L9396 datasheet(43/109 Pages) STMICROELECTRONICS

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DS12539 Rev 6

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L9396

Remote sensor interface

108

Remote sensor interface

The device contains 4 remote sensor interfaces, capable of supporting active wheel speed

sensors or operating as an independent 2-channel tracking regulation supply.

The interface supply is internally connected to the VPREREG pin. The circuitry consists of a

power interface delivering a dedicated output voltage on RSUHx pins. This output could be

voltage regulated in case of operation as tracking supply (pins RSUH0 and RSUH1). When

WSS operation is selected, the function mirrors the current flowing in the external sensor

and transmits this current information to the decoder, which produces a digital value for

each sensor channel. RSULx pins are used as ground returns from the sensors and current

sense is carried out in low side.

Data are then output through SPI registers. Received signals can be processed to the

corresponding discrete logic output pin WSO0-WSO3.

5.1

Active wheel speed sensor

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

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

supported and selected through SPI configuration:



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



A 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 4.0);



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 SPI or the four WSOx output pins. For all sensors, other than

the standard active 2- level sensor, additional sensor data (diagnostics, etc…) are decoded

and available within SPI registers. The user may select to have all sensor data processed

on WSOx pins through the microcontroller by selecting pass through mode. In pass through

mode, the remote sensor interface simply conditions the incoming sensor current pulses to

digital pulses, no decoding is performed.

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

be configured (from 8 µs to 50 µs). Filters can be selected individually for each channel,

through the RS_CFG_x_y registers, bits [9:6].

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

signal can be processed directly to the WSOx output pins. This is done in the RS_CFG_x_y

registers, bit [4].

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 WSOx output pins and

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

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