A1242LUA-I2-T【PDF 8/12 页】IC LATCH HALL EFFECT 3-SIP

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Two-Wire Chopper-Stabilized Hall Effect Latch

A1242

Allegro MicroSystems, Inc.

115 Northeast Cutoff

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

1.508.853.5000; www.allegromicro.com

Functional Description

Operation

The output, I

, of the A1242 switches to the high current state

when a magnetic field perpendicular to the Hall element exceeds

the operate point threshold, B

. Note that the device latches,

that is, a south pole of sufficient strength towards the branded

surface of the device switches the device output to I

CC(H)

. The

device retains its output state if the south pole is removed. When

the magnetic field is reduced to below the release point thresh-

old, B

, the device output goes to the low current state. The dif-

ference between the magnetic operate and release points is called

the hysteresis of the device, B

HYS

. This built-in hysteresis allows

clean switching of the output even in the presence of external

mechanical vibration and electrical noise.

Typical Application Circuit

The A1242 should be protected by an external bypass capaci-

tor, C

BYP

, connected between the supply, V

, and the ground,

GND, of the device. C

BYP

reduces both external noise and the

noise generated by the chopper-stabilization function. As shown

in figure 2, a 0.01 糉 capacitor is typical.

Installation of C

BYP

must ensure that the traces that connect it to

the A1242 pins are no greater than 5 mm in length.

All high-frequency interferences conducted along the supply

lines are passed directly to the load through C

BYP

, and it serves

only to protect the A1242 internal circuitry. As a result, the load

ECU (electronic control unit) must have sufficient protection,

other than C

BYP

, installed in parallel with the A1242.

A series resistor on the supply side, R

(not shown), in combina-

tion with C

BYP

, creates a filter for EMI pulses.

When determining the minimum V

requirement of the A1242

device, the voltage drops across R

and the ECU sense resistor,

SENSE

, must be taken into consideration. The typical value for

SENSE

is approximately 100 ?

Extensive applications information on magnets and Hall-effect

devices is available in:

" Hall-Effect IC Applications Guide, AN27701,

" Guidelines for Designing Subassemblies

Using Hall-Effect Devices, AN27703.1

" Soldering Methods for Allegro Products SMD and Through-

Hole, AN26009

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

the Allegro Web site: www.allegromicro.com.

Figure 1. Switching Behavior of the A1242. 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).

HYS

CC(H)

CC(L)

B+

I+

GND

A1242

VCC

V+

0.01 uF

GND

ECU

Package UA Only

Maximum separation 5 mm

SENSE

BYP

Figure 2. Typical Application Circuit

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