Datasheet

1
2
3
4
5
6
7
8
14
13
12
9,10
IN
EN
GND NC
OUT
1
3
5
42
ISO1050
TPS76350
RXD
V
CC1
NC
TXD
GND1
GND1
GND1
NC
NC
CANH
GND2
4
3
2 6
51
CANL
NC
11
7
8
16
V
CC2
15
RXD
TXD
MCU
Vdd
DGND
PSU
L1
N
PE
3.3V
0V
Protective
Earth
Chasis
Ground
Digital
Ground
ISO
Ground
Optional Bus
protection
function
SN6501
V
CC
D2
D1
GND2
GND1
Galvanic
Isolation
Barrier
ISO1050
www.ti.com SLLS983H –JUNE 2009–REVISED JUNE 2013
APPLICATION INFORMATION
Figure 25. Application Circuit
BUS LOADING, LENGTH AND NUMBER OF NODES
The ISO11898 Standard specifies a maximum bus length of 40m and maximum stub length of 0.3m with a
maximum of 30 nodes. However, with careful design, users can have longer cables, longer stub lengths, and
many more nodes to a bus. A high number of nodes requires a transceiver with high input impedance such as
the ISO1050.
Many CAN organizations and standards have scaled the use of CAN for applications outside the original
ISO11898 standard. They have made system level trade offs for data rate, cable length, and parasitic loading of
the bus. Examples of some of these specifications are ARINC825, CANopen, CAN Kingdom, DeviceNet and
NMEA200.
A CAN network design is a series of tradeoffs, but these devices operate over wide –12-V to 12-V common-
mode range. In ISO11898-2 the driver differential output is specified with a 60Ω load (the two 120Ω termination
resistors in parallel) and the differential output must be greater than 1.5V. The ISO1050 is specified to meet the
1.5V requirement with a 60Ω load, and additionally specified with a differential output of 1.4V with a 45Ω load.
The differential input resistance of the ISO1050 is a minimum of 30KΩ. If 167 ISO1050 transceivers are in
parallel on a bus, this is equivalent to a 180Ω differential load. That transceiver load of 180Ω in parallel with the
60Ω gives a total 45Ω. Therefore, the ISO1050 theoretically supports over 167 transceivers on a single bus
segment with margin to the 1.2V minimum differential input at each node. However for CAN network design
margin must be given for signal loss across the system and cabling, parasitic loadings, network imbalances,
ground offsets and signal integrity thus a practical maximum number of nodes is typically much lower. Bus length
may also be extended beyond the original ISO11898 standard of 40m by careful system design and data rate
tradeoffs. For example, CANopen network design guidelines allow the network to be up to 1km with changes in
the termination resistance, cabling, less than 64 nodes and significantly lowered data rate.
This flexibility in CAN network design is one of the key strengths of the various extensions and additional
standards that have been built on the original ISO11898 CAN standard. In using this flexibility comes the
responsibility of good network design.
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