Continuous-Time Bipolar Switch

A1205

8

Allegro MicroSystems, Inc.

115 Northeast Cutoff, Box 15036

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

www.allegromicro.com

back to the low state.

The typical output behavior of the A120x devices is latching.

However, the A120x family is designed to attain a small hys-

teresis, and thereby provide more sensitive switching. Although

this means that true latching behavior cannot be guaranteed in all

cases, proper switching can be ensured by use of both south and

north magnetic fields, as in a ring magnet. The hysteresis of the

A120x family allows clean switching of the output, even in the

presence of external mechanical vibration and electrical noise.

Bipolar devices adopt an indeterminate output state when pow-

ered-on in the absence of a magnetic field or in a field that lies

within the hysteresis band of the device.

For more information on Bipolar switches, refer to Application

Note 27705, Understanding Bipolar Hall Effect Sensors.

CONTINUOUS-TIME BENEFITS

Continuous-time devices, such as the A120x family, offer the

fastest available power-on settling time and frequency response.

DuetooffsetsgeneratedduringtheICpackagingprocess,contin-

uous-time devices typically require programming after packaging

totightenmagneticparameterdistributions.Incontrast,chop-

per-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-

mentisanexamplewherecontinuous-timeisoftenrequired.In

inordertoconservepower(refertofigure2).Thedutycycle

valid, a control unit reads the output. Position 5, power is removed from the device.

Output Sampled

1

5

4

2

t

t

3