L9779WD-SPI datasheet(88/141 Pages) STMICROELECTRONICS

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Functional description

L9779WD-SPI

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DocID027721 Rev 2

6.14

Flying wheel interface function

Figure 59. Flying wheel interface circuit

6.14.1

Flying wheel interface functionality description

The flying wheel interface is an interface between the microprocessor and the flying wheel

sensor: it handles signals coming from magnetic pick-up sensor or Hall Effect sensor and

feeds the digital signal to Microcontroller that extracts flying wheel rotational position,

angular speed and acceleration.

This circuit implements an auto adaptative hysteresis and filter time algorithm that can be

configured via SPI using VRS_mode bit.

If the auto adaptive hysteresis is OFF the hysteresis value can be selected using VRS_Hyst

bit.

If fault is present (OL / SC GND / SC VB) the functionality is not guaranteed.

6.14.2

Auto-adaptive sensor filter

Two main VRS configuration sets are available for VRS, by mans of CONFIG_REG1

Auto-adaptative hysteresis (fully adaptive mode)

When enabled the auto adaptative hysteresis works as described below.

Input signals difference is obtained through a full differential amplifier; its output, DV signal,

is fed to peak detection circuit and then to A/D converter implemented with 4 voltage

comparators (5 levels) (Pvi).

Output of A/D is sent to Logic block (Table 43: Hysteresis threshold precision) that

implements correlation function between Peak voltage and hysteresis value; hysteresis

value is used by square filtering circuit which conditions DV signal.

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