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TMS320C5515: Can the WAKEUP pin be open?

Expert 2780 points
Part Number: TMS320C5515

Hi,

I have a question about the WAKEUP pin.

The WAKEUP pin is in the document as follows.
If it is left open, will the device be destroyed by latchup etc. or will it only increase power consumption?

Regards,
Da

  • Hi,
    We're looking into this.

    Best Regards,
    Yordan
  • Hi Da,

    The WAKEUP pin defaults to an input. Floating inputs can oscillate if not terminated with an external resistor (or driven by some output). Oscillating inputs consume power. See http://processors.wiki.ti.com/index.php/C5000_DSP_based_Low-power_system_design#Overview_of_CMOS_IO 

    However, to avoid this, WAKEUP can be configured as an open-drain output in the RTC Power Management Register (RTCPMGT, 1930h). If you drive a "high", the open drain output becomes Hi-Z and will still oscillate if there is no external resistor (pull-up recommended to let the signal float high). But if you drive a low, then the open drain output will be controlled at a logic low and will not oscillate.

    There is no internal pull-up that you can use with WAKEUP.

    [EDIT] - Also, in order to access this RTCPMGT register, the RTC must be powered and clocked. CVDDRTC, DVDDRTC, and RTC oscillator supplied and populated. Any pull-up on WAKEUP should go to DVDDRTC level (and DVDDRTC must be supplied).

    Another solution is not to use RTC - ground DVDDRTC and terminate RTC_XI and RTC_XO per the datasheet. In this case, WAKEUP can be left floating as the voltage to the IO buffer is grounded. However, CVDDRTC must always be supplied and must not be supplied by any on-chip LDO.

    Hope this helps,
    Mark

  • Thank you for your reply.

    When the WAKEUP pin is not processed, current consumption increases.
    I understand that C5515 will not break, but is there a problem?

    Also, if the RTC clock is valid, we understood that setting the WAKEUP pin to output in the program does not increase the power consumption by that, but is there a problem?

    Regards,
    Da
  • Hallow,

    If the wakeup pin remains open, is your understanding that power consumption increases?

    Regards,
    Da

  • Hi Da,

    Did you observe any difference in current going into the DVDDRTC supply pin when wakeup was left floating but was configured as an open drain output and driven low? I expect to see slightly less current in this case than when the wakeup pin is left floating and configured as an input.

    Regards,
    Mark

  • The problem was whether the device did not break if the wakeup terminal was open as I had written before.
    It was a reply that we wanted to measure power consumption, so we decided that the device will not break soon.

    Since the customer is supplying the clock of RTC, it is set by software to deal with it.

    Regards,
    Da