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TPS929240-Q1: Communication Loss Diagnostic in NORMAL state

Ivy Jin
Expert 4565 points
Part Number: TPS929240-Q1

Tool/software:

Hi team,

The customer is simulating loss of communication by testing as follows：

Watchdog time is set to 500ms, FS mode to illuminate the LED.

A.  When CAN-H shorted to CAN-L, the 929240 enters FS mode.

B. However, the 929240 will not enter FS mode when CAN-H is shorted to GND or CAN-L is shorted to VCC. Is this a normal result?

According to the datasheet, there are two conditions for entering FS mode: 1. WDTimer overflows or 2. FORCEFS = 1.

For customer's B test, the address and CRC are theoretically incorrect and should trigger a timer overflow. However, the actual test result of the customer is that when CAN-H is shorted to VCC or CAN-L is shorted to GND, the LEDs no longer show the flow effect, but stop at the moment, the 929240 does not enter FS mode. 

Could you please share some comments? Thanks

Regards,

Ivy

  • +1
    TI__Genius 17590 points

    Hi, Ivy, 

    TPS929240 runs into FS mode when there is no toggling on communication bus for > WDTimer, 

    Customer can monitor RX signal to see if there is still toggling. If so, MCU need to stop sending data for > WDTimer to make sure that the bus is in idle to have the device runs into FS.