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PCA9515A: communication is not smooth,

Depeng Man
Intellectual 2030 points
Part Number: PCA9515A
Other Parts Discussed in Thread: ISO1540, , TCA9803, TCA9517

Hi Team，

Now the communication is not smooth,

The hardware circuit is described as follows:

Single chip microcomputer STM32F103C8 pin I2C comes out and is directly connected to I2C of ISO1540 as shown in the figure above_ SDA、I2C_ SCL. Now the waveform of direct communication is as follows

The yellow one is SDA, and the low level of the back is about 600mV. The USB to IIC connected to the computer can communicate, and the communication with other devices is unstable. If you want to use PCA9515A as a buffer, you will not be able to communicate with the computer after adding PCA9515A between the computer and ISO1540. If yes, you can help to see if it is a level compatibility problem and if there is a good way. Thank you for your hard work.

Best Regards

James 

  • 0
    Guru 287370 points

    Both devices use a static voltage offset (see section 4 of the PCA9515A datasheet and section 8.4 of the ISO1540 datasheet), so they are indeed not compatible.

    To make this work, use a buffer that has special restrictions only on one side (e.g., TCA9803, TCA9517).

  • 0
    TI__Guru 60850 points

    Clemen's is correct. 

    PCA9515A has a static offset on both sides (of around 600mV) so it is incompatible with any device that uses a static voltage offset like ISO1540 if it is paired on side 1. 

    TCA9517 can pair with ISO1540 if A side of TCA9517 is paired with eitherside of ISO1540. You will still see a ~600mV offset on side 1 of ISO1540 and side B of TCA9517.

    -Bobby