Civil Engineering Reference
In-Depth Information
• CAN_H comparator: Single-ended comparator to monitor CAN_H only.
• CAN_L Vbatt Comp: Comparator to monitor high voltage on CAN_L > 7 V.
• CAN_H Vbatt Comp: Comparator to monitor high voltage on CAN_H > 7 V.
2.6.1.4
Differential Receiver
The differential receiver has a high common-mode range (−2-6V). This guarantees
an EMC and ground shift robust communication. This comparator is active if there
is no short on the bus.
2.6.1.5
CAN_L, CAN_H Single-Ended Comparator
These comparators monitor one bus CAN_H or CAN_L only. In case of a short
of one bus wire, the corresponding comparator on the short-free wire receives
the data. The robustness against EMC and ground shift is low compared with the
performance of the differential mode.
2.6.1.6
CAN_H, CAN_L Vbat Comparator
These comparators monitor the voltage on CAN_H and CAN_L to detect overvolt-
age on these wires (V > 7 V).
If the voltage on CAN_H or CAN_L is higher than 7 V, this indicates a failure on
the bus wire (for example, short to Vbatt) in sleep mode and CAN_L will be terminated
to Vbatt. In this mode, a high voltage is a normal situation. The Vbatt comparator will
be disabled in this mode to reduce current consumption and to avoid a failure report.
2.6.1.7
Bus Failure Detection
To detect the kind of failure on the bus all comparators are used. The combination of
the information allows the failure detection logic (Fig.
2.56
) to find out which kind
of failure is on the bus. Depending on the type of failure, the hidden output stage
can be switched off to protect them.
2.6.1.8
Application Circuit
Figure
2.57
shows the typical application circuit of a low-speed CAN application.
Sometimes CAN coils are used to improve the emission and EMC robustness. The
termination resistors are different. Minimum on two nodes 500 Ω are set. The value
for the termination resistors on the other nodes depends on the number of node in
the network. In total, the value of all resistors must be above 100 Ω. For example, if
