Functional Description and Application Information

Switching Behavior

The output of the A1225, A1227, and A1229 devices switches

low (turns on) when a magnetic field perpendicular to the Hall

After turn-on, the output is capable of sinking 25 mA and the

a south pole of sufficient strength towards the branded surface

of the device turns the device on, and the device remains on with

removal of the south pole.

the device output goes high (turns off). The difference between

the magnetic operate point and release point is the hysteresis,

ing of the output, even in the presence of external mechanical

vibration and electrical noise.

When the device is powered-on in the hysteresis range, less than

Application Information

The simplest form of magnet that will operate these devices is a

ring magnet, as shown in figure 2. Other methods of operation

are possible.

In three-wire applications the device output is connected through

a pull-up resistor to the supply pin or separate battery voltage

(figure 3). Switching of the output signal indicates sufficient

change of the magnetic field.

B+

B–

V+

0

Figure 1. Output switching characteristics

Figure 2. Typical magnetic target configuration using a ring magnet

Figure 3. Typical 3-wire application circuit

A122x

VOUT

GND

(Optional)

V+

VCC

Device

Output

Hall Effect Latch for High Temperature Operation

A1225, A1227

and

A1229

9

Allegro MicroSystems, Inc.

115 Northeast Cutoff

Worcester, Massachusetts 01615-0036 U.S.A.

1.508.853.5000; www.allegromicro.com