ADA4528-2ARMZ Datasheet, PDF (24/29 Pages) Analog Devices – Precision, Ultralow Noise, RRIO, Zero-Drift Op Amp

Data Sheet
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
V_SY (V)
Figure 72. Supply Current vs. Supply Voltage (Comparator A and
Comparator B)
For more details on op amps as comparators, refer to the
AN-849 Application Note, Using Op Amps as Comparators.
PRINTED CIRCUIT BOARD LAYOUT
The ADA4528-1/ADA4528-2 are high precision devices with
ultralow offset voltage and noise. Therefore, care must be taken
in the design of the printed circuit board (PCB) layout to achieve
the optimum performance of the ADA4528-1/ADA4528-2 at
board level.
To avoid leakage currents, keep the surface of the board clean
and free of moisture. Coating the board surface creates a barrier
to moisture accumulation and reduces parasitic resistance on
the board.
To minimize power supply disturbances caused by output current
variation, properly bypass the power supplies and keep the supply
traces short. Connect bypass capacitors as close as possible to the
device supply pins.
Stray capacitances are a concern at the outputs and the inputs of
the amplifier. It is recommended that signal traces be kept at a
distance of at least 5 mm from supply lines to minimize coupling.
A potential source of offset error is the Seebeck voltage on the
circuit board. The Seebeck voltage occurs at the junction of two
dissimilar metals and is a function of the temperature of the
ADA4528-1/ADA4528-2
junction. The most common metallic junctions on a circuit
board are solder-to-board trace and solder-to-component lead.
Figure 73 shows a cross section of a surface-mount component
soldered to a PCB. A variation in temperature across the board
(where TA1 ≠ TA2) causes a mismatch in the Seebeck voltages at
the solder joints, thereby resulting in thermal voltage errors
that degrade the ultralow offset voltage performance of the
ADA4528-1/ADA4528-2.
COMPONENT
LEAD
V_SC1
V_TS1
SURFACE-MOUNT
COMPONENT
+ ^{VSC2 SOLDER}
+ ^VTS2
PC BOARD
COPPER
TRACE
T_A1
T_A2
IF T_A1 ≠ T_A2, THEN
V_TS1 + V_SC1 ≠ V_TS2 + V_SC2
Figure 73. Mismatch in Seebeck Voltages Causes
Seebeck Voltage Error
To minimize these thermocouple effects, orient resistors so that
heat sources warm both ends equally. Where possible, the input
signal paths should contain matching numbers and types of com-
ponents to match the number and type of thermocouple junctions.
For example, dummy components, such as zero value resistors, can
be used to match the thermoelectric 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 canceling thermal errors. Additionally, use
leads of equal length to keep thermal conduction in equilibrium.
Keep heat sources on the PCB as far away from the amplifier
input circuitry as practical.
It is highly recommended that a ground plane be used. A ground
plane helps to distribute heat throughout the board, maintains a
constant temperature across the board, and reduces EMI noise
pickup.
Rev. D | Page 23 of 28