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Last Post 27 Aug 2010 02:50 PM by  kurtl@logicpd.com
MCF5329EVB Supply Voltage Sequencing
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tom.evans@motec.com.au
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--
25 Aug 2010 07:54 PM
    My Base Board is the "SDK-DRG-!0", "MCF53xx SDK", "Zoom SDK Application Board Rev 7".

    Freescale specify:

    MCF5329DS.pdf MCF532x ColdFire® Microprocessor Data Sheet, Rev. 5
    3.3.1 Power Up Sequence
    "IVDD should not lead the EVDD, SDVDD, or PLLVDD by
    more than 0.4 V during power ramp-up or there is
    high current in the internal ESD protection diodes."


    When powered from the supplied Plug Pack and the plug pack is then plugged in, the voltage waveforms for the 5V, 3.3V, 2.5V and 1.5V rails take about 1600us to ramp up and they're fine. I have oscilloscope traces of this, but this board doesn't seem to allow attachments, so I can't show what it looks like. Maybe I can...



    **********************
    *** 5.0V
    ***
    ***
    *** 3.3V
    *** ******************************
    *** ***
    *** *** 2.5V
    *** *** ***********************************
    *** *** *** 1.5V
    *** *** *** ***********************************
    *** *** ***
    *** *** *** ***
    *** *** *** *
    *********************************** Rise Time about 2.5 milliseconds



    When the plug-pack is already powered and the power cable is then plugged into the baseboard, the waveform is like the following. The 5V rises immediately and the other rails ramp up a lot faster. The 2.5V regulator lags way behind though:


    ************************************************************
    * 5.0V
    *
    *
    * 3.3V
    * *******************************
    * ***
    * *** 2.5V
    * *** *********************
    * *** * 1.5V
    * *** ***********************************
    * *** *** *
    * *** *** **
    *** * ***
    ************************************************* Rise Time about 500us



    The 1.5V rail reaches 1.5V before the 2.5V Core supply has started to turn on. IVdd is thus 1.5V above SD_Vdd, way higher than the 0.4v specified. The VCORE voltage on the Fire Engine board at TP120 is even worse due to the FET in series with the power rail.

    This doesn't cause a problem for units powered from the supplied plug-pack, but could cause problems if powered from any other supply. If used as a reference, this design might cause problems for products powered from batteries or other fast-turn-on power sources.

    The LM317S regulator seems to take too long to turn on compared with the LM1086 used for the 3.3V supply. It might be better matched if replaced by another LM1086.
    richard.laborde@logicpd.com
    Basic Member
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    Posts:247


    --
    26 Aug 2010 06:51 PM
    Thanks Tom, nice rendering. ; ) I've forwarded to the HW team.
    kurtl@logicpd.com
    New Member
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    Posts:


    --
    27 Aug 2010 02:50 PM
    The kit power supply is one of many ways to power a design. This is good feedback for all designers using this product. Care should be taken to ensure proper power sequencing on power up and power down of all products to prevent shortening the life of the components.

    p.s. I love the ASCII art!
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