HAL810
2.2. Digital Signal Processing and EEPROM
The DSP is the main part of this sensor and performs
the signal conditioning. The parameters for the DSP
are stored in the EEPROM registers. The details are
shown in Fig. 2–3.
DATA SHEET
Filter = 2 kHz
2000
1500
ADC-
READOUT
1000
500
0
Terminology:
MIN-DUTY: name of the register or register value
Min-Duty:
name of the parameter
The EEPROM registers consist of three groups:
Group 1
contains the registers for the adaptation of
the sensor to the magnetic circuit: Mode for selecting
the magnetic field range and filter frequency, TC and
TCSQ for the temperature characteristics of the mag-
netic sensitivity.
Group 2
contains the registers for defining the output
characteristics: DCSENSITIVITY, DCOQ, MIN-DUTY,
and MAX-DUTY. The output characteristic of the sen-
sor is defined by these four parameters (see Fig. 2–5
and Fig. 2–6 for examples).
– The parameter DC
OQ
(Output Quiescent Duty Cycle)
corresponds to the duty cycle at B = 0 mT.
– The parameter DCSensitivity defines the magnetic
sensitivity:
DCSensitivity =
ΔDC
OUT
* 2048
ΔADC-Readout
* 100%
–500
–1000
–1500
–2000
–200–150–100 –50
Range 150 mT
Range 90 mT
Range 60 mT
Range 30 mT
0
50 100 150 200 mT
B
Fig. 2–6:
Example for output characteristics
– The output duty cycle can be calculated as follows:
DC
OUT
=
DCSensitivity * ADC-Readout / 2048 * 100% + DC
OQ
The output duty cycle range can be clamped by setting
the registers MIN-DUTY and MAX-DUTY in order to
enable failure detection (such as short-circuits to V
DD
or GND and open connections).
Group 3
contains the Micronas registers and LOCK
for the locking of all registers. The Micronas registers
are programmed and locked during production and are
read-only for the customer. These registers are used
for oscillator frequency trimming, A/D converter offset
compensation, and several other settings.
An external magnetic field generates a Hall voltage on
the Hall plate. The ADC converts the amplified positive
or negative Hall voltage (operates with magnetic north
and south poles at the branded side of the package) to
a digital value. Positive values correspond to a mag-
netic north pole on the branded side of the package.
The digital signal is filtered in the internal low-pass fil-
ter and is readable in the ADC-READOUT register.
Depending on the programmable magnetic range of
the Hall IC, the operating range of the A/D converter is
from
−
30 mT…+30 mT up to
−
150 mT…+150 mT.
During further processing, the digital signal is multi-
plied with the sensitivity factor, added to the quiescent
output duty cycle and limited according to Min-Duty
and Max-Duty. The result is converted to the duty
cycle of a pulse width modulated signal and stabilized
by a push-pull output transistor stage.
The ADC-READOUT at any given magnetic field
depends on the programmed magnetic field range but
also on the filter frequency. Fig. 2–6 shows the typical
ADC-READOUT values for the different magnetic field
ranges with the filter frequency set to 2 kHz. The rela-
tionship between the minimum and maximum
ADC-READOUT values and the filter frequency setting
is listed in the following table.
Filter Frequency
80 Hz
160 Hz
500 Hz
1 kHz
2 kHz
ADC-READOUT Range
−
3968…3967
−
1985…1985
−
5292…5290
−
2646…2645
−
1512…1511
8
Feb. 6, 2009; DSH000034_003EN
Micronas
MICRONAS [ MICRONAS ]
