MCP2561 datasheet(3/30 Pages) MICROCHIP

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DS25167B-page 3

MCP2561/2

1.0

DEVICE OVERVIEW

The MCP2561/2 is a high-speed CAN, fault-tolerant

device that serves as the interface between a CAN

protocol

controller

and

the

physical

bus.

The

MCP2561/2 device provides differential transmit and

receive capability for the CAN protocol controller, and

is fully compatible with the ISO-11898-5 standard. It will

operate at speeds of up to 1 Mb/s.

Typically, each node in a CAN system must have a

device to convert the digital signals generated by a

CAN controller to signals suitable for transmission over

the bus cabling (differential output). It also provides a

buffer between the CAN controller and the high-voltage

spikes that can be generated on the CAN bus by

outside sources.

1.1

Mode Control Block

The MCP2561/2 supports two modes of operation:

•Normal

• Standby

These modes are summarized in Table 1-1.

1.1.1

NORMAL MODE

Normal mode is selected by applying a low-level to the

STBY pin. The driver block is operational and can drive

the bus pins. The slopes of the output signals on CANH

and

CANL

are

optimized

produce

minimal

electromagnetic emissions (EME).

The high speed differential receiver is active.

1.1.2

STANDBY MODE

The device may be placed in Standby mode by

applying a high-level to the STBY pin. In Standby

mode, the transmitter and the high-speed part of the

receiver

are

switched

off

minimize

power

consumption. The low-power receiver and the wake-up

filter block are enabled in order to monitor the bus for

activity. The receive pin (RXD) will show a delayed

representation of the CAN bus, due to the wake-up

filter.

1.2

Transmitter Function

The

CAN

bus

has

two

states: Dominant

and

Recessive. A Dominant state occurs when the

differential voltage between CANH and CANL is

greater than VDIFF(D)(I). A Recessive state occurs

when the differential voltage is less than VDIFF(R)(I).

The Dominant and Recessive states correspond to the

Low and High state of the TXD input pin, respectively.

However, a Dominant state initiated by another CAN

node will override a Recessive state on the CAN bus.

1.3

Receiver Function

In Normal mode, the RXD output pin reflects the differ-

ential bus voltage between CANH and CANL. The Low

and High states of the RXD output pin correspond to the

Dominant and Recessive states of the CAN bus,

respectively.

1.4

Internal Protection

CANH and CANL are protected against battery short-

circuits and electrical transients that can occur on the

CAN bus. This feature prevents destruction of the

transmitter output stage during such a fault condition.

The device is further protected from excessive current

loading by thermal shutdown circuitry that disables the

output drivers when the junction temperature exceeds

a nominal limit of +175°C. All other parts of the chip

remain operational, and the chip temperature is low-

ered due to the decreased power dissipation in the

transmitter outputs. This protection is essential to

protect against bus line short-circuit-induced damage.

TABLE 1-1:

MODES OF OPERATION

Mode

STBY Pin

RXD Pin

LOW

HIGH

Normal

LOW

Bus is dominant

Bus is recessive

Standby

HIGH

Wake-up request is detected

No wake-up request detected

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