L9788 datasheet(139/264 Pages) STMICROELECTRONICS

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DS12308 Rev 4

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L9788

Inductive sensor interface

263

11.2.3

VRS_A - Fully Adaptive Hysteresis

To set the adaptive hysteresis on VRS_A configuration, bit VRS_MODE[0] has to be set to

'1'. In this configuration, VRS input differential signal is fed into a peak detector circuit and

then quantized on 5 different voltage levels, based on 4 PVi thresholds (see Table 59).

Default hysteresis current after exiting reset is HI3.

The quantized output is sent to a logic block (Hysteresis Selection Table) that chooses the

proper hysteresis value (HIi) depending on the input peak voltage (PVi), see Table 60.

Peak detector and Hysteresis Selection Table circuits are enabled by VRS_FB signal

according to HYS_FB_SEL in CONFIG-REG 8 bit value that establishes if the feedback

signal is before or after the filter time.

VRS input differential voltage is continuously acquired: its max value, reached during time-

frame VRS_FB signal is asserted (hysteresis current is off), is latched through a peak

detector; such a peak defines a specific value of hysteresis current, turned on as soon as

the VRS_FB falls to zero and switches OFF when next rising edge occurs.

Based on the hysteresis current, the signal is processed by a squaring circuit which

processes the output signal of the comparator, see Figure 58.

Table 59. Peak voltage value ranges

Peak voltage [PVi]

Min

Typ

Max

Unit

PV1

600

930

1300

PV2

1200

1600

1950

PV3

2000

2300

2650

PV4

2600

3000

3300

Table 60. Insert title here

Input peak voltage range

Selected hysteresis (HIi)

0 - PV1

HI1

PV1 – PV2

HI2

PV2 – PV3

HI3

PV3 – PV4

HI4

> PV4

HI5

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