PCA89C250

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© 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

VCC

3

supply voltage

RXD

4

receive data output

Vref

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