MCP2551

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 8 RS CANH CANL VREF MCP2551 VDD VSS 2 3 4 7 6 5 Block Diagram VDD TXD Slope Control TXD Dominant Detect Thermal Shutdown Driver Control Power-On Reset CANH 0.5 VDD GND Reference Voltage Receiver RS RXD VREF CANL © 2007 Microchip Technology Inc. DS21667E-page 1 MCP2551 NOTES: DS21667E-page 2 © 2007 Microchip Technology Inc. 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 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 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 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 (RS) to ground, with the slope proportional to the current output at RS, further reducing 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 RS pin to VSS. 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 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). 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 (REXT) between RS and VOL (usually ground). The slope is proportional to the current output at the RS pin. Since the current is primarily determined by the slope-control resistance value REXT, a certain slew rate is achieved by applying a respective 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 shortcircuits 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 lowered 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 RS. 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 RS pin (at higher bus rates, the first CAN message may be lost). © 2007 Microchip Technology Inc. DS21667E-page 3 MCP2551 TABLE 1-1: Mode Standby Slope-control High-speed MODES OF OPERATION Current at Rs Pin -IRS < 10 µA 10 µA < -IRS < 200 µA -IRS < 610 µA Resulting Voltage at RS Pin VRS > 0.75 VDD 0.4 VDD < VRS < 0.6 VDD 0 < VRS < 0.3VDD TABLE 1-2: VDD TRANSCEIVER TRUTH TABLE VRS VRS < 0.75 VDD TXD 0 1 or floating X 0 1 or floating X X CANH CANL Bus State( 1) RXD( 1) 0 1 1 0 1 1 X HIGH LOW Dominant Not Driven Not Driven Recessive Not Driven Not Driven Recessive VRS > 0.75 VDD VRS < 0.75 VDD HIGH LOW Dominant VPOR < VDD < 4.5V (See Note 3) Not Driven Not Driven Recessive Not Driven Not Driven Recessive VRS > 0.75 VDD 0 < VDD < VPOR X Not Driven/ Not Driven/ High Impedance No Load No Load 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. 4.5V ≤ VDD ≤ 5.5V FIGURE 1-1: SLEW RATE VS. SLOPE-CONTROL RESISTANCE VALUE 25 20 Slew Rate V/uS 15 10 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 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 kΩ to VDD). 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 (VSS) Ground supply pin. 1.6 Power-on Reset 1.7.3 SUPPLY VOLTAGE (VDD) When the device is powered on, CANH and CANL remain in a high-impedance state until VDD reaches the voltage-level VPORH. In addition, CANH and CANL will 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 enter a high-impedance state if the voltage level at VDD falls below VPORL, providing voltage brown-out protection during normal operation. Positive supply voltage pin. 1.7.4 RECEIVER DATA OUTPUT (RXD) 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 (VREF) Reference Voltage Output (Defined as VDD/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 VSS VDD RXD VREF CANL CANH RS 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 (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 2.1 ELECTRICAL CHARACTERISTICS Terms and Definitions 2.1.5 DIFFERENTIAL VOLTAGE, VDIFF (OF CAN BUS) Differential voltage of the two-wire CAN bus, value VDIFF = VCANH - VCANL. A number of terms are defined in ISO-11898 that are used to describe the electrical characteristics of a CAN transceiver device. These terms and definitions are summarized in this section. 2.1.6 INTERNAL CAPACITANCE, CIN (OF A CAN NODE) 2.1.1 BUS VOLTAGE 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). VCANL and VCANH denote the voltages of the bus line wires CANL and CANH relative to ground of each individual CAN node. 2.1.7 INTERNAL RESISTANCE, RIN (OF A CAN NODE) 2.1.2 COMMON MODE BUS VOLTAGE RANGE 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). Boundary voltage levels of VCANL and VCANH with respect to ground, for which proper operation will occur, if up to the maximum number of CAN nodes are connected to the bus. FIGURE 2-1: PHYSICAL LAYER DEFINITIONS ECU 2.1.3 DIFFERENTIAL INTERNAL CAPACITANCE, CDIFF (OF A CAN NODE) RIN CANL RIN RDIFF CIN CIN GROUND CDIFF CANH 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, RDIFF (OF A CAN NODE) Resistance seen between CANL and CANH during the recessive state when the CAN node is disconnected from the bus (see Figure 2-1). © 2007 Microchip Technology Inc. DS21667E-page 7 MCP2551 Absolute Maximum Ratings† VDD .............................................................................................................................................................................7.0V DC Voltage at TXD, RXD, VREF and VS ............................................................................................ -0.3V to VDD + 0.3V 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, TVJ (Note 3).............................................................................................-40°C to +150°C 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 and functional operation of the device at those or any other conditions above those indicated in the operational listings of this specification is not implied. Exposure to maximum rating conditions for extended periods may affect device reliability. DS21667E-page 8 © 2007 Microchip Technology Inc. MCP2551 2.2 DC Characteristics Electrical Characteristics: Industrial (I): TAMB = -40°C to +85°C VDD = 4.5V to 5.5V Extended (E):TAMB = -40°C to +125°C VDD = 4.5V to 5.5V Characteristic Min Max Units Conditions DC Specifications Param No. Supply D1 D2 D3 IDD Supply Current Sym — — — — 75 10 365 465 4.3 4.0 0.8 mA mA µA µA V V V Dominant; VTXD = 0.8V; VDD Recessive; VTXD = +2V; RS = 47 kΩ -40°C ≤ TAMB ≤ +85°C, Standby; (Note 2) -40°C ≤ TAMB ≤ +125°C, Standby; (Note 2) CANH, CANL outputs are active when VDD > VPORH CANH, CANL outputs are not active when VDD < VPORL Note 1 D4 D5 D6 VPORH VPORL VPORD High-level of the power-on reset comparator Low-level of the power-on reset comparator Hysteresis of power-on reset comparator 3.8 3.4 0.3 Bus Line (CANH; CANL) Transmitter D7 D8 D9 D10 D11 D12 D13 D14 D15 D16 D17 IO(SC)(CANL)l VDIFF(r)(i) CANL short-circuit output current Recessive differential input voltage VO(CANH) VO(CANL) VDIFF(r)(o) VDIFF(d)(o) IO(SC)(CANH) CANH dominant output voltage CANL dominant output voltage Recessive differential output voltage Dominant differential output voltage CANH short-circuit output current VCANH(r);VCANL(r) CANH, CANL Recessive bus voltage IO(CANH)(reces) IO(CANL)(reces) Recessive output current 2.0 -2 -10 2.75 0.5 -500 1.5 — — — -1.0 -1.0 D18 VDIFF(d)(i) Dominant differential input voltage 0.9 1.0 D19 D20 D21 VDIFF(h)(i) RIN RIN(d) Differential input hysteresis CANH, CANL common-mode input resistance Deviation between CANH and CANL common-mode input resistance 100 5 -3 3.0 +2 +10 4.5 2.25 +50 3.0 -200 -100 (typical) 200 +0.5 +0.4 5.0 5.0 200 50 +3 V mA mA V V mV V mA mA mA V V V V mV kΩ % VCANH = VCANL VTXD = VDD; no load. -2V < V(CAHL,CANH) < +7V, 0V