Datasheet

ADA4522-1/ADA4522-2/ADA4522-4 Data Sheet
Rev. F | Page 30 of 33
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 k 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.
ADA4522-1/
ADA4522-2/
ADA4522-4
+V
SY
R
F
R
S
V
OUT
–V
SY
V
IN
13168-200
Figure 89. Insert R
F
When Large R
S
is Used
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 (R
S
).
 Insert a feedback resistor (R
F
).
Table 11. Amplifier Output Railing Workaround
Recommendations
Condition Recommendation
1.5 V ≤ V
SY
− V
IN
< 2.5 V
R
F
= 200 Ω or R
F
≥ 50 R
S
, whichever is
greater
2.5 V ≤ V
SY
− V
IN
< 3.5 V R
S
≤ 200 Ω or R
F
≥ 2 R
S
V
SY
− V
IN
≥ 3.5 V R
S
≤ 500 Ω or R
F
≥ 0.5 R
S
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