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# Running 3.3V MCU from 12V battery efficiently

## Running 3.3V MCU from 12V battery efficiently

(OP)
Hey,

I have been trying to get my head around how to tackle the problem of powering a microcontroller that runs on 3.3V from a 12V supply.  The power supply is a simple battery and will be deployed 'in the field' for long periods of time (1 or 2 years) so it is essential that the 12V to 3.3V conversion is efficient.

The microcontrollwe will be duty cycled i.e. it will be asleep for the large majority of the time.  The entire circuit not including the power supply in question would be drawing only a few microamps when asleep and up to a maximum of 100 milliamps when active (although it will generally be more like 10mA).

Obviously a simple linear regulator could be used however dropping 12V down to 3.3V over a resistive load is far from efficient.

This lead me to look into a DC-DC buck converter however I couldn't find any parts that were suitable for my application.  The main problem with the buck converters I found was that ones that could handle an input voltage of 12V were all rated for high currents and had low switching frequencies (i'd prefer one with a high switching frequency to minimise the size of the components).  These traits seemed to lead to them all having high quiescent currents in the range of a milliamp or two.

If I were to use a buck converter with such a high quiescent current it would be less efficient than using a linear regulator.

So my question(s) is(are), is there a buck converter out there that will power my circuit and retain a very low quiescent current when the MCU is asleep?  Alternatively is there a way to have the buck converter shut down when the MCU is asleep? (obviously the MCU still needs power.. would a combination of a buck converter and a regulator be the best solution?) Is there an 'industry standard' way of achieving what I am trying to do?

Thanks
Matt.

### RE: Running 3.3V MCU from 12V battery efficiently

You can also check out energy harvesting chips that are newly out.  Most are oriented towards processes that include CPU usage that is short and sporadic while saving every possible erg of energy.

Keith Cress
kcress - http://www.flaminsystems.com

### RE: Running 3.3V MCU from 12V battery efficiently

Plenty of chips out there that will provide 2.8V, 3.3V, etc. from 12V supplies, some running in the MHz range.  Fast, efficient, and often have "sleep" pins.

Dan - Owner
http://www.Hi-TecDesigns.com

### RE: Running 3.3V MCU from 12V battery efficiently

(OP)
Hey,

Thanks for the feedback.  Yeah that first chip mentioned by IRstuff, the MAX1836 looked good but I couldn't find it for sale anywhere.  With a bit of extra searching I found the TPS54331 which seems to do everything I wanted and is readily available for me to purchase.

Thanks again for the replies.

Matt

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