ADVANCE INFORMATION
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.
Terminology:
SENSITIVITY: name of the register or register value
Sensitivity:
name of the parameter
Filter = 2 kHz
2000
1500
ADC-
READOUT
1000
500
0
–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
The EEPROM registers consist of three groups:
Group 1 contains the registers for the adaption of the
sensor to the magnetic system: 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: SENSITIVITY, VOQ, CLAMP-LOW,
and CLAMP-HIGH. The output characteristic of the
sensor is defined by these 4 parameters (see Fig. 2–4
and Fig. 2–5 for examples).
– The parameter V
OQ
(Output Quiescent Voltage) cor-
responds to the output voltage at B = 0 mT.
– The parameter Sensitivity defines the magnetic sen-
sitivity:
Sensitivity =
∆
V
OUT
∆
B
Fig. 2–6:
Typical ADC-READOUT
versus magnetic field for filter = 2 kHz
– The output voltage can be calculated as:
V
OUT
∼
Sensitivity
×
B + V
OQ
The output voltage range can be clamped by setting
the registers CLAMP-LOW and CLAMP-HIGH 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 special 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 voltage and limited according to the clamping
voltage. The result is converted to an analog 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
Micronas
7
MICRONAS [ MICRONAS ]
