Large Air Gap, Vibration-Tolerant,
GMR Transmission Speed and Direction Sensor IC
A19571
12
Allegro MicroSystems
955 Perimeter Road
Manchester, NH 03103-3353 U.S.A.
www.allegromicro.com
Calibration and Direction Validation
When power is applied to the A19571, the built-in algorithm per-
forms an initialization routine. For a short period after power-on,
the device calibrates itself and determines the direction of target
rotation. For the -xxxPx variant, the output transmits nondirection
pulses during calibration (Figure 14). For the -xxxBx variant, the
output does not transmit any pulses during calibration.
Once the calibration routine is complete, the A19571 will trans-
mit accurate speed and direction information.
Figure 14: Calibration Behavior of the -xSxPH Variant
t
I
CC
Target
Differential
Magnetic
Profile
Target Rotation
Opposite
north pole
Opposite
N→S boundary
Opposite
south pole
Opposite
S→N boundary
Device Location at Power-On
t
W(FWD)
or
t
W(REV)
t
W(ND)
t
W(ND)
t
W(ND)
t
W(ND)
t
W(FWD)
or
t
W(REV)
t
W(FWD)
or
t
W(REV)
t
W(ND)
t
W(FWD)
or
t
W(REV)
t
W(FWD)
or
t
W(REV)
t
W(ND)
t
W(ND)
t
W(FWD)
or
t
W(REV)
t
W(FWD)
or
t
W(REV)
t
W(FWD)
or
t
W(REV)
N S
N S
N
S
N S N