Micropower Ultrasensitive 3D Hall-Effect Switch
A1266
10
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
FUNCTIONAL DESCRIPTION
Low Average Power
To keep average power low, internal timing circuitry activates
the sensor of each axis for 100 µs (followed by a low power
sleep time, t
sleep
, of 54.9 ms). This awake and sleep cycle occurs
three times for each t
period
, such that all three axes are sampled
in t
period
. The short “awake” time allows for stabilization prior
to the sensor sampling and data latching at the end of each t
awake
cycle. The outputs during each t
sleep
cycle are latched in the last
sampled state. The supply current is not affected by the output
states.
Operation
For the single output option of the A1266, the output switches
low (turns on) when a magnetic field perpendicular to one of the
three Hall sensors, either the X, Y, or Z direction, exceeds the
operate point, B
OPS
(or is less than B
OPN
). The A1266 triple out-
put option is configured with three separate outputs (X, Y, or Z),
which switch low (turns on) when a magnetic field perpendicular
to the corresponding Hall sensor (X, Y, or Z) exceeds the oper-
ate point, B
OPS
(or is less than B
OPN
). When the magnetic field is
reduced below the release point, B
RPS
(or increased above B
RPN
),
the device output switches high (turns off). The difference in the
magnetic operate and release points is the hysteresis, B
HYS
, of
the device. This built-in hysteresis allows clean switching of the
output even in the presence of external mechanical vibration and
electrical noise.
After turn-on, the output voltage is V
OUT
. Powering-on the device
in the hysteresis region, between B
OP
and B
RP
, allows an inde-
terminate output state. The correct state is attained after the first
excursion beyond B
OP
or B
RP
.
Device
Power-On
t
awake
X Axis
t
awake
Z Axis
t
awake
Y Axis
Sleep
Sleep Sleep
I
DD(EN)
I
DD(DIS)
t
period
t= 300 µs [t (X) + t (Y) + t (Z)]
awake awake awake awake
t= 165 ms (t + 3 × t)
period awake sleep
t
sleep period awake
= (t –t )/3
= 54.9 mst
sleep
Awake
Sleep
Sample X Sample Y Sample Z Sample X
Latch Output Latch Output Latch Output Latch Output
Figure 2: Device Sleep and Awake Mode Cycle
