OPA2381 Datasheet, PDF (9/19 Pages) Burr-Brown (TI) – Precision, Low Power, 18MHz Transimpedance Amplifier

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OUTPUT RANGE
The OPA381 is specified to swing within at least 600mV
of the positive rail and 50mV of the negative rail with a
10kΩ load while maintaining good linearity. Swing to the
negative rail while maintaining 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 OPA381 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—see
Figure 2.
25
20 ^{VS = 5.5V}
15
10
5
0
−5
−10
−15
−20
−25
−1
0
1
2
3
V_OUT (V)
R_P = 10kΩ to −5V
R_L = 10kΩ to V_S/2
4
5
6
Figure 2. Effect of High-Speed Overload
Recovery Clamp on Output Voltage
OVERLOAD RECOVERY
The OPA381 has been designed to prevent output
saturation. After being overdriven to the positive rail, it
will typically require only 200ns to return to linear
operation. The time required for negative overload
recovery is greater, unless a pulldown 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.
OPA381
OPA2381
SBOS313B − AUGUST 2004 − REVISED NOVEMBER 2004
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 OPA381 can be made to swing to 0V,
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
pulldown 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
OPA381
V_OUT
R_P
=
−V_S
500µA
V− = Gnd
R_P = 10kΩ
−V_S = −5V
Negative Supply
Figure 3. Amplifier with Pull-Down Resistor to
Achieve V_OUT = 0V
The OPA381 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 OPA381 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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