TCAN330 Datasheet, PDF (27/39 Pages) Texas Instruments – CAN Transceivers

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TCAN330, TCAN332, TCAN334, TCAN337
TCAN330G, TCAN332G, TCAN334G, TCAN337G
SLLSEQ7A – DECEMBER 2015 – REVISED JANUARY 2016
Typical Application (continued)
11.2.1 Design Requirements
11.2.1.1 CAN Termination
The ISO 11898 standard specifies the interconnect to be a twisted-pair cable (shielded or unshielded) with 120-Ω
characteristic impedance (Z_O). Resistors equal to the characteristic impedance of the line should be used to
terminate both ends of the cable to prevent signal reflections. Unterminated drop lines (stubs) connecting nodes
to the bus should be kept as short as possible to minimize signal reflections. The termination may be on the
cable or in a node, but if nodes may be removed from the bus the termination must be carefully placed so that it
is not removed from the bus.
11.2.2 Detailed Design Procedure
Termination is typically a 120-Ω resistor at each end of the bus. If filtering and stabilization of the common mode
voltage of the bus is desired, then split termination may be used (see Figure 8). Split termination uses two 60-Ω
resistors with a capacitor in the middle of these resistors to ground. Split termination improves the
electromagnetic emissions behavior of the network by eliminating fluctuations in the bus common mode voltages
at the start and end of message transmissions.
Care should be taken in the power ratings of the termination resistors used. Typically the worst case condition
would be if the system power supply was shorted across the termination resistance to ground. In most cases the
current flow through the resistor in this condition would be much higher than the transceiver's current limit.
Node 1
MCU or DSP
CAN
Controller
Node 2
MCU or DSP
CAN
Controller
Node 3
MCU or DSP
CAN
Controller
Node n
(with termination)
MCU or DSP
CAN
Controller
CAN Transceiver
CAN Transceiver
CAN Transceiver
CAN Transceiver
RTERM
RTERM
Figure 35. Typical CAN Bus
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