IC Power Consumption
IC Power Consumption
(OP)
Hi,
How do IC manufacturers come up with a power consumption rating?? How do I check their numbers??
swb1
How do IC manufacturers come up with a power consumption rating?? How do I check their numbers??
swb1





RE: IC Power Consumption
It will specify "output pins not connected", "Oscillator pin held low", "Vcc = 5.0V", 25C, etc.,etc.
Some IC data sheets will specify quiescent current as a function of clock frequency and provide an equation.
Why are you bothering to check an IC? Usually you want to know a product's draw not just an IC. The data sheets are rarely wrong in their statements as this can be easily checked.
Like all things IC, measuring one instead of using the data sheet is not usually a good idea.
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: IC Power Consumption
If you add up all the worst case power requirements from all the devices and design a power supply to meet this requirement, more often than not, you will wind up with a significantly oversized power supply (not that there is necessarilly anything wrong with this). The worst case consumption from the data sheets assumes that the device is operating at full capacity, which is not usually the case.
RE: IC Power Consumption
Finally, the validity of the data sheet numbers are directly related to the age of the design. In other words, early versions of IC (pre-production releases) may not always meet the final data sheet numbers.
RE: IC Power Consumption
The best advice we can give is "know your system". The data sheets are based upon laboratory settings where the chip manufacturers can push the chips to the limits and create an envelope of failure rates. If your chip ever goes outside of that envelope, you're beyond the 'X'-sigma it was designed for... the chances of that happening are extremely small, and if you absolutely must have a higher sigma, you'll pay for it.
For example, I know the typical PIC can source 20mA per line, but the entire chip with five 8-line ports may have a limit of 200mA. Since I know my lines are almost always used for sub-mA signaling, I never worry about that worst-case scenario, and therefore I don't design for it. I know my system. I don't bother checking the manufacturer's numbers, because if I was ever knocking at the door of the limits I know the datasheet values are going to be correct in 99.999% of the chips that roll across my desk. If one unit fails out of 10k, that number is acceptable in most cases... if it's not, I underdesigned the system.
Dan - Owner

http://www.Hi-TecDesigns.com
RE: IC Power Consumption
With MCUs, take into account which peripherals are you using. Most IDE packages allow simulating the program, even watching thread duration in machine cycles, so you may calculate current x thread time for each peripheral, thus getting average power estimates for your specific firmware. As said before, it will be likely lower than that shown in the datasheet.
If you want nWatt accuracy, keep in mind that IC 'thinking' drains power too. We know CMOS devices spend more power when switching between states, so any firmware with a tight loop ("loop: goto loop;") may give you a close figure of the highest power consumption in idle mode.
Good Luck!