve, Output
Voltage Swing vs Output Current.
The OPA380 can swing slightly closer than specified to
the positive rail; however, linearity will decrease and a
high-speed overload recovery clamp limits the amount
of positive output voltage swing available, as shown in
Figure 2.
OFFSET VOLTAGE vs OUTPUT VOLTAGE
20
V_S = 5V
15
10 _{RP = 2kΩ connected to −5V}
5
0
−5
R_L = 2kΩconnected to V_S /2
−10
−15
Effect of clamp
−20
0
1
2
3
4
5
V_OUT (V)
Figure 2. Effect of High-Speed Overload
Recovery Clamp on Output Voltage
OVERLOAD RECOVERY
The OPA380 has been designed to prevent output
saturation. After being overdriven to the positive rail, it
will typically require only 100ns to return to linear
operation. The time required for negative overload
recovery is greater, unless a pull-down resistor
connected to a more negative supply is used to extend
the output swing all the way to the negative rail—see the
following section, Achieving Output Swing to Ground.
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ACHIEVING OUTPUT SWING TO GROUND
Some applications require output voltage swing from
0V to a positive full-scale voltage (such as +4.096V)
with excellent accuracy. With most single-supply op
amps, problems arise when the output signal
approaches 0V, near the lower output swing limit of a
single-supply op amp. A good single-supply op amp
may swing close to single-supply ground, but will not
reach 0V.
The output of the OPA380 can be made to swing to
ground, or slightly below, on a single-supply power
source. This extended output swing requires the use of
another resistor and an additional negative power
supply. A pull-down resistor may be connected between
the output and the negative supply to pull the output
down to 0V. See Figure 3.
R_F
λ
V+ = +5V
OPA380
V_OUT
V− = Gnd
R_P = 2kΩ
V_P = −5V
Negative Supply
Figure 3. Amplifier with Optional Pull-Down
Resistor to Achieve V_OUT = 0V
The OPA380 has an output stage that allows the output
voltage to be pulled to its negative supply rail using this
technique. However, this technique only works with
some types of output stages. The OPA380 has been
designed to perform well with this method. Accuracy is
excellent down to 0V. Reliable operation is assured over
the specified temperature range.
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