E-L9637D Datasheet, PDF (9/15 Pages) STMicroelectronics – Monolithic bus driver with ISO 9141 interface

L9637
3
Functional description
Functional description
The L9637 is a monolithic bus driver designed to provide bidirectional serial communication
in automotive diagnostic applications according to the specification "Diagnostic Systems
ISO9141".
The device provides a bidirectional link, called K, to the V_Bat related diagnosis bus. It also
includes a separate comparator L which is also able to be linked to the V_Bat bus. The input
TX and output RX of K are related to V_CC with her integrated pull up resistances. Also the L
comparator output LO has a pull up resistance connected to V_CC.
The maximum external pull up resistance at K related to V_S should not be higher than R_KO ≤
5 kΩ to achieve clear output ON conditions.
All V_Bat bus defined inputs LI and K have supply voltage dependent thresholds together with
sufficient hysteresis to suppress line spikes. These pins are protected against overvoltages,
shorts to GND and V_S and can also be driven beyond V_S and GND.
These features are also given for TX, RX and LI only taking into account the behavior 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 temperature must decrease below the K switch ON temp. To achieve no fault for
V_S undervoltage conditions the outputs will be switched OFF and stay at high impedance.
The device is also protected against reverse battery condition. During lack of V_S or GND all
pins shows high impedance characteristic. To realize a lack of the V_S related bus line LI and
K the outputs LO and RX shows defined ON status.
Suppressing all 4 classes of "Schaffner" signals all pins can be load with short energy
pulses of max. ±0.2 mJ. All these features together with a high possible baud rate
>50Kbaud, controlled output slopes for low EMI, a wide power supply voltage range and a
very small quiescent current during OFF (TX LI K=High) condition IS_{off typ} ≤ 120 µA, and a
real standby function with zero power consumption IS_{SB typ} ≤ 1 µA during system de
powering V_CC ≤ 0.5 V make this device high efficient for automotive bus system.
After wake up of the system from OFF or SB condition the first output signal will have an
additional delay time td_typ ≤ 5 µs see also Figure 5.
The typical output voltage behavior for the K, LO, RX outputs as a function of the output
current is shown in Figure 6. Figure 7 shows a waveform of the output signal when the low
level changes from R_ON * I_OUT to I_OUT * 2 * R_ON + U_BE state. This variation occurs due to too
low output current or after a negative transient forced to the output or to the supply voltage
line.
Doc ID 1765 Rev 7
9/15