P82B715: Vehicle CAN bus application

Hey Daniel,

Just to be sure I understand what you are trying to do here, are you planning on sending CAN data over cables with the P82B715 (bypassing the CAN controller/transceivers)?

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P82B715 was intended to be used with I2C protocol. If I understand your use for this device correctly (as above) then I see some potential disadvantages to using this device.

1) Though the datasheet doesn't specifically say it, this device was created with the max frequency of 400kHz in mind. (Judging from the max cap allowable of 400pF on the S pins). If I am correct, CAN is expected to operate faster than this which could be a limitation if you are not allowed to operate at lower speeds in CAN. [I am not a CAN expert]

2) The distance limitation will be dictated by the capacitance of your cables and if you plan on using multiple nodes this will further limit your distance.

3) You may be driving large currents if your distance is far therefore if your GND return is through cables, you may see the GND potential shift which could affect signal integrity as a low could be mistaken as a high because it was not pulled low enough in respect to the shifted GND.

4) Using a single ended solution like this means the signal integrity could be affected by EMI. (With CAN as a differentiated output solution, the common mode noise of EMI is greatly attenuated). In a noisy environment like a car, you could corrupt your signal.

5) Driving large current is power intensive and not an efficient solution.

6) Parasitic inductance could damage this device if not accounted for. When pulling low, the inductance could cause inductive kickback and pull the bus way below the absolute max of -0.3V.

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I am not saying it is impossible to get this device to work but there are some things you would need to keep in mind to make sure it worked properly (6 points above).

A) May I ask why you are looking to use this device to pass a CAN signal (are you trying to save cost by trying to get rid of some CAN transceivers or is there a remote sensor you are trying to communicate with and looking to bypass the mcu)?

B) How far of a distance are you looking to go (cable distance)?

C) Will there be multiple nodes? (How many?)

D) What devices will be communicating on this bus? (Sensors, mcus, ect.)

-Bobby