tle4982c Infineon Technologies Corporation, tle4982c Datasheet - Page 3

• Manufacturer Part Number: tle4982c
• Description: Programmable True Power On Hall Sensor
• Manufacturer: Infineon Technologies Corporation

Initial mode:
The magnetic information is derived from a chopped Hall amplifier. The threshold
information comes from a PROM-register that may be programmed at any time, but only
once (no EEPROM). The magnetic information is compared against the threshold and
the output state is set correspondingly. Some hysteresis is introduced in order to avoid
false switching due to noise.
In case that there is no PROM-value available (PROM has not been programmed
before) the chip starts an auto-search for the actual magnetic value. The initial threshold
value is set to this magnetic value. This feature can be used to find a TPO-value for
providing correct programming information to the chip simply by setting the chip in front
of a well-defined static target. In this case a moving target wheel is not necessary.
In case there is a PROM value available, the open drain output will be turned on or off
by comparing the magnetic field against the pre-programmed value.
During rotation of the target wheel a self-calibration procedure is started in the
background. The IC memorises magnetic field values for adjusting the threshold to an
optimum value. The exact way of threshold adjustment is described in more detail in the
precalibrated mode. Once the IC has sufficient information for improving the accuracy
(typically after 2-3 teeth) the device threshold value is adjusted and the device is
switched into the precalibrated mode.
Precalibrated mode:
In the precalibrated mode the IC permanently monitors the magnetic signal. To say it in
more detail, it searches for minimum (caused by a notch) and maximum (caused by a
tooth) values in the signal. Once the IC has found a pair of min / max values it calculates
the optimum threshold level and adjusts the system offset in such a way, that the
switching occurs on this level. The threshold adjustment is limited to increments of
approx. 1,5mT (up to 32 updates possible) per calibration in order to avoid totally wrong
updates caused by large signal disturbances (EMC-events or similar). The optimum
threshold level may differ depending on the target wheel. For example, for regular
gearwheels the magnetic signal is close to a sinusoid and the optimum threshold value
can be considered as 50% value, which is the mean value between minimum and
maximum signal. For camshaft wheels an optimum threshold may be at a different
percent-value in order to have minimum phase error over airgap variations. See fig.4 for
definition of this dynamic switching level. Up to 32 updates with 1.5mT steps give a total
range of max. 48mT for the possible threshold update.
In case that the initial PROM-value does not lead to a switching of the IC because it is
slightly out of the signal range the IC nevertheless does its switch value correction in the
background. After having corrected for a sufficient amount the IC will start its output
switching. The output switching includes some hysteresis in order to avoid false
switching.
If the IC has not been programmed yet, it uses the default 50% value between the
minimum and the maximum as switching level.
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