MCP2557FD datasheet(3/36 Pages) MICROCHIP

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 2016 Microchip Technology Inc.

DS20005533A-page 3

MCP2557FD/8FD

1.0

DEVICE OVERVIEW

The MCP2557FD/8FD CAN transceiver family is

designed for high-speed CAN FD applications with up

to 8 Mbps communication speed. The product offers a

Silent mode controlled by the Silent mode pin. The

Silent mode is used to disable the CAN transmitter.

This ensures that the device doesn’t drive the CAN

bus.

The

MCP2557FD/8FD

device

provides

differential transmit and receive capability for the CAN

protocol controller, and is fully compatible with

specification ISO/DIS-11898-2:2015.

The loop delay symmetry is tested to support data rates

that are up to 8 Mbps for CAN FD (Flexible Data rate).

The maximum propagation delay was improved to

support longer bus length.

Typically, each node in a CAN system must have a

device 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

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 states of the TXD input pin, respectively.

However, a Dominant state initiated by another CAN

node will override a Recessive state on the CAN bus.

1.2

Receiver Function

The RXD output pin reflects the differential 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.

1.3

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 lowered due to the decreased

power dissipation in the transmitter outputs. This

protection is essential to guard against bus line short-

circuit-induced damage. Thermal protection is only

active during Normal mode.

1.4

Permanent Dominant Detection

The MCP2557FD/8FD device prevents a permanent

dominant condition on TXD.

In Normal mode, if the MCP2557FD/8FD detects an

extended Low state on the TXD input, it will disable the

CANH and CANL output drivers in order to prevent

data corruption on the CAN bus. The drivers will remain

disabled until TXD goes High. The high-speed receiver

is active, and data on the CAN bus is received on RXD.

The condition has a time-out of 1.9 ms (typical). This

implies a maximum bit time of 128 µs (7.8 kHz),

allowing up to 18 consecutive dominant bits on the bus.

1.5

Power-on Reset (POR) and

Undervoltage Detection

The MCP2557FD/8FD have POR detection on both

supply pins, VDD and VIO. Typical POR thresholds to

deassert the reset are 1.2V and 3.0V for VIO and VDD,

respectively.

When the device is powered on, CANH and CANL

remain in a high-impedance state until VDD exceeds its

undervoltage level. Once powered on, CANH and

CANL will enter a high-impedance state if the voltage

level at VDD drops below the undervoltage level,

providing voltage brown-out protection during normal

operation.

The receiver output is forced to a Recessive state

during an undervoltage condition on VDD.

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