A1222 Ver la hoja de datos (PDF) - Allegro MicroSystems

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A1222

solid state crowbar devices

Allegro MicroSystems 

A1220, A1221,

A1222, and A1223

Chopper Stabilized Precision Hall Effect Latches

Functional Description

Operation

The output of these devices switches low (turns on) when a mag-

netic field perpendicular to the Hall element exceeds the operate

point threshold, BOP (see panel A of figure 1). After turn-on, the

output voltage is VOUT(SAT) . The output transistor is capable of

sinking current up to the short circuit current limit, IOM, which is

a minimum of 30 mA. When the magnetic field is reduced below

the release point, BRP , the device output goes high (turns off).

The difference in the magnetic operate and release points is the

hysteresis, BHYS , of the device. This built-in hysteresis allows

clean switching of the output even in the presence of external

mechanical vibration and electrical noise.

Removal of the magnetic field will leave the device output

latched on if the last crossed switchpoint is BOP, or latched off if

the last crossed switch point is BRP.

Powering-on the device in the hysteresis range (less than BOP and

higher than BRP) will give an indeterminate output state. The cor-

rect state is attained after the first excursion beyond BOP or BRP.

Applications

It is strongly recommended that an external bypass capacitor be

connected (in close proximity to the Hall element) between the

supply and ground of the device to reduce both external noise

and noise generated by the chopper stabilization technique. As is

shown in panel B of figure 1, a 0.1 μF capacitor is typical.

Extensive applications information for Hall effect devices is

available in:

• Hall-Effect IC Applications Guide, Application Note 27701

• Guidelines for Designing Subassemblies Using Hall-Effect

Devices, Application Note 27703.1

• Soldering Methods for Allegro’s Products – SMT and Through-

Hole, Application Note 26009

All are provided in Allegro Electronic Data Book, AMS-702, and

the Allegro Web site, www.allegromicro.com.

V+

VCC

0

B–

0

VOUT(SAT)

B+

VS

CBYP

0.1 μF

VCC

A122x

VOUT

GND

RL

Output

BHYS

(A)

(B)

Figure 1. Switching behavior of latches. In panel A, on the horizontal axis, the B+ direction indicates increasing south polarity magnetic field strength,

and the B– direction indicates decreasing south polarity field strength (including the case of increasing north polarity). This behavior can be exhibited

when using a circuit such as that shown in panel B.

Allegro MicroSystems, Inc.

10

115 Northeast Cutoff

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

1.508.853.5000; www.allegromicro.com

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