A1214LUA-T Allegro, A1214LUA-T Datasheet - Page 8

• Manufacturer Part Number: A1214LUA-T
• Manufacturer: Allegro

OPERATION
The output of these devices switches low (turns on) when a
magnetic field perpendicular to the Hall sensor exceeds the
operate point threshold, B
of sinking 25 mA and the output voltage is V
that the device latches; that is, a south pole of sufficient strength
towards the branded surface of the device turns the device on,
and the device remains on with removal of the south pole. When
the magnetic field is reduced below the release point, B
the device output goes high (turns off). The difference in the
magnetic operate and release points is the hysteresis, B
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 the hysteresis range, less than B
and higher than B
correct state is attained after the first excursion beyond B
B
CONTINUOUS-TIME BENEFITS
Continuous-time devices, such as the A121x family, offer the
fastest available power-on settling time and frequency response.
Figure 1. Switching Behavior of Latches. 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). This behavior can be exhibited when
using a circuit such as that shown in Panel B.
A1210-DS
RP
.
V+
RP
0
, allows an indeterminate output state. The
B–
OP
A1210, A1211, A1212, A1213, and A1214
. After turn-on, the output is capable
B
(A)
0
HYS
Continuous-Time Latch Family
B+
OUT(SAT)
V
V
CC
OUT(SAT)
Functional Description
. Notice
hys
RP
OP
, of
,
OP
or
Due to offsets generated during the IC packaging process,
continuous-time devices typically require programming after
packaging to tighten magnetic parameter distributions. In con-
trast, chopper-stabilized switches employ an offset cancellation
technique on the chip that eliminates these offsets without the
need for after-packaging programming. The tradeoff is a longer
settling time and reduced frequency response as a result of the
chopper-stabilization offset cancellation algorithm.
The choice between continuous-time and chopper-stabilized
designs is solely determined by the application. Battery manage-
ment is an example where continuous-time is often required. In
these applications, V
in order to conserve power (refer to figure 2). The duty cycle
is controlled by the power-on time, t
continuous-time devices have the shorter power-on time, they
are the clear choice for such applications.
For more information on the chopper stabilization technique,
refer to Technical Paper STP 97-10, Monolithic Magnetic Hall
Sensor Using Dynamic Quadrature Offset Cancellation and
Technical Paper STP 99-1, Chopper-Stabilized Amplifiers with a
Track-and-Hold Signal Demodulator.
V
S
CC
is chopped with a very small duty cycle
A121x
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 [phone]
www.allegromicro.com
VCC
GND
(B)
VOUT
PO
, of the device. Because
R
L
Sensor Output
8