TLE4926C-HTNE6747 Datasheet, PDF (3/27 Pages) Infineon Technologies AG – Dynamic Differential Hall Effect Sensor

VS
clamping & reverse
voltage protection
power supply regulator
analog
supply
digital
supply
hyst
comp
main
comp
Hall probes
+_{a+mplifier +}
--
-
filter
Offset
DAC
actual switching level
bias for temperature
& technology
compensation
oscillator
TLE4926C-HTN E6747
Q
overtemperature
& short-circuit
protection
clamping
enable
n-channel
open
drain
Tracking ADC
interface
digital
min
max
algorithm
GND
reset
Figure 2: Block Diagram of TLE4926C
Basics of self-calibration
A magnetic signal generated by a typical toothed wheel looks somewhat like a
sinusoid. Optimum switching points lie near the zero crossings of the curve. Due to
backbiasing conditions and imperfections in the IC the signal is superposed by an
offset. Therefore the main task to accomplish is to remove this offset. This is done by
measuring the minimum and maximum values of the curve and by calculating the
resulting offset. By subtracting this offset from the original signal, the signal is
centered on its zero crossings and these can be detected by a normal comparator.
The detection of the minimum and maximum values as well as the complete signal
correction strategy is implemented in a digital way. Therefore first the signal has to
be digitized.
Digitizing the signal
A tracking A/D converter basically does signal conversion from analog into digital
domain. The converter has a resolution of 6 bits. This (including some averaging
calculation described later on) is sufficient for characterizing the signal if the signal is
not too small. Therefore, a programmable gain amplifier (PGA) enhances the A/D
converter. Its amplification can be modified by powers of two. 7 different positions are
possible; the amplification range lies between ½ and 32 (Full scale A/D converter
range referred to full-scale range of the offset- Dac). The gain of the PGA tracks the
amplitude of the signal so that sufficient resolution of the converter is ensured. The
gain of the PGA is decreased by 1 step (a factor of 2) whenever a signal overrun in
the tracking converter is detected. On the other hand, the gain of the PGA is
increased by 1 step, when during an offset update low signal amplitude is detected.
This means, that the actual minimum value is larger or equal 50H (on an 8 bit base
referred to the averaged Gain- Dac) and the actual maximum value is smaller than
Data Sheet
Page 3 of 27