Using a LDO to go from 13v DC to 3.3v DC, bad idea?

[ZeroAviation]

All,

I am building a little project, it will be used in the automotive environment so I know there will be a lot of AC noise from the alternator.

The project will consist of several LED's, STM32F4 MCU, Can Transceiver, and FT232... Should be about 800-900ma of current draw.

My question is, would it be ok to use a LDO such as MIC39100-3.3WS with a wide input voltage range to step down from 13-14vDC to 3.3V for VCC with plenty of filter caps? I'm thinking i will have about 9w of dissipation, which I think is probably too much to dissipate with the pcb.

I am tight on space, is there a better switching solution with a small inductor?

Thanks

[Dave_PT]

9W is a lot!
This regulator will not take it!

Use a step-down circuit. There are a lots to suit all tastes and prices.

Look for in this link the circuit that best suits what you want to do.

http://www.digikey.pt/products/en/integrated-circuits-ics/pmic-voltage-regulators-dc-dc-switching-regulators/739?FV=ffe002e3&mnonly=0&newproducts=0&ColumnSort=0&page=1&stock=0&pbfree=0&rohs=0&quantity=0&ptm=0&fid=0&pageSize=25

[retrolefty]

All,

I am building a little project, it will be used in the automotive environment so I know there will be a lot of AC noise from the alternator.

The project will consist of several LED's, STM32F4 MCU, Can Transceiver, and FT232... Should be about 800-900ma of current draw.

My question is, would it be ok to use a LDO such as MIC39100-3.3WS with a wide input voltage range to step down from 13-14vDC to 3.3V for VCC with plenty of filter caps? I'm thinking i will have about 9w of dissipation, which I think is probably too much to dissipate with the pcb.

I am tight on space, is there a better switching solution with a small inductor?

Thanks

 At that current requirement only a SM DC/DC regulator makes sense. Size of the inductor is dictated
by the current requirement, not negotiable. So it will either fit or have to go off board.

[Dave_PT]

For example the MC34063 is very cheap and simple to use.

I use it frequently...

[Dave_PT]

I am tight on space, is there a better switching solution with a small inductor?

If you find a DC/DC with a high working frequency (1 MHz for example), the inductors are smaller ...

[Dave_PT]

Have you looked at this regulator?

AP3211KTR-G1
http://www.diodes.com/_files/datasheets/AP3211.pdf

Do the math and see if it suits your project.

[JPortici]

one i'm going to play with is AP3211 (and the companion app note for design)
SOT23-6
1.5A peak
1 MHz frequency
then as already said inductor size is also a of acceptable ripple current/voltage
you may also do 3.6 - 4V then LDO

[mariush]

Use a switching regulator at a high frequency, which allows you to use small inductors and ceramic capacitors or polymer capacitors. If you go with ceramic capacitors, make sure you keep in mind the big fluctuations in temperature that may happen inside the box that will be in your car... the capacitance of ceramic capacitors could vary a lot with temperature.

Don't use cheap mc34063 and variations, it's ancient chip running at low frequency and with barely any protections.

Get something that can handle voltages higher than 13-15v, because you may have higher voltages at some moments due to car's alternator and other things.

Have a look at something like MIC4680 from Micrel / Microchip  or  CS5173 from ON Semi (which is pin-to-pin compatible with LT1372/1373 (that are great but more expensive)
 

[ZeroAviation]

Thank you all for your input!

I will go with the MIC4680, I have limited knowledge of switching regulators, but this one seems to be the best option! I will probably use a UP2B-680-R inductor, the size isn't terrible for my PCB footprint

Cheers!

[suicidaleggroll]

Make sure you put in PLENTY of protection on that input rail.  Automotive electrical systems are horrible environments for electronics.  The circuit should be able to handle up to 60V, down to ~6V, reverse voltage, and should be able to withstand brief pulses of +/- a couple hundred volts.  See here for more recommendations, especially regarding fusing, ceramics on the input rail, and large package parts (eg: 1206).

https://www.eevblog.com/forum/projects/design-of-automotive-electronics/

[langwadt]

All,

I am building a little project, it will be used in the automotive environment so I know there will be a lot of AC noise from the alternator.

The project will consist of several LED's, STM32F4 MCU, Can Transceiver, and FT232... Should be about 800-900ma of current draw.

My question is, would it be ok to use a LDO such as MIC39100-3.3WS with a wide input voltage range to step down from 13-14vDC to 3.3V for VCC with plenty of filter caps? I'm thinking i will have about 9w of dissipation, which I think is probably too much to dissipate with the pcb.

I am tight on space, is there a better switching solution with a small inductor?

Thanks

for a one-off a module like this http://www.ebay.com/itm/321829513465 is cheaper than the components,
just make a footprint for it and solder on board

[JPortici]

Ah! i missed the automotive part.
where will the board be located? all those LEDs and current make me think that it will be inside the body, not under the hood.
if this was the case the environment is much more forgiving
900 mA seems a lot even if you have a screen