HAL855 datasheet(9/42 Pages) MICRONAS

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DATA SHEET

HAL855

Micronas

Nov. 26, 2008; DSH000149_003EN

2.2. Digital Signal Processing and EEPROM

The DSP is the major 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 on page 8.

Terminology:

SLOPE:

name of the register or register value

Slope:

name of the parameter

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.

The parameters SLOPE and SHIFT are used for the

individual calibration of the sensor in the magnetic cir-

ucit.

– The parameter Shift corresponds to the output sig-

nal at B = 0 mT.

– The parameter Slope defines the magnetic sensitiv-

ity.

Group 2 contains the registers for defining the output

characteristics: OUTPUT FORMAT, OUTPUT PERIOD

or OUTPUT BITTIME, SLEW RATE and OUTPUT

CHARACTERISTIC.

The shape of the output signal is determined by the

output characteristic, which, in turn, is defined by the

32 setpoints of the sensor. A value for each of the set-

points must be defined. The setpoints are distributed

evenly along the magnetic field axis allowing linear

interpolation between the 32 setpoints (see Fig. 2–4).

Group 3 contains the PARTNUMBER, the Micronas

registers, and LOCK for the locking of all registers.

After locking, the PARTNUMBER register is only avail-

able in Biphase-M output mode. The Micronas regis-

ters are programmed and locked during production

and are read-only for the customer. These registers

are used for oscillator frequency trimming and several

other special settings.

An external magnetic field generates a Hall voltage on

the Hall plate. The A/D-converter converts the ampli-

fied positive or negative Hall voltage (operates with

magnetic north and south poles at the branded side of

the package) to a digital value. The digital signal is

filtered in the internal low-pass filter and manipulated

according to the settings stored in the EEPROM. The

digital value after signal processing is readable in the

DIGITAL OUTPUT register. Depending on the pro-

grammable 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 calcu-

lated based on the values of slope, shift, and the

defined output characteristic. The result is converted to

the

different

digital

output

formats

(PWM

and

Biphase-M) and stabilized by a open-drain output tran-

sistor stage.

The DIGITAL OUTPUT value at any given magnetic

field depends on the settings of the magnetic field

range, the low-pass filter, TC, TCSQ values and the

programmed

output

characteristic.

The

DIGITAL

OUTPUT range is min. 0 to max. 4095.

Note: During application design, it should be taken

into

consideration

that

DIGITAL

OUTPUT

should not saturate in the operational range of

the specific application.

Setpoint

PWM

HAL 855

121620242832

100

Logarithmic

Sine

Linear

Logarithmic

Sine

Linear

Fig. 2–4: Example for different

output characteristics

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