AD8622/AD8624

Data Sheet

Rev. D | Page 16 of 20

HALL SENSOR SIGNAL CONDITIONING

The AD8622/AD8624 is also highly suitable for high accuracy,

low power signal conditioning circuits. One such use is in Hall

sensor signal conditioning (see Figure 57). 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/AD8624,

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

magnetic 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/AD8624 then increases the

sensitivity to 55 mV/mT. The key to high CMRR for this in-amp

configuration are resistors that are well matched (where R1/R2

= R3/R4) from both the resistive ratio and relative drift. The

resistors are important in determining the performance over

manufacturing tolerances, time and temperature. At least 1% or

better resistors are recommended. Using the AD8622/AD8624 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.

VSY

VSY

VSY

R6

9.9kΩ

R3

9.9kΩ

R5

9.9kΩ

R1

9.9kΩ

R2

9.9kΩ

R7

200Ω

R8

4.12kΩ

R9

98.8kΩ

R4

9.9kΩ

ADR121 – 2.5V

400Ω

×4

HALL

ELEMENT

VOUT = 2.5V +

× MAGNETIC FIELD (mT)

55mV

mT

+

–

+

–

VSY

–

+

VSY

AD862x

AD862x

AD862x

AD862x

–

+

+

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 57. Hall Sensor Signal Conditioning