Datasheet

70
60
50
40
30
20
10
0
0
3000
CapacitiveLoad(pF)
Overshoot(%)
2500
500 1000 1500 2000
G=1,V =1.8V
S
G=1,V =5.5V
S
G=10,V =1.8V
S
G=10,V =5.5V
S
1
0.5
0
0.5
1
1.5
2
2.5
3
-
-
-
-
-
-
9.75
11
Time(250ns/div)
Voltage(V)
10 10.25 10.5 10.75
Output
Input
V = 2.75V
G= 10
±
-
S
10 toW
20W
V+
V
IN
V
OUT
R
S
R
L
C
L
OPA320
3
2.5
2
1.5
1
0.5
0
0.5
1
-
-
9.75
11
Time(250ns/div)
Voltage(V)
10 10.25 10.5 10.75
Input
Output
V = 2.75V
G= 10
±
-
S
OPA320, OPA2320
OPA320S, OPA2320S
www.ti.com SBOS513E –AUGUST 2010–REVISED JUNE 2013
The equivalent series resistance (ESR) of some very OVERLOAD RECOVERY TIME
large capacitors (C
L
> 1µF) is sufficient to alter the
Overload recovery time is the time it takes the output
phase characteristics in the feedback loop such that
of the amplifier to come out of saturation and recover
the amplifier remains stable. Increasing the amplifier
to the linear region. Overload recovery is particularly
closed-loop gain allows the amplifier to drive
important in applications where small signals must be
increasingly larger capacitance. This increased
amplified in the presence of large transients.
capability is evident when observing the overshoot
Figure 38 and Figure 39 show the positive and
response of the amplifier at higher voltage gains, as
negative overload recovery times of the OPA320,
shown in Figure 37. One technique for increasing the
respectively. In both cases, the time elapsed before
capacitive load drive capability of the amplifier
the OPA320 comes out of saturation is less than
operating in unity gain is to insert a small resistor
100ns. In addition, the symmetry between the positive
(R
S
), typically 10Ω to 20Ω, in series with the output,
and negative recovery times allows excellent signal
as shown in Figure 36.
rectification without distortion of the output signal.
This resistor significantly reduces the overshoot and
ringing associated with large capacitive loads. A
possible problem with this technique is that a voltage
divider is created with the added series resistor and
any resistor connected in parallel with the capacitive
load. The voltage divider introduces a gain error at
the output that reduces the output swing. The error
contributed by the voltage divider may be
insignificant. For instance, with a load resistance, R
L
= 10kΩ and R
S
= 20Ω, the gain error is only about
0.2%. However, when R
L
is decreased to 600Ω,
which the OPA320 is able to drive, the error
increases to 7.5%.
Figure 38. Positive Recovery Time
Figure 36. Improving Capacitive Load Drive
Figure 39. Negative Recovery Time
Figure 37. Small-Signal Overshoot versus
Capacitive Load (100mV
PP
output step)
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