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  1. #1
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    Power estimation of IC's

    Hello Guys,

    I want to calculate the Approximately Power required for the IC (LM339 or KZ8081RNA)

    Which parameters are taken consideration while calculating the same..?

    Kindly help for the Same by giving datasheet reference as an example so it would be easier to understand me as well the ppl who use this Forum.


    Regards,
    Marx

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  2. #2
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    Re: Power estimation of IC's

    Quiescent or operating?
    With or without load?
    At its minimum or maximum voltage?

    I will be looking at TI's datasheet revision E when I mention figures.

    1) I would start by reading the datasheet's supply current vs. voltage and temperature. Figure 1. Multiply by supply voltage.
    2) Then take all the output load currents (which include the pullup resistors, use ohm's law), and multiply it by the output saturation voltage, figure 3.
    3) The losses dissipated by the actual switching....that will be a tough one as it is not specified. But as a ballpark value, if you are switching slowly, below 1 KHz, leave the sum of 1 and 2 as is. Add 10% for each additional decade of switching frequency. Again, this is only a ballpark value.
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    Re: Power estimation of IC's

    Hi..
    Coming to the Controller.
    I am using controller STM32F417IGH6.

    Now i want to make a proper calculation for the same.
    http://www.st.com/en/microcontrollers/stm32f417ig.html

    Now the controller will be operated on the +3.3V
    i want to understand the current so i will design the Power supply of the same by keeping 20% margin of approximately result.

    Regards,
    Marx



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    Re: Power estimation of IC's

    Hi

    In my eyes it makes no sense to use a power supply just for the microcontroller.
    I recommend to deign the power supply for the complete circuit, including all other ICs, resistors, LEDs, interfaces...that are connected to the microcontroller.

    And take care of proper input voltage levels.
    Usually the supply current is specified with all inputs tied to VCC or GND.
    If in your application there are input pins floating or connected to voltage levels far away fro VCC or GND, then the Icc may be increased. Don't be surprised if you see twice or more the ICC given in the datasheet (depending on microcontroller operating state).

    Usually this is also explained in the microcontroller datasheet.

    Klaus
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    Re: Power estimation of IC's

    The datasheets are pretty plain about maximum and
    typical Icc. I am not going to post them, datasheets360
    has everything you could want.

    Add to this the load (pullup) resistor current although
    this is not truly -IC- power dissipation and depends
    on circuit state and is often a different supply than
    the IC's operating supply.

    You're talking tens of milliamps including load current
    if you do the arithmetic.



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    Re: Power estimation of IC's

    Quote Originally Posted by KlausST View Post
    Hi

    And take care of proper input voltage levels.
    Usually the supply current is specified with all inputs tied to VCC or GND.
    If in your application there are input pins floating or connected to voltage levels far away fro VCC or GND, then the Icc may be increased. Don't be surprised if you see twice or more the ICC given in the datasheet (depending on microcontroller operating state).

    Usually this is also explained in the microcontroller datasheet.

    Klaus
    Hi Klauss.

    if the Input pins will be floating, then how it can consume current.

    Another, I want to Make specification for the Micro controller.
    Where i am conflicting between the Max power Dissipation..? and Max current ICC..??

    Which current need to be taken into consideration..

    or Are there any other ways..?



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    Re: Power estimation of IC's

    If you are concerned about thermal issues then think
    in terms of power.

    If you are specifying or designing power delivery then
    think in terms of current draw in each supply voltage
    branch, and work up your budget subtotals.

    Floating inputs mean an undefined internal state
    while supply current is specified and tested under
    very specific (often, only one) condition which has
    everything defined.

    For your linear comparator you might see no supply
    current difference (if open inputs drift apart and
    create an opportunistic "signal" that happens to be
    close to test conditions) or you could see greatly
    elevated current draw from the comparators
    "chattering" when inputs happen to be close together
    and back-coupled ground noise sets up a ground
    loop oscillation (output->gnd->input->output).

    Your options are to enforce known conditions that
    are known not-crazy, or to accommodate a worst
    case supply current that exceeds datasheet (by
    how much, is an exercise that includes some amount
    of fog and futility). And to tolerate any output
    uncertainty / activity (which might well impose not-
    as-spec'd input conditions on downstream stuff).



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    Re: Power estimation of IC's

    Hi,

    if the Input pins will be floating, then how it can consume current.
    It's not input current, it's supply current that increases, caused by crowbar currents in the input stage, when both transistors, the highside and the lowside are (slightly) conductive at the same time.

    Klaus
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    Re: Power estimation of IC's

    Hi,
    Here i have attached the OPAMP snapshot to understand the Better.

    I am using the OP-AMP 393 in Comparator mode.

    Where output is pulled up with the +5V with 2.1K resistor.

    Now attached figure is giving me confusion while Current consumption.
    Where they have Mentioned the ICC (Supply Current) and If opamp configured in the Comparator.

    Which value needs to take for the Power consumption part..?
    Click image for larger version. 

Name:	OPAMP.PNG 
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    Re: Power estimation of IC's

    Multiply current by supply voltage.

    The datasheet snippet is for the LMV393, is that what you are using?
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    Re: Power estimation of IC's

    Hi Schmitt,

    I have been confused in the Supply Current (ICC) & INPUT Sink current.

    For the, Power consumption which parameters are corrent to take in account and why..??



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  12. #12
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    Re: Power estimation of IC's

    No need to be confused.
    Just follow the steps I outlined in post #2
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