TLE4942-2, TLE4942-2C Supplement

TLE4942-2 - TLE4942-2C Data sheet supplement

February 2002

5

Example: The 14th row describes the behaviour shown in Fig. 1: The standstill pulse length

can be cut by the first detected speed pulse, therefore the minimum distance between the

rising edges will be 45µs. The distance between the first and second detected speed pulse is

determined by the initial signal phase and amplitude and a possible first PGA switching. As

the first pulse length also can theoretically be cut off by the following pulse, the minimum

distance could be 45µs. The rising edge between the first signal minimum and the first signal

maximum can cause the PGA switching into a lower gain range. As a result the digital noise

constant value can increase in relation to the signal amplitude. That typically leads to an

increased delay between the second and the third pulse, its maximum value is 260°. The

following minimum and maximum are necessary for peak detection. After offset correction,

the delay between the 5

the transition from uncalibrated to calibrated mode, the following consecutive pulses (4, 5, 6

...) will be spaced 180° nominally.

Same example with numbers:

∆B = 10mT sin (ωt + ϕ). ϕ = 30°

Typical startup-behaviour at a sinusoidal input signal of 10mT amplitude, initial phase= 30°.

ϕ

1

43,6°

2

133,9°

3

333,2°

4

513,2°

5

693,2°

6

900°

7

1080°

8

1260°

9

1440°

10

...

∆

ϕ

90,3°

(PGA,

uncal)

199,3°

(PGA,

uncal)

180°

(uncal)

180°

(uncal)

206,8°

(Offset-

correction)

180°

(cal)

180°

(cal)

180°

(cal)

180°

(cal)

→ This corresponds to row 14 in the table, behaviour similar to Fig. 1

As a special (and rare) case instead of an offset correction after edge number 5, a further

(extra) PGA switching could occur before edge number 5. PGA switching inhibits an

immediate

offset update. It can happen if one of the signal peaks is exactly at a PGA

switching threshold (speed-ADC overflow). In this case the offset update (switching from

uncalibrated mode to calibrated mode) would be delayed by two to three further edges. The

referring phase shifts of the example would then be as follows:

ϕ

1

43,6°

2

133,9°

3

333,2°

4

513,2°

5

727,5°

6

907,5°

7

1087,5°

8

1260°

9

1440°

10

...

∆

ϕ

90,3°

(PGA,

uncal)

199,3°

(PGA,

uncal)

180°

(uncal)

214,3°

(extra PGA)

180°

(uncal)

180°

(uncal)

172,5°

(Offset-

correction)

180°

(cal)

180°

(cal)

→ This corresponds to row 13 of the table.