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Launchpad standalone power supply?


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While it's nice to have USB power while debugging, at some point the Launchpad has to stand on its own feet.

I thought I've seen a blog or so evaluating the options, but I can't seem to find it.

 

Using a 5V supply as with USB would have the advantage of the onboard regulator, but how much power does the FET use?

How much power does the regulator need for itself? What is the minimal voltage required to get the 3.5 V output?

Connect a wall wart or 3-cell battery pack to the USB power lines would be ideal, but with batteries it may not be feasable.

Does powering the MSP430 directly (Pin headers) cause problems with the FET if it's not disconnected?

This would allow a direct 2-cell battery pack, everything else would require another regulator.

 

Somebody surely has come up with a few good ideas!?

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If you want to run launchpad from battery, it is possible to connect 3,6V li-ion battery to launchpad Vcc and GND pins.

I use nokia battery all the time like this. But you must be careful and remember to disconnect battery before connecting launchpad through USB to computer.

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I've powered the launchpad via the header pins with 2xAA batteries - it didn't cause any problems.

 

Rather amazingly (I find anyway), I could also run it with 2 x rechargeable AA batteries, so the (nominal) voltage being supplied was 2.4V.

 

With the minimal external component requirements of the launchpad chips, I find it easier to breadboard all circuits with the uC - one 33k resistor between Vcc and the RST pin and you're good to go!

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The launchpad uses a TI LDO http://focus.ti.com/lit/ds/symlink/tps77301.pdf. Dropout voltage depends on a few factors, but it should not be much more than 100 mV (values given for 250 mA load).

It has a back-diode for protection, it also has Enable and Power-Good IO. Standby around 1 uA.

So if the regulator is used (10 V max) the MSP could control power to the board (switch it off).

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