Datasheet

Data Sheet ADA4522-1/ADA4522-2/ADA4522-4
Rev. F | Page 29 of 33
performance of the ultralow offset voltage of the ADA4522-1/
ADA4522-2/ADA4522-4.
SOLDER
+
+
+
+
COMPONENT
LEAD
COPPER
TRACE
V
SC1
V
TS1
T
A1
SURFACE-MOUNT
COMPONENT
PC BOARD
T
A2
V
SC2
V
TS2
IF T
A1
 T
A2
, THEN
V
TS1
+ V
SC1
 V
TS2
+ V
SC2
13168-081
Figure 85. Mismatch in Seebeck Voltages Causes Seebeck Voltage Error
In Figure 85, V
SC1
and V
SC2
are the Seebeck voltages due to solder to
component at Junction 1 and Junction 2, respectively. V
TS1
and
V
TS2
are the Seebeck voltages due to solder to trace at Junction 1
and Junction 2. T
A1
and T
A2
are the temperatures of Junction 1
and Junction 2, respectively.
To minimize these thermocouple effects, orient resistors so
that heat sources warm both ends equally. Where possible, it
is recommended that the input signal paths contain matching
numbers and types of components to match the number and type
of thermocouple junctions. For example, dummy components,
such as zero value resistors, can be used to match the thermo-
electric error source (real resistors in the opposite input path).
Place matching components in close proximity and orient them
in the same manner to ensure equal Seebeck voltages, thus
cancelling thermal errors. Additionally, use leads that are of
equal length to keep thermal conduction in equilibrium. Keep
heat sources on the PCB as far away from amplifier input circuitry
as is practical.
It is highly recommended to use a ground plane. A ground
plane helps distribute heat throughout the board, maintain a
constant temperature across the board, and reduce EMI noise
pickup.
COMPARATOR OPERATION
An op amp is designed to operate in a closed-loop configuration
with feedback from its output to its inverting input. In contrast to
op amps, comparators are designed to operate in an open-loop
configuration and to drive logic circuits. Although op amps are
different from comparators, occasionally an unused section of a
dual op amp is used as a comparator to save board space and
cost; however, this is not recommended for the ADA4522-1/
ADA4522-2/ADA4522-4.
Figure 86 and Figure 87 show the ADA4522-1/ADA4522-2/
ADA4522-4 configured as a comparator, with 10 kΩ resistors in
series with the input pins. Any unused channels are configured as
buffers with the input voltage kept at the midpoint of the power
supplies. The ADA4522-1/ADA4522-2/ADA4522-4 have input
devices that are protected from large differential input voltages by
Diode D5 and Diode D6, as shown in Figure 72. These diodes
consist of substrate PNP bipolar transistors, and conduct whenever
the differential input voltage exceeds approximately 600 mV;
however, these diodes also allow a current path from the input
to the lower supply rail, resulting in an increase in the total
supply current of the system. Both comparator configurations yield
the same result. At 30 V of power supply, I
SY
+ remains at 1.55 mA
per dual amplifier, but I
SY
− increases close to 2 mA in magni-
tude per dual amplifier.
ADA4522-1/
ADA4522-2/
ADA4522-4
A1
10k

10k

I
SY
+
+V
SY
V
OUT
–V
SY
I
SY
–
A2
13168-082
Figure 86. Comparator Configuration A
A1
10k

10k
I
SY
+
+
V
SY
V
OUT
–V
SY
I
SY
–
A2
ADA4522-1/
ADA4522-2/
ADA4522-4
13168-083
Figure 87. Comparator Configuration B
2.2
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
0 6 12 18 24 304 101622282 8 14 20 26
I
SY
PER DUAL AMPLIFIER (mA)
V
SY
(V)
I
SY
+
I
SY
–
13168-084
Figure 88. Supply Current (I
SY
) per Dual Amplifier vs. Supply Voltage (V
SY
)
(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.
Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.