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Designing low-power embedded devices requires careful consideration of power consumption, especially during sleep modes. Accurate calculations help optimize battery life and ensure device reliability.
Understanding Power Consumption
Power consumption in embedded devices is primarily determined by the current draw during active and sleep states. Measuring and calculating these values allows engineers to estimate battery life and identify areas for optimization.
Calculating Sleep Mode Current
The current during sleep mode, often denoted as I_sleep, is a critical factor. To estimate the battery life, use the formula:
Battery Life (hours) = Battery Capacity (mAh) / I_sleep (mA)
Estimating Total Power Consumption
To determine overall power consumption, consider both active and sleep periods. The average current, I_avg, can be calculated as:
I_avg = (I_active × t_active + I_sleep × t_sleep) / (t_active + t_sleep)
Practical Calculation Example
Suppose a device has a battery capacity of 2000mAh, a sleep current of 10μA, and an active current of 20mA. If the device spends 90% of the time sleeping and 10% active, the average current is:
- I_sleep = 0.01mA
- I_active = 20mA
- t_sleep = 90%
- t_active = 10%
Calculating I_avg:
I_avg = (20mA × 0.10 + 0.01mA × 0.90) / 1 = 2.001mA
Estimated battery life:
2000mAh / 2.001mA ≈ 999 hours