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ISO9141 Transceiver (K-Line)

L9679P

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DocID029275 Rev 1

ISO9141 Transceiver (K-Line)

A block diagram of the function is shown below. Data transmitted by the main

microcontroller is sent via the ISOTX pin and data is received via the ISORX pin. The bus

output is ISOK.

Figure 67. ISO9141 block diagram

When the ISOTX pin is asserted, logic high, the ISOK output will be disabled (pulled up by

an external resistor). When the ISOTX pin is logic low, the ISOK output will be enabled

(pulled down by the internal driver). This input pin contains an internal pull-up to command

the output to the disabled state in the event of an open circuit condition.

The ISORX pin has a push-pull output stage referenced to VDDQ voltage. This output is

asserted high when the voltage on the ISOK pin is above the ISOK input receiver threshold,

VBATMON, as defined in the electrical tables, while it is low when the voltage on the ISOK

pin is below the ISOK input receiver threshold with hysteresis.

ISOK output is a low side driver compatible with ISO9141 physical layer.

The output stage is protected against short circuits and diagnostics provide feedback for

current limit and thermal shutdown. While in current limit, the output stage will continue to

function until thermal limit is reached. If the thermal limit occurs, the output stage will shut

down until the temperature decreases below the limit threshold with hysteresis. The fault

status is reported in the ISO9141 Fault Status Register (ISOFLTSR).

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