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TPS659037: Vcc slew rate and LDORTC OFF period

Yuto Sakai
Mastermind 6100 points
Part Number: TPS659037

Hi,

Application note (SWCA302) describes Vcc slew rate and LDOVRTC_OFF condition for POR generation.
Our customers designed this application note before it was released.
Therefore, they do not consider those conditions.

I understand that if those conditions are not met, the POR will not generate successfully.
What issue does that cause?

Best regards,
Yuto Sakai

  • 0
    TI__Genius 10000 points

    Sakai-san,

    If the VCCA slew rate or VRTC discharge level was not considered at time of design, there is the chance for the device to not turn back on during fast off/on conditions. One of these conditions must be met to guarantee a POR event in fast off/on events.

    Please note that the TPS659037 is changing silicon revision over the next year (part number staying the same) that will resolve this issue for future builds and designs.

    Thanks,

    Nastasha

  • 0 in reply to Nastasha
    Mastermind 6100 points

    Hi Nastasha-san,

    Thank you for your reply.
    How fast is "fast off / on"?
    If either Vcc slew rate or LDOVRTC_OFF condition is met, is the POR event guaranteed?

    Best regards,
    Yuto Sakai

  • 0 in reply to Yuto Sakai
    TI__Genius 10000 points

    Sakai-san,

    The timing of the fast on/off if system dependent, based off your VCCA slew rate (which may not be linear and depends on your board loading and capacitance).

    The POR detection mechanism samples every 1ms. If the VCCA supply falls faster than 90mV/ms between 1.9V and 1.8V, than the POR may not be detected. The LDOVRTC discharging can also allow the device to detect POR if it discharges below 300mV. Depending on how long your system takes to reach that voltage after an off event, you will have an idea of how fast the off/on timing can be for your system.

    Any off/on event that is faster than the discharge time of the LDOVRTC if your VCCA is dropping too fast, could cause a POR to not be detected.

    Thanks,

    Nastasha

  • 0 in reply to Nastasha
    Mastermind 6100 points

    Hi Nastasha-san,

    Thank you for your support.
    Let me ask you an additional question.
    What's the problem caused by missing POR events?

    Best regards,
    Yuto Sakai

  • 0 in reply to Yuto Sakai
    TI__Genius 10000 points

    Sakai-san,

    If the POR event is not detected, the device will not start up. It will need to be reset again.

    Thanks,

    Nastasha