Datasheet
ADA4528-1/ADA4528-2 Data Sheet
Rev. D | Page 22 of 26
Residual Voltage Ripple
Although autocorrection feedback (ACFB) suppresses the chop-
ping related voltage ripple, higher noise spectrum exists at the
chopping frequency and its harmonics due to the remaining ripple.
Figure 67 shows the voltage noise density of the ADA4528-1/
ADA4528-2 configured in unity gain. A noise energy spectrum
of 50 nV/√Hz can be seen at the chopping frequency of 200 kHz.
This noise energy spectrum is significant when the op amp has a
closed-loop frequency that is higher than the chopping frequency.
1
10
100
1
10
100 1k 10k 100k 1M 10M
VOLTAGE NOISE DENSITY (nV/
√
Hz)
F
R
E
Q
U
E
N
C
Y
(
H
z
)
09437-063
V
SY
=
5
V
V
CM
=
V
SY
/
2
A
V
=
1
Figure 67. Voltage Noise Density vs. Frequency
To further suppress the noise at the chopping frequency, it is
recommended that a post filter be placed at the output of the
amplifier. For more information about residual voltage ripple,
see the AN-1114 Application Note, Lowest Noise Zero-Drift
Amplifier Has 5.6 nV/√Hz Voltage Noise Density.
COMPARATOR OPERATION
Figure 68 shows the ADA4528-2 configured as a voltage
follower with an input voltage that is always kept at midpoint
of the power supplies. The same configuration is applied to the
unused channel. A1 and A2 indicate the placement of ammeters
to measure supply current. As shown in Figure 69, as expected,
in normal operating condition, I
SY
+ = I
SY
− = 3 mA for the dual
ADA4528-2 at 5 V of supplies.
A1
1kΩ
1kΩ
I
SY
+
+
V
SY
V
OUT
–V
SY
I
SY
–
A2
ADA4528-2
1/2
09437-065
Figure 68. Voltage Follower
09437-066
0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
I
SY
PER DU
A
LAMPLIFIER (mA)
V
SY
(V)
Figure 69. Supply Current vs. Supply Voltage (Voltage Follower)
Figure 70 and Figure 71 show the ADA4528-2 configured as
comparators, with 1kΩ resistors in series with the input pins.
Figure 72 shows the supply currents for both configurations.
Supply currents increase slightly to 3.2 mA per dual amplifier at
5 V of supplies.
V
OUT
A1
1k
Ω
1k
Ω
I
SY
+
+
V
SY
–V
SY
I
SY
–
A2
ADA4528-2
1/2
09437-067
Figure 70. Comparator A
V
OUT
A1
1kΩ
1kΩ
I
SY
+
+
V
SY
–V
SY
I
SY
–
A2
ADA4528-2
1/2
09437-068
Figure 71. Comparator B