03-30-2012 05:46 AM
I need test an automotive component that operates on 28V LIN bus. This is the operating voltage of a LIN bus in trucks. The voltage will be raised to 32V in an overvoltage test. The VBAT voltage specification of the NI 9866 is 8V to 18V, although the XNP TJA1028 LIN driver that is used in this modul allows 40V supply voltage. Is there a way I can use this modul on 32V? Are there other reasons the VBAT pin is limited to 18V?
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03-30-2012 12:57 PM
The reason why we spec the module to 8-18 is for two reasons:
1) The LIN standard indicates that the operating voltage of the bus is 8-18V.
2) Our current NI-XNET PXI/PCI LIN hardware (and legacy NI-CAN USB LIN hardware) use a different transceiver that is only rated to 8-18V. If you use something beyond this range, it will not be portable to our other solutions.
The TJA1028 data sheet does have some conflicting information. They are clear that 40V is their absolute max. In the one place they mention that it may not work > 18V (Table 7, note 5 says "For VBAT > 18 V, the LIN transmitter might be suppressed."), but in other places they indicate that the working range is 4.5-28V (Section 7.2.1: "The operating range is from 4.5 V to 28 V.").
If you are running between 18V and 28V, the Application Hint AH1003 indicates that it should work, but is also not fully guaranteed to run correctly "LIN functional specified. Voltage regulator full specified"
If you are running > 28 V (overvoltage test), you are outside of the working range of the TJA1028. The TJA1028 is not guaranteed to run correctly. It should be safe from damage, but it is not guaranteed to run correctly. (from AH1003, "SBC not damaged. Functionality will be ok, but no parameters are guaranteed".)
The other components contained in the NI 9866 Module that connect to VBAT should tolerate the 40V as well without any issues. I am still looking up one thing (power dissipation), but I believe even at 40V we will not be exceeding the allowable power dissipation.
04-02-2012 12:43 AM
Thank you. I'll try to get a module and test it. Now I know I won't burn it if I connect it to 32V. Since you are familiar with the NI 9866 circuit diagram, I would like to ask one more question. One of the tests I need to run is also a reverse polarity test. If I don't disconnect the Vbat and COM from the NI 9866 while running this test, the module will be supplied with a reverse polarity voltage. Does the NI 9866 has a reverse polarity diode or do I need a relay to disconnect the lines from the module?