Battery specifications

[scrabble80]

Hi,

I have a small circuit that needs to be powered at 3.6V and draws a continuous 35mA current.. The problem is that in the circuit is also a CC2420 transceiver with a max. absolute rating of 3.6V.

I was thinking of combining 3 x 1.2V NiMH cells I already have to make the 3.6V battery but I am worried that the voltage of the fully charged cell connected to the circuit (potentially around 4V, as 1.2V is the 'nominal' voltage for a NiMH cell) might fry the transceiver. I'm I justified in thinking this ?

I understand that the battery voltage will drop when its connected to the load but its the first few seconds of operation that worry me.

 

[IRstuff]

I don't see anything on the datasheet that says the CC2420 needs to be powered at 3.6V. According to the front page, the chip will run off its internal regulator if supplied with >2.1V, and will run at an externally regulated 1.6V.

And yes, you'll need to regulate or crowbar the supply voltages to be less than 3.6V.

TTFN

FAQ731-376

 

[scrabble80]

Wow, that was a fast response, Thanks !

The circuit (not mine unfortunately) uses the internal voltage regulator , so CC2420 is powered by VREG_IN.If you look at page 8 of the datasheet it quotes the maximum ratings for this setup. The 3.6V supply is dictated by other parameters irrelevant to CC2420 so there is no alternative.

Any quick ideas on how to regulate it at this voltage ? (Fixed linear regulator maybe ?)

 

[IRstuff]

There are lots of suppliers and chips. This is one of many:

http://datasheets.maxim-ic.com/en/ds/MAX6469-MAX6484.pdf

You could get one that's preset to 1.6V, and the regulator will continue to work down to about 1.8V.

Others:

http://para.maxim-ic.com/en/search.mvp?fam=linear_reg&tree=powersupplies

TTFN

FAQ731-376