Datasheet

 2014 Microchip Technology Inc. DS20005284A-page 3
MCP2561/2FD
1.0 DEVICE OVERVIEW
The MCP2561/2FD is a high-speed CAN device,
fault-tolerant device that serves as the interface
between a CAN protocol controller and the physical
bus. The MCP2561/2FD device provides differential
transmit and receive capability for the CAN protocol
controller, and is fully compatible with the ISO-11898-2
and ISO-11898-5 standards.
The Loop Delay Symmetry is guaranteed to support
d
ata rates that are up to 5 Mbps for CAN FD (Flexible
D
ata rate). The maximum propagation delay was
improved to support longer bus length.
Typically, each node in a CAN system must have a
d
evice 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 MCP2561/2FD supports two modes of operation:
• Normal Mode
• Standby Mode
These modes are summarized in Tabl e 1-1.
1.1.1 NORMAL MODE
Normal mode is selected by applying low-level voltage
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 to 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 high-level voltage to the STBY pin. In Standby
mode, the transmitter and the high-speed part of the
receiver are switched off to minimize power
consumption. The low-power receiver and the wake-up
filter blocks are enabled to monitor the bus for activity.
The receive pin (R
XD) will show a delayed
representation of the CAN bus, due to the wake-up
filter.
The CAN controller gets interrupted by a negative edge
on
the R
XD pin (Dominant state on the CAN bus). The
CAN controller must put the MCP2561/2FD back into
Normal mode, using the STBY pin, in order to enable
high speed data communication.
The CAN bus wake-up function requires both supply
v
oltages, V
DD and VIO, to be in valid range.
1.2 Transmitter Function
The CAN bus has two states:
• Dominant State
• Recessive State
A Dominant state occurs when the differential voltage
b
etween CANH and CANL is greater than V
DIFF(D)(I).
A Recessive state occurs when the differential voltage
is less than V
DIFF(R)(I). The Dominant and Recessive
states correspond to the Low and High state of the T
XD
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
differential bus voltage between CANH and CANL. The
Low and High states of the R
XD 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
l
oading 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
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