L9779WD datasheet(103/170 Pages) STMICROELECTRONICS

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L9779WD

Functional description

169

Auto-adaptative time filter (fully adaptive mode)

This characteristic is useful to set the best internal filter time depending on the input signal

frequency.

Tfilter time depends on duration of the previous period Tn according to the following

formula:

Tfilter(n+1) = 1/32*Tn if Int_vrs > Tfilter(n)

The filtering time purpose is filtering very short spikes.

The digital filtering time is applied to internal squared signal (int_vrs), obtained by Voltage

comparators.

The output of time filtering block is out_vrs signal.

The filtering time Tfilter is applied to int_vrs signal in two different ways:



Rising edge: if int_vrs high level lasts less than Tfilter out_vrs is not set to high level

In absence of any spikes during input signal rising edge out_vrs signal is expected with

a delay of Tfilter time



Falling edge: the falling edge of int_vrs is not delayed through time filtering block: after

falling edge for a time Tfilter any other transition on int_vrs signal is ignored.

Tmaxfilter = 200 µs typ.

Tmin filter = 4 µs typ.

The default value after reset is Tmaxfilter.

The Tfilter function is reset by the enable of FLYING WHEEL function.

Figure 65. Auto-adaptive time filter (rising edge)

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