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TPS61099: Usage with small MCU/RF load and coin cell supply: any advise?

Genius 3985 points
Part Number: TPS61099
Other Parts Discussed in Thread: CC115L, TPS61299, TPS63900,

Hi,

we plan a small keyfob with a MCU and CC115L RF, driven by a CR2032 coin cell. RF pulses will be at about 20-50ms long.

As CC115L consumes up to 30mA, any native CR2032 will 'die' within a few hundred cycles: internal resistance increases fast and under load output voltage will drop fast below 2V.

Now we want to operate CC at about 2.2V, which helps to some extend (~25% less current than at 3.3V, with a few less dB PA).

In addition such a boost circuit like this TPS might help: set to e.g. 2.2V VOUT, with the coin cell supplying 3V -> down to 1V, its always guaranteed that my circuit is provided with 2.2V.
The power consumption of the circuit will vary between some uA in sleep mode, waiting for a button press; a few mA if the MCU is operating alone and up to ~25mA including the RF.

Questions: is this TPS (due to budget we can't afford anything more expensive than this one) the right choice to help us out?
And: as long as the coin cell deliver more than 2.2V, the TPS is in DOWN-mode and 'destroys' the valueable energy in its internal circuits - I can't believe that this would be the right strategy...

So please advise

Thanks in advance

  • Hi 

    The down mode of TPS61099 is too wide. f the Vin is higher than 2.2V, is the Vout expected as 2.2V. Or can follow Vin? If the answer is the former, I recommend to use a buck boost TPS63900. It the answer is the later, you could choose TPS61299, whcih down mode range is more tight. The price is a little more expessive than 099.

  • Thx!

    Considering that a coin cell easily drops to 2.5V under load, if we set the TPS61099 to 2.5V fixed output, could we use the coin cell on its 1V extension?

    Is there anything against it?

  • Do you mean the Vin is 1V and still want to keep Vout at 2.5V. If so, it's possible.