Texas Instruments SN65HVD257, Руководство пользователя

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SN65HVD257 EVM Setup and Operation for Redundant (Parallel Networks)
3.2 Using CAN Bus Load and Termination Configuration
Each bus of the EVM is populated with two 120 Ω power resistors selectable via jumpers between CANH
and CANL. By using one of the resistors, 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 120
Ω resistors in parallel to
give the standard 60 Ω load for parametric measurement. The EVM also has footprints for customer
installation of split termination if the application requires it. 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 / (2 π R C). Normally, the split capacitance is in the
range of 4.7nF to 100nF. Keep in mind that this is the common-mode filter frequency, not a differential
filter that will impact the differential CAN signal directly.
Table 3. CAN Bus Termination Configuration
Split Termination CM Stabilizing
120 Ω Resistors
Footprints Capacitor
"Termination Configuration Bus 1"
JMP4 JMP6 R5 R13 C3
Standard Termination (120 Ω ) shorted open NA NA NA
60
Ω
load - Electrical Parameterics shorted shorted NA NA NA
Split Termination (Common Mode
open open 60 Ω 60 Ω populated
Stabilization)
Split Termination CM Stabilizing
"Termination Configuration Bus 2" 120 Ω Resistors
Footprints Capacitor
JMP9 JMP11 R29 R37 C23
Standard Termination (120 Ω ) shorted open NA NA NA
60 Ω load - Electrical Parameterics shorted shorted NA NA NA
Split Termination (Common Mode
open open 60 Ω 60 Ω populated
Stabilization)
9 SLLU172 – August 2012 SN65HVD257 CAN EVM: Functional Safety and Redundant CAN Network
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