L9637 Functional description
Doc ID 1765 Rev 8 9/15
3 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
Ba
t related diagnosis bus. It also
includes a separate comparator L which is also able to be linked to the V
Ba
t 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 kto 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.
