IC Power Consumption

[LearnMore]

HI,

I would like to seek for advice for measuring the actual power consumption of a chip.

The idea in my mind is to tap the VCC line of the chip and measure the current flowing through since the voltage is set accordingly. So the power = VI. Is that a correct method.

The IC i am going to measure the power consumption is LCD display Driver. Please give some advice. THank

 

[Skogsgurra]

Yes, that is how to do it. But be aware that drivers mostly consume power when switching outputs (charging capacitive traces in the display), and that is done in microseconds or less. So you need to either measure with a high-bandwidth scope and current transducer - difficukt at these low current levels. Or you must put a capacitor across your ammeter to smooth out the current peaks. Since that would be a rather large capacitor (because of low internal resistance in ammeter) it is better to put a good decoupling capacitor across Vdd and Vss on the driver. That will give the same effect.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[LearnMore]

For ammeter portion, i will have a very good meter. the high end HP DVM.

One more thing to top up, the driver have two power supply which one is vcc(AC), vdd(DC) for logic driver... means i have to measure both? to get the separate power consumption?

 

[Skogsgurra]

Vdd is the positive supply, usually +5 V. Vss is ground rail.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[itsmoked]

A "good meter" doesn't actually mean it will read uS current pulses.

I'd put a 1 or 10 Ohm resistor in the supply lines and then look at the voltage across it with a scope.
I=V/R

An alternative would be measure the whole circuit assembly's current then yank that chip and measure it again.
I_driver = I_system - I_{system w/o driver}

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[jimkirk]

Be sure whether you want to measure the IC consumption alone, or the consumption along with whatever the chip is driving. For an LCD display that might be miniscule, but as an example, an audio amplifier might be drawing 10 watts from the power supply, but if it is delivering 2 watts to a load, the amp itself is only dissipating 8 watts. If you're doing thermal measurements trying to calculate die temperature, it's important.