Micropower Ultrasensitive Hall Effect Switch
A1171
5
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Low Average Power
Internal timing circuitry activates the IC for a short period of
time, t
Awake
, and deactivates it for the remainder of the period
(t
Period
). A short awake state duration allows stabilization prior
to the sampling and data-latching on the falling edge of the tim-
ing pulse. The output during the sleep state is latched in the last
sampled state. The supply current is not affected by the output
state.
Operation
The VOUTPS output switches low (turns on) when the magnetic
field received at the Hall element in the A1171 exceeds the oper-
ate point, B
OPS
(or is less than B
OPN
). After turn-on, the output
voltage is V
OUT(SAT)
. The output transistor is capable of sinking
current up to the short circuit current limit, I
OM
. When the mag-
netic field is reduced below the release point, B
RPS
(or increased
above B
RPN
), the device output switches high (turns off). The
pull-up transistor brings the output voltage to V
OUT(HIGH)
.
VOUTPN operates with the opposite output polarity. That is, the
output is low (on) in the absence of a magnetic field. The output
goes high (turns off) when sufficient field, or either north or
south polarity, is presented to the device.
The difference between 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.
Powering-on the device in a hysteresis region, between B
OPX
and B
RPX
, allows an indeterminate output state. The correct state
is attained after the first excursion beyond B
OPX
or B
RPX
.
B
OPS
B
OPN
B
RPN
B
RPS
B
B
V
OUT(HIGH)
OUT
V
OUT(SAT)
Switch to Low
Switch to Low
Switch to High
Switch to High
B+
B–
0
0
Figure 1. Switching Behavior of Omnipolar Switches. On the horizontal axis, the B+ direction indicates increasing south polarity magnet-
ic field strength, and the B– direction indicates decreasing south polarity field strength (including the case of increasing north polarity).
This output switching profile applies when the SELECT line is allowed to float, selecting omnipolar operation.
(A) VOUTPS (B) VOUTPN
B
OPS
B
OPN
B
RPN
B
RPS
B
HYS
B
HYS
V
OUT(HIGH)
OUT
V
OUT(SAT)
Switch to Low
Switch to Low
Switch to High
Switch to High
B+
B–
0
0
Functional Description
0
I
DD(EN)
I
DD(DIS)
t
Period
Sleep
Awake
Sample and Output Latched
