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Wednesday, May 12, 2010

Strange Blog may Disclose Something

There is a new post on TI's  Bluetooth Low Energy blog, Bluetooth low energy and coin cells

I felt strange when I first read the blog, but could not tell what it was. Is Bluetooth Low Energy supposed to be operated by a coin cell? Definitely! This is what BLE is all about.

Now I just  had a second read, the conclusion of the TI blog says "The most interesting thing, though, is that the effective battery capacity is the same for both the 15 mA load and the 30 mA load. The effective battery capacity turns out to be approximately 120 mAh (there is some variation battery to battery) for both 15 mA and 30 mA max loads using CR2032 cells at room temperature. Now, this means that the cell is used for pulsed operation, it must be de-rated from the 230 mAh that is typically given for constant current (usually given for a <1 mA load), but it does seems to disprove the theory that you cannot use coin cells if your (pulsed) load current is higher than 15 or 20 mA."

Take a look of the competitors of CC2540:

1. Nordic uBlue. The peak current is 15mA.

2. EM Micro EM9301. The peak current is 14.5mA

Now, can you deduce something?

I guess that CC2540's peak current is much higher, probably 30mA as the test alluded, but the sleep current is on par with or better than the Nordic and EM Micro products, thus the average current of CC2540 for a normal Bluetooth Low Energy operation is still competitive. This makes the TI post a lot of sense. All TI is doing is probably to prove that the high peak current of their CC2540 actually does not matter for a real BLE application.

Anyway, this is an interesting test if the results hold true. I bet most of the coin cell suppliers does not know this fact. But high peak current is after all not a good thing. Even though CR2032 is fine, how about other types of batteries? how about energy harvesting?



  1. Normally, CR2032's have around a 15-20 mA discharge capability due to the high internal resistance of lithium batteries. I have had problems running coin cells at higher than around 25 mA of constant discharge. I'm not sure about pulsed discharge.

    Here's some Wikipedia info on coin cells. You'll need to scroll down to the coin cell sections:

  2. It is worth pointing out theat the TI devices include a microprocessor on chip. Nordic and EM require an additional micro processor. So total current consumption for Nordic and EM solutions may also exceed 16mA

    I work for CSR - our devices (with on chip micro) operate withing the 16mA peak discharge threshold.