# Power calculations for Controller

Discussion in 'Embedded Systems and Microcontrollers' started by Abhinavrajan, Aug 22, 2016.

1. ### Abhinavrajan Thread Starter Member

Aug 7, 2016
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1
I have an microcontroller. MSP430FR2310.
I am supposed to interface this microcontroller with a temperature sensor (TMP100)and Level translator (3.3V to 1.8v).

I have selected the chips. I am asked to do power calculations for this system.

How should I do it ?
Should I just take in the supply voltage of each chip and multiply with the load current?

But it doesn't seem that simple to just multiply the voltage and current.
It seems that we have to calculate the current at each pin of the peripheral device ( TMP100) and then take the total current and multiply it with the supply voltage?

Can someone explain it clearly in step by step process with an example on how should my calculation look?

2. ### dannyf Well-Known Member

Sep 13, 2015
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Would it help to ask the person who asked you to do this? That person would know best.

3. ### ErnieM AAC Fanatic!

Apr 24, 2011
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The current is not a single number. It is less when no readings are being acquired. It is high when acquiring thru the I2C. It is lower for a lower frequency bus over a higher freq bus.

Providing a quiescent and acquisition current should satisfy the request.

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4. ### shteii01 AAC Fanatic!

Feb 19, 2010
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If peripherals are powered from uC, then all the power is going through uC, the power needed to run uC + power needed to run peripherals + power consumed by various signals between uC and peripherals. I would measure how much current the uC draws, you already know the voltage the uC needs, use these numbers to find total power of the system.

The others are correct about conditions, like higher frequency signals draw more power than lower frequency signals, higher ambient temperature might have an effect. So you will likely need to choose several operating conditions/situations and calculate power for each situation. Or you can take an easy way out, define one situation and say that this one operating situation is the only one that is allowed, then take measurements and calculate power.

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5. ### ErnieM AAC Fanatic!

Apr 24, 2011
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I don't know of any peripheral powered by a uC, except perhaps those on the very same chip.

It's it's external it gets it's power from some other place.

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6. ### dannyf Well-Known Member

Sep 13, 2015
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Calculate the time weighted average.

7. ### ErnieM AAC Fanatic!

Apr 24, 2011
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1) Look at every connection to Vss.
2) Make an educated guess for the current down each leg.
3) add everything found in #2 together