TLE4941-2, TLE4941-2C Supplement

TLE4941-2 - TLE4941-2C

February 2002

Datasheet supplement

2

1

Functional description

offset correction

= peak detection

offset= (max + min) / 2

uncalibrated mode

calibrated mode

d1

initial

settling

time

d1

d2

PGA

switching

1

2

3

4

5

6

7

d2

d2

phase shift change

Fig. 1: example for startup behaviour

Uncalibrated mode:

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

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.