TJA1021 bug...?

gicking — Fri, 18 Mar 2022 16:16:28 GMT

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

Re: TJA1021 bug...?

dietmarschmid — Fri, 25 Mar 2022 15:19:05 GMT

Hello Mr Icking, think this was answered already by me via tec support

Re: TJA1021 bug...?

Tarloth — Sun, 30 Oct 2022 06:01:33 GMT

Please @dietmarschmid , can you answer here to this post, I like to see the answer to this problem. Thanks

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