Micropower Ultra-Sensitive Hall-Effect Switch
A1172
8
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 50 s and deacti-
vates it for the remainder of the period (50 ms). A short awake
time allows stabilization prior to the sampling and data-latching
on the falling edge of the timing 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 a magnetic
field perpendicular to the Hall element exceeds the operate 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 cur-
rent up to the short circuit current limit, I
OM
, which is a mini-
mum of 1 mA. 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 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, of either north or
south polarity, is presented to the device.
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.
The push-pull outputs are capable of sourcing or sinking a maxi-
mum of 1 mA.
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
HYS
B
HYS
V
OUT(HIGH)
V
OUT
V
OUT(SAT)
Switch to Low
Switch to Low
Switch to High
Switch to High
B+
B–
V+
0
0
Figure 1. Switching Behavior of Omnipolar Switches. On the horizontal axis, the B+ direction indicates increasing
south polarity magnetic field strength, and the B– direction indicates decreasing south polarity field strength
(including the case of increasing north polarity).
(A) VOUTPS (B) VOUTPN
B
OPS
B
OPN
B
RPN
B
RPS
B
HYS
B
HYS
V
OUT(HIGH)
V
OUT
V
OUT(SAT)
Switch to Low
Switch to Low
Switch to High
Switch to High
B+
B–
V+
0
0
Functional Description
0
I
DD(EN)
I
DD(DIS)
t
Period
Sleep
Awake
Sample and Output Latched
