TLIN1039-Q1: Internal pull down resistor at TXD pin

HIrata-san,

Akihiro Hirata said:

1. The TLIN1039-Q1 has internal pull down.

And In the customer schematic EN is always pulled high. (not controlled by MCU)

Therefore when the MCU is under the initialization and the output port becomes HiZ state, the LIN pin drives the LIN bus to dominant accidentally.

I think this situation should be avoided. What usage does TI assume for the proper operation?

I think this situation can be avoided by controlling EN pin...right? If not please could you let me know the detail?

If the MCU is powering up and becomes high-Z on its signal lines, then I would expect both EN and TXD to fall low, so this would put the transceiver to sleep mode.

If EN is still high, the pull-down brings TXD to a known state when the pin floats. Given TXD dominant time-out, the driver ends up disabled if TXD floats, but RXD is still active.

Akihiro Hirata said:

What is the reason/background that TLIN1028-Q1 has pull up and TLIN1039-Q1(+ other TI LIN portfolio) has pull down at TXD?

The TLIN1028-Q1 has an internal VCC, but the other devices do not. They cannot be pulled high to VSUP, since this would not be safe for logic-level microcontrollers connected to the data lines.

Akihiro Hirata said:

3. My customer would like to keep the EN pin high (= don't want to control EN pin by MCU) if possible.

If the external pull up resistor is added on the TXD line, are there any issue or concern?

If this is no issue what resistor range is appropriate? 1-10kOhm?

Did you mean to say a pull-up resistor to the *EN line? Either way, there is no issue with a pull-up resistor to VCC for either the EN or TXD lines. This would help ensure that your pins are in a known state if the MCU leaves these inputs floating.

Any resistor in that 1k-10k range would be acceptable. I have seen all of these work. When designing, the consideration would be the current consumption resulting from stronger pull-up resistor usage.

Best,

Danny