Not Recommended for New Designs
Please use MCP2561
MCP2551
High-Speed CAN Transceiver
Features
• Supports 1 Mb/s operation
• Implements ISO-11898 standard physical layer
requirements
• Suitable for 12V and 24V systems
• Externally-controlled slope for reduced RFI
emissions
• Detection of ground fault (permanent Dominant)
on TXD input
• Power-on Reset and voltage brown-out protection
• An unpowered node or brown-out event will not
disturb the CAN bus
• Low current standby operation
• Protection against damage due to short-circuit
conditions (positive or negative battery voltage)
• Protection against high-voltage transients
• Automatic thermal shutdown protection
• Up to 112 nodes can be connected
• High-noise immunity due to differential bus
implementation
• Temperature ranges:
- Industrial (I): -40°C to +85°C
- Extended (E): -40°C to +125°C
Package Types
PDIP/SOIC
TXD
V
SS
V
DD
RXD
1
2
3
4
8
R
S
CANH
CANL
V
REF
MCP2551
V
DD
7
6
5
Block Diagram
V
DD
TXD
Slope
Control
TXD
Dominant
Detect
Thermal
Shutdown
Driver
Control
Power-On
Reset
CANH
0.5 V
DD
GND
Reference
Voltage
Receiver
R
S
RXD
V
REF
CANL
V
SS
2001-2016 Microchip Technology Inc.
DS20001667G-page 1
MCP2551
1.0
DEVICE OVERVIEW
1.4
Operating Modes
The MCP2551 is a high-speed CAN, fault-tolerant
device that serves as the interface between a CAN
protocol controller and the physical bus. The MCP2551
device provides differential transmit and receive
capability for the CAN protocol controller, and is fully
compatible with the ISO-11898 standard, including 24V
requirements. 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 (EMI, ESD, electrical transients, etc.).
The R
S
pin allows three modes of operation to be
selected:
• High-Speed
• Slope-Control
• Standby
These modes are summarized in
Table 1-1.
When in High-Speed or Slope-Control mode, the
drivers for the CANH and CANL signals are internally
regulated to provide controlled symmetry in order to
minimize EMI emissions.
Additionally, the slope of the signal transitions on
CANH and CANL can be controlled with a resistor
connected from pin 8 (R
S
) to ground. The slope must
be proportional to the current output at R
S
, which will
further reduce EMI emissions.
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 a defined voltage (e.g.,1.2V). A Recessive
state occurs when the differential voltage is less than a
defined voltage (typically 0V). 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.
1.4.1
HIGH-SPEED
High-Speed mode is selected by connecting the R
S
pin
to V
SS
. In this mode, the transmitter output drivers have
fast output rise and fall times to support high-speed
CAN bus rates.
1.4.2
SLOPE-CONTROL
1.1.1
MAXIMUM NUMBER OF NODES
The MCP2551 CAN outputs will drive a minimum load
of 45
,
allowing a maximum of 112 nodes to be
connected (given a minimum differential input
resistance of 20 k and a nominal termination resistor
value of 120
Slope-Control mode further reduces EMI by limiting the
rise and fall times of CANH and CANL. The slope, or
slew rate (SR), is controlled by connecting an external
resistor (R
EXT
) between R
S
and V
OL
(usually ground).
The slope is proportional to the current output at the R
S
pin. Since the current is primarily determined by the
slope-control resistance value R
EXT
, a certain slew rate
is achieved by applying a specific resistance.
Figure 1-1
illustrates typical slew rate values as a
function of the slope-control resistance value.
1.2
Receiver Function
1.4.3
STANDBY MODE
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 165°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.
The device may be placed in Standby or SLEEP mode
by applying a high-level to the R
S
pin. In SLEEP mode,
the transmitter is switched off and the receiver operates
at a lower current. The receive pin on the controller side
(RXD) is still functional, but will operate at a slower
rate. The attached microcontroller can monitor RXD for
CAN bus activity and place the transceiver into normal
operation via the R
S
pin (at higher bus rates, the first
CAN message may be lost).
2001-2016 Microchip Technology Inc.
DS20001667G-page 3
MCP2551
1.5
TXD Permanent Dominant
Detection
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
output 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 to V
DD
).
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
maximum 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.
1.7.2
GROUND SUPPLY (V
SS
)
Ground supply pin.
1.6
Power-on Reset
1.7.3
SUPPLY VOLTAGE (V
DD
)
RECEIVER DATA OUTPUT (RXD)
When the device is powered on, CANH and CANL
remain in a high-impedance state until V
DD
reaches the
voltage level V
PORH
. In addition, CANH and CANL will
remain in a high-impedance state if TXD is Low when
V
DD
reaches V
PORH
. 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 V
DD
falls below V
PORL
, providing
voltage brown-out protection during normal operation.
Positive supply voltage pin.
1.7.4
RXD is a CMOS-compatible output that drives high or
low depending on 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
Pin Descriptions
1.7.5
REFERENCE VOLTAGE (V
REF
)
Reference Voltage Output (defined as V
DD
/2).
The 8-pin pinout is listed in
Table 1-3.
1.7.6
TABLE 1-3:
Pin
Number
1
2
3
4
5
6
7
8
CAN LOW (CANL)
MCP2551 PINOUT
Pin
Name
TXD
V
SS
V
DD
RXD
V
REF
CANL
CANH
R
S
Ground
Supply Voltage
Receive Data Output
Reference Output Voltage
CAN Low-Level Voltage I/O
CAN High-Level Voltage I/O
Slope-Control Input
Pin Function
Transmit Data Input
The CANL output drives the low side of the CAN
differential 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
differential bus. This pin is also tied internally to the
receive input comparator.
1.7.8
SLOPE RESISTOR INPUT (R
S
)
The R
S
pin is used to select High-Speed, Slope-Control
or Standby modes via an external biasing resistor.
2001-2016 Microchip Technology Inc.
DS20001667G-page 5
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