nice little switcher

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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 

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John Larkin
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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
Reply to
Winfield Hill

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 

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Reply to
John Larkin

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

Reply to
Klaus Kragelund

Yes, small is not always beautiful.

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 Thanks, 
    - Win
Reply to
Winfield Hill

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.

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 

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Reply to
John Larkin

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 

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Reply to
John Larkin

First hit on Digikey:

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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

Reply to
klaus.kragelund

You should sync the SMPS to you signal, to switch in the quiet periods

Reply to
klaus.kragelund
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

Reply to
klaus.kragelund

Vom = BoM

Reply to
klaus.kragelund

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 

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Reply to
John Larkin

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.

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

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John Larkin   Highland Technology, Inc   trk 

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Reply to
John Larkin

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

Reply to
Klaus Kragelund

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