A1211LUA-T【PDF 9/14 页】IC LATCH HALL EFFECT 3-SIP

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Continuous-Time Latch Family

A1210, A1211,

A1212, A1213,

and A1214

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 perpendicular to the Hall element exceeds the

operate point threshold, B

. After turn-on, the output is capable

of sinking 25 mA and the output voltage is V

OUT(SAT)

. Notice

that the device latches; that is, 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. When

the magnetic field is reduced below the release point, B

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

magnetic operate and release points is the hysteresis, B

hys

, of

the device. This built-in hysteresis allows clean switching of the

output, even in the presence of external mechanical vibration and

electrical noise.

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

and higher than B

, allows an indeterminate output state. The

correct state is attained after the first excursion beyond B

CONTINUOUS-TIME BENEFITS

Continuous-time devices, such as the A121x 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 Latches. 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

A121x

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