A1354KKT-T Datasheet, PDF (13/23 Pages) Allegro MicroSystems – High Precision 2-Wire Linear Hall Effect Sensor IC With Pulse Width Modulated Output

A1354
High Precision 2-Wire Linear Hall Effect Sensor IC
with Pulse Width Modulated Output
Typical Application Drawings
V_CC
CBYPASS
0.01 μF
1
VCC
A1354
V_CC
R_SENS
CBYPASS
0.01 μF
1
VCC
A1354
R_SENS
GND
4
GND
4
Chopper Stabilization Technique
When using Hall-effect technology, a limiting factor for
switchpoint accuracy is the small signal voltage developed
across the Hall element. This voltage is disproportionally small
relative to the offset that can be produced at the output of the
Hall element. This makes it difficult to process the signal while
maintaining an accurate, reliable output over the specified operat-
ing temperature and voltage ranges. Chopper stabilization is a
unique approach used to minimize Hall offset on the chip. The
patented Allegro technique, namely Dynamic Quadrature Offset
Cancellation, removes key sources of the output drift induced by
thermal and mechanical stresses. This offset reduction technique
is based on a signal modulation-demodulation process. The
undesired offset signal is separated from the magnetic field-
induced signal in the frequency domain, through modulation.
The subsequent demodulation acts as a modulation process for
the offset, causing the magnetic field-induced signal to recover
its original spectrum at base band, while the DC offset becomes
a high frequency signal. The magnetic-sourced signal then can
pass through a low-pass filter, while the modulated DC offset is
suppressed. The chopper stabilization technique uses a 200 kHz
high frequency clock. For demodulation process, a sample and
hold technique is used, where the sampling is performed at twice
the chopper frequency (400 kHz). This high-frequency operation
allows a greater sampling rate, which results in higher accuracy
and faster signal-processing capability. This approach desensi-
tizes the chip to the effects of thermal and mechanical stresses,
and produces devices that have extremely stable quiescent Hall
output voltages and precise recoverability after temperature
cycling. This technique is made possible through the use of a
BiCMOS process, which allows the use of low-offset, low-noise
amplifiers in combination with high-density logic integration and
sample-and-hold circuits.
Regulator
Hall Element
Clock/Logic
Amp
Low-Pass
Filter
Allegro MicroSystems, Inc.
12
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com