An external 32 kHz crystal will give lower average current consumption than using the RC oscillator, at the expense of cost and board space. There are primarily 3 reasons the current consumption is lower:
The RC oscillator must be calibrated every 4 seconds to be accurate enough. Calibration normally takes about 17 ms, and requires the 16 MHz to be running, giving an average current consumption increase of about 6-7 µA.
The receive window must be widened to account for the worse accuracy. Since the RC is 250 ppm, compared with typically 20-30 ppm for an external crystal, the radio must receive for a slightly longer time, giving an increase of 1-2 µA average
The run current or the RC is 0.8 µA instead of 0.4 µA for a typical crystal.
In total, this gives 8-10 µA extra average current consumption. Depending on application, this may be enough to justify the cost and board space for a crystal.
Is it only about 10uA of current dissipated by not using the 32.768Khz crystal?
I do not want to use crystal, but this should not cause any processor delay.
Current consumption is not a problem for my development. Of course, we won't use the RTC timer either. It is just important to make the PCB lighter. Is it right to remove the 32k crystal in this case?
Is it only about 10uA of current dissipated by not using the 32.768Khz crystal?
I do not want to use crystal, but this should not cause any processor delay.
Current consumption is not a problem for my development. Of course, we won't use the RTC timer either. It is just important to make the PCB lighter. Is it right to remove the 32k crystal in this case?
