MCP2551 - SparkFun Electronics

1 MCP2551 . High-Speed CAN Transceiver Features Package Types Supports 1 Mb/s operation Implements ISO-11898 standard physical layer PDIP/SOIC. requirements Suitable for 12V and 24V systems TXD 1 8 RS. Externally-controlled slope for reduced RFI. MCP2551 . emissions VSS 2 7 CANH. Detection of ground fault (permanent Dominant). on TXD input VDD 3 6 CANL. Power-on Reset and voltage brown-out protection RXD 4 5 VREF. 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.

2 - Extended (E): -40 C to +125 C. Block Diagram VDD. TXD Thermal Dominant Shutdown VDD Detect TXD Driver Control Slope Power-On CANH. RS. Control Reset VDD. RXD GND. CANL. Reference Receiver VREF. Voltage VSS. 2010 Microchip Technology Inc. DS21667F-page 1. MCP2551 . NOTES: DS21667F-page 2 2010 Microchip Technology Inc. MCP2551 . DEVICE OVERVIEW Operating Modes The MCP2551 is a high-speed CAN, fault-tolerant The RS pin allows three modes of operation to be device that serves as the interface between a CAN selected: protocol controller and the physical bus. The MCP2551 High-Speed device provides differential transmit and receive Slope-Control capability for the CAN protocol controller, and is fully compatible with the ISO-11898 standard, including 24V Standby requirements.

3 It will operate at speeds of up to 1 Mb/s. These modes are summarized in Table 1-1. Typically, each node in a CAN system must have a When in High-Speed or Slope-Control mode, the device to convert the digital signals generated by a drivers for the CANH and CANL signals are internally CAN controller to signals suitable for transmission over regulated to provide controlled symmetry in order to the bus cabling (differential output). It also provides a minimize EMI emissions. buffer between the CAN controller and the high-voltage Additionally, the slope of the signal transitions on spikes that can be generated on the CAN bus by CANH and CANL can be controlled with a resistor outside sources (EMI, ESD, electrical transients, etc.). connected from pin 8 (RS) to ground.

4 The slope must be proportional to the current output at RS, which will Transmitter Function further reduce EMI emissions. The CAN bus has two states: Dominant and HIGH-SPEED. Recessive. A Dominant state occurs when the differential voltage between CANH and CANL is High-Speed mode is selected by connecting the RS pin greater than a defined voltage ( , ). A Recessive to VSS. In this mode, the transmitter output drivers have state occurs when the differential voltage is less than a fast output rise and fall times to support high-speed defined voltage (typically 0V). The Dominant and CAN bus rates. Recessive states correspond to the Low and High state of the TXD input pin, respectively. However, a SLOPE-CONTROL. Dominant state initiated by another CAN node will Slope-Control mode further reduces EMI by limiting the override a Recessive state on the CAN bus.

5 Rise and fall times of CANH and CANL. The slope, or slew rate (SR), is controlled by connecting an external MAXIMUM NUMBER OF NODES resistor (REXT) between RS and VOL (usually ground). The MCP2551 CAN outputs will drive a minimum load The slope is proportional to the current output at the RS. of 45 , allowing a maximum of 112 nodes to be pin. Since the current is primarily determined by the connected (given a minimum differential input slope-control resistance value REXT, a certain slew rate resistance of 20 k and a nominal termination resistor is achieved by applying a specific resistance. value of 120 ). Figure 1-1 illustrates typical slew rate values as a function of the slope-control resistance value. Receiver Function STANDBY MODE. The RXD output pin reflects the differential bus voltage The device may be placed in Standby or SLEEP mode between CANH and CANL.

6 The Low and High states of by applying a high-level to the RS pin. In SLEEP mode, the RXD output pin correspond to the Dominant and the transmitter is switched off and the receiver operates Recessive states of the CAN bus, respectively. at a lower current. The receive pin on the controller side (RXD) is still functional, but will operate at a slower Internal Protection rate. The attached microcontroller can monitor RXD for CAN bus activity and place the transceiver into normal CANH and CANL are protected against battery short- operation via the RS pin (at higher bus rates, the first circuits and electrical transients that can occur on the CAN message may be lost). CAN bus. This feature prevents destruction of the transmitter output stage during such a fault condition.

7 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. 2010 Microchip Technology Inc. DS21667F-page 3. MCP2551 . TABLE 1-1: MODES OF OPERATION. Mode Current at Rs Pin Resulting Voltage at RS Pin Standby -IRS < 10 A VRS > VDD. Slope-Control 10 A < -IRS < 200 A VDD < VRS < VDD. High-Speed -IRS < 610 A 0 < VRS < TABLE 1-2: TRANSCEIVER TRUTH TABLE. VDD VRS TXD CANH CANL Bus State( 1) RXD( 1).

8 0 HIGH LOW Dominant 0. VRS < VDD. VDD 1 or floating Not Driven Not Driven Recessive 1. VRS > VDD X. Not Driven Not Driven Recessive 1. 0 HIGH LOW Dominant 0. VPOR < VDD < VRS < VDD. 1 or floating Not Driven Not Driven Recessive 1. (See Note 3). VRS > VDD X. Not Driven Not Driven Recessive 1. Not Driven/ Not Driven/. 0 < VDD < VPOR X X High Impedance X. 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. FIGURE 1-1: SLEW RATE VS. SLOPE-CONTROL RESISTANCE VALUE. 25. 20. Slew Rate V/ s 15. 10. 5. 0. 10 20 30 40 49 60 70 76 90 100 110 120. Resistance (k ). DS21667F-page 4 2010 Microchip Technology Inc.

9 MCP2551 . TXD Permanent Dominant TRANSMITTER DATA INPUT (TXD). Detection TXD is a TTL-compatible input pin. The data on this pin is driven out on the CANH and CANL differential output If the MCP2551 detects an extended Low state on the pins. It is usually connected to the transmitter data TXD input, it will disable the CANH and CANL output output of the CAN controller device. When TXD is Low, drivers in order to prevent the corruption of data on the CANH and CANL are in the Dominant state. When TXD. CAN bus. The drivers are disabled if TXD is Low for is High, CANH and CANL are in the Recessive state, more than ms (minimum). This implies a provided that another CAN node is not driving the CAN. maximum bit time of s (16 kb/s bus rate), bus with a Dominant state.

10 TXD has an internal pull-up allowing up to 20 consecutive transmitted Dominant resistor (nominal 25 k to VDD). bits during a multiple bit error and error frame scenario. The drivers remain disabled as long as TXD remains GROUND SUPPLY (VSS). Low. A rising edge on TXD will reset the timer logic and enable the CANH and CANL output drivers. Ground supply pin. SUPPLY VOLTAGE (VDD). Power-on Reset Positive supply voltage pin. When the device is powered on, CANH and CANL. remain in a high-impedance state until VDD reaches the RECEIVER DATA OUTPUT (RXD). voltage-level VPORH. In addition, CANH and CANL will RXD is a CMOS-compatible output that drives High or remain in a high-impedance state if TXD is Low when Low depending on the differential signals on the CANH.