ADA4522-4ARUZ-R7 datasheet(40/48 Pages) AD

40 / 48 page

Data Sheet

ADA4522-1/ADA4522-

2/ADA4522-4

analog.com

Rev I 40 of 48

Printed Circuit Board Layout

The ADA4522-1/ADA4522-2/ADA4522-4 are high precision devices with ultralow offset voltage and noise. Therefore,

take care in the design of the PCB layout to achieve optimum performance of the ADA4522-1/ADA4522-2/ADA4522-4

at the board level.

To avoid leakage currents, keep the surface of the board clean and free of moisture.

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 traces and solder to component leads. Figure 85 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 performance of the ultralow offset voltage of the ADA4522-1/ADA4522-2/ADA4522-4.

Figure 85.Mismatch in Seebeck Voltages Causes Seebeck Voltage Error

In Figure 85, VSC1 and VSC2 are the Seebeck voltages due to solder to component at Junction 1 and Junction 2,

respectively. VTS1 and VTS2are the Seebeck voltages due to solder to trace at Junction 1 and Junction 2. TA1 and TA2 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 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 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

COMPONENT

LEAD

COPPER

TRACE

VSC1

VTS1

TA1

SURFACE-MOUNT

COMPONENT

PC BOARD

TA2

VSC2

VTS2

IF TA1 ≠ TA2, THEN

VTS1 + VSC1 ≠ VTS2 + VSC2

ADA4522-4ARUZ-R7 Datasheet(PDF) 40 Page - Analog Devices

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