PCA89C250 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2011. All rights reserved.
Product data sheet Rev. 06 — 25 August 2011 3 of 18
NXP Semiconductors
PCA82C250
CAN controller interface
7.2 Pin description
8. Functional description
The PCA82C250 is the interface between a CAN protocol controller and the physical bus.
It is primarily intended for high-speed automotive applications (up to 1 MBd). The device
provides differential transmit capability to the bus and differential receive capability to the
CAN controller. It is fully compatible with the “ISO 11898” standard.
A current limiting circuit protects the transmitter output stage against short-circuit to
positive and negative battery voltage. Although the power dissipation is increased during
this fault condition, this feature will prevent destruction of the transmitter output stage.
If the junction temperature exceeds a value of approximately 160 C, the limiting current
of both transmitter outputs is decreased. Because the transmitter is responsible for the
major part of the power dissipation, this will result in reduced power dissipation and hence
a lower chip temperature. All other parts of the PCA82C250 will remain in operation. The
thermal protection is needed, in particular, when a bus line is short-circuited.
The CANH and CANL lines are also protected against electrical transients which may
occur in an automotive environment.
Pin 8 (Rs) allows three different modes of operation to be selected: High-speed, Slope
control and Standby.
For high-speed operation, the transmitter output transistors are simply switched on and off
as fast as possible. In this mode, no measures are taken to limit the rise and fall slope.
Use of a shielded cable is recommended to avoid RFI problems. The High-speed mode is
selected by connecting pin 8 to ground.
For lower speeds or shorter bus length, an unshielded twisted pair or a parallel pair of
wires can be used for the bus. To reduce RFI, the rise and fall slope should be limited. The
rise and fall slope can be programmed with a resistor connected from pin 8 to ground. The
slope is proportional to the current output at pin 8.
If a HIGH level is applied to pin 8, the circuit enters a low-current Standby mode. In this
mode, the transmitter is switched off and the receiver is switched to a low current. If
dominant bits are detected (differential bus voltage >0.9 V), RXD will be switched to a
Table 3. Pin description
Symbol Pin Description
TXD 1 transmit data input
GND 2 ground
V
CC
3 supply voltage
RXD 4 receive data output
V
ref
5 reference voltage output
CANL 6 LOW-level CAN voltage input/output
CANH 7 HIGH-level CAN voltage input/output
Rs 8 slope resistor input
