Continuous-Time Bipolar Switch Family

A1202

and A1203

7

Allegro MicroSystems, LLC

115 Northeast Cutoff, Box 15036

Worcester, Massachusetts 01615-0036 (508) 853-5000

www.allegromicro.com

FUNCTIONAL DESCRIPTION

Bipolar Device Switching

The devices of the A120X family provide highly sensitive switch-

ing for applications using magnetic fields of alternating polarities,

such as ring magnets. There are three switching modes for bipolar

devices, referred to as latch, unipolar switch, and negative switch.

Mode is determined by the switchpoint characteristics of the indi-

is the difference in the relative magnetic strength and polarity

of the switchpoints of the device. (Note that, in the following

descriptions, a negative magnetic value indicates a north polar-

ity field, and a positive magnetic value indicates a south polarity

B = 0 indicates the absence of a magnetic field.)

Bipolar devices typically behave as latches. In this mode,

magnetic fields of opposite polarity and equivalent strengths

are needed to switch the output. When the magnetic fields are

removed (B → 0) the device remains in the same state until a

magnetic field of the opposite polarity and of sufficient strength

causes it to switch. The hysteresis of latch mode behavior is

shown in panel A of Figure 1.

In contrast to latching, when a device exhibits unipolar switch-

ing, it only responds to a south magnetic field. The field must be

the high state, as shown in panel B of Figure 1. Devices exhibit-

ing negative switch behavior operate in a similar but opposite

state.

The typical output behavior of the A120x devices is latching.

That is, switching to the low state when the magnetic field at the

Figure 1: Bipolar Device Output Switching Modes

These behaviors can be exhibited when using a circuit such as that shown in panel D. Panel A displays the hysteresis when a device exhibits

ate in any of the three modes.

B

HYS

V

OUT(SAT)

V+

0

B

HYS

V

OUT(SAT)

V+

0

B

HYS

V

OUT(SAT)

V+

0

V

CC

V

CC

V

CC

B+

B–

B+

B– 0

0

B+

B–

0

(A)

(B)

(C)

VCC

Output

GND

VOUT

A120x

(D)