NXP CAN Transceiver: TJA1051 RXD pin's VOH and VOL are not clear

[YUANYUAN1]

Hi all, 

I am a Hardware engineer in the field of autonomous driving, I found one point was not so clear in the datasheet when I designed the circuit with chip TJA1051:

1. could you share me what is the internal structure of pin RXD? I think it should be either OD structure or CMOS structure but it is not written in the datasheet.

This may affect me design the output voltage level VOH and VOL, and I think this value should be included in the datasheet just like the TXD pin. Thank you.

Best Regards,

Yuanyuan

[TomasVaverka · Accepted solution]

Hi Yuanyuan,

You are right, that is not clearly stated in the datasheet.

The RXD pin is driven to VCC on devices without the "/3" suffix, and VIO for devices with the "/3" suffix.

For the output voltage levels you can refer to the following values:

1. Device without the "/3" suffix: VOH min 4V. VOL max 0.4V.

2. Device with the "/3" suffix: VOH min 0.8 x VIO. VOL max 0.2 x VIO.

Best regards,

Tomas

[YUANYUAN1]

Hi Tomas,

thank you for your reply, your solution is meaningful for me.

Here is another question that puzzles me:

1. Is there any power on sequence bewteen VIO and VCC?

For example, now I choose to use TJA1051T/3, the VIO pin I will give it 1.8V power supply, and VCC pin will get 3.3V power supply, will there be any problem if I give the VIO power supply firstly, then comes the VCC power supply? I find no answer in the datasheet.

Best Regards,

Yuanyuan

[TomasVaverka]

Hi Yuanyuan,

First off, please keep in mind that VIO min is 2.8V and VCC min 4.5V.

As for the power-up sequence, there is no difference if VCC starts early or VIO does.

Basically, TJA1051/3 is suitable to application that VCC and VIO start same time as indicated in the figure below.

But, it can also be used in the case VCC and VIO start in different timing.

If one of VCC or VIO was in under-voltage, the TJA1051/3 is in OFF mode and just wait for the under-voltage release.

Best regards,

Tomas

[YUANYUAN1]

Thank you Tomas, I get your meaning, and I mixed up the voltage value with my other project, sorry about it haha.