Kontron COMe Starterkit Eval T2 - Manual (Page 128)

COM Express Interfaces
2.21.2. Reference Schematics
2.21.2.1. CAN Bus Example
Figure 50: CAN Bus Example
Figure 50: CAN Bus Example shows the schematics of a CAN Bus implementation with the CAN
Transceiver TJA10407 (U25). The transistor / inverter combination at the CAN_TX and CAN_RX
line coming from the Module is necessary to handle the protection against VCC_12V connection
according to chapter 5.10 of COM.0 Rev. 2.1. The Diodes D31 and D32 accomplish ESD
protection.
J33 is a DSUB-9 connector in standardized CAN pin-out. Please refer to Table 41: Pin-out Table
DSUB-9 CAN Connector below.
If an ODB-II adapter is used pin 9 carries the car battery voltage. The automotive power rail is a
difficult rail to work with. It is nominally a 12V rail but may dip to 6V when the engine is cranking
and may be up to 16V when the engine is running and there may be transients in excess of +/-
100V.
Table 41: Pin-out Table DSUB-9 CAN Connector
J33 (9 positions) Pin description
2 CAN_L
7 CAN_H
9 VCC
3 GND
The COM Express Specification conform 12V protection will decrease the maximum transfer rate
to about 10kbaud. For higher speed please contact your Module vendor to find a solution.
2.21.3. Routing Considerations
It should be routed as a differential pair signal with 120 Ohm differential impedance. The end
points of CAN bus should be terminated with 120 Ohms or with 60 Ohms from the CAN_H line
and 60 Ohms from the CAN_L line to the CAN Bus reference voltage. Check your CAN
transceiver application notes for further details on termination.
PICMG ® COM Express ® Carrier Board Design Guide Rev. 2.0 / December 6, 2013
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CEX
SER1_TX_Q
SER1_RX_Q CAN_SPLIT
CAN_STB
CAN_L
CAN_H
V5.0_CAN
SER1_TX#
SER1_RX# SER1_RX_R
CAN_L
CAN_H
VCC_5V0
VCC_5V_SBY
VCC_3V3
VCC_3V3
CAN_TX
CAN_RX
R187
R1%0R0S02
D32
EZAEG2A50AX
R350
R1k006
R230
R1%0R0S02
U25
TJA1040T
VCC
3
TXD
1 CANH
7
GND
2
SPLIT
5
RXD
4
CANL
6
STB
8
R184
R1%10K0S02
C151
C47UV16S10
R183
R1%10K0S02
C262
C100N02V16
nc
U45A
NC7SZ14
1
2
4
U45B
NC7SZ14
GND
3
VCC
5
R247
R1%0R0S02
Q43
BSS138W
3
1
2
C150
C100N02V16
R185
R1%60R4S02
R186
R1%60R4S02
Q16
BSS138W
3
1
2
R337
R1%4K7S02
Q18
BSS138W
3
1
2
R342
R1%4K7S02
J33
STDB9
D31
EZAEG2A50AX
R343
R1%4K7S02
C152
C470PS02
CEX
D
N
I
1
2
3
4
5
6
7
8
9
VCC_3V3