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TLIN1028-Q1: The affecting of lower voltage use for VSUP.

?? ?
Prodigy 20 points
Part Number: TLIN1028-Q1
Other Parts Discussed in Thread: TLIN10283-Q1, TLIN10285-Q1

Hi Team,

I want to confirm about the possibility to use lower voltage for VSUP.

This is just confirmation to use LIN Transceiver.
For example, TLIN1028 is possible to use around 5.5V for VSUP.
However, it is lower than the voltage of LIN Bus line.
If LIN Bus line is using around 12V, the device: TLIN1028 is possible to use on around 5.5V for VSUP?
Because some of internal circuit is operating on VSUP, but the input voltage is according to LIN Bus.

Therefore, I am warrying about the leakage the current to VSUP from LIN Bus.
Also, it may make some damage to the device, I concern.

Could you give me the usage in the lower voltage for VSUP about the LIN transceiver.

Regards,

Toru

  • +1
    TI__Guru 74172 points

    Toru,

    In general, this kind of implementation isn't ideal, and depending on the difference in VSUP vs. LIN bus voltage, won't work without some external circuitry added. This is because the bus thresholds for dominant and recessive get set by the VSUP voltage. In your case, it should be okay because the thresholds are 1.1V for dominant and 4.675V for recessive, both of which are achievable with a 12V LIN bus. The problem can come when the VSUP voltage is significantly higher than the LIN bus voltage. 

    Also, since the TLIN1028-Q1 is rated down to 5.5V VSUP, this is an acceptable supply voltage range.

    I am curious though, why is the VSUP voltage lower than the LIN bus voltage?

    Regards,

    Eric Hackett 

  • +1 in reply to Eric Hackett
    Prodigy 20 points

    Hi Eric,

    Thank you for your kindly reply.
    I suspected the reverse current to VSUP line from LIN BUS line because VSUP is lower than LIN Bus line in this case.
    I got your information, and I am relieved to use low voltage for VSUP.
    And about the reason of such case, basically 12V is unstable and it is so noisy.
    Generally, LDO transform to heat the gap of voltage and its current.
    In this time, I am considering to use its intenal LDO for the system regulator.
    However, Micro-controller and some of LED will consume some current.
    Therefore, to reduce the heating up of TLIN1028-Q1 and to be stable the voltage,
    I think it is good to supress the input voltage for VSUP.

    Currently, this is just idea.
    At the time of implementation, I will confirm this again.

    Thank you for your support.

    Regards,

    Toru

  • +1 in reply to ?? ?
    TI__Mastermind 26796 points

    Toru,

    Thank you for your explanation! As Eric mentioned, the device is capable of operation with a VSUP as low as 5.5 V. Regarding your point of the LDO operation, if you are using the DRB (VSON) or DDA (SOIC) package, this is rarely an issue. If you take a look at Figure 7-2 and Figure 7-3 (for the TLIN10283-Q1) or Figure 7-5 and Figure 7-6 (for the TLIN10285-Q1) in the data sheet, you will see that ICC vs VSUP vs Temperature is unaffected for voltage ranges from 5.5 V to 12 V.

    This, of course, is related to the performance of the TLIN1028-Q1 itself. Your point about system-level heat generation is still valid. Power dissipation from the device will include the LDO's dissipation: ICC × (VSUP - VCC), so reducing VSUP would help reduce this.

    It is important to note that this implementation would potentially be a violation of the LIN specification ISO 17987-4, which calls for an integrated pull-up to the supply, which would be 12 V, on each node. Here, this node would not provide this pull-up. As mentioned above, you also do not risk current flowing from LIN to VSUP thanks to the serial diode between the two that prevents current flow in this direction.

    To summarize, this should work if needed for your design's heat requirements, but might not follow ISO 17987-4.

    Best,

    Danny