Pro Micro regulator issues

Development Boards Arduino
1

I’m trying to run a chain of LED matrices using the newer Pro Micro (DEV-11098) and some MAX7219 based circuits. When using an Arduino Pro Mini and a 5V regulator (from a 12V power source) the whole thing draws from 120-160mA. Since the Pro Micro is rated for 16V and can supposedly put out 500mA with it’s onboard MIC5219 regulator, I thought it might let me eliminate my external regulator.

However, when I supply the Pro Micro with 12.3V into RAW, the LED matrix chain will only run for about 4 seconds and then the Pro Micro resets, then run for another 4 seconds, resets etc.

Disconnecting some parts of my matrix chain (reducing the current needed to under 100mA) the Pro Micro runs with the smaller load just fine.

I then tested with a 9V battery connected to the Pro Micro’s RAW and the whole matrix chain runs perfectly. That’s odd. :think:

Does the MIC5219 regulator’s output current go down as the input voltage is increased or something?

2

No, the onboard regulator is probably overheating, shutting down, cooling off, powering up, heating up, shutting down, wash/later/rinse/repeat.

(12.3v - 5v = 7.3v…7.3v @ 160mA = 1.168watts of heat dumping off the regulator)

(9v - 5v = 4v…4v @ 160mA = .64watts of heat dumping off the regulator, almost 1/2 as much as the 12volt case)

For the heck of it, hook up the 12.3v source and blow on the regulator itself and see if it runs longer between resets.

3

Ah! That makes sense. I’ll try blowing on the regulator (when nobody’s looking!).

I wonder if I could clip the worlds smallest heatsink to it?

4

I’d doubt that would work. Small chip, not a lot of surface area to dissipate heat in the first place. 1 watt doesn’t sound like much, but it adds up if it can’t get outta there. Still might be worth a try if you can find the right piece of metal the slap on there.

If you WANT to run the board from 12v, get something like a 7808 (or 7809) regulator and preregulate the 12v down to 8 (or 9) volts. But, over time, maybe even mounted in a case, the 9v might even cause the onboard regulator to heat up also.

Also, if you look at the MIC5219 datasheet, page9, it shows that it’ll generate 220C per watt and a maximum temp of 125C. So, at an ambient temp of 25C, you’re only going to get 100C of temp rise before it goes into shutdown. At 220C per watt, limited to 100C, you’re looking at only .45watts of heat before you hit the limits (assuming a sealed case, no air blowing, no heat sink, no other copper on the PCB helping to dissipate heat, etc), which means at 160mA, you’d be limited to about a maximum of 8volts input.

8volts - 5volts = 3volts @ 160mA = .48 watts.

220C per watt = .48 * 220C = 105.6C.

(At 120mA…9v - 5v = 4v @ 120mA = .48watts…same end result at 9volts input)

It’s also a low dropout regulator, 500mV at full load, which means you could power it with 6v (preregulate 12v down to 6v with a 7806)…

6v - 5v = 1v @ 160mA = .16watts

220C per watt = 35.2C temp rise.

5

Yeah, those SMD regulators aren’t able to dissipate much heat so even a modest current with 7V or more drop will fry the Vreg. I’d look for a 6 or 7V wall wart. Maybe even a 5V WW with a low dropout Vreg will work. Thrift stores usually have a pile of wall warts for like $.50 ea.

6

Agreed, I’ll never get the onboard regulator running on 12V with this much current.

I was machining some acrylic and aluminum today, so decided to make a teeny heatsink that would just make contact with the regulator and Mega32U4 chip. It does allow the regulator to do it’s thing for a little longer; about a minute , maybe more if I could find my thermal compound. I lowered the intensity of my LEDs to give it a little more life too. Still not a solution, but it does look kind of cool…

7

OK, I’ll give that cool+ rating. Too bad it hides some pins.

8

Philba:
OK, I’ll give that cool+ rating. Too bad it hides some pins.

Thanks! They’re extra long pins and poke out just as much on the other side, so I tie into them there.

9

I’ll go with the cool points too…however…it’s not a very efficient heat sink.

Gotta have surface area…lots of it! Whether it’s from holes, slots, tabs, whatever. Gots ta have lots of surface area.

Drill some holes thru the side, thru the top, etc.etc. Bunches and bunches of tiny holes. Do that and your homemade heat sink might just do the job without breaking a sweat.