L9637 datasheet(5/11 Pages) STMICROELECTRONICS

5 / 11 page

FUNCTIONAL DESCRIPTION

The L9637 is a monolithic bus driver designed to

provide bidirectional serial communication in auto-

motive diagnostic applications according to the

specification ”Diagnostic Systems ISO9141”.

The device provides a bidirectional link, called K,

to the VBat related diagnosis bus. It also includes

a separate comparator L which is also able to be

linked to the VBat bus. The input TX and output

RX of K are related to VCC with her integrated pull

up resistances. Also the L comparator output LO

has a pull up resistance connected to VCC.

The maximum external pull up resistance at K re-

lated to VS should not be higher than RKO

≤ 5KΩ

to achieve clear output ON conditions.

All VBat bus defined inputs LI and K have supply

voltage dependent thresholds together with suf-

ficent hysteresis to suppress line spikes. These

pins are protected against overvoltages, shorts to

GND and VS and can also be driven beyond VS

and GND. These features are also given for TX,

RX and LI only taking into account the behaviour

of the internal pull up resistances. The thermal

shut down function switches OFF the K output if

the chip temperature increases above the thermal

shut down threshold. To reactivate K again the

chip temperature must decrease below the K

switch ON temp. To achieve no fault for VS under-

voltage conditions the outputs will be switched

OFF and stay at high impedance. The device is

also protected against reverse battery condition.

During lack of VS or GND all pins shows high im-

pedance characteristic. To realize a lack of the VS

related bus line LI and K the outputs LO and RX

shows defined ON status.

40V

I/O

VCC

VDD

ECU1

ECU2

GND

VCC

1,75V

RTX

RLO

RRX

510 Ohm

Diagnostic

Tester

ILI

0.4 Ohm

IK OFF

R KO

C K

Figure 2: ISO Application Circuit

L9637

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