參數(shù)資料
型號: LOG112
元件分類: 跨阻放大器
英文描述: Precision, High-Speed Transimpedance Amplifier
中文描述: 精密,高速互阻抗放大器
文件頁數(shù): 10/18頁
文件大?。?/td> 362K
代理商: LOG112
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SBOS291E NOVEMBER 2003 REVISED NOVEMBER 2004
www.ti.com
10
OUTPUT RANGE
The OPA380 is specified to swing within at least 600mV
of the positive rail and 100mV of the negative rail with
a 2k
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—see
Figure 2.
20
15
10
5
0
5
10
15
20
OFFSET VOLTAGE vs OUTPUT VOLTAGE
V
OUT
(V)
V
O
(
μ
V
0
1
2
3
4
5
V
S
= 5V
R
P
= 2k
connected to
5V
R
L
= 2k
connected to V
S
/2
Effect of clamp
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 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
.
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 pulldown resistor may be connected between
the output and the negative supply to pull the output
down to 0V. See Figure 3.
OPA380
V
OUT
R
F
R
P
=2k
V+ = +5V
V
= Gnd
V
=
5V
Negative Supply
λ
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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