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29th January 2005, 14:15 #1
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Calculate power consumption/ life times
I found that the datasheet of electronic device have the power consumption details. But I not clear that how the manufacturer calculate the life times for the devices.
For example:
Operating Voltage: 5V or 3.3V
• TX consumption: 300mA (Max)
• RX consumption: 200mA (Max)
• Sleep Mode: 50mA
If we are using the normal 5Volt battery. How can we calculate the life times?
If possible, please show the example or the relevant resource to answer this question.
Thanks you.

29th January 2005, 14:15

29th January 2005, 14:53 #2
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Calculate power consumption/ life times
i hope u r asking for battery life time...
well in the worst case..the max current is 300mA (Assuming the chip is semi duplex operation)
obviously if the chip is in sleep mode for long(ie no tx or rx) the power consumed is totally different..
so u can say the battery life time corresponds to 50mA when no call is made and corresponds to 250mA(average) when a call is going on

29th January 2005, 14:53

29th January 2005, 15:48 #3
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Re: Calculate power consumption/ life times
Usually rechargeables come with chargestorage capacities, something like 2100mAh. Nonrechargeable batteries typically have larger capacities than rechargeable ones, but they are normally not stated. You'll have to give an estimate.
Now, mAh stands for milliAmpere hours. So 2100mAh translates to 2.1x60x60C of charges.
Now assuming 50mA current drawn, since I = dQ/dt, you can roughly compute the dt.
Note that these figures are normally gross estimates, and losses are usually significant. So use these figures with a pinch of salt. The best way is still to do a lifetime test.

29th January 2005, 15:48

29th January 2005, 17:16 #4
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Calculate power consumption/ life times
for example if there are 3 ICs in my circuit. to calculate the total power consumption, is it right to add all of the IC's power consumption directly?

29th January 2005, 21:35 #5
Re: Calculate power consumption/ life times
Yes, of course you add all the currents drawn by all devices in your circuit.
The current drawn from the battery can be the same if there is no regulator between the battery and your circuit. If there is a linear regulator you ave to add its quiescent current to the circuit current to get the battery current.
If there is a switching regulator between the battery and the circuit, then this will draw a constant POWER from the battery. Its input current (=battery current) can be calculated if you know its efficiency and output voltage and current:
Ibat=(Vcircuit*Icircuit)/η/Vbat, where η is the efficiency of the regulator. This current is an approximation, since it increases as the battery discharges. Plus, the efficiency of the regulator can also change as the battery voltage or output current change. But it should give you a fair ESTIMATE of the input current.
Once you have established the current the battery needs to supply, just use the formula given by checkmate to calculate the time.
If the circuit current varies, which it probably will, you have to use a best estimate as to how much average current it draws.

30th January 2005, 21:23 #6
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Re: Calculate power consumption/ life times
Thanks you for quick and nice reply.
But I still not clear about the standard that used for manufacture to do the calculation for the life times.
Can help me?

30th January 2005, 21:23

2nd February 2005, 18:11 #7
Re: Calculate power consumption/ life times
If you are referring to lifetime of a product, there are standards for calculating the expected life from failure rates of different components, based on their ratings and the stresses in the circuit. It is pretty much a statistical calculation, based on numerous data sets collected over a number of years to establish these failure rates. One of the companies that does this kind of work is Telcordia.
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