OP207 データシートの表示（PDF） - Analog Devices
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OP207 Datasheet PDF : 21 Pages
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Data Sheet
CAPACITIVE LOAD DRIVING AND POWER SUPPLY
CONSIDERATIONS
The OP270 is unity-gain stable and capable of driving large
capacitive loads without oscillating. Nonetheless, good supply
bypassing is highly recommended. Proper supply bypassing
reduces problems caused by supply line noise and improves the
capacitive load driving capability of the OP270.
In the standard feedback amplifier, the output resistance of the
op amp combines with the load capacitance to form a low-pass
filter that adds phase shift in the feedback network and reduces
stability. A simple circuit to eliminate this effect is shown in
Figure 39. The components C1 and R3 decouple the amplifier
from the load capacitance and provide additional stability. The
values of C1 and R3 shown in Figure 39 are for a load capacitance
of up to 1000 pF when used with the OP270.
V+
R1
VIN
C3
0.1µF
+ C2
10µF
R2
C1
200pF
R3
50Ω
OP270
VOUT
C1
1000pF
C5
C4
0.1µF + 10µF
V–
PLACE SUPPLY DECOUPLING
CAPACITOR AT OP270
Figure 39. Driving Large Capacitive Loads
OP270
UNITY-GAIN BUFFER APPLICATIONS
When Rf ≤ 100 Ω and the input is driven with a fast, large signal
pulse (>1 V), the output waveform looks like the one in Figure 40.
During the fast feedthrough-like portion of the output, the input
protection diodes effectively short the output to the input, and
a current, limited only by the output short-circuit protection, is
drawn by the signal generator. With Rf ≥ 500 Ω, the output is
capable of handling the current requirements (IL ≤ 20 mA at 10 V);
the amplifier stays in its active mode and a smooth transition occurs.
When Rf > 3 kΩ, a pole created by Rf and the input capacitance
(3 pF) of the amplifier creates additional phase shift and reduces
phase margin. A small capacitor (20 pF to 50 pF) in parallel with
Rf helps eliminate this problem.
Rf
OP270
2.4V/µs
Figure 40. Pulsed Operation
Rev. F | Page 15 of 20
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