Other Parts Discussed in Thread: TCA9517, TCA9800
Hi,
I am currently facing a problem with the TCA9406 driver that I use as an SMBus driver to communicate with a battery.
I attach the layout of the SMBus to this message. On the schematic, one of the pairs of pull-up resistors is displayed with a dotted line. For these resistors, I have made some test without them, with some of 4.7kOhms and with another pair of 1kOhm each.
When communicating over the SMBus with the battery, we measure weird noise in the signal of both data lines.In order to show the difference, I measured the clock before the driver and after the driver. I also attach them to this message. As you can see, the rising time of the clock before the driver is much better than the one after the driver. By reading the datasheet I understood that the rise time is accelerated on the second part of the rise as the output resistance of the driver is decreased to approximately 50Ohms. This acceleration of the rise seems to introduce a spike in the voltage of the line.
I used additional pull-up resistors to reduce the rising time of the lines between the driver and the battery. I have made some tests without them, with resistors of 4.7kOhm and 1kOhm. The tests without the resistors and with the 4.7kOhm resistors gave a result similar to the one presented in the PDF document. The tests with the 1kOhm resistors was unsuccessful as the equivalent pull-up resistance was too low and the voltage of the logic zero of the slave was too high and was not considered as a logic zero by the master anymore.
The communication is done at 50 kHz and should not be too quick for the TCA9406 as it is supposed to work for up to 1 MHz.
