Continuous-Time Switch Family

A1101, A1102, A1103,

A1104, and A1106

7

Allegro MicroSystems, Inc.

115 Northeast Cutoff, Box 15036

Worcester, Massachusetts 01615-0036 (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 sen-

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

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

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

vibration and electrical noise.

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

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

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

Sensor 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.

B+

B–

V+

0

0

(A)

(B)

VCC

Sensor Output

GND

VOUT

A110x