MCP2551ESLASHP datasheet(5/20 Pages) MICROCHIP

5 / 20 page

 2002 Microchip Technology Inc.

Preliminary

DS21667C-page 5

MCP2551

1.5

TXD Permanent Dominant

Detection

If the MCP2551 detects an extended low state on the

TXD input, it will disable the CANH and CANL output

drivers in order to prevent the corruption of data on the

CAN bus. The drivers are disabled if TXD is low for

more than 1.25 ms (minimum). This implies a maxi-

mum bit time of 62.5 µs (16 kb/s bus rate) allowing up

to 20 consecutive transmitted dominant bits during a

multiple bit error and error frame scenario. The drivers

remain disabled as long as TXD remains low. A rising

edge on TXD will reset the timer logic and enable the

CANH and CANL output drivers.

1.6

Power-on Reset

When the device is powered on, CANH and CANL

remain in a high-impedance state until VDD reaches the

voltage level VPORH. In addition, CANH and CANL will

remain in a high-impedance state if TXD is low when

VDD reaches VPORH. CANH and CANL will become

active only after TXD is asserted high. Once powered

on, CANH and CANL will enter a high-impedance state

if the voltage level at VDD falls below VPORL, providing

voltage brown-out protection during normal operation.

1.7

Pin Descriptions

The 8-pin pinout is listed in Table 1-3.

TABLE 1-3:

MCP2551 PINOUT

1.7.1

TRANSMITTER DATA INPUT (TXD)

TXD is a TTL compatible input pin. The data on this pin

is driven out on the CANH and CANL differential output

pins. It is usually connected to the transmitter data out-

put of the CAN controller device. When TXD is low,

CANH and CANL are in the dominant state. When TXD

is high, CANH and CANL are in the recessive state,

provided that another CAN node is not driving the CAN

bus with a dominant state. TXD has an internal pull-up

resistor (nominal 25 k

Ω to VDD).

1.7.2

GROUND SUPPLY (VSS)

Ground supply pin.

1.7.3

SUPPLY VOLTAGE (VDD)

Positive supply voltage pin.

1.7.4

RECEIVER DATA OUTPUT (RXD)

RXD is a CMOS-compatible output that drives high or

low depending upon the differential signals on the

CANH and CANL pins and is usually connected to the

receiver data input of the CAN controller device. RXD

is high when the CAN bus is recessive and low in the

dominant state.

1.7.5

REFERENCE VOLTAGE (VREF)

Reference Voltage Output (Defined as VDD/2).

1.7.6

CAN LOW (CANL)

The CANL output drives the low side of the CAN differ-

ential bus. This pin is also tied internally to the receive

input comparator.

1.7.7

CAN HIGH (CANH)

The CANH output drives the high side of the CAN dif-

ferential bus. This pin is also tied internally to the

receive input comparator.

1.7.8

SLOPE RESISTOR INPUT (RS)

The RS pin is used to select High-Speed, Slope-Control

or Standby modes via an external biasing resistor.

Number

Name

Pin Function

TXD

Transmit Data Input

2VSS

Ground

3VDD

Supply Voltage

RXD

Receive Data Output

5VREF

Reference Output Voltage

CANL

CAN Low-Level Voltage I/O

CANH

CAN High-Level Voltage I/O

8RS

Slope-Control Input

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