L9903

14/17

tCCP= RPR · CPR · ln NPR

with NPR= VPRH / VPRL = 2

tCCP= 0.69 · RPR · CPR

3.14 ISO-Interface

The ISO-Interface provides the communication between the micro controller and a serial bus with a baud rate

up to 60kbit/s via a single wire which is VBAT and GND compatible. The logic level transmission input TX drives

the open drain K-output. The K output can be connected to a serial bus with a pull up resistor to VBAT. The K-

pin is protected against overvoltage, short to GND and VS and can be driven beyond VVS and GND. During lack

of VVS or GND the output shows high impedance characteristic. The open drain output RX with an internal pull

up resistor monitors the status at the K-pin to read the received data and control the transmitted data. Short

circuit condition at K-pin is recognized if the internal open drain transistor isn't able to pull the voltage potential

at K-pin below the threshold of 0.45·VVS. Then the RX stays in high condition. A timer starts and switches the

open drain transistor after typ. 20µs off. A next low at the TX input resets the timer and the open drain transistor

switches on again.

Figure 11. Functional schematic of the ISO-interface

RX

TX

K

VCC

R RX

0.5

V

VS

TX

R

TSH

delay

=

R

S

Q

R

I KH