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SMPS will cause spike current ?

Discussion in 'Electronic Design' started by Boki, May 24, 2007.

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  1. Boki

    Boki Guest

    Hi All,

    Our wireless short range communication is in standby mode now,
    however, the software is working, should be no anything to do. ( I
    want to indicate the s/w level is still alive, but nothing to do )

    I got spike current in the duration of standby mode, I can't make sure
    that is because NOP command ( or other not really important
    commands) in the s/w level or h/w components effect it.

    Any idea about read / write a EEPROM value will cause spike current
    about 7mA, is it possible ?

    Any idea about change a PIO will cause a spike current about 7mA ?


    The module work at 1.8V at core chip, however, it accept 4.2V battery
    voltage, it should has its own regulator. The PIO output I got is 3V.
    The normal normal standby current is 1.5mA range.

    Please let me know if I have to input more info.

    Thanks!

    Best regards,
    Boki.
     
  2. Guest

    At least some switched mode power supplies operate in the
    "intermittent mode" when lightly loaded - they draw a signifcant
    current for a short time, charge up their output reservoir capacitor
    to the upper threshold output voltage then wait until it discharges
    discharges to the lower threshold.

    A really cheap crude switching step-down regulator would always
    operate this way - the 4.2V battery charges up the reservoir capacitor
    to a certain voltage which is less than the highest output voltage,
    storing a certain amount of energy in the inductor in the process.
    Once the reservoir capacitor hits this voltage, the input side of the
    inductor is switched from the 4.2V down to ground, and the current
    through the inductor proceeds to decrease to zero, charging up the
    resevoir capacitor even further in the process.

    At this point the system designer could elect to open circuit the
    input side of the inductor (but this needs a sensor for the current
    through the inductor, which costs money) and wait until the reservoir
    capacitor has discharged itself to the lower output voltage threshold
    before starting to recharge the inductor.

    The cheaper solution is to let the current through the inductor go
    negative and start discharging the output capacitor until it hits a
    threshold voltage somewhat higher than the lowest acceptable output
    voltage, and then reconnect the input side of the inductor to the
    battery. It will take a while for the battery to increase the current
    through the inductor back to zero, and the voltage across the resevoir
    capacitor continues to decrease untl you get to this point.
     
  3. Winfield

    Winfield Guest

    Any part numbers for us to evaluate, boki?
     
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