ADA4528-2ARMZ-R7 datasheet(22/24 Pages) AD

22 / 24 page

ADA4528-1/ADA4528-2

Data Sheet

Rev. F | Page 22 of 24

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VSY (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

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.

SOLDER

COMPONENT

LEAD

COPPER

TRACE

VSC1

VTS1

TA1

SURFACE-MOUNT

COMPONENT

PC BOARD

TA2

VSC2

VTS2

IF TA1 ≠ TA2, THEN

VTS1 + VSC1 ≠ VTS2 + VSC2

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 must 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.

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