TJA1028T/5V0/20 Communication cannot function properly

[gududexiaolu]

At present, LIN is communicating normally, VBAT is 12V, VCC is 5V, LIN waveform is normal, EN is 5V, REST is 5V, TX is 5V. Why is RX 0V causing communication to fail? Please provide a solution.

@guoweisun   #TJA1028T/5V0/20

目前，LIN正常通讯，VBAT为12V，VCC为5V，LIN波形正常，EN为5V，REST为5V,TX为5V,RX为什么是0V导致通讯无法正常运行

[JozefKozon]

Dear 善逸科技李 善逸科技李,

the reason could be, that the RXD pin is reporting remote wake-up. Please confirm if the RXD 0V is happening in Normal mode or in Standby/Sleep modes. 

With Best Regards,

Jozef

[gududexiaolu]

May I ask if you can provide me with your email? I would like to communicate with you via instant messaging

[gududexiaolu]

Thank you for your answer RX is experiencing this situation in normal operating mode

[JozefKozon]

Dear Gududexiaolu,

thank you for confirmation of the operation level. I am sorry, we are not allowed to share email addresses. 

Please share your schematic with voltage levels and part values. 

Please connect an oscilloscope probes on the RXD and LIN pins and please share the scope with their waveform during the unwanted RXD 0V. To check if the LIN signal is not holding the RXD low with LIN dominant signal.

Please check if the TXD pin is not held low for longer then tto(dom)TXD. If yes, then the TXD dominant time-out function is triggered and the transceiver is disabled. 

Please disconnect the RXD pin from your MCU and check if it is still pulled low. Your MCU might drive the RXD pin unwantedly low.

With Best Regards,

Jozef

[gududexiaolu]

LIN waveform is normal, both RX and TX should be high at the same time, but the failure issue is that RX is low level
The circuit diagram is not convenient to display here. I have already sent it to your forum email, please check it

[JozefKozon]

Dear Gududexiaolu,

thank you for the schematic. I have only one comment. There is no need to have pull-up resistors on the TXD and RXD lines. The TXD pin has an internal pull-up resistor to VCC and the RXD is driven by the LIN level. Please try to remove to pull-up resistors. The pull-up resistors might cause overtemperature on the TJA1028, which result in transition to off mode.

Please download and refer to the AH1003, section 5 "Mode control".

It is available in the TJA1028 product page, under the Secure files. 

With Best Regards,

Jozef

[gududexiaolu]

What does it mean that adding a resistor to TX and RX can cause overheating abnormalities? Can you explain it in detail?

I am temporarily unable to open the security file you mentioned

[JozefKozon]

Dear Gududexiaolu,

please follow the datasheet and the application hints, and other documents. Everywhere the TXD and RXD pins are connected without external pull-up resistors. If you will use parallel external resistor to the internal resistor, it will lower overall resistance value, resulting in more current flowing in the component. We do not have any document for this, so I cannot confirm if this is the case or not, but using external resistors is not according to the documents. 

Please connect an oscilloscope probes on the RXD and LIN pins and please share the scope with their waveform during the unwanted RXD 0V. To check if the LIN signal is not holding the RXD low with LIN dominant signal.

  Please disconnect the RXD pin from your MCU and check if it is still pulled low. Your MCU might drive the RXD pin unwantedly low.

With Best Regards,

Jozef

[gududexiaolu]

Thank you for your answer.

Under what circumstances will TX and RX power on faster than VCC?

[JozefKozon]

Dear Gududexiaolu,

could you please elaborate on your question? The VCC can be powered via the external pull-up resistors from RXD or TXD or both. 

With Best Regards,

Jozef