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TCAN1043-Q1: UVLO of VSUP and VCC/VIO

Shaofeng Luo
Intellectual 1650 points
Part Number: TCAN1043-Q1

Hi experts

Our customer is using TCAN1043-Q1 in their system, and they use INH to enable/disable the LDO for VCC/VIO. But we found a potential issue here is:

When the VBAT drops to about 4.2V(It may not trigger UVsup), but it may trigger UVCC since there is ~200mV dropout voltage through LDO. In this case, TCAN1043-Q1 will enter sleep mode and INH goes to Hi-Z, which will disable the LDO.

When Vsup recover from this point(no UVsup), it will not be a cold start and TCAN1043-Q1 stays in sleep mode. Only WUP can wake up the device.

Our point is, do we have any workarounds to avoid this issue? OEM asks for staying standby mode instead of Sleep mode when the VBAT recovers. 

One way from our side is to change the power rail, use SEPIC/buck-boost to generate the VCC, it will make VCC stable even Vsup is lower than VCC. But we want your insights, expect for your reply, thanks!

  • +1
    TI__Guru 53555 points

    Hi Shaofeng,

    When Vcc becomes unavailable due to this undervoltage condition, reliable CAN communication will not be possible as the 5V supply is needed by the CAN driver. If the UVcc condition remains for tUV (159ms) the device will assume there has been some issue with the local supply and move to the lowest power state (sleep mode) in order to have minimal impact on the system. If this takes place while the CAN bus is idle then the transceiver will remain in sleep mode with INH off until a wake source is detected, as you described above. If the CAN bus becomes active at any point, the WUP contained in any CAN frame will wake the transceiver into standby mode and cause INH to assert high again. At this time, the tUV will start again and Vcc and Vio must clear their undervoltage thresholds in order for the device to remain in standby or any other active state with INH high. 

    How long is the undervoltage condition on Vsup expected to last in this fault case? If it is less than the tUV time, this scenario will not occur as the supply should recover before the transceiver times out. It may also be acceptable for this case to happen on an active CAN bus as the node will immediately attempt to re-enter standby mode on receiving the WUP for the CAN bus. 

    Let me know if this scenario is problematic and if the customer has any more questions. 

    Regards, 
    Eric Schott 

  • 0 in reply to Eric Schott1
    TI__Intellectual 1650 points

    Hi Eric

    Well noted and it's very clear, thanks sincerely!