ada4528-1 Analog Devices, Inc., ada4528-1 Datasheet - Page 17

• Manufacturer Part Number: ada4528-1
• Description: Precision, Ultralow Noise, Rrio, Zero-drift Op Amp Ada4528-1
• Manufacturer: Analog Devices, Inc.

PRINTED CIRCUIT BOARD LAYOUT
The ADA4528-1 is a high precision device with ultralow offset
voltage and noise. Therefore, care must be taken in the design of
the printed circuit board (PCB) layout to achieve optimum
performance of the ADA4528-1 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.
Properly bypassing the power supplies and keeping the supply
traces short minimizes power supply disturbances caused by
output current variation. 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
junction. The most common metallic junctions on a circuit board
are solder-to-board trace and solder-to-component lead. Figure 60
shows a cross section of a surface-mount component soldered
to a PCB. A variation in temperature across the board (where T
T
thereby resulting in thermal voltage errors that degrade the per-
formance of the ultralow offset voltage of the ADA4528-1.
A2
) causes a mismatch in the Seebeck voltages at the solder joints,
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A1
≠
V
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 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, maintains a
constant temperature across the board, and reduces EMI noise
pick up.
COPPER
TS1
TRACE
V
COMPONENT
SC1
+
LEAD
+
T
A1
Figure 60. Mismatch in Seebeck Voltages Causes
SURFACE-MOUNT
Seebeck Voltage Error
COMPONENT
PC BOARD
IF T
V
TS1
A1
+ V
≠ T
SC1
T
A2
A2
, THEN
ADA4528-1
≠ V
+
TS2
V
SC2
+
+ V
V
TS2
SC2
SOLDER