I keep reading that the Bluetooth Low Energy modules are capable of working with a CR2032 battery for years, but their consumption is around 20mA and the max discharge of a CR2032 is around 3mA (200uA standard). How could this be possible?
I'm pretty sure it has something to do with the pulse discharge current, but the datasheets usually don't have a lot of information about that. In this case how can I determine the relation between the discharge current and the duration of the pulse?
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2 Answers
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Basically: the answer is: yes, they can work on a CR2032 power budget, but a lot of factors come into play when dealing with low power systems. A pretty good overview on the general issues (not especially for BLE) is outlined here: http://www.ganssle.com/reports/ultra-low-power-design.html.
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You can do it if you switch the chip on at long intervals. The standby currents of BLE modules is something like a microampere. Surprisingly, at least with some devices you can, within that power consumption, run a timer to automatically power up the device at a chosen time. I don't know how well this would work if the other end is some generic BLE device such as a cellphone.
CR2032's can be drained with significantly higher currents than 3mA. Consider for example this test report from TI: http://www.ti.com/lit/wp/swra349/swra349.pdf, there were no significant differences when draining a button cell with 30mA. You should use a capacitor to smooth out the voltage ripple during the active period, however.
