OP270 Analog Devices, OP270 Datasheet - Page 15

• Manufacturer Part Number: OP270
• Description: Low Noise Precision Dual Op Amp
• Manufacturer: Analog Devices

Specifications of OP270

• -3db Bandwidth: 5MHz
• Slew Rate: 2.4V/µs
• Vos: 50µV
• Ib: 15nA
• # Opamps Per Pkg: 2
• Input Noise (nv/rthz): 3.2nV/rtHz
• Vcc-vee: 9V to 36V
• Isy Per Amplifier: 3.25mA
• Packages: DIP,SOIC

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
IN
R1
Figure 39. Driving Large Capacitive Loads
OP270
V+
V–
200pF
C5
0.1µF
C3
0.1µF
C1
+
+
PLACE SUPPLY DECOUPLING
CAPACITOR AT OP270
C2
10µF
C4
10µF
50Ω
R2
R3
V
C1
1000pF
OUT
Rev. E | Page 15 of 20
UNITY-GAIN BUFFER APPLICATIONS
When R
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 R
capable of handling the current requirements (I
the amplifier stays in its active mode and a smooth transition occurs.
When R
(3 pF) of the amplifier creates additional phase shift and reduces
phase margin. A small capacitor (20 pF to 50 pF) in parallel with
R
f
helps eliminate this problem.
f
f
≤ 100 Ω and the input is driven with a fast, large signal
> 3 kΩ, a pole created by R
OP270
R
f
Figure 40. Pulsed Operation
f
and the input capacitance
f
≥ 500 Ω, the output is
L
≤ 20 mA at 10 V);
2.4V/µs
OP270