General Description The MAX351 interfaces between the CAN protocol controller and the physical wires of the bus lines in a controller area network (CAN). The MAX351 provides differential transmit capability to the bus and differential receive capability to the CAN controller. The MAX351 is primarily intended for +3.3 single-supply applications that do not require the stringent fault protection specified by the automotive industry (ISO 11898). The MAX351 features four different modes of operation: high-speed, slope-control, standby, and shutdown mode. High-speed mode allows data rates up to 1Mbps. The slope-control mode can be used to program the slew rate of the transmitter for data rates of up to 5kbps. This reduces the effects of EMI, thus allowing the use of unshielded twisted or parallel cable. In standby mode, the transmitter is shut off and the receiver is pulled high, placing the MAX351 in lowcurrent mode. In shutdown mode, the transmitter and receiver are switched off. The MAX351 input common-mode range is from -7 to +12, exceeding the ISO 11898 specification of -2 to +7. These features, and the programmable slew-rate limiting, make the part ideal for nonautomotive, harsh environments. The MAX351 is available in 8-pin SO and SOT23 packages and operates over the -4 C to +85 C extended temperature range. Features Low +3.3 Single-Supply Operation ESD Protection ±12k Human Body Model Wide -7 to +12 Common-Mode Range Small SOT23 Package Four Operating Modes High-Speed Operation Up to 1Mbps Slope-Control Mode to Reduce EMI (Up to 5kbps) Standby Mode Low-Current Shutdown Mode Thermal Shutdown Current Limiting PART Ordering Information TEMP RANGE PIN- PACKAGE TOP MARK MAX351ESA+ -4 C to +85 C 8 SO MAX351EKA+T -4 C to +85 C 8 SOT23-8 AEKF +Denotes a lead(pb)-free/rohs-compliant package. T = Tape and reel Printers JetLink Industrial Control and Networks Telecom Backplane Consumer Applications Applications TOP IEW + TXD 1 Pin Configuration 8 RS GND 2 3 MAX351 7 6 CANH CANL 4 5 SHDN SO/SOT23 Typical Operating Circuit at end of data sheet. For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim s website at www.maximintegrated.com. 19-3274; Rev 2; 1/12
ABSOLUTE MAXIMUM RATINGS to GND...-.3 to +6 TXD, RS, SHDN to GND...-.3 to +6 to GND...-.3 to +6 CANH, CANL to GND...-7.5 to +12.5 Continuous Power Dissipation (T A = +7 C) 8-Pin SO (derate 5.9mW/ C above +7 C)...47mW 8-Pin SOT23 (derate 5.1mW/ C above +7 C)...48.2mW Operating Temperature Range...-4 C to +85 C Maximum Junction Temperature...+15 C Storage Temperature Range...-65 C to +15 C Lead Temperature Range (soldering, 1s)...+3 C Soldering Temperature (reflow)...+26 C Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. ELECTRICAL CHARACTERISTICS ( = +3.3 ±5%, R L = 6Ω, C L = 1pF, T A = T MIN to T MAX, unless otherwise noted. Typical values are at = +3.3 and T A = +25 C.) (Note 1) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS Dominant 35 7 ma Supply Current I S Recessive 2 5 Standby 8 15 µa Shutdown Current I SHDN SHDN =, TXD = or unconnected 1 µa Thermal-Shutdown Threshold TSH +16 C Thermal-Shutdown Hysteresis 25 C TXD INPUT LEELS High-Level Input oltage IH 2 Low-Level Input oltage IL.8 Input Capacitance C IN 5 pf Pullup Resistor R INTXD 5 1 kω CANH, CANL TRANSMITTER Recessive Bus oltage CANH, CANL +.3 TXD =, no load 2 2.3 3 TXD =, no load, RS = (standby mode) -1 +1 m Off-State Output Leakage -2 < CANH, CANL < +7, SHDN = HIGH -25 +25 µa Input Leakage Current =, CANH = CANL = 5-25 +25 µa CANH Output oltage CANH TXD = 2.45 CANL Output oltage CANL TXD = 1.25 Differential Output ( CANH - CANL ) TXD = 1.5 3. TXD =, R L = 45Ω 1.2 3. TXD =, no load -5 +5 TXD =, R L = 6Ω -12 +12 m 2 Maxim Integrated
