HAL401 datasheet(6/20 Pages) MICRONAS

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HAL401

DATA SHEET

Micronas

2. Functional Description

Temp.

Dependent

Bias

Offset

Compensation;

Hallplate

Switching

Matrix

OUT1

OUT2

Fig. 2–1: Block diagram of the HAL 401 (top view)

VDD

Protection

Device

Chopper

Oscillator

GND

The Linear Hall Sensor measures constant and low fre-

quency magnetic flux densities accurately. The differen-

tial output voltage VOUTDIF (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 VCM (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 (+VOffs). In case of a magnetic field, V13 is

the sum of the Hall voltage (VH) and VOffs.

V13 = VH + VOffs

– 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 (–VOffs). In case of

a magnetic field, V24 is the difference of the Hall volt-

age (VH) and VOffs.

V24 = VH – VOffs

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 VOUT1 and

VOUT2 (VOUTDIF) is equivalent to VHall.

Fig. 2–2: Hall Offset Compensation

Note: The numbers do not

represent pin numbers.

VOffs

VCM

for B

u0 mT

VOUT1

VOUT2

VOUTDIF

VOUTDIF/2

1/fCH = 6.7 μs

VOUTAC

a) Offset Voltage

b) Switched Current Supply

c) Output Voltage

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