The TPS78233 from Texas Instruments looks like a standard LDO linear voltage regulator:
It takes an input voltage up to 5.5V and regulates it down to 3.3V (the above image from the datasheet is the 2.7V regulator). Not a spectacular voltage range, but it has a very nifty trick up its sleeve:
This regulator only draw 450 nA, i.e. 0.45 µA, when unloaded!
That’s about a quarter of the current consumption of the already-spectacular MCP1702 and MCP1703 used in JeeNodes – a ridiculously low 2.5 microwatts.
Here’s a little test setup (yep, those SMD’s are small – can you see the two 10 µF caps?):
To get a sense of this level of current consumption: 3x AA batteries of 2000 mAh would last 5 centuries (ehm, well, except for their pesky self-discharge) – which is a bit silly, of course.
To get another idea: when I measure the output voltage with a multi-meter, the current consumption “jumps” to about 750 nA. Why this relatively big change? Because most multi-meters have a 10..11 MΩ input impedance, and 3.3V over 11 MΩ is… 300 nA!
In case you’re wondering: measuring minute currents is easy with Dave Jones’ µCurrent.
The fascinating thing about the TPX82xx series is that it achieves this extremely low idle current while still being able to regulate and supply up to 150 mA. Furthermore, that enable pin might come in very handy for certain ultra-low energy harvesting scenario’s.
But I’m not going to replace the regulator on JeeNodes for a number of reasons:
The MCP1702 can handle input voltages up to 13V (vs only 5.5V for the TPS78233).
There’s no through-hole version, so this would not work for standard JeeNode kits.
Those extra savings only kick in when you get everything into the few-µA range, and so far, things like Room Nodes still draw a few dozen µA’s.
In many cases, when the max is 5.5V anyway, no regulator will be needed at all (note that running only the RFM12B on it may create a problem with signal levels).
But hey, it’s good too know that these chips exist. A few microwatts… wow!