ELECTRICAL CHARACTERISTICS (continued) MAX351 ( = +3.3 ±5%, R L = 6Ω, C L = 1pF, T A = T MIN to T MAX, unless otherwise noted. Typical values are at = +3.3 and T A = +25 C.) (Note 1) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS -7 CANH -2 CANH Short-Circuit Current I CANHSC Minimum foldback current -35 CANL Short-Circuit Current I CANLSC CANL 12 2 ma OUTPUT LEELS High Output-oltage Level OH I = -1mA ma.8 x Low Output-oltage Level OL I = 4mA.4 D C BU S R EC EI ER ( T XD = C C ; C A N H a n d C A N L e x t e r n a l l y dr iv e n ; - 7 C A N H, C A N L + 1 2, un le s s ot h e r w i s e sp e c if i e d ) Differential Input oltage -7 CM +12.5 DIFF (Recessive) RS = (standby mode).5 Differential Input oltage Dominant.9 DIFF (Dominant) RS = (standby mode) 1.1 Differential Input Hysteresis D IF F( H Y S T ) 2 m CANH and CANL Input Resistance R I 2 5 kω Differential Input Resistance R DIFF 4 1 kω MODE SELECTION (RS).3 x Input oltage for High Speed SLP Input oltage for Standby STBY.75 x Slope-Control Mode oltage SLOPE R RS = 25kΩ to 2kΩ High-Speed Mode Current I HS RS = -5 µa SHUTDOWN (SHDN) SHDN Input oltage High SHDNH 2 SHDN Input oltage Low SHDNL.8 SHDN Pulldown Resistor R INSHDN 5 1 kω.4 x.6 x Maxim Integrated 3
TIMING CHARACTERISTICS ( = +3.3 ±5%, R L = 6Ω, C L = 1pF, T A = T MIN to T MAX, unless otherwise noted. Typical values are at = +3.3 and T A = +25 C.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS Delay TXD to Bus Active (Figure 1) RS = ( 1Mbps) 5 t ONTXD R RS = 25kΩ ( 5kbps) 183 R RS = 1kΩ ( 125kbps) 77 ns Delay TXD to Bus Inactive (Figure 1) Delay Bus to Receiver Active (Figure 1) RS = ( 1Mbps) 7 t OFFTXD R RS = 25kΩ ( 5kbps) 226 R RS = 1kΩ ( 125kbps) 834 RS = ( 1Mbps) 8 t ON R RS = 25kΩ ( 5kbps) 2 R RS = 1kΩ ( 125kbps) 73 ns ns Delay Bus to Receiver Inactive (Figure 1) RS = ( 1Mbps) 1 t OFF R RS = 25kΩ ( 5kbps) 245 R RS = 1kΩ ( 125kbps) 8 ns RS = ( 1Mbps) 96 Differential-Output Slew Rate SR R RS = 25kΩ ( 5kbps) 12.5 R RS = 1kΩ ( 125kbps) 2.9 /µs R RS = 2kΩ ( 62.5kbps) 1.6 Bus Dominant to Active t DL RS >.8 x, standby, Figure 2 1 µs Standby to Receiver Active t SBL BUS dominant, Figure 2 4 µs SHDN to Bus Inactive t OFFSHDN TXD = GND, Figure 3 (Note 2) 1 µs S H DN to Recei ver Acti ve t ONSHDN BUS dominant, Fi gur e 3 (Note 3) 4 µs S H D N to S tand b y t SHDNSB Fi g ur e 4 2 µs ESD Protection Human Body Model ±12 k Note 1: All currents into device are positive; all currents out of the device are negative. All voltages are referenced to device ground, unless otherwise noted. Note 2: No other devices on the BUS. Note 3: BUS externally driven. 4 Maxim Integrated
Timing Diagrams TXD /2 /2 RS x.75 BUS EXTERNALLY DRIEN t ONTXD t OFFTXD DIFF.9.5 DIFF t SBL 1.1 t ON t OFF t DL /2 /2 /2 /2 Figure 1. Timing Diagram Figure 2. Timing Diagram for Standby Signal SHDN /2 /2 SHDN t OFFSHDN t ONSHDN /2 DIFF t SHDNSB.5 BUS EXTERNALLY DRIEN.75 /2 RS Figure 3. Timing Diagram for Shutdown Signal Figure 4. Timing Diagram for Shutdown-to-Standby Signal Maxim Integrated 5
