Datasheet MCP2551 Datasheet
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
VSS
VDD
RXD
1
2
3
4
8
RS
7
CANH
6
CANL
MCP2551
5
VREF
Block Diagram
VDD
TXD
VDD
TXD
R
S
RXD
V
REF
© 2007 Microchip Technology Inc. DS21667E-page 1
Slope
Control
Reference
Voltage
Dominant
Detect
Power-On
Reset
Receiver
Thermal
Shutdown
Driver
Control
DD
0.5 V
GND
CANH
CANL
VSS
MCP2551
NOTES:
DS21667E-page 2 © 2007 Microchip Technology Inc.
MCP2551
1.0 DEVICE OVERVIEW
The MCP2551 is a high-speed CAN, fault-tolerant
device that serves as the interface between a CAN
protocol controller an d the physical bus. The MCP2551
provides differential transmit and receive capability for
the CAN protocol controlle r and is fully com pati ble with
the ISO-1 1898 standard, including 2 4V requiremen ts. 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 signa ls suit able for trans missio n over
the bus cabling (differential output). It also provides a
buffer between the C AN controlle r and the high-vol tage
spikes that can be generated on the CAN bus by
outside sources (EMI, ESD, electrical transients, etc.).
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 w h en the di fferential volt age 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, res pectively . Howe ver , a dominant
state initiated by another CAN node will override a
recessive state on the CAN bus.
1.1.1 MAXIMUM NUMBER OF NODES
The MCP2551 CAN outputs will drive a minimum load
of 45Ω
, allowing a maximum of 112 nodes to be
connected (given a minimum differential input
resistance of 20 kΩ and a nominal termination resistor
value of 120Ω).
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 shortcircuits and electrical transients that can occur on the
CAN bus. This feature prevents destruction of the
transmitter output sta ge duri ng such a fault condi tio n.
The device is further protected from excessive current
loading by thermal shutdown circuitry that disables the
output driv ers w hen the j uncti on te mperat ure e xceeds
a nominal limit of 165°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.
1.4 Operating Modes
The RS 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 dri vers
for the CANH and CANL signals are i nternally 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
proportional to the current output at R
reducing EMI emissions.
1.4.1 HIGH-SPEED
High-speed mode is s el ect ed by connecting the RS pin
SS. In this mode, the transm itter output drivers have
to V
fast output rise and fall times to support high-speed
CAN bus rates.
1.4.2 SLOPE-CONTROL
Slope-control mode further reduces EMI by limitin g th e
rise and fall times of CANH and CANL. The slope, or
slew rate (SR), is controlled by connecting an external
resistor (R
The slope is proportional to th e current outpu t at the R
pin. Since the current is primarily determined by the
slope-control resis tance value R
is achieved by applying a respective resistance.
Figure 1-1 illustrates typical slew rate values as a
function of the slope-control resistance value.
EXT) between RS and VOL (usually ground).
1.4.3 STANDBY MODE
The device may be placed in standby or “SLEEP” mod e
by applying a high-level to R
transmitter is switched off and the receiver operates at
a lower current. The receive pin on the controller side
(RXD) is still function al but w ill opera te at a slow er rate.
The attached mi crocontroller can monitor RXD for CAN
bus activity and place the transceiver into normal
operation via the R
CAN message may be lost).
S) to ground, with the slope
S, further
EXT, a certain slew rate
S. In SLEEP mode, the
S pin (at higher bus rates, the first
S
© 2007 Microchip Technology Inc. DS21667E- page 3
MCP2551
TABLE 1-1: MODES OF OPERATION
Mode Current at Rs Pin Resulting Voltage at RS Pin
Standby -I
Slope-control 10 µA < -IRS < 200 µA 0.4 VDD < VRS < 0.6 VDD
High-speed -IRS < 610 µA 0 < VRS < 0.3VDD
TABLE 1-2: TRANSCEIVER TRUTH TABLE
VDD VRS TXD CANH CANL Bus State
4.5V ≤ VDD ≤ 5.5V VRS < 0.75 VDD 0 HIGH LOW Dominant 0
POR
< VDD < 4.5V
V
(See Note 3)
0 < VDD < VPOR X X Not Driven/
Note 1: If another bus node is transmitting a dominant bit on the CAN bus, then RXD is a logic ‘0’.
2: X = “don’t care”.
3: Device drivers will function, although outputs are not ensured to meet the ISO-11898 specification.
RS < 10 µA VRS > 0.75 VDD
(1)
1 or floating Not Driven Not Driven Recessive 1
RS > 0.75 VDD X Not Driven Not Driven Recessive 1
V
VRS < 0.75 VDD 0 HIGH LOW Dominant 0
1 or floating Not Driven Not Driven Recessive 1
RS > 0.75 VDD X Not Driven Not Driven Recessive 1
V
No Load
Not Driven/
No Load
High Impedance X
RXD
(1)
FIGURE 1-1: SLEW RATE VS. SLOPE-CONTROL RESISTANCE VALUE
25
20
15
10
Slew Rate V/uS
5
0
10 20 30 40 49 60 70 76 90 100 110 120
Resistance (kΩ)
DS21667E-page 4 © 2007 Microchip Technology Inc.
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 prev en t th e c orrup tion of data on the
CAN bus. The d rivers 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 c onsecutive tran smitted dominant bits
during a multiple bit error a nd error fram e scenario. The
drivers remain disabl ed as lo ng as TXD rem ains low. A
rising edge on T XD will re set the t imer logi c and en able
the CANH and CANL output drivers.
