Part Number: ISO1500
We have this question: If we are not using a bus speed of 1Mbps (ISO1500) and we stay at today 4.8 to 19,6 kbps, can we increase the stub length calculated according to the TI AppNote? > this length is ~5 meters max for Tr/Tf = 210ms typ.
It may impact our Bus system if we must reduce with this new driver our stubs length (10 ~15 meters today)
As this value calculation depends on Trise/Tfall of the transceiver, and in the case of the new ISO1500 (only available @1Mbps max and not 200KBps) this time is quite low. That’s may mean lower length of stub? I have a doubt and I’m not sure to be right ! May the Tr/Tf will increase if we use this transceiver at lower speeds (up to 19600bds max).
Thanks in advance for your reply and confirmation
The rise and fall times are more dependent on line resistance and capacitance rather that communication speed. The driver rise and fall times are speced at a line resistance and capacitance of 54ohms and 50pF respectively. So based on the equation in the datasheet, then the ideal stub length should shorten as rise and fall times reduce.
We are glad that we were able to resolve this issue, and will now proceed to close this thread.
If you have further questions related to this thread, you may click "Ask a related question" below. The newly created question will be automatically linked to this question.
In reply to Lucas Schulte9:
Thanks for your answer. All right, So it seems not so easy to quantify in concrete terms of stubs length.. but we can hope to have also proper communications with little bit longer stubs @lower speed. We usually use CAT-5e cable (100R) and 2 termination résistors 120R on the bus.
All content and materials on this site are provided "as is". TI and its respective suppliers and providers of content make no representations about the suitability of these materials for any purpose and disclaim all warranties and conditions with regard to these materials, including but not limited to all implied warranties and conditions of merchantability, fitness for a particular purpose, title and non-infringement of any third party intellectual property right. No license, either express or implied, by estoppel or otherwise, is granted by TI. Use of the information on this site may require a license from a third party, or a license from TI.
TI is a global semiconductor design and manufacturing company. Innovate with 100,000+ analog ICs andembedded processors, along with software, tools and the industry’s largest sales/support staff.