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TCAN4550: Use of inexpensive peripheral parts

Kenji Ohno1
Genius 5095 points
Part Number: TCAN4550


Hi Team,

The recommended upper voltage limit for Vsup is 24V.

When used at 24Vin, the recommended voltage will be exceeded considering the voltage fluctuation of 24V+5%.

If it reaches 25.2V, will the specified specifications not be met?

You don't guarantee it, but basically it doesn't deviate significantly?

In addition, I have the following questions.

・ Regarding recommended cables

　　The datasheet states that a 120Ω twisted pair cable is recommended. Is it possible to transmit 5m using an AWG cable?

・ Should I choose 20MHz as the clock when I want a speed of 2Mbps?

・When should nINT pin be used?

・Please tell us the intended use of these. (INH, WAKE, nWKRQ, GP01, GP02)

・Is the signal line on the board a differential 120Ω wiring?

・In EVM, the terminating resistor is 3225 size. Can I use a smaller size resistor? For example, are both sizes 1608 and 2110 OK?

Best Regards,

Kenji

  • 0
    TI__Guru 74322 points

    Kenji,

    Thanks for bringing this to our attention. If the customer is using the TCAN4550 and not the TCAN4550-Q1, then yes we can't guarantee the datasheet specifications beyond 24V. If the customer uses TCAN4550-Q1, the datasheet parameters are guaranteed up to 30V. Even in the case of TCAN4550 where it is only guaranteed up to 24V, the majority of parameters will be fine, the one most affected will be the self-heating of the device due to the LDO drop from 25.2V to 5V.

    • It's possible but signal integrity will be affected, especially at that distance and at 2Mbps. The twisted pair cabling helps with signal integrity through impedance matching (120-ohm characteristic impedance) as well as RF emissions from the CAN bus with equal and opposite magnetic fields from the CAN signals canceling each other out.
    • You can use 20MHz for 2Mbps data rate, though 40MHz would give you more resolution when setting the sample point and other timing parameters for each individual bit. If you want to run at a data rate higher than 2Mbps, 40MHz must be used.
    • nINT will toggle low for any interrupt that is enabled and asserted by the TCAN4550-Q1. The user can disable certain interrupts from being indicated by the device, so that if nINT is asserted it will be known from a shorter list of interrupts available. This can be used to indicate a new message in memory, a message transmitted, or fault conditions.
    • INH is meant to be an enable for a power supply providing power to the TCAN4550-Q1 and other parts of the system. It is low when the device is in sleep mode, and high in every other mode. WAKE is used to wake the device by toggling from low to high or high to low. It's another method to wake the TCAN4550-Q1 besides using the CAN bus. nWKRQ is a logic level signal that toggles low when a wake request has occurred on the device. GPIO1 and GPO2 can be configured for MCAN interrupt outputs, or other functions. Look into the datasheet for more specific information on these pins.
    • The EVM has a differentially routed signal matched to 60 ohms since that is the overall impedance of the CAN bus by definition and specification.
    • Yes, but you must pay attention to the power dissipation that will occur over these resistors and size them correctly.

    Please let me know if you have any other questions.

    Regards,

  • 0 in reply to Eric Hackett
    Genius 5095 points

    Hi Eric,

    Thank you for your answer.

    Is the only difference between the TCAN4550 and TCAN4550-Q1 is the internal LDO?

    I have another question.

    How fast should SPI operate in order to operate CAN FD at 2Mbps? 

    Best Regards,

    Kenji

  • 0 in reply to Kenji Ohno1
    TI__Guru 74322 points

    Kenji,

    No, the only difference between TCAN4550 and the TCAN4550-Q1 is the qualification level. The TCAN4550-Q1 is automotive qualified and certified through EMC testing. The TCAN4550 is meant for industrial applications and does not have these same qualifications.

    The SPI shouldn't have a direct affect on the CAN bus data rate, only the external oscillator. However, the SPI will work up to 18MHz on this device. 

    Regards,