1.6 Power-on Reset
When the device is powered on, CANH and CANL
remain in a high-impeda nce state until V
voltage-level V
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 e nter a high-i mpeda nce s ta te
if the voltage level at V
voltage brown-out protection during normal operation.
PORH. In addition, CANH and CANL will
DD falls below VPORL, providing
DD reaches the
1.7 Pin Descriptions
The 8-pin pinout is listed in Table1-3.
TABLE 1-3: MCP2551 PINOUT
Pin
Number
1 TXD Transmit Data Input
2V
3V
4 RXD Receive Data Output
5VREF Reference Output Voltage
6 CANL CAN Low-Level Voltage I/O
7 CANH CAN High-Level Voltage I/O
8R
Pin
Name
SS Ground
DD Supply Voltage
S Slope-Control Input
Pin Function
1.7.1 TRANSMITTER DATA INPUT (TXD)
TXD is a TTL-comp atible in put pin. Th e data on this pi n
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 dominan t state. Wh en TXD
is high, CANH and CANL are in the recessive state,
provided that ano ther C AN no de is not d riving the CA N
bus with a dominant state. TXD has an internal pull-up
resistor (nominal 25kΩ to V
DD).
1.7.2 GROUND SUPPLY (VSS)
Ground supply pin.
1.7.3 SUPPLY VOLTAGE (VDD)
Positive supply voltage pin.
1.7.4 RECEIVER DATA OUTPU T (RXD)
RXD is a CMOS -com patible outpu t that driv es high or
low depending on the differential signals on the CANH
and CANL pins and is usua lly connected to the receiver
data input of the CAN controller device. RXD is high
when the CAN bus i s recessive and lo w in the domina nt
state.
1.7.5 REFERENCE VOLTAG E (VREF)
Reference Voltage Output (Defined as VDD/2).
1.7.6 CAN LOW (CANL)
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 (RS)
The RS pin is used to select High-speed, Slope-control
or Standby modes via an external biasing resistor.
© 2007 Microchip Technology Inc. DS21667E- page 5
MCP2551
NOTES:
DS21667E-page 6 © 2007 Microchip Technology Inc.
MCP2551
2.0 ELECTRICAL
CHARACTERISTICS
2.1 Terms and Definitions
A number of terms are defined in ISO-11898 that are
used to describe the e lectri cal ch aracte ristics o f a CAN
transceiver device. These terms and definitions are
summarized in this section.
2.1.1 BUS VOLTAGE
VCANL and VCANH denote the voltages of the bus line
wires CANL and CANH relative to ground of each
individual CAN node.
2.1.2 COMMON MODE BUS VOLTAGE
RANGE
Boundary voltage levels of VCANL and VCANH with
respect to ground, for which prope r operation will oc cur ,
if up to the maximum number of CAN nodes are
connected to the bus.
2.1.3 DIFFERENTIAL INTERNAL
CAPACITANCE, C
NODE)
Capacitance seen between CANL and CANH during
the recessive state when the CAN node is
disconnected from the bus (see Figure 2-1).
2.1.4 DIFFERENTIAL INTERNAL
RESISTANCE, R
NODE)
Resistance see n betwe en CANL an d CANH du ring the
recessive state when the CAN node is disconnected
from the bus (see Figure 2-1).
DIFF (OF A CAN
DIFF (OF A CAN
2.1.5 DI FFERENTIAL V OLTAG E, VDIFF (OF CAN BUS)
Differential voltage of the two-wire CAN bus, value
DIFF = VCANH - VCANL.
V
2.1.6 INTERNAL CAPACITANCE, CIN (OF A CAN NODE)
Capacitance seen between CANL (or CANH) and
ground during the recessive state when the CAN node
is disconnected from the bus (see Figure 2-1).
2.1.7 INTERNAL RESISTANCE, RIN (OF A CAN NODE)
Resistance seen between CANL (or CANH) and
ground during the recessive state when the CAN node
is disconnected from the bus (see Figure 2-1).
FIGURE 2-1: PHYSICAL LAYER
DEFINITIONS
ECU
RIN
CANL
RIN
RDIFF
CIN CIN
CDIFF
CANH
GROUND
© 2007 Microchip Technology Inc. DS21667E- page 7
MCP2551
Absolute Maximum Ratings†
VDD.............................................................................................................................................................................7.0V
DC Voltage at TXD, RXD, V
DC Voltage at CANH, CANL (Note 1)..........................................................................................................-42V to +42V
Transient Voltage on Pins 6 and 7 (Note 2).............................................................................................-250V to +250V
Storage temperature ...............................................................................................................................-55°C to +150°C
Operating ambient temperature................................................. ...... ...... ..... ............................................-40°C to +125°C
Virtual Junction Temperature, T
Soldering temperature of leads (10 seconds).......................................................................................................+300°C
ESD protection on CANH and CANL pins (Note 4) ...................................................................................................6 kV
ESD protection on all other pins (Note 4) ..................................................................................................................4 kV
Note 1: Short-circuit applied when TXD is high and low.
2: In accordance with ISO-7637.
3: In accordance with IEC 60747-1.
4: Classification A: Human Body Model.
† NOTICE: Stresses above those listed under “Maximum ratings” may cause permanent damage to the device. This
is a stress rating only a nd fu nc tional operation of the d evi ce at tho se or an y ot her c ond itions above those indi ca ted in
the operational li stings of thi s specificatio n is not imp lied. Exposure to maximum ra ting conditi ons for extend ed periods
may affect device reliability.
REF and VS............................................................................................ -0.3V to VDD + 0.3V
VJ (Note 3).............................................................................................-40°C to +150°C
DS21667E-page 8 © 2007 Microchip Technology Inc.
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