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TCAN4550: Power sequence btw Vwake, Vsup and Vio?

[FAE] Andrew Wang
Genius 10685 points
Part Number: TCAN4550
Other Parts Discussed in Thread: TCAN1043-Q1, TCAN1043,

Hi Team,

Quick question regarding TCAN4550 power sequence.

Any special sequence btw: Vwake, Vsup  and Vio?

Which rail Vwake refering to?

Thanks.

Andrew

  • 0
    TI__Intellectual 2090 points

    Hi Andrew,

    Thank  you for your question.  

    The only power supply inputs for the TCAN4550 device are the VSUP and VIO pins.  The main power supply is VSUP.  The VIO rail supplies the SPI interface and other logic inputs.  Each supply may be ramped in any order, although the main power sequence of the device will depend on VSUP.  With both rails supplied, the TCAN4550 device will provide a 5V LDO power output through the VCCOUT pin that can support load currents up 70mA.

    One note, there is an under voltage lockout timer (t_UV/TSD) within the device that will put the TCAN4550 in sleep mode if the supplies are not established in time.  The timer lasts between 200ms and 500ms.  As long as your power supplies are up and running within that time, then you should be fine.  

    When you say Vwake, I assume that you are referring to the WAKE pin on the TCAN4550.  This pin is not a power supply.  Rather, it is a high voltage logic input, which can swing between ground and VSUP.  This pin is used to stimulate a local-wake-up (LWU) request when the TCAN4550 is in sleep mode.  Another high voltage logic pin, the INH pin, will also swing between VSUP and ground.  The INH output will be used to enable system-level power regulators during sleep mode for extra current savings should the system designer choose to use it.  

    Let me know if you have any questions regarding the above comments. 

    Best Regards,

    Max Megee

    TI Transceiver Interface

  • 0 in reply to Max Megee
    TI__Genius 10685 points

    Hi Max,

    Thanks for the detail feedback!!

    Yes Vwake = WAKE, I was trying to ask if Vsup and Vio has not settled, and WAKE pin has voltage come in, will it cause problem?

    That's why I was wondering if any relationship btw them.

    I assume, Vsup should be up first, wait for tPower_Up (250uS min)

    then Vio up then WAKE input can be received correctly, is my understanding sound ok to you? 

    Thanks!

    Andrew

  • 0 in reply to [FAE] Andrew Wang
    TI__Intellectual 2090 points

    As far as the power up sequence goes, the voltage on the WAKE pin will not cause a disturbance if it comes up before VSUP.  However, this really is very rare, since most systems derive the WAKE voltage off of the VSUP rail anyway.  Therefore normally you will see WAKE rise with VSUP or slightly delayed from VSUP.

    Max

  • 0 in reply to Max Megee
    TI__Genius 10685 points

    Hi Max,

    Thanks!

    I think this is exactly the thing I am confused about. Please allow me to ask more. 

    Usually, how is WAKE (signal transition) event is used in below typical application circuit? VBAT is always there? How is the sequence looks like with WAKE signal, Vsup and Vio? Appreciate your help!

    Andrew

  • 0 in reply to [FAE] Andrew Wang
    TI__Intellectual 2090 points

    Hi Andrew,

    Gotcha!  

    I'm not sure what application space you are designing for, but the typical application space (among others) for the TCAN1043-Q1 is automotive.  In an automotive system, the car battery (12-14V) will provide the VSUP (or VBAT) rail.  The WAKE input is derived from the VSUP rail through the resistor, capacitor, and switch network that you see in the diagram provided above.  So when the system powers up, the VSUP and WAKE signals will rise together, typically.  

    The WAKE signal is used for what is called Local Wake Up (LWU).  Local Wake Up is one of two wake schemes used to bring the TCAN1043 device out of sleep mode.  The other wake scheme is called the Wake Up Pattern (WUP), which is defined by a certain bit pattern on the CAN bus signals (CANH/CANL).  

    For Local Wake Up, the TCAN1043 will transition out of sleep mode whenever an edge (either rising or falling) is detected on the WAKE input.  As you can see from the block diagram above, this is usually implemented by a switch that will toggle WAKE from VSUP to ground.  This can be either a manual push button switch, or a micro-controller operated switch.  Typically it is a manual push button though.  

    If a designer elects not to use the Local Wake Up functionality, they may choose to tie off the WAKE pin to either VSUP or ground.  This would ensure that no toggles happen on the WAKE input, and an LWU will never be detected.  The WAKE input circuit is designed to draw minimal current when it is tied to either VSUP or ground.  

    Does that help to answer your question for how WAKE related to VSUP? 

    Best Regards,

    Max

  • 0 in reply to Max Megee
    TI__Intellectual 2090 points

    Clarification to the above:  

    I meant to write TCAN4550-Q1 for all of the above device references instead of TCAN1043-Q1.  The same explanation applies for WAKE and VSUP.

    My mistake! 

    Thanks,

    Max

  • 0 in reply to Max Megee
    TI__Genius 10685 points

    Max,

    This is so helpful, your info is like the missing puzzle in the datasheet...many thank taking time to explain the whole idea,. I wish TCAN4550 datasheet can explain things like you did not just register control,  have a good day!!!

    Andrew