L9680 datasheet(184/277 Pages) STMICROELECTRONICS

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Remote sensor interface

L9680

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DocID029257 Rev 1

9.2.1

Wheel speed data register formats

When programmed as a wheel speed sensor interface, only four data registers are used

(Remote Sensor Data Register RSDR0-RSDR3).

Independent data registers are defined for each wheel speed channel and their contents are

determined by sensor type. Three level VDA sensors have eight data bits and. At fast wheel

speed not all bits may be transmitted by the sensor: the IC is able both to process normal or

either truncated frames by providing together with data, a 4 bit counter to inform the

microcontroller about the number of received valid bits.

For PWM encoded sensors, each pulse length is written to the sensor data register with a

typical resolution of 5 μs per bit. In case of pulse width duration equal or higher than

TSTANDSTILL_TH_L and less or equal than TSTANDSTILL_TH_H2, the standstill condition will be

recognized and bit 15 in the corresponding register will be set.

The register is updated when a PWM falling edge is detected; in case of stuck-at 1 of the

PWM signal the register is updated when the counter reaches the overflow value (0x1FF): in

this case the standstill bit not set and the counter in overflow will signal a fault to the

microcontroller.

9.2.2

Test mode

In order test the input structures of the connected microcontroller, the L9680 features a

wheel speed test mode that allows test patterns to be applied on the four wheel speed

outputs WS0-WS3. The test mode can be entered via SPI and the test patterns can also be

controlled via SPI commands. Test patterns can be composed only of static high or low

signals, which can be selected via SPI. For failsafe reasons only one channel at a time can

be switched into test mode.

9.3

Remote sensor interface fault protection

9.3.1

Short to ground, current limit

Each output is short circuit protected by an independent current limit. Should the output

current level reach or exceed the ILIMTH for a time period greater than TILIMTH or the

remote sensor interface the output stage is disabled. An internal up-down counter will count

in 25 μs increment up to TILIMTH. The filter time is chosen in order to avoid false current

limit detection for in-rush current that may happen at interface switch-on. When the output is

turned off due to current limit, the appropriate fault code STG is set in the Remote Sensor

Data Register (RSDR). The fault timer latch is cleared when the sensor channel is first

disabled and then re-enabled through the Remote Sensor Control Register (RSCTRL). This

fault condition does not interfere neither with the normal operation of the IC, nor with the

operation of the other channels. When a sensor fault is detected, the RSFLT bit of the GSW

is set indicating a fault occurred and can be decoded by addressing the RSDR register.

In order to fulfill the blanking time requirement at channel activation as per PSI-5

specification, a dedicated masking time is applied to the current limitation fault detection

each time a channel is activated.

L9680 Datasheet(PDF) 184 Page - STMicroelectronics

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