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Extended Power Management

Discussion in 'Electronic Design' started by Myauk, Sep 22, 2008.

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  1. Myauk

    Myauk Guest

    Dear All,


    Could anybody explain to me the details of Extended Power Management
    Scheme? Or could anybody suggest any good link for all the details on
    tolerances of 1.2V and 1.8 V supply rails on PCBAs?

    Extended Power Management Scheme is normally found in a System On Chip
    solutions using low drop series pass transistors for 1.8 V and 1.2 V
    supply rails.

    Here is the reason why I would like to know in every details of it:


    I am now working on power up testing of a typical PCBA by using Bed of
    Nails style test fixture.

    In one typical testing scheme, I have to measure 1.2V and 1.8V power
    rails.

    The Manufacture Specified that the voltage measurement on 1.2V and
    1.8V in given Golden PCBA should not exceed 1.26 V and 1.89 V
    respectively.

    I could verify that by supplying power directly to the PCBA and
    measuring the rails by Agilent DMM 34401A. I measured more than 10
    times.

    However, after putting the PCBAs onto the Bed of Nail style test
    fixture, I found that the measurements are exceeding the limits quite
    often.

    For 9 out of 10 times. 1.8 V rail measures 1.891 ~ 1.894. For 6 out of
    10 times 1.2V rail measures 1.260025 to 1.272.

    Checking the PCBA schematics, I found that 1.2V and 1.8V rails are
    controlled by extended power management part of the main processor
    IC.

    It looks like a Linear Voltage Control scheme. 10V adaptor supply is
    converted to 3.3V by a DC to DC converter. This 3.3V is passing
    through a low drop series pass transistor (controlled by core
    processing IC) to give the output of 1.8V. This 1.8V is passing
    through another low drop series pass transistor to give the output
    1.2V.

    I am checking on the PCBA and Test System now to find the root cause
    of it.

    Thanks and Best Regards
    Aung
     
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