L9678P datasheet(157/203 Pages) STMICROELECTRONICS

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L9678P, L9678P-S

ISO9141 transceiver

202

ISO9141 transceiver

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 56. ISO9141 block diagram

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

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

enabled (pulled low 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. This output is deasserted 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. Should thermal limit occur, 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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