Best Way to go from 12V to 3.3V to power an MSP430G2231?

[777funk 0]

I'm going to be powering the chip mentioned from vehicle voltage power (10-14.5 Volts). Curious what I should use to get the voltage down to 3.3V?

 

I'm not concerned with battery savings or efficiency as much as I am with ease of use.

 

thanks!

Nick

[RobG 1,892]

LM1117 should work well for you. LM1117T-3.3 or LM1117T-ADJ (if you need 3.6V)

[chibiace 46]

i second lm1117t-3.3 and also suggest lm317

[Nytblade 24]

I am also working on a project that taps into the wiring in a vehicle. I am making something to switch a 12 volt light on and off.

 

Regarding voltage regulators, I found the linear regulator I was using was getting too hot when I tested it (LM2937ET I think). I got some DE-SW033 switching regulators from dimensionengineering-d0t-com*. I have not had a chance to use them yet though since I have been spending all my time learning how the MSP430 works.

 

I am not sure if the LM1117 would have the same heat problem or not. I a newbie at this stuff so I am still learning and have not really had time to go back and experiment with voltage regulators more to see which ones are best.

 

*(weird link due to forum spam filter).

[RobG 1,892]

Since we are on this subject, my two favorite LDOs are LM1117 (SOT-223 package) and TPS7xxxx (5SOT-23,) but couple of my projects required something in between, smaller package than SOT-223 and higher current than TPS7xxxx.

When placing my order with Avnet few days ago, I came across a perfect LDO for my use, AP1117Y33L-13 from Diodes. It's SOT-89 (unfortunately, TI does not make 1117 in SOT-89,) 1A, and 18V max Vin. And the best part, it's on sale for $0.14!

 

@Nytblade, you have to remember that the current your circuit draws times voltage drop (14V - 3.3V = 10.7V) cannot exceed regulator's maximum Pd (power dissipation.) If it does, you will have to use heat sink or switch to DC-DC converter.

For example, LM2937 TO-220 without a heat sink, can dissipate ~1W @ 60deg, which means your circuit can draw no more than 100mA (regulator will get really hot.)

[chibiace 46]

depending on your application you could use one of nationals simple switcher products then either smooth out the output with caps or a linear reg.

 

i have a launchpad running with a lm2576-3.3 just using their standard circuit though they arent exactly jelly bean parts.

[gordon 229]

Careful with vehicle power systems. oPossum tells me

Use a TVS, 35 or 50 volt cap, and automotive grade regulator.

It should tolerate 40V continuous, and shunt spikes above that.

So basically be ready for anything between <6V to 70+V on the input side. I faintly remember a TI app note about that, but all I can find at the moment is a DP post made of Unobtanium.

[TomKraut 17]

Here is what I would do:

 

get a cheap car USB charger from eBay, crack it open and then use something like a LM317 (easily obtainable LDO) to convert the 5V to 3.3V. That way, the nasty irregularities from the car supply have already been taken care of without you having to build a protection circuit yourself.

 

Cheers

TomKraut

[cde 334]

Here is what I would do:

 

get a cheap car USB charger from eBay, crack it open and then use something like a LM317 (easily obtainable LDO) to convert the 5V to 3.3V. That way, the nasty irregularities from the car supply have already been taken care of without you having to build a protection circuit yourself.

 

Cheers

TomKraut

 

Or realize that most of those regulators are variable based on a pair of resistors. Even the fixed ones tend to be variable if you ignore the tie-feedback-pin-directly-to-ground rule.

[777funk 0]

I actually had a package of 317's in my bin and used one. It got pretty hot and after a certain time dropped the voltage a bit until it cooled. Is it supposed to get this hot? MAybe I have something wrong in the circuit.

[RobG 1,892]

Yes, this is how linear regulators work, they turn excess power into heat. Attach a heat sink and you should be fine.

How much current does your circuit require?

[chibiace 46]

I actually had a package of 317's in my bin and used one. It got pretty hot and after a certain time dropped the voltage a bit until it cooled. Is it supposed to get this hot? MAybe I have something wrong in the circuit.

 

make sure you have stuff connected to the right pins,

 

the datasheet circuit may mislead you by saying Vi ADJ VO

 

while the chip's pinout ADJ VO VI :

 

and if you have quite abit of load its gonna heat up more.

[777funk 0]

I actually had a package of 317's in my bin and used one. It got pretty hot and after a certain time dropped the voltage a bit until it cooled. Is it supposed to get this hot? MAybe I have something wrong in the circuit.

 

make sure you have stuff connected to the right pins,

 

the datasheet circuit may mislead you by saying Vi ADJ VO

 

 

while the chip's pinout ADJ VO VI :

 

 

and if you have quite abit of load its gonna heat up more.

 

I did that by mistake when I first tested the regulator and chose resistors. Then I looked at the datasheet again when I couldn't get 3.5V for the life of me. moment at myself.

 

Still generating a lot of heat and I don't know if I have heatsinks. I'll have to look through the junk pile. I'm sure there are some that will fit in something.

[GeekDoc 226]

Yes, this is how linear regulators work, they turn excess power into heat. Attach a heat sink and you should be fine.

How much current does your circuit require?

If you're going from 12v to 3.3v, even a low amperage quickly adds up to a lot of heat to dissapate. :?

[RobG 1,892]

Yeah, that's why DC-DC converter should be considered if higher current is required.