L9680 datasheet(182/277 Pages) STMICROELECTRONICS

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Remote sensor interface

L9680

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DocID029257 Rev 1

9.2

Active wheel speed sensor

The remote sensor interface circuit conditions and decodes active wheel speed sensor

signals with various pulse widths and output currents. The following sensor types are

supported and selected through the Remote Sensor Configuration Register (RSCR)



Standard active 2-level wheel speed sensors (7/14 mA)



Three level (7/14/28 mA) VDA compliant sensor with direction and air gap information

(‘Requirement Specification for Standardized Interface for Wheel Speed Sensor with

Additional Information’, Version 2.0)



PWM encoded 2-level sensors with 2 edges per tooth (see data sheet Infineon® IC

TLE4942/BOSCH DF11)



PWM encoded 2-level sensors with 1 edge per tooth (see data sheet Allegro®

ATS651LSH/BOSCH DF11)

Received wheel speed frames from all the above sensors are decoded into signals suitable

for the microcontroller through the four WSx output pins (WS0-WS3). Specific information is

shown in Figure 44.

For all sensors, other than the standard active 2- level sensor, additional sensor data

(diagnostics, etc…) are decoded and available within the Remote Sensor Data Registers

(RSDR0, RSDR1, RSDR3, RSDR4). If standard active 2- level sensor is selected the

content of the Remote Sensor Data Registers will be NO DATA fault.

Only for 2-level sensors (STD or PWM encoded) the user may choose to have all sensor

data processed through the microcontroller by selecting pass through mode, WSPTEN,

within the Remote Sensor Configuration Register (RSCR). In pass through mode, the

remote sensor interface simply transforms the incoming sensor current pulses to digital

voltage pulses on the WSx pins, no decoding is performed.

The sensor input filter time, deglitch filter (delay until a threshold crossing is detected) can

be configured in 15 steps. Filters can be selected individually for each channel, through the

Remote Sensor Configuration Register, WSFILT bits.

For PWM encoded sensors with 2 edges per tooth not in pass through mode, the standstill

signal can be processed directly to the WSx output pins. This is done in the Remote Sensor

Configuration Register, SSEN bit.

Since the decoder has to measure the pulses in order to determine, whether they are stand-

still pulses or not, the first standstill pulse will always be seen on the WSx output pins and

the first not stand-still pulse after a stand-still period will be suppressed.

For 3-levels VDA sensors the device performs parity check on the received data frame. In

case a parity error is detected, the INVALID fault bit of the RSDRx register will be set.

Data from the sensor are not latched: last incoming frame overwrites the previous one once

validated. Faults coming from diagnostic (i.e. over current, short to ground or battery) are

latched until the microcontroller reads them.

Sensor signal decoding is done according to two possible algorithms:



Auto-adjusting current trip points.

With this option, the IC is able to find sensor DC current value (named IB0) in the range

from 2.5 mA to 21 mA (default is 7 mA).

The IC is also able to detect the current value of the data pulse and compute the first

threshold (named Ith1): Ith1 = IB0 +

Ith1/2 where Ith1 is in the range from 5 mA to

9.3 mA (default is 7 mA).

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