hello all,
in a project I use a TJA1021 LIN transceiver. Today I found something weird, which seems to deviate from the state diagram on page 6 in the TJA1021 datasheet. Maybe you can explain that to me...
In my circuit the pins are connected as follows:
- RXD <-> µController Rx with 10k pull-up to 5V
- TXD <-> µController Tx
- SLP_N <-> 5Vreg --> no sleep used
- WAKE_N <-> open
- INH <-> open
- Vbat <-> supply voltage (normally 12V)
- LIN <-> LIN bus with 1R pull-up to Vbat
If I switch on Vbat=12V, everything works as expected. However, if I first plug in board USB (Vbat~4.4V) and afterwards Vbat=12V supply, there is no traffic on LIN or RxD. The µContoller is sending via TxD, but neither LIN nor RxD show any activity. I checked with an oscilloscope, and see TxD is active, LIN static at ~12V, and Rx~5V. Also, manually connecting LIN to GND (-> bus wake) has no effect.
The state diagram on page 6 in the TJA1021 datasheet shows that the chip switches to normal mode if SLP_N=HIGH, independent of the initial condition. But apparently that is not the case. What am I missing...?
I searched the internet but found no errata or other report of this strange behavior. Any help is highly appreciated! Thanks a lot in advance!
Regards, Georg
