My New Favorite Switching