Forums

nice little switcher

Started by John Larkin December 25, 2019

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.



-- 

John Larkin   Highland Technology, Inc   trk

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

John Larkin wrote...
> >https://www.digikey.com/product-detail/en/linear-technology-analog-devices/LTM8078IY-PBF/161-LTM8078IY-PBF-ND/10668252 > > I wonder if it can be persuaded to convert a > positive rail to two negative outputs.
I'll say, of course, connect the GND pin to your desired most negative output voltage, and Vout of that buck converter to ground. -- Thanks, - Win
On 25 Dec 2019 06:52:24 -0800, Winfield Hill <winfieldhill@yahoo.com>
wrote:

>John Larkin wrote... >> >>https://www.digikey.com/product-detail/en/linear-technology-analog-devices/LTM8078IY-PBF/161-LTM8078IY-PBF-ND/10668252 >> >> I wonder if it can be persuaded to convert a >> positive rail to two negative outputs. > > I'll say, of course, connect the GND pin to your > desired most negative output voltage, and Vout > of that buck converter to ground.
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. -- John Larkin Highland Technology, Inc trk jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Why don&rsquo;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
Klaus Kragelund wrote...
> > 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.
Yes, small is not always beautiful. -- Thanks, - Win
On 25 Dec 2019 13:12:19 -0800, Winfield Hill <winfieldhill@yahoo.com>
wrote:

>Klaus Kragelund wrote... >> >> 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. > > Yes, small is not always beautiful.
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. -- John Larkin Highland Technology, Inc trk jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
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
You should sync the SMPS to you signal, to switch in the quiet periods 
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 
Vom = BoM