True Zero-Speed, High Accuracy, Ring Magnet Sensor IC

A1667

10

Allegro MicroSystems, LLC

955 Perimeter Road

Manchester, NH 03103-3353 U.S.A.

www.allegromicro.com

1

4

2

3

Start Mode

If exceed PO

HYS

on high side

If exceed PO

HYS

on low side

IC Position

Relative to Target

Target Magnetic Profile

Target, Ring Magnet

N

S

S

START MODE HYSTERESIS

This feature helps to ensure optimal self-calibration by rejecting

electrical noise and low-amplitude target vibration during

initialization.ThispreventsAGCfromcalibratingtheIConsuch

spurious signals. Calibration can be performed using the actual

target features.

Atypicalscenarioisshowninfigure6.TheStartModeHysteresis,

before the A1667 starts to compute switchpoints.

Figure 6. Operation of Start Mode Hysteresis

Mode Hysteresis can be generated either by a legitimate target feature or by excessive vibration.

• In either case, because the switchpoint is immediately passed as soon as it is established, the A1667 enables switching:

As this example demonstrates, initial output switching occurs with the same polarity, regardless of whether the Start Mode Hysteresis is exceeded on the

high side or on the low side.