A1101, A1102, A1103,
A1104, and A1106
Continuous-Time Switch Family
Functional Description
OPERATION
The output of these devices switches low (turns on) when a
magnetic field (south polarity) perpendicular to the Hall sen-
sor exceeds the operate point threshold, B
OP
. After turn-on, the
output is capable of sinking 25 mA and the output voltage is
V
OUT(SAT)
. When the magnetic field is reduced below the release
point, B
RP
, the device output goes high (turns off). The differ-
ence in the magnetic operate and release points is the hysteresis,
B
hys
, of the device. This built-in hysteresis allows clean switch-
ing of the output, even in the presence of external mechanical
vibration and electrical noise.
Powering-on the device in the hysteresis region, less than B
OP
and
higher than B
RP
, allows an indeterminate output state. The correct
state is attained after the first excursion beyond B
OP
or B
RP
.
CONTINUOUS-TIME BENEFITS
Continuous-time devices, such as the A110x family, offer the
fastest available power-on settling time and frequency response.
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
CC
is chopped with a very small duty cycle
in order to conserve power (refer to figure 2). The duty cycle
is controlled by the power-on time, t
PO
, of the device. Because
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.
(A)
V+
Switch to High
Switch to Low
V
S
(B)
V
CC
VCC
R
L
Sensor Output
V
OUT
A110x
VOUT
0
V
OUT(SAT)
B
RP
B– 0
B+
B
OP
B
HYS
GND
Figure 1. Switching Behavior of Unipolar 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). This behavior can
be exhibited when using a circuit such as that shown in Panel B.
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
7
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