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OMAPL138 RTC

VA
Prodigy 30 points
Other Parts Discussed in Thread: OMAPL138

I have a board with OMAPL138. I am using RTC and connect a battery to RTC_CVDD pin. There is no problem, my board works well. Then I forgot to connect the battery (mean: RTC_CVDD pin is floating) and some peripherals dont work regularly. For example I am using SPI, and sometimes SPI reads wrong datas. Also there are problems about I/O pins. After connecting the battery the problems are continue.

I want to ask, if  RTC_CVDD pin is floating and powered the board on this state, it can be cause damage on interface and I/Os ? I mean permanent damage.

  • 0
    TI__Mastermind 43660 points

    Hello,

    Welcome to the TI E2E forum. I hope you will find many good answers here and in the TI.com documents and in the TI Wiki Pages (for processor issues). Be sure to search those for helpful information and to browse for the questions others may have asked on similar topics (e2e.ti.com).

    I do not think RTC_CVDD floating would affect the other peripherals functionality. There is no interconnection between them and i guess something else happened which cause this issue. I would suggest you to first check all the power rails, reset, clock and ensure all are within the limits. Then try to figure out what is the exact problem you are facing in your board. 

    I want to ask, if  RTC_CVDD pin is floating and powered the board on this state, it can be cause damage on interface and I/Os ? I mean permanent damage.

    RTC_CVDD may be connected to CVDD if no battery is used. But leave it floating does not damage other peripherals, it only stops the RTC functionality.

    Regards,

    Senthil

  • 0 in reply to Senthilkumar Srinivasan
    Prodigy 30 points
    Thanks for your quick reply. I am also checking the other possibilities.
    You wrote "there is no interconnection...". I am using only one GND net on all board. The RTC_VSS pin is connected to the same GND too. Is it broken the isolation of RTC power ? What can you suggest about RTC_VSS if using RTC with battery ?
  • 0 in reply to VA
    TI__Mastermind 43660 points

    Hello,

    The recommendations on RTC connections are given in the section 6.31.1 Clock Source of device data manual.

    In addition to that there is a note, 

    When an external crystal is used oscillator (OSC_VSS, RTC_VSS) ground must be kept separate from other grounds and connected directly to the crystal load capacitor ground. These pins are shorted to VSS on the device itself and should not be connected to VSS on the circuit board. If a crystal is not used and the clock input is driven directly, then the oscillator VSS may be connected to board ground.

    Regards,

    Senthil

  • 0 in reply to VA
    TI__Mastermind 43660 points

    Hello,

    You can also find some relevant guidelines in OMAPL138 schematic checklist.

    http://processors.wiki.ti.com/index.php/OMAP-L13x_/_C674x_/_AM1x_Schematic_Review_Checklist

    Regards,

    Senthil

     

  • 0 in reply to Senthilkumar Srinivasan
    Prodigy 30 points

    Hello,

    Our design contains a battery and a 1.2V LDO working together. If the board powered up with system voltage (5V) the LDO is working, so the battery's life time does not finish. Below picture.  

    I checked the power sequence of my board. The RTC_CVDD wake up after the CVDD (1.2V) and before the DVDD (1.8V). So when I forgot to using battery the power sequence was wrong. Now I correct the sequence but the problem is continue (permanant damage).

    The wrong squence can cause the problem ?

    VA

  • 0 in reply to VA
    TI__Mastermind 43660 points
    Hello VA,

    I would like you to go through the power on sequence given in section 6.3.1 in the device data manual.

    RTC (RTC_CVDD) may be powered from an external device (such as a battery) prior to all other supplies being applied or powered-up at the same time as CVDD. If the RTC is not used, RTC_CVDD should be connected to CVDD. RTC_CVDD should not be left unpowered while CVDD is powered.

    When you forgot to connect the battery, the power sequence was wrong. This would have affect the device functionality. We strongly recommend you to follow the proper power sequence to get the device functions normally and reliably.

    Regards,
    Senthil