A1250LUA-T Datasheet, PDF (7/12 Pages) Allegro MicroSystems – Hall Effect Latch / Bipolar Switch

A1250
Hall Effect Latch / Bipolar Switch
Functional Description
The output of this device switches low (turns on) when a magnetic The other two modes of operation are the unipolar switch and the
field perpendicular to the Hall sensor IC exceeds the operate point negative switch, shown in panels 1b and 1c, respectively. The
threshold, B_OP . After turn-on, the output voltage is V_OUT(SAT) . unipolar switch type operates only in a south polarity field, and
The output transistor is capable of sinking current up to the short ^{will switch to the high state if the magnetic field is removed. The}
circuit current limit I_OM , which is a minimum of 30 mA. When ^{negative switch operates only in a north polarity field, and will}
the magnetic field is reduced below the release point, B_RP , the
switch to the low state if the magnetic field is removed.
device output goes high (turns off). The difference in the magnetic _{Individual bipolar switch devices exhibit any one of the three}
operate and release points is the hysteresis, B_HYS , of the device. _{switching behaviors: latch, unipolar, or negative switch. Because}
This built-in hysteresis allows clean switching of the output even _{these devices are not guaranteed to behave as latches, magnetic}
in the presence of external mechanical vibration and electrical
fields of sufficient magnitude and alternate polarity are required to
noise.
ensure output switching.
Given the magnetic parameter specifications (refer to Magnetic _{Powering up the device in the hysteresis band, that is in a mag-}
Characteristics table), bipolar switches will operate in one of three _{netic field less than BOP and higher than BRP , allows an indeter-}
modes, depending on switchpoints. For typical values of B_OP and _{minate output state. Note that this hysteresis band encompasses}
B_RP , the device will operate as a latch, as shown in figure 1a.
zero magnetic field on devices that exhibit latch behaviors. The
Note that, when the magnetic flux density exceeds a switchpoint, correct state is determined after the first magnetic excursion
the output will retain its state when the magnetic field is removed. beyond B_OP or B_RP.
(A)
V+
V_CC
(B)
(C)
V+
V+
V_CC
V_CC
0
B–
0
V_OUT(SAT)
B+
0
B– 0
V_OUT(SAT)
B+
0
B–
V_OUT(SAT)
0 B+
B_HYS
B_HYS
B_HYS
Figure 1. Bipolar Device Output Switching Modes. These behaviors can be exhibited when using a circuit such as
that shown in figure 1. Panel A displays the hysteresis when a device exhibits latch mode (note that the B_HYS band
incorporates B = 0), panel B shows unipolar switch behavior (the B_HYS band is more positive than B = 0), and panel
C shows negative switch behavior (the B_HYS band is more negative than B = 0). Bipolar devices, such as the A1250,
can operate in any of the three modes.
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