ADA4522-4ARZ-R7 datasheet(28/32 Pages) AD

28 / 32 page

ADA4522-1/ADA4522-2/ADA4522-4

Data Sheet

Rev. E | Page 28 of 32

OUT+

SENSE–

SENSE+

OUT–

VEXC

1/2

V+

R1 11.3kΩ

C1 3.3µF

1/2

ADA4522-2

R2 11.3kΩ

C2 3.3µF

60.4Ω

1kΩ

1µF

10µF

1µF

AIN(+)

REF(–)

REF(+)

DOUT/

RDY

DIN

AIN(–)

GND

VDD

+5V

AD7791

100pF

1µF

100pF

SCLK

LOAD

CELL

Figure 83. Precision Weigh Scale Measurement System

PRECISION LOW-SIDE CURRENT SHUNT SENSOR

Many applications require the sensing of signals near the

positive or negative rails. Current shunt sensors are one such

application and are mostly used for feedback control systems.

They are also used in a variety of other applications, including

power metering, battery fuel gauging, and feedback controls in

industrial applications. In such applications, it is desirable to

use a shunt with very low resistance to minimize series voltage

drop. This configuration not only minimizes wasted power, but

also allows the measurement of high currents while saving power.

A typical shunt may be 100 mΩ. At a measured current of 1 A,

the voltage produced from the shunt is 100 mV, and the ampli-

fier error sources are not critical. However, at low measured current

in the 1 mA range, the 100 μV generated across the shunt demands

a very low offset voltage and drift amplifier to maintain absolute

accuracy. The unique attributes of a zero drift amplifier provide

a solution. Figure 84 shows a low-side current sensing circuit

using the ADA4522-1/ADA4522-2/ADA4522-4. The ADA4522-1/

ADA4522-2/ADA4522-4 are configured as difference amplifiers

with a gain of 1000. Although the ADA4522-1/ADA4522-2/

ADA4522-4 have high CMRR, the CMRR of the system is

limited by the external resistors. Therefore, as mentioned in the

Single-Supply Instrumentation Amplifier section, the key to

high CMRR for the system is resistors that are well matched

from both the resistive ratio and relative drift, where R1/R2 =

R3/R4.

Any unused channel of the ADA4522-1/ADA4522-2/

ADA4522-4 must be configured in unity gain with the input

common-mode voltage tied to the midpoint of the power

supplies.

100kΩ

VSY

VOUT*

*VOUT = AMPLIFIER GAIN × VOLTAGE ACROSS RS

= 1000 × RS × I

= 100 × I

0.1Ω

100Ω

ADA4522-1/

ADA4522-2/

ADA4522-4

100kΩ

100Ω

Figure 84. Low-Side Current Sensing Circuit

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

ADA4522-4ARZ-R7 Datasheet(PDF) 28 Page - Analog Devices

ADA4522-4ARZ-R7 Datasheet(HTML) 28 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

Datasheet Download

Link URL