L9788 datasheet(140/264 Pages) STMICROELECTRONICS

140 / 264 page

Inductive sensor interface

L9788

140/264

DS12308 Rev 4

Figure 58. VRS_A fully adaptive hysteresis

11.2.4

VRS_A - Adaptive filter time

In VRS_A mode, it is possible to enable the filter time on the output of the zero crossing

comparator through the bit VRS_MODE[1] of CONFIG-REG 8.

Once enabled, the most suitable internal filter based on the input signal frequency is

determined.

According to VRS previous output period, filter time value is updated as follows:

If the value of the previous period is lower than 128 µs, the filter time would be saturated at

4 µs fixed value. After reset Tfilter = 200 µs (TYP)

Through EN_FALLING_FILT CONFIG-REG8 bit in VRS register, it is possible to configure

two different strategies for the filtering algorithm.

VRS_OUT rising edge: the transition depends on the hysteresis crossing of differential

signal Vdiff; VRS output is set if Vdiff remains asserted and stable for a period longer than

Tfilter.

VRS OUT falling edge: the transition depends on the zero crossing of differential signal

Vdiff:



EN_FALLING_FILT = 1: VRS_OUT is deasserted when the signal is low and remains

stable for at least Tfilter; see Figure 59



EN_FALLING_FILT = 0: VRS_OUT is de-asserted at first zero crossing transition of

differential signal and next eventual commutations are ignored for Tfilter time. see

Figure 60.

GADG0612161130PS

FLW_IN_P

FLW_IN_N

Peak Detector

Hysteresis

Square circuit

int_vrs

VRS_HYST_FB

Filter Time

VRS_CONF_MODE_1

FLW_OUT

VRS_FB

ADC

PVi

Selection

Table

(n)

Tfilter

Tperiod (n-1)

GADG0612161215PS

L9788 Datasheet(PDF) 140 Page - STMicroelectronics

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