A1101LUA-T【PDF 7/13 页】IC SWITCH HALL EFFECT 3-SIP

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Continuous-Time Switch Family

A1101, A1102, A1103,

A1104, and A1106

Allegro MicroSystems, LLC

115 Northeast Cutoff

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

1.508.853.5000; www.allegromicro.com

Functional Description

OPERATION

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

magnetic field (south polarity) perpendicular to the Hall ele-

ment exceeds the operate point threshold, B

. After turn-on,

the output is capable of sinking 25 mA and the output voltage is

OUT(SAT)

. When the magnetic field is reduced below the release

point, B

, the device output goes high (turns off). The differ-

ence in the magnetic operate and release points is the hysteresis,

hys

, of the device. This built-in hysteresis allows clean switch-

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

vibration and electrical noise.

Powering-on the device in the hysteresis region, less than B

and

higher than B

, allows an indeterminate output state. The correct

state is attained after the first excursion beyond B

or B

CONTINUOUS-TIME BENEFITS

Continuous-time devices, such as the A110x family, offer the

fastest available power-on settling time and frequency response.

Due to offsets generated during the IC packaging process,

continuous-time devices typically require programming after

packaging to tighten magnetic parameter distributions. In con-

trast, chopper-stabilized switches employ an offset cancellation

technique on the chip that eliminates these offsets without the

need for after-packaging programming. The tradeoff is a longer

settling time and reduced frequency response as a result of the

chopper-stabilization offset cancellation algorithm.

The choice between continuous-time and chopper-stabilized

designs is solely determined by the application. Battery manage-

ment is an example where continuous-time is often required. In

these applications, V

is chopped with a very small duty cycle

in order to conserve power (refer to figure 2). The duty cycle

is controlled by the power-on time, t

, of the device. Because

continuous-time devices have the shorter power-on time, they

are the clear choice for such applications.

For more information on the chopper stabilization technique,

refer to Technical Paper STP 97-10, Monolithic Magnetic Hall

Sensing Using Dynamic Quadrature Offset Cancellation and

Technical Paper STP 99-1, Chopper-Stabilized Amplifiers with a

Track-and-Hold Signal Demodulator.

Figure 1. Switching Behavior of Unipolar Switches. 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.

HYS

OUT(SAT)

B+

V+

(A)

(B)

VCC

Output

GND

VOUT

A110x

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