LINE DRIVER WITH SLEW-RATE CONTROL

摘要

A line driver for a LIN-bus. The line driver has a current source output transistor (T1) for pulling down the LIN-bus wire (LB) to ground (GND). The LIN-bus wire (LB) is connected to a positive supply voltage (VBAT) through a pull-up resistor (R1). The output transistor (T1) provides a ramp shaped output current, under control of a ramp generator (RG). The output current, in combination with the pull-up resistor (R1), imposes a ramp-shaped output voltage on of the pull-up resistor may vary between 500 Ohm and 1 kOhm. When the resistance is 1 kOhm, the output voltage is clamped to signal ground (GND) and a delay occurs between the edge in the data signal (TXD) and the corresponding rising ramp in the output voltage. This delay is reduced by a comparator (CMP, T2) which monitors the output voltage and which increases the slew rate of the ramp generator (RG) when the output voltage is clamped and drops below a certain threshold.