HAL401 Datasheet, PDF (6/20 Pages) Micronas – Linear Hall-Effect Sensor IC

HAL401
DATA SHEET
2. Functional Description
GND
4
Chopper
Oscillator
Temp.
Dependent
Bias
Offset
Compensation;
Hallplate
Switching
Matrix
Protection
Device
V_DD
OUT1
1
2
OUT2
3
Fig. 2–1: Block diagram of the HAL 401 (top view)
The Linear Hall Sensor measures constant and low fre-
quency magnetic flux densities accurately. The differen-
tial output voltage V_OUTDIF (difference of the voltages on
pin 2 and pin 3) is proportional to the magnetic flux densi-
ty passing vertically through the sensitive area of the
chip. The common mode voltage V_CM (average of the
voltages on pin 2 and pin 3) of the differential output am-
plifier is a constant 2.2 V.
The differential output voltage consists of two compo-
nents due to the switching offset compensation tech-
nique. The average of the differential output voltage rep-
resents the magnetic flux density. This component is
overlaid by a differential AC signal at a typical frequency
of 147 kHz. The AC signal represents the internal offset
voltages of amplifiers and hall plates that are influenced
by mechanical stress and temperature cycling.
External filtering or integrating measurement can be
done to eliminate the AC component of the signal. Re-
sultingly, the influence of mechanical stress and temper-
ature cycling is suppressed. No adjustment of magnetic
offset is needed.
The sensitivity is stabilized over a wide range of temper-
ature and supply voltage due to internal voltage regula-
tion and circuits for temperature compensation.
Offset Compensation (see Fig. 2–2)
The Hall Offset Voltage is the residual voltage measured
in absence of a magnetic field (zero-field residual volt-
age). This voltage is caused by mechanical stress and
can be modeled by a displacement of the connections
for voltage measurement and/or current supply.
Compensation of this kind of offset is done by cyclic
commutating the connections for current flow and volt-
age measurement.
– First cycle:
The hall supply current flows between points 4 and 2.
In the absence of a magnetic field, V₁₃ is the Hall Off-
set Voltage (+V_Offs). In case of a magnetic field, V₁₃ is
the sum of the Hall voltage (V_H) and V_Offs.
V₁₃ = V_H + V_Offs
– Second cycle:
The hall supply current flows between points 1 and 3.
In the absence of a magnetic field, V₂₄ is the Hall Off-
set Voltage with negative polarity (–V_Offs). In case of
a magnetic field, V₂₄ is the difference of the Hall volt-
age (V_H) and V_Offs.
V₂₄ = V_H – V_Offs
In the first cycle, the output shows the sum of the Hall
voltage and the offset; in the second, the difference of
both. The difference of the mean values of V_OUT1 and
V_OUT2 (V_OUTDIF) is equivalent to V_Hall.
Note: The numbers do not
represent pin numbers.
I_C
1
1
I_C
V_Offs
2
4
V_Offs ²
4
3
3
a) Offset Voltage
V
V
b) Switched Current Supply
Fig. 2–2: Hall Offset Compensation
V
for Bu0 mT
V_OUT1
V_CM
V_OUTDIF/2
V_OUTDIF/2
V_OUTDIF
V_OUTAC
1/f_CH = 6.7 μs
V_OUT2
t
c) Output Voltage
6
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