Datasheet

www.ti.com 2 EVM Setup and Operation
2.2 Using CAN Bus Load, Termination and Protection Configurations
The CAN EVM is populated with two 120Ω power resistors selectable via jumpers between CANH and
CANL. By using one, the EVM may be used as a terminated end of a bus. For electrical measurements to
represent the total loading of the bus, use both 120Ω resistors in parallel to give the standard 60Ω load for
parametric measurement. The EVM also has footprints is split termination is needed for the application.
The table below summarizes how to use these termination options. If split termination is used, care must
be taken to match the resistors. The common mode filter frequency may be calculated by: f
C
= 1/(2πRC).
Normally, the split capacitance is in the range of 4.7nF to 100nF. Keep in mind this is the common mode
filter frequency, not a differential filter that will impact the differential CAN signal directly.
Table 3. Bus Termination Configuration
Split Termination Split Termination
Termination Configuration 120Ω Resistors
Footprints Footprints
JMP4 JMP5 R7 R15 C4
Standard Termination (120Ω) shorted open
N/A N/A N/A
60Ω load - Electrical Parameterics shorted shorted
Split Termination (Common Mode
open open 60Ω 60Ω populated
Stabilization)
The EVM also has footprints for various protection schemes to enhance robustness for extreme system
level EMC requirements. The table below summarizes these options.
Table 4. Protection and Filtering Configuration
Configuration Footprint Reference Use Case Population & Description
Direct CAN transceiver to bus R9 and R14 populated with 0Ω
connection (default population)
Series resistance protection R9 and R14 populated with
Series Resistors or Common R9 / R14 or L1 (common CAN transceiver to bus MELF resistor as necessary for
Mode Choke footprint) connection harsh EMC environment
L1 populated with CM choke to
CM choke (bus filter) filter noise as necessary for
harsh EMC environment
Filter noise as necessary for
Bus Filtering Caps Transient harsh EMC environment. Filter
C2 / C7 Bus filter
Protection caps may be used in
combination with L1 CM choke.
To add extra protection for
system level transients and
ESD protection TVS diode
C2 / C7 or D1 / D2 Transient & ESD Protection
population option via D1/D2
footprint or varistor population
via C2 / C7 footprint.
7
SLLU158– December 2011 CAN EVM User Guide
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