really nice little switcher

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http://www.ti.com/product/tps54302?keyMatch=TPS54302&tisearch=Search-EN-Everything

The data sheet doesn't say much about thermals, and it looks scary to
me to make a 15 watt switcher in a SOT23-6 without a power pad, so I
got the eval board and tried it.

It's unusual in that it accepts 28 volts input and has internal
soft-start and spread-spectrum. And it's cheap.


https://dl.dropboxusercontent.com/u/53724080/Parts/VREGS/TPS54302/DSC06829.JPG

https://dl.dropboxusercontent.com/u/53724080/Parts/VREGS/TPS54302/DSC06826.JPG

https://dl.dropboxusercontent.com/u/53724080/Parts/VREGS/TPS54302/DSC06825.JPG

https://dl.dropboxusercontent.com/u/53724080/Parts/VREGS/TPS54302/DSC06828.JPG

https://dl.dropboxusercontent.com/u/53724080/Parts/VREGS/TPS54302/TPS54302EVB_WB.JPG

https://dl.dropboxusercontent.com/u/53724080/Parts/VREGS/TPS54302/TPS54302_rise.JPG

https://dl.dropboxusercontent.com/u/53724080/Parts/VREGS/TPS54302/IR_0057_3A.jpg


I think 3 amps is pushing this little guy pretty hard, but 2 amps,
maybe even 2.5, looks reasonable. I don't know where the heat comes
out... most likely pin 1, ground. I guess I'll put a lot of copper on
all the pins.




--  

John Larkin         Highland Technology, Inc

lunatic fringe electronics  


Re: really nice little switcher
On Thu, 01 Sep 2016 19:16:13 -0700, John Larkin

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Looks similar to their TPS6xxx inverting charge pumps. They work
pretty good too. Not much noise.

Cheers


Re: really nice little switcher
On Thu, 01 Sep 2016 22:23:41 -0400, Martin Riddle

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This one will work in the inverting configuration, but it can't quite
do +24 to -5... that's one volt over its abs max rating.

I can switch down to +5 with one of these, and flip it to -5 with one
more. I need some +5 anyhow.




--  

John Larkin         Highland Technology, Inc

lunatic fringe electronics  


Re: really nice little switcher
John Larkin wrote...
Quoted text here. Click to load it

 They don't mention inverting mode.  I always worry
 about using parts in the inverting mode if they
 do 100% duty cycle, when the output is lower than
 programmed, "the TPS54302 is designed to operate
 at 100% duty cycle as long as the BOOT to SW pin
 voltage is greater than 2.1 V."  You have to rely
 on a maximum-input-current shutoff.  They specify
 5A for that, which is pretty ugly.


--  
 Thanks,
    - Win

Re: really nice little switcher
wrote:

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That statement is sort of ambiguous.

 You have to rely
Quoted text here. Click to load it

I'll certainly have to breadboard that. It would be nice if it
inverts, and I didn't have to use another part. The soft start might
help.

The data sheet does lack a lot of details. We'll have to learn on the
bench, like the thermal tests.

Certain Parties want to add a winding to, say, the +5 switcher
inductor, and rectify that to make -5. Gotta think about that one.
I've done that before, but just to make a little bit of
not-well-regulated negative.



--  

John Larkin         Highland Technology, Inc

lunatic fringe electronics  


Re: really nice little switcher

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or this: https://www.maximintegrated.com/en/images/appnotes/3740/3740Fig05 .
gif



Re: really nice little switcher
On Sat, 3 Sep 2016 14:06:48 -0700 (PDT), Lasse Langwadt Christensen


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I've done that too; the negative output is the p-p input voltage minus
two diode drops minus other losses. That 5.6r resistor adds loss but
most switchers need it to prevent current-spike shutdown.






--  

John Larkin         Highland Technology, Inc

lunatic fringe electronics  


Re: really nice little switcher
John Larkin wrote...
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 Uggggh!  Throw up!

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 Use a coupled inductor.  Provide a Schottky
 diode on the plus side to match one on the
 minus side.  Symmetry is your friend.  Get
 better than 1% matching.


--  
 Thanks,
    - Win

Re: really nice little switcher
Quoted text here. Click to load it


Yup.  This.

Also works for non-synchronous converters, but you need a minimum load on  
the straight-through (buck) output.

Tim

--  
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Contract Design
We've slightly trimmed the long signature. Click to see the full one.
Re: really nice little switcher
"John Larkin"  wrote in message  

http://www.ti.com/product/tps54302?keyMatch=TPS54302&tisearch=Search-EN-Everything

The data sheet doesn't say much about thermals, and it looks scary to
me to make a 15 watt switcher in a SOT23-6 without a power pad, so I
got the eval board and tried it.

It's unusual in that it accepts 28 volts input and has internal
soft-start and spread-spectrum. And it's cheap.


https://dl.dropboxusercontent.com/u/53724080/Parts/VREGS/TPS54302/DSC06829.JPG

https://dl.dropboxusercontent.com/u/53724080/Parts/VREGS/TPS54302/DSC06826.JPG

https://dl.dropboxusercontent.com/u/53724080/Parts/VREGS/TPS54302/DSC06825.JPG

https://dl.dropboxusercontent.com/u/53724080/Parts/VREGS/TPS54302/DSC06828.JPG

https://dl.dropboxusercontent.com/u/53724080/Parts/VREGS/TPS54302/TPS54302EVB_WB.JPG

https://dl.dropboxusercontent.com/u/53724080/Parts/VREGS/TPS54302/TPS54302_rise.JPG

https://dl.dropboxusercontent.com/u/53724080/Parts/VREGS/TPS54302/IR_0057_3A.jpg


I think 3 amps is pushing this little guy pretty hard, but 2 amps,
maybe even 2.5, looks reasonable. I don't know where the heat comes
out... most likely pin 1, ground. I guess I'll put a lot of copper on
all the pins.
===============================================================================

Can't you just take a pic with your IR camera and see how hot each pin is  
where it enters the body?  If not on the eval board, do a proto with the  
same pad area at each pin and drive it just hard enough to make it warm up a  
little and see  which pin(s) get hottest.

-----
Regards,
Carl Ijames



Re: really nice little switcher
On Thu, 1 Sep 2016 22:47:30 -0400, "Carl Ijames"

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The pins themselves are shiny in the thermal IR, so their temperature
display is very wrong. I didn't quite have enough resolution to image
the epoxy around each pin. Maybe I'll paint the pins with something
with high emissivity to try to resolve pin temps. I wish I could image
the heat flow!

I probably don't need over 2 amps on any supply, so I'll just lay out
the real board. These are cheap enough that I can use a lot of them
for the various supplies.






--  

John Larkin         Highland Technology, Inc

lunatic fringe electronics  


Re: really nice little switcher
On 02/09/16 13:02, John Larkin wrote:
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The NXP RF PA's (see recent discussion) show some thermal photos
after the entire reference design was sprayed with a uniform black.
The actual paint used was unlike any black I've seen - I suspect
because it was extremely thin and high-conductivity, to avoid
changing the heat flow. Does anyone know what it is?

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You know the approximate thermal conductivity, and the heat flow
is just the temperature derivative multiplied by the conductivity.
Even just convolving the raw image to produce the derivative would
be enlightening. I think most image manipulation tools have such a
thing.

Clifford Heath.

Re: really nice little switcher
wrote:

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Black whiteboard marker seems to have high emissivity, and it wipes or
washes off easily without making a mess. I have a Testor model paint
set, and I suspect that's high e, so I could paint the pins and just
leave it that way. Most paints are high e.


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I'd need pretty high imaging resolution to see the temp gradient along
a pin. The FLIR could probably manage that, but not handheld! Maybe I
could hack up a tripod sort of thing to hold it steady. It would be
interesting to compara the temp gradients on all six pins.

But the heat flow will still depend on the board layout. TI should
better discuss heat flow on a SOT23 part that can switch 30 watts. Oh
well, playing with parts like this is fun, a break from being a
grownup.





--  

John Larkin         Highland Technology, Inc

lunatic fringe electronics  


Re: really nice little switcher
"John Larkin"  wrote in message  

wrote:

Quoted text here. Click to load it

Black whiteboard marker seems to have high emissivity, and it wipes or
washes off easily without making a mess. I have a Testor model paint
set, and I suspect that's high e, so I could paint the pins and just
leave it that way. Most paints are high e.


Quoted text here. Click to load it

I'd need pretty high imaging resolution to see the temp gradient along
a pin. The FLIR could probably manage that, but not handheld! Maybe I
could hack up a tripod sort of thing to hold it steady. It would be
interesting to compara the temp gradients on all six pins.

But the heat flow will still depend on the board layout. TI should
better discuss heat flow on a SOT23 part that can switch 30 watts. Oh
well, playing with parts like this is fun, a break from being a
grownup.
=========================================================================

I would be afraid of the variable thicknesses you will get with any kind of  
hand painting.  I'd just give it a light spritz with some aerosol flat black  
paint, from a foot or more away.  Should give a nice even coat, and you can  
hit it a few times if you think it's not dense enough.  Doesn't matter so  
much exactly what the emissivity is, so long as it is the same everywhere  
and much less shiny than the metal pins, and you are getting the same  
insulation value everywhere.  You should also be able to look at the package  
where the pins exit, instead of the pins, for an accurate temp (given  
sufficient resolution in the flir).  Anyway, just some thoughts since I knew  
you had that nice ir camera, but I should have known that you would already  
have tried it :-).

-----
Regards,
Carl Ijames



Re: really nice little switcher
On Fri, 2 Sep 2016 11:10:52 -0400, "Carl Ijames"

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The problem with the eval board is that the pins have various amounts
of heat sinking. A better thermal breadboard would have identical
traces on all pins, to estimate the heat flow from each. Too much
work. I'll just put lots of copper on the ground pin and the output
node, probably the main heat dumps, which I would have dome for
electrical reasons anyhow.  

This chip should come in a power-pad version.


--  

John Larkin         Highland Technology, Inc

lunatic fringe electronics  


Re: really nice little switcher
John Larkin wrote...
Quoted text here. Click to load it

 The datasheet, page 21, shows large copper areas
 for Vin and Gnd, and four vias on the SW pin to
 "internal SW node copper".  Those are the 3 pins
 connected to the MOSFETs.  Isn't that the SW pin
 that's overheating?  I see their PCB has a long
 SW trace before reaching 12 vias to a bottom
 trace, which it fails to make as big as it could.
 It should be easy to do better than that.


--  
 Thanks,
    - Win

Re: really nice little switcher
wrote:

Quoted text here. Click to load it

Pin 2, SW, looks hot in the IR image, but it has a long trace, which
confuses things.

The eval board layout looks fine at 2 amps, which is probably all I
need. It runs, pretty hot, at 3.5 amps out and thermal cycles at 4.

There are little cheap potted switching 78XX drop-in equivalents, and
they invert, so I could use one of them.

http://www.cui.com/product/power/dc-dc-converters/non-isolated/0.5-a-output-current/p7805-s-series


I'm trying to keep this box clean and simple, which is why this sort
of thing is appealing, as compared to making a Cuk or something with a
lot of parts.




--  

John Larkin         Highland Technology, Inc

lunatic fringe electronics  


Re: really nice little switcher
John Larkin wrote...
Quoted text here. Click to load it

 John, read my other comment and Tim's followup.


--  
 Thanks,
    - Win

Re: really nice little switcher
wrote:

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I just tested a CUI potted-blob 7805 style switcher, as a +24 to -5
converter.

http://www.digikey.com/product-detail/en/cui-inc/P7805-Q24-S5-S/102-2705-ND/4009632

This works great. It's hardly worth designing something when this is
under $5.

Here's measurements if anyone is interested:

https://dl.dropboxusercontent.com/u/53724080/Parts/VREGS/CUI_P7805.zip

This, plus the cute little TI synchronous switchers, pretty much
solves my zillions-of-rails power supply problems.





--  

John Larkin         Highland Technology, Inc
picosecond timing   precision measurement  

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Re: really nice little switcher
On Tuesday, 6 September 2016 21:51:53 UTC+2, John Larkin  wrote:
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Would be nice if someone took one apart and reverse engineered it.

Seems like a high price for a small switcher, maybe one should setup a company doing small switchers like that

Cheers

Klaus

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