AD8672 Analog Devices, AD8672 Datasheet - Page 13

• Manufacturer Part Number: AD8672
• Description: Dual Precision Very Low Noise, Low Input Bias Current Operational Amplifier
• Manufacturer: Analog Devices

Specifications of AD8672

• -3db Bandwidth: 10MHz
• Slew Rate: 4V/µs
• Vos: 20µV
• Ib: 3nA
• # Opamps Per Pkg: 2
• Input Noise (nv/rthz): 2.8nV/rtHz
• Vcc-vee: 10V to 36V
• Isy Per Amplifier: 3.5mA
• Packages: SOIC,SOP

TOTAL HARMONIC DISTORTION (THD) AND NOISE
The AD8671/AD8672/AD8674 exhibit low total harmonic
distortion (THD) over the entire audio frequency range. This
makes them suitable for applications with high closed-loop
gains, including audio applications. Figure 35 shows
approximately 0.0006% of THD + N in a positive unity gain, the
worst-case configuration for distortion.
DRIVING CAPACITIVE LOADS
The AD8671/AD8672/AD8674 can drive large capacitive loads
without causing instability. However, when configured in unity
gain, driving very large loads can cause unwanted ringing or
instability.
Figure 36 shows the output of the AD8671 with a capacitive
load of 1 nF. If heavier loads are used in low closed-loop gain or
unity-gain configurations, it is recommended to use external
compensation as shown in the circuit in Figure 37. This
technique reduces the overshoot and prevents the op amp from
oscillation. The trade-off of this circuit is a reduction in output
swing. However, a great added benefit stems from the fact that
the input signal and the op amp’s noise are filtered, and thus the
overall output noise is kept to a minimum.
The output response of the circuit is shown in Figure 38.
0.1000
0.0500
0.0200
0.0100
0.0050
0.0020
0.0010
0.0005
0.0002
0.0001
20
Figure 35. Total Harmonic Distortion and Noise
50
100
200
Hz
500
1k
LT1007
2k
AD8671
5k
V
V
R
S
IN
L
= ±5V
= 600Ω
= 2.5V
10k
20k
Rev. E | Page 13 of 20
500Ω
R
G
Figure 37. Recommended Capacitive Load Circuit
Figure 36. AD8671 Capacitive Load Drive
Figure 38. Compensated Load Drive
V
C
220pF
IN
TIME (10μs/DIV)
F
TIME (10μs/DIV)
AD8671/AD8672/AD8674
V
V
EE
CC
500Ω
R
F
10Ω
R
S
V
R
C
V
A
V
R
C
C
V
A
SY
L
L
IN
V
SY
IN
L
L
F
V
= 2kΩ
= 1nF
= +1
= 100mV
= ±15V
= 2kΩ
= 1nF
= 220pF
= +2
= 100mV
= ±15V
C
1nF
L
CH2 +OVER
39.80%
CH2 –OVER
39.80%
CH2 +OVER
5.051%
CH2 –OVER
6.061%
R
2kΩ
L