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A while back Chip designed a <a
href="https://oshpark.com/shared_projects/WRmW4AQU">little
breakout board</a> for this regulator chip that puts out a
constant 3.3v with about 2-5.5v input. Before going to the UK I did
a couple quick tests to see how the chip performed under heavy load,
finding that it very quickly shuts itself off due to overheating
when asked to put out it's rated maximum current in room air.<br>
<br>
Here's some data showing how hot the chip gets for a given input
voltage and a few moderate load current values. This is for board
"example 1". Hopefully these tests can be repeated with Chip's
examples two and three to see if there is variation due to how well
the chip's thermal pad soldered. We were cautious with the paste to
avoid bridging the .5mm lead pitch pins, but close inspection
suggested there was adequate solder available for the pad joint (and
this joint slurped solder off the traces connected to the pad,
suggesting it wetted nicely). <br>
<br>
But this is crude data just aimed at suggesting what applications
would be likely to work and what would be asking too much of this
board. The load was a piece of nichrome wire with alligator clips to
set the current. The current varied up to perhaps 2% as the wire
heated up and changed resistance. The input voltage was provided by
an LM2596S-based adjustable supply. The temp was measured with a
cheapo IR thermometer, holding it as close to the chip as possible
and giving each test case time to reach a final temperature. <br>
<br>
My takeaway is that for this example of the board I could use it
with a single lithium cell with confidence up to 200ma and after
that I'd have to consider what the ambient temperature conditions
might be. For example, with an almost flat battery and a 300ma
output it wouldn't take much in terms of ambient heat before the
package temp gets very high. Also notice that at 2 volts input the
chip dropped out of regulation, so with other battery types that
drop much below 2.5 volts that would be a problem. Interestingly, in
this case the chip made no attempt to regulate and didn't exhibit
the "run properly, then drop out, then run properly" cycles of
overheating/cooling I saw at much higher current levels, but in
those cases I was driving the thing with a much higher input
voltage.<br>
<br>
I did some checks at 50ma load levels but didn't bother plotting
them, as temperature rise was negligible. <br>
<br>
<img src="cid:part2.03000500.08070102@soper.us" alt=""><br>
<br>
-Pete<br>
<br>
<br>
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