TLE4942-2, TLE4942-2C Supplement

TLE4942-2 - TLE4942-2C Data sheet supplement

February 2002

2

1

Functional description

offset correction

peak detection

offset= (m ax + min) / 2

uncalibrated mode

calibrated mode

d1

initial

settling

time

d1

d2

d2

d2

standstill

pulse

(cut off)

PGA

switching

0

1

2

3

4

5

6

7

Fig. 1: example for start-up 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 comparator is triggered. The comparator is triggered again as soon as a

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.