nice little switcher

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https://www.digikey.com/product-detail/en/linear-technology-analog-devices/LTM8078IY-PBF/161-LTM8078IY-PBF-ND/10668252

It has a nice combination of input and output range, and the size is
insane: about 1/4" square. It will do forced synchronous, burst, or
synchronized switching.

I wonder if it can be persuaded to convert a positive rail to two
negative outputs. Sadly, LT Spice does not yet include a model for
this one. My designs often need a few negative supplies, and negative
switchers a neglected area.

I'd love to xray one of these. I can't imagine how they crammed the
inductors inside.



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John Larkin   Highland Technology, Inc   trk

jlarkin att highlandtechnology dott com
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Re: nice little switcher
John Larkin wrote...
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 I'll say, of course, connect the GND pin to your
 desired most negative output voltage, and Vout
 of that buck converter to ground.


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 Thanks,
    - Win

Re: nice little switcher
wrote:

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That works for one of the negative outputs. Make, say, -8 volts first
from +24, which is what I need now. But I also need -1.5. The second
regulator section has +24 as its V+ input, and -8 as its ground. If
its feedback pin is a resistor to ground, it thinks it's a +6.5 volt
reg riding on -8, with a +32 supply. I think that will work, but the
tolerance stackup is awful for the -1.5. I'm powering some THS4303
opamps at their abs max supply voltage, +4.5 and -1.5. The -8 is for
something else.

I could make, say, -8 and -2.5, and LDO the -2.5 down to -1.5, which
takes one more chip but is reasonably efficient.

Or use an opamp to create the feedback to the second switcher. Do the
math to make the second switcher really regulate to -1.5.

Hard to think about at 7AM and 6400 feet. I might Spice it with two
LTM8023's.




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John Larkin   Highland Technology, Inc   trk

jlarkin att highlandtechnology dott com
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nice little switcher
Why don?t you select another switcher?

It is expensive, has bad efficiency, hard to solder and what not

Could roll your own for a tenth of the price with a lot better performance
  

Cheers  

Klaus

Re: nice little switcher
Klaus Kragelund wrote...
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 Yes, small is not always beautiful.


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 Thanks,
    - Win

Re: nice little switcher
wrote:

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We want complex designs to work first pass. Design spins and added
time to market are expensive. Noisy switchers make jitter in fast
circuits. The LTM bricks are small and quiet.

I don't want to compromise a $4000 box by saving a few dollars.


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John Larkin   Highland Technology, Inc   trk

jlarkin att highlandtechnology dott com
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Re: nice little switcher
You should sync the SMPS to you signal, to switch in the quiet periods  

Re: nice little switcher
4000 USD is your sales price, right?  

With 5x mark up you are at 80

Production CTP is probably 10

So a 10 USD switcher would be 14% of your Vom

Cheers  

Klaus  

Re: nice little switcher
Vom = BoM  

Re: nice little switcher
On Thu, 26 Dec 2019 04:45:21 -0800 (PST), snipped-for-privacy@gmail.com
wrote:

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That 14% number is mostly meaningless. The absolute dollars are in the
noise. Besides, just one of the other parts costs $220. Our total BOM
is maybe $400 or so.

If the rev A board has jitter from EMI or ground loops or something,
it might cost $20K to spin the rev B board. The LTC things are really
quiet.


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John Larkin   Highland Technology, Inc   trk

jlarkin att highlandtechnology dott com
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Re: nice little switcher
On Wed, 25 Dec 2019 13:03:32 -0800 (PST), Klaus Kragelund



Because this one looks like the best choice for a few upcoming
projects. Very small timing or electro-optical boxes that need
multiple, efficient, quiet power supplies.

Quoted text here. Click to load it

The little LTM bricks are small and quiet and easy to use. This dual
switcher is really tiny (0.25" square) and costs about $9.50 at 100
pieces. Efficiency peaks at about 92%.

We don't have problems soldering BGAs. BGAs are generally more
reliable than most other packages.

I could roll my own dual spread-spectrum synchronous switcher for 95
cents? How?




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John Larkin   Highland Technology, Inc   trk

jlarkin att highlandtechnology dott com
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Re: nice little switcher
First hit on Digikey:

https://www.digikey.com/product-detail/en/microchip-technology/MIC28513-2YFL-T5/576-4885-1-ND/5216764

Add an inductor and cap and your set

For you 10 dollar switcher we do a complete motor control including RFI filter, PCB, power supplies, oh and also the motor and all pump hydraulics and mechatronics

But yes, we spend some time on it

Cheers  

Klaus

Re: nice little switcher
On Thu, 26 Dec 2019 01:08:24 -0800 (PST), snipped-for-privacy@gmail.com
wrote:

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That's a single buck for $2, without inductors. The LTC thing is a
dual with inductors for about $10. I'm not seeing a 10:1 cost
advantage here. Absolutely a loser on board area and probably EMI.

Quoted text here. Click to load it

Different market, obviously. What's your selling price/cost ratio?


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John Larkin   Highland Technology, Inc   trk

jlarkin att highlandtechnology dott com
We've slightly trimmed the long signature. Click to see the full one.
Re: nice little switcher
It might be just a 5 to 1 improvement, but the one I found was a turn key solution, no fiddling needed

If you do your own cost is a lot lower but as you stated dev cost is then significant

Standard industry mark up is 5 to 1 for a sound company  

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