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Ideally I’d like to have valid, hard data on the actual components on the Sparkfun Pro Mini - the regulator, the caps, everything, which I don’t recall seeing on the schematic where one would expect to find it. I presume the traces are usable at any voltage / current the components themselves support; if that’s not the case it would be important to know.
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Sparkfun and about all “user grade” literature says the raw voltage input has a max of 12v. I accepted that at face value until I stumbled across what is supposed to be the datasheet for the regulator used by the Pro Mini in this thread:
viewtopic.php?f=7&t=13370&p=0&e=0
That datasheet (which does match the markings on my pro mini regulator) says the regulator will accept up to 16v.
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I want to run my Pro Mini from a standard “12v” car battery, which can actually put out near 14v on a fresh charge, but I’d prefer not to have to pre-regulate that “12v” just because it’s a few over the user grade literature. Yet this datasheet is the only reference I’ve seen that does not say 12v, which makes me leery of trusting it as the only data point that lists a limit I prefer. (grin)
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But it could be the “user grade” literature really means the consumer variation of “12v”, such as that put out by a car battery, rather than a literal limit of 12v as read by a multimeter. In that regard I don’t trust even Sparkfun saying it’s 12v means rigidly 12v, but “sort of” 12v.
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Be that as it may, I’m not interesting in zatching my Pro Mini. Anyone else would simply pre-regulate the voltage <12v literal and be done with it. I’m not wanting any more parts that I have to and consider it wasteful to toss in regulation if the device really can take a car battery’s max output.
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If that datasheet is in fact accurate, then it also has all the information necessary to compute thermal safety limits, so if it will take 14v from a battery I can also make sure the regulator doesn’t fail due to overheating.
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I do have a variable bench supply and I could run it up to 14v and check temps with the IR thermometer. I don’t like that approach because it doesn’t address long-term circuit stress - for instance if the regulator has a “max” voltage of 16v I can likely run it on 20v at low current as long as I don’t mind severely reducing its usable life span. So knowing it “works” at 14v isn’t sufficient. I need to know what the specs are on the parts and Pro Mini itself.
Thanks for your time…
The SFE store says 12V http://www.sparkfun.com/products/9218
The schematic says 16V http://www.sparkfun.com/datasheets/DevT … 28-v11.pdf
The MIC5205 datasheet says 20V, but the note on the schematic could be due to capacitor ratings or something. I’d think it’d be ok on a 12V lead-acid battery. I suppose an over-achieving charging system could drive it up to more than 16V, but that’s a risk I’d probably take.
Page 8-9 of the datasheet gives you the maths to work out the max current/voltage you can draw from the regulator verses the input voltage whilst keeping within the max die junction temperature. 
Ragnorok:
- I want to run my Pro Mini from a standard “12v” car battery, which can actually put out near 14v on a fresh charge, but I’d prefer not to have to pre-regulate that “12v” just because it’s a few over the user grade literature. Yet this datasheet is the only reference I’ve seen that does not say 12v, which makes me leery of trusting it as the only data point that lists a limit I prefer. (grin)
Never, ever connect anything in an automotive application without LOTS of protection against spikes, load-dumps etc, or it won't last a day. Even if this is just the car battery, there's no way I'd just connect it to the battery without additional protection. Even with MOVs / Tranzorbs it isn't realistic to try to clamp a 12V supply to protect a regulator with 16V max rating (you don't want them conducting under normal operation, but they do have a finite impedance when they do start conducting). I suggest using a pre-regulator (say 9V), and clamping the input voltage to (say) 25V or so.
The “absolute max” voltage of the regulator might be 16V, but the figure of 12V is probably given more because of heat dissipation in the regulator than anything else.
JChristensen:
http://www.sparkfun.com/datasheets/DevT … 28-v11.pdf
- Totally missed this. (pout) I had v10. Thanks!
MichaelN:
Even if this is just the car battery, there’s no way I’d just connect it to the battery without additional protection.
- Hurm. I have to say I’ve never heard of horrid spikes from a stand-alone car battery, but that doesn’t mean I’m the be all and end all of car battery knowledge, and this argument smacks of reason. Gosh Darn! ™ I so don’t want to pre-regulate it, and the power draw will be well under the 150mA regulator limit.
sigh
Thanks all for your input!..
Ragnorok:
MichaelN:
Even if this is just the car battery, there’s no way I’d just connect it to the battery without additional protection.
- Hurm. I have to say I’ve never heard of horrid spikes from a stand-alone car battery,
Well, of course you are correct - a simple battery by itself won't have any voltage spikes. I was more thinking of the general lack of input protection that people (including Sparkfun) put on the power input to their designs. I've seen many, many cases where hardware was damaged by spikes, even in an apparently benign environment. As a bare minimum, no matter what the power supply, I include a tranzorb on the input of any board I design.