Inquire about TJA1042

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Inquire about TJA1042

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sjpark17
Contributor I
Inquire about TJA1042.

In standby mode of TJA1042, CAN BUS line is biased to 0V.

When connected to CAN H, L to the SBC of a specific vehicle, the CAN bus level of the vehicle drops from 2.5V to 1.1V.
When the TJA1042 is disconnected, it operates normally at 2.5V.
I wonder why it affects the vehicle CAN bus level in standby mode.
thank you.
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lukaszadrapa
NXP TechSupport
NXP TechSupport

Hi,

this is known and expected behavior. The datasheet explicitly says that the bus is biased to GND in standby mode to minimize current consumption:

pastedImage_1.png

The application hints AH1014 then also describes how to deal with this situation using SPLIT pin. Of course, this needs to be handled by nodes which are not in standby mode:

pastedImage_2.png

pastedImage_3.png

Regards,

Lukas

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sjpark17
Contributor I

Hi

Thank you for your reply.

Voltage drop occurs in standby mode, and it is necessary to use standby mode due to current consumption.

Also, there is no SPLT pin because TJA1042T / 3 is currently used.

Is it possible to pull up to the CAN bus line with a resistor like 100K?

Please inquire whether it can be solved by attaching a pull-up resistor to the bus line in normal mode or standby mode.
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lukaszadrapa
NXP TechSupport
NXP TechSupport

I don't think this can be solved by pull up resistor. This is the reason why there are devices with SPLIT pin.

Regards,

Lukas

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sjpark17
Contributor I

Does SPLIT pin keep VCC/2 level in Standby mode?

If I look at the AH1014, SPLIT in standby mode appears to be floating, so can bus is gnd bias isn't the same?

Thank you for your help.

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lukaszadrapa
NXP TechSupport
NXP TechSupport

No, it doesn't keep VCC/2 level. As I already mentioned somewhere above, this is up to devices which are not in standby mode.

Regards,

Lukas

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