Typical Operating Characteristics ( = +3.3, R L = 6Ω, C L = 1pF, T A = +25 C, unless otherwise specified.) SLEW RATE (/µs) 35 3 25 2 15 1 5 SLEW RATE vs. R RS AT 1kbps MAX351toc1 SUPPLY CURRENT (ma) 25 22 19 16 13 SUPPLY CURRENT vs. DATA RATE T A = -4 C T A = +25 C T A = +85 C MAX351toc2 SHUTDOWN SUPPLY CURRENT (na) 12 1 8 6 4 2 SHUTDOWN SUPPLY CURRENT vs. TEMPERATURE (SHDN = ) MAX351toc3 2 4 6 8 1 12 14 16 18 2 R RS (kω) 1 2 4 6 8 1 DATA RATE (kbps) -4-15 1 35 6 85 TEMPERATURE ( C) STANDBY SUPPLY CURRENT (µa) 11. 1.5 1. 9.5 9. 8.5 STANDBY SUPPLY CURRENT vs. TEMPERATURE (RS = ) 8. -4-15 1 35 6 85 TEMPERATURE ( C) MAX351toc4 RECEIER PROPAGATION DELAY (ns) 5 45 4 35 3 25 2 15 1 RECEIER PROPAGATION DELAY vs. TEMPERATURE RECESSIE DOMINANT 5 R RS = GND -4-15 1 35 6 85 TEMPERATURE ( C) MAX351toc5 DRIER PROPAGATION DELAY (ns) 5 4 3 2 1 DRIER PROPAGATION DELAY vs. TEMPERATURE RECESSIE DOMINANT R RS = GND, DATA RATE = 1kbps -4-15 1 35 6 85 TEMPERATURE ( C) MAX351toc6 OLTAGE () 1.6 1.4 1.2 1..8.6.4.2 RECEIER OUTPUT LOW vs. OUTPUT CURRENT T A = -4 C T A = +25 C T A = -85 C 5 1 15 2 25 3 35 4 45 OUTPUT CURRENT (ma) MAX351toc7 6 Maxim Integrated
Typical Operating Characteristics (continued) ( = +3.3, R L = 6Ω, C L = 1pF, T A = +25 C, unless otherwise specified.) RECEIER OUTPUT HIGH (CC - ) () 1.8 1.6 1.4 1.2 1..8.6.4.2 RECEIER OUTPUT HIGH vs. OUTPUT CURRENT MAX351toc8 DIFFERENTIAL OLTAGE () 3.5 3. 2.5 2. 1.5 1..5 DIFFERENTIAL OLTAGE vs. DIFFERENTIAL LOAD T A = -4 C T A = +25 C T A = -85 C MAX351toc9 1 2 3 4 5 6 7 8 OUTPUT CURRENT (ma) 1 2 3 DIFFERENTIAL LOAD R L (Ω) RECEIER PROPAGATION DELAY DRIER PROPAGATION DELAY RS = GND MAX351toc1 CAHN - CANL MAX351toc11 TXD 2/div R RS = 24kΩ 1v/div R RS = 75kΩ R RS = 1kΩ 2ns/div 2ns/div DRIER PROPAGATION DELAY MAX351toc12 TXD 1/div CAHN - CANL LOOPBACK PROPAGATION DELAY (ns) 12 1 8 6 4 2 LOOPBACK PROPAGATION DELAY vs. R RS MAX351toc13 2ns/div RS = GND 2 4 6 8 1 12 14 16 18 2 R RS (kω) Maxim Integrated 7
PIN NAME FUNCTION 1 TXD 2 GND Ground Pin Description Transmit Data Input. TXD is a CMOS/TTL-compatible input from a CAN controller. TXD has an internal 75kΩ pullup resistor. 3 Supply oltage. Bypass to GND with a.1µf capacitor. 4 Receive Data Output. is a CMOS/TTL-compatible output. 5 SHDN 6 CANL CAN Bus Line Low 7 CANH CAN Bus Line High 8 RS Shutdown Input, CMOS/TTL-Compatible. Drive SHDN high to put the MAX351 in shutdown. SHDN has an internal 75kΩ pulldown resistor to GND. Mode-Select Input. Drive RS low or connect to GND for high-speed operation. Connect a resistor between RS and GND to control output slope. Drive RS high to put into standby mode (see the Mode Selection section). THERMAL SHUTDOWN MAX351 CANH TXD TRANSMITTER CONTROL CANL RS MODE SELECTION GND RECEIER SHUTDOWN SHDN.75 Figure 5. MAX351 Functional Diagram 8 Maxim Integrated
Detailed Description The MAX351 interfaces between the CAN protocol controller and the physical wires of the bus lines in a CAN. It provides differential transmit capability to the bus and differential receive capability to the CAN controller. It is primarily intended for +3.3 single-supply applications that do not require the stringent fault protection specified by the automotive industry (ISO 11898) The MAX351 features four different modes of operation: high-speed, slope-control, standby, and shutdown mode. High-speed mode allows data rates up to 1Mbps. The slope-control mode can be used to program the slew rate of the transmitter for data rates of up to 5kbps. This reduces the effects of EMI, thus allowing the use of unshielded twisted or parallel cable. In standby mode, the transmitter is shut off and the receiver is pulled high, placing the MAX351 in lowcurrent mode. In shutdown mode, the transmitter and receiver are switched off. The MAX351 input common-mode range is from -7 to +12, exceeding the ISO 11898 specification of -2 to +7. These features, and the programmable slew-rate limiting, make the part ideal for nonautomotive, harsh environments. The transceivers operate from a single +3.3 supply and draw 35µA of supply current in dominant state and 2µA in recessive state. In standby mode, supply current is reduced to 8µA. In shutdown mode, supply current is less than 1µA. CANH and CANL are output short-circuit current limited and are protected against excessive power dissipation by thermal-shutdown circuitry that places the driver outputs into a high-impedance state. Receiver The receiver reads differential inputs from the bus lines (CANH, CANL) and transfers this data as a singleended output () to the CAN controller. It consists of a comparator that senses the difference DIFF = (CANH - CANL) with respect to an internal threshold of +.75. If this DIFF is greater than.75, a logic-low is present at. If DIFF is less than.75, a logic-high is present. The receiver always echoes the CAN BUS data. The CANH and CANL common-mode range is -7 to +12. is logic-high when CANH and CANL are shorted or terminated and undriven. Mode Selection High-Speed Mode Connect RS to ground to set the MAX351 to highspeed mode. When operating in high-speed mode, the MAX351 can achieve transmission rates of up to 1Mbps. In high-speed mode, use shielded twisted pair cable to avoid EMI problems. Slope-Control Mode Connect a resistor from RS to ground to select slopecontrol mode (Table 2). In slope-control mode, CANH and CANL slew rates are controlled by the resistor connected to the RS pin. Maximum transmission speeds are controlled by RRS and range from 4kbps to 5kbps. Controlling the rise and fall slopes reduces EMI and allows the use of an unshielded twisted pair or a parallel pair of wires as bus lines. The equation for selecting the resistor value is given by: RRS (kω) 12 / (maximum speed in kbps) Transmitter The transmitter converts a single-ended input (TXD) from the CAN controller to differential outputs for the bus lines (CANH, CANL). The truth table for the transmitter and receiver is given in Table 1. See the Slew Rate vs. RRS graph in the Typical Operating Characteristics. Standby Mode If a logic-high is applied to RS, the MAX351 enters a low-current standby mode. In this mode, the transmitter Table 1. Transmitter and Receiver Truth Table When Not Connected to the Bus TXD RS SHDN CANH CANL BUS STATE Low RS <.75 x Low High Low Dominant Low High or float RS <.75 x Low 5kΩ to 25kΩ to / 2 5kΩ to 25kΩ to / 2 Recessive High X RS >.75 x Low 5kΩ to 25kΩ to GND 5kΩ to 25kΩ to GND Recessive X X High Unconnected Unconnected Unconnected High High Maxim Integrated 9
is switched off and the receiver is switched to a lowcurrent/low-speed state. If dominant bits are detected, switches to low level. The microcontroller should react to this condition by switching the transceiver back to normal operation. When the MAX351 enters standby mode, goes high for 4µs (max) regardless of the BUS state. However, after 4µs, goes low only when the BUS is dominant, otherwise remains high (when the BUS is recessive). For proper measurement of standbyto-receiver active time (tsbl), the BUS should be in dominant state (see Figure 2). Shutdown Drive SHDN high to enter shutdown mode. Connect SHDN to ground or leave unconnected for normal operation. Thermal Shutdown If the junction temperature exceeds +16 C, the device is switched off. The hysteresis is approximately 25 C, disabling thermal shutdown once the temperature drops below 135 C. In thermal shutdown, CANH and CANL go recessive and all IC functions are disabled. Applications Information Reduced EMI and Reflections In slope-control mode, the CANH and CANL outputs are slew-rate limited, minimizing EMI and reducing reflections caused by improperly terminated cables. In multidrop CAN applications, it is important to maintain a direct point-to-point wiring scheme. A single pair of wires should connect each element of the CAN bus, and the two ends of the bus should be terminated with 12Ω resistors (Figure 6). A star configuration should never be used. Any deviation from the point-to-point wiring scheme creates a stub. The high-speed edge of the CAN data on a stub can create reflections back down the bus. These reflections can cause data errors by eroding the noise margin of the system. Although stubs are unavoidable in a multidrop system, care should be taken to keep these stubs as small as possible, especially in high-speed mode. In slope-control mode, the requirements are not as rigorous, but stub length should still be minimized. Power Supply and Bypassing The MAX351 requires no special layout considerations beyond common practices. Bypass CC to GND with a.1µf ceramic capacitor mounted close to the IC with short lead lengths and wide trace widths. Table 2. Mode Selection Truth Table CONDITION FORCED AT PIN RS MODE RESULTING CURRENT AT RS RS <.3 x High Speed I RS < 5µA.4 x < RS <.6 x Slope Control 1µA < I RS < 2µA RS >.75 x Standby I RS < 1µA 1 Maxim Integrated
TXD MAX351 CANH TWISTED PAIR R L = 12Ω R L = 12Ω TRANSCEIER 3 CANL STUB LENGTH KEEP AS SHORT AS POSSIBLE TRANSCEIER 1 TRANSCEIER 2 Figure 6. Multiple Receivers Connected to CAN Bus Typical Operating Circuit 12Ω.1µF CAN CONTROLLER TX RX TXD MAX351 CANH CANL GND 25kΩ TO 2kΩ RS GND 12Ω PROCESS: BiCMOS Chip Information Package Information For the latest package outline information and land patterns (footprints), go to www.maximintegrated.com/packages. Note that a +, #, or - in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing pertains to the package regardless of RoHS status. PACKAGE TYPE PACKAGE CODE OUTLINE NO. LAND PATTERN NO. 8 SO S8+4 21-41 9-96 8 SOT23 K8F+4 21-78 9-176 Maxim Integrated 11
REISION NUMBER REISION DATE DESCRIPTION Revision History PAGES CHANGED 2 1/12 Added lead-free part information to the data sheet 1 13 Maxim Integrated cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim Integrated product. No circuit patent licenses are implied. Maxim Integrated reserves the right to change the circuitry and specifications without notice at any time. The parametric values (min and max limits) shown in the Electrical Characteristics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance. 12 Maxim Integrated 16 Rio Robles, San Jose, CA 95134 USA 1-48-61-1 212 Maxim Integrated Products, Inc. Maxim Integrated and the Maxim Integrated logo are trademarks of Maxim Integrated Products, Inc.
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