ADA4522-4ARZ-R7 datasheet(42/48 Pages) AD

42 / 48 page

Data Sheet

ADA4522-1/ADA4522-

2/ADA4522-4

analog.com

Rev I 42 of 48

Figure 88.Supply Current (ISY) per Dual Amplifier vs. Supply Voltage (VSY) (ADA4522-1/ADA4522-2/ADA4522-4 as a Comparator)

Note that 10 kΩ resistors are used in series with the input of the op amp. If smaller resistor values are used, the supply

current of the system increases much more. For more details on op amps as comparators, see the AN-849 Application

Note

, Using Op Amps as Comparators.

Use of Large Source Resistance

The ADA4522-1/ADA4522-2/ADA4522-4 are designed to work with low value source resistance. Note that the amplifier

has an ultralow voltage noise density of 6 nV/√Hz. A 1 kΩ resistor contributes 4 nV/√Hz; therefore, placing a 1 kΩ

resistor at the input increases total noise to 7.2 nV/√Hz. For this noise reason, it is recommended to avoid using large

source resistance.

Unity Gain Follower with Large Source Resistance

When the ADA4522-1/ADA4522-2/ADA4522-4 are configured in a unity-gain follower configuration with a large source

resistance and slow power supply ramp rate, the amplifier output may rail to the positive supply.

Figure 89.Insert RF When Large RS is Use

Workaround

To avoid the amplifier output railing to the positive supply, implement one of the following actions (see Table 11

and Figure 89):



Reduce the value of the source resistance (RS).



Insert a feedback resistor (RF).

2.2

2.0

1.8

1.6

1.4

1.2

1.0

0.8

0.6

0.4

0.2

VSY (V)

ISY+

ISY–

ADA4522-1/

ADA4522-2/

ADA4522-4

+VSY

VOUT

–VSY

VIN

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