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Original question:

TCAN1043-Q1: TCAN1043 wake up problem

TCAN1043-Q1: WAKE question

Wonder Fang
Prodigy 265 points
Part Number: TCAN1043-Q1
Other Parts Discussed in Thread: TCAN1043

Tool/software:

Hi team,

I’d like to confirm the WAKE pin behavior on TCAN1043xx-Q1:

It's said in Datasheet that "the WAKE automatically configures itself based on the applied voltage to have either an internal pull-up or pull-down current source.".

  • How does "automotically configures" work? Does it means if V_wake > VSUP - 1.9( high level input), WAKE block turns on the internal pull-up current source, and vice versa?
  • How quickly does the WAKE module detect the input voltage and turn on the current source?

Best Regards,

Wonder Fang

  • 0
    TI__Genius 13952 points

    Hi Wonder,

    Wonder Fang said:
    How does "automotically configures" work? Does it means if V_wake > VSUP - 1.9( high level input), WAKE block turns on the internal pull-up current source, and vice versa?

    Effectively, yes.

    What is your goal with understanding how this Wake pin functions? Does the customer intend to switch from high to low level wake signals while the device is powered and operational?

    In application, only one particular configuration should be used. For example, the Wake pin should be biased to VSUP only, such that a low level voltage signal (i.e. GND) wakes the device. We do not provide the time it takes to detect the input voltage and use the appropriate current source.

    Best,

    Ethan 

  • 0 in reply to Ethan Sempsrott
    TI__Prodigy 265 points

    HI Ethan,

    Thanks for your relpy!

    In my customer's application, the WAKE signal is 1K PWM, which looks like below. I want to understand how this Wake pin functions to explain why the voltage drops down a little.

    And it's baised to VSUP to 100K，directly connect to WAKE pin without R_series as below.

    Because PWM is not only used for wake function, but also send infomation by duty. So the whole system works like:

    1. PWM wake signal come in, wake TCAN1043, then next wake PMIC and MCU.
    2. After work be done, MCU try to pull low NSTB to make TCAN1043 go to sleep mode. But, TCAN1043 will keep wake up the system because PWM wake signal is still exist and its voltage is higher than VSUP - 1.9. 

    I think this issue didn't show up because the PWM wake signal may drop as you can see in the first picture. And TCAN1043 will not be waken if it drop enough to below VSUP - 1.9. This may be in a relatively critical state.

    So I want to confirm some points with you here. 

    1. Does the PWM signal drop down because the 100K pull up resistor is too big, which is required as  to keep the valid V_IH? 
    2. Is there any risk to apply PWM signal to WAKE pin?  I think it's OK if current is limited under the IO(WAKE).
    3. Any suggestion on how to make it work with the PWM wake signal? I know it's not recommanded way to use it but customer seems can not change it in this point.

    Best,

    Wonder

  • +1 in reply to Wonder Fang
    TI__Genius 13952 points

    Hi Wonder,

    The Wake pin was not designed for a PWM signal. We strongly do not recommend using a PWM here. Even if this did properly wake the device, my main concern is that the Wake pin will constantly read a local wake up source preventing TCAN1043 from switching into particular modes on the state machine. For instance, if the PWM stays active while the transceiver is powered on, it will never be able to enter Sleep mode from Go-to-Sleep mode. 

    Best,

    Ethan

  • 0 in reply to Ethan Sempsrott
    TI__Prodigy 265 points

    Understood, thanks for your support!

    Best,

    Wonder