AD8622

Rev. 0 | Page 16 of 20

HALL SENSOR SIGNAL CONDITIONING

The AD8622 is also highly suitable for high accuracy, low power

signal conditioning circuits. One such use is in Hall sensor

signal conditioning (see Figure 55). The magnetic sensitivity of

a Hall element is proportional to the bias voltage applied across

it. With 1 V bias voltage, the Hall element consumes about

2.5 mA of supply current and has a sensitivity of 5.5 mV/mT

typical. To reduce power consumption, bias voltage must be

reduced, but at the risk of lower sensitivity. The only way to

achieve higher sensitivity is by introducing a gain using a

precision micropower amplifier. The AD8622, with all its

features, is well suited to amplify the sensitivity of the Hall

element.

The ADR121 is a precision micropower 2.5 V voltage reference.

A precision voltage reference is required to hold a constant current

so that the Hall voltage only depends on the intensity of the mag-

netic field. Using the 4.12k:98.8k resistive divider, the bias

voltage of the Hall element is reduced to 100 mV, leading to only

250 μA of power consumption. The 3-op-amp in-amp

configuration of the AD8622 then increases the sensitivity to

55 mV/mT. Using the AD8622 to amplify the sensor signal can

reduce power while also achieving higher sensitivity. The total

current consumed is just 1.2 mA, resulting in 21× improvement in

sensitivity/power.

9.9kΩ

9.9kΩ

9.9kΩ

9.9kΩ

9.9kΩ

200Ω

4.12kΩ

98.8kΩ

9.9kΩ

ADR121 –2.5V

400Ω

×4

HALL

ELEMENT

× MAGNETIC FIELD (mT)

55mV

mT

1/2

AD8622

+

–

1/2

AD8622

+

–

1/2

AD8622

–

+

1/2

AD8622

–

+

+

C3

0.1µF

TO 10µF

C2

0.1µF

C1

1µF TO 10µF

NOTES

1. USE MATCHED RESISTORS FOR IN-AMP.

2. FOR INFORMATION ON C1, C2, AND C3, REFER TO ADR121 DATA SHEET.

Figure 55. Hall Sensor Signal Conditioning