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TCAN4550: Expected ripple on VCCOUT?

Igor Orlovich
Prodigy 180 points
Part Number: TCAN4550

What kind of ripple is expected to be present on VCCOUT while CAN  bus is running? We noticed some curving of the CANH signal and traced it to VCCOUT doing same.

Everything still works, so not sure if this is just the expected behavior.

If bus is off, VCCOUT is happy/steady.

The overall bounce is maybe 50mv in each direction

VSUP is at 12V and has 22uF  and 0.1uF ceramics

FLTR has 1uF 10V ceramic 

VIO is 3.3V has 1uF 0402 ceramic

VCCOUT has a 10uF 10V 0805 cap and no other load

Tried adding a second 10 uF cap to VCCOUT and it cleared things a little bit

 

Schematic:

  • +1
    TI__Guru 53535 points

    Hi Igor,

    Yes, this ripple on the Vccout is expected. The device's internal CAN transceiver is supplied by the same LDO that provides Vccout. When there is no load on the Vccout pin, the only load on the LDO is presented by the switching CAN driver. Drawing current from Vccout will allow the external filtering components to have a greater impact on the Vccout voltage and the ripple will decrease in magnitude. I have also observed this ripple decrease when higher data rates are used as the switching noise moves to higher frequencies which are more easily filtered out by the external capacitance. 

    Let me know if you have any more questions. 

    Regards,
    Eric Schott