TLE4941-2 Datasheet, PDF (2/8 Pages) Infineon Technologies AG – Differential Two-Wire Hall Effect Sensor IC

TLE4941-2, TLE4941-2C Supplement
1 Functional description
= peak detection
offset= (max + min) / 2
d1
d1
d2
offset correction
initial
settling
d2
d2
time
12
3
PGA
switching
4
5
6
7
phase shift change
uncalibrated mode
calibrated mode
Fig. 1: example for startup behaviour
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 trigger pulse is issued to a comparator. A second trigger pulse is issued 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 start-up 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,
related to the corresponding PGA states), leading to a change in phase shift between
magnetic input signal and output signal. After that consecutive output edges should
have a nominal delay of about 180°. In rare cases one further switching of PGA can
occur (see appendix B).
During the uncalibrated mode the offset value is calculated by the peak detection
algorithm as described in the TLE 4941 data sheet.
TLE4941-2 - TLE4941-2C
2
Datasheet supplement
February 2002