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TCAN1043-Q1: Supply ripples requirement for TCAN1043-Q1

Ted Zhang
Intellectual 2280 points
Part Number: TCAN1043-Q1
Other Parts Discussed in Thread: TCAN1043

Hi,

A quick question regarding supply TCAN1043, currently my customer is using our LDO TPS7B82 to supply the CAN TCAN1043, and found that the load transient(~10mA- 40mA) when CAN is in communication lead to large over/under shoot, around 200mV. Customer is concerned if any risk on this large over/under shoot supply on TCAN1043's Vcc and how it affects.

Thanks.

Below yellow is the LDO output current(supplying CAN PHY TCAN1043), and purple is the LDO output voltage(AC coupled).

  • 0
    TI__Guru 62920 points
    Hi Ted,

    This should not lead to any functional issues as long as the voltage remains above the UVVCC threshold for the TCAN1043. However, since ripple on the VCC rail will transfer onto the CANH output line, you may want to address this so that it does not result in EMI problems. Is it possible to improve the LDO performance by increasing its output capacitance?

    Max
  • 0 in reply to Miguel Robertson
    TI__Intellectual 2280 points

    Hi Max,

    Thanks for the reply. So normally what range of the over/undershoot as thumb of rule that is more acceptable and not lead to big EMI issue(like below 50mV or else?)? We've tried to increase the output capacitor to a relatively large value, and still has 150mV... 

    Thanks

  • 0 in reply to Ted Zhang
    TI__Guru 62920 points
    Ted,

    It's hard to give an exact answer, but I believe most applications target <100 mV. Could you please check to see what the CANH and CANL waveforms look like? I'm curious how much of this noise is actually transferring through the IC. Also, is the voltage ripple measured at the VCC pin of the transceiver or at the output of the LDO? And, what does the routing look like on the PCB between these two points - is a wide plane used, narrow trace, etc.? Is a low-ESR capacitor (like a ceramic) used on the LDO output? That would help with load regulation.

    Regards,
    Max