TLE4942-2 Datasheet, PDF (2/9 Pages) Infineon Technologies AG – Differential Two-Wire Hall Effect Sensor IC

1 Functional description
initial
settling
d2
time
TLE4942-2, TLE4942-2C Supplement
peak detection
d2
offset= (m ax + min) / 2
d1
d1
offset correction
d2
01 2
3
4
5
s ta n d s t i l l
pulse
(cut off)
PGA
switching
6
7
uncalibrated mode
Fig. 1: example for start-up behaviour
calibrated mode
Uncalibrated mode:
Occasionally a short initial offset settling time t_d,input might delay the detection of the
input signal. (The sensor is "blind").
The magnetic input signal is tracked by the speed ADC and monitored within the
digital circuit. For detection the signal transient needs to exceed a threshold (digital
noise constant d1). When the signal slope is identified as a rising edge (or falling
edge), a comparator is triggered. The comparator is triggered again as soon as a
falling edge (or rising edge respectively) is detected (and vice versa). Depending on
the initial state of the comparator the IC output is first triggerd on the first or second
detected edge.
Between the startup of the magnetic input signal and the time when its second
extreme is reached, the PGA (programmable gain amplifier) will switch to its
appropriate position. This value is determined by the signal amplitude and initial
offset value. The digital noise constant value is changing accordingly (d1 → d2),
leading to a change in phase shift between magnetic input signal and output signal.
After that consecutive output pulses should have a nominal delay of about 180°.
During the uncalibrated mode the offset value is calculated by the peak detection
algorithm as described in the TLE4942 data sheet.
Transition to calibrated mode:
In the calibrated mode the phase shift between input and output signal is no longer
determined by the ratio between digital noise constant and signal amplitude.
Therefore a sudden change in the phase shift may occur during the transition from
uncalibrated to calibrated mode.
TLE4942-2 - TLE4942-2C Data sheet supplement 2
February 2002