ADA4528-1ACPZ-R2 datasheet(23/29 Pages) AD

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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.

100

10k

100k

10M

FREQUENCY (Hz)

VSY = 5V

VCM = VSY/2

AV = 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, ISY+ = ISY− = 3 mA for the dual

ADA4528-2 at 5 V of supplies.

1kΩ

ISY+

+VSY

VOUT

–VSY

ISY–

ADA4528-2

1/2

Figure 68. Voltage Follower

0.5

1.0

1.5

2.0

2.5

3.0

3.5

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

VSY (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.

VOUT

1kΩ

ISY+

+VSY

–VSY

ISY–

ADA4528-2

1/2

Figure 70. Comparator A

VOUT

1kΩ

ISY+

+VSY

–VSY

ISY–

ADA4528-2

1/2

Figure 71. Comparator B

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