How to read datasheets
A microcontroller's operating current is specified as "120 µA/MHz." When it runs at 16 MHz, roughly what is its operating current?
- AAbout 1.9 mA
- BAbout 7.5 µA
- CAbout 19 mA
Show answer and explanation
Answer: A. About 1.9 mA
The µA/MHz notation indicates that operating current is roughly proportional to clock frequency. 120 µA × 16 = 1920 µA, or about 1.9 mA. This is because dynamic power in CMOS circuits is proportional to the capacitance being charged and discharged, the square of the supply voltage and the frequency. However, this value is typically measured under specific conditions, such as running a particular program with peripherals stopped, so add the current of the peripherals in use and leakage current separately in the estimate. About 7.5 µA is the mistake of dividing 120 by 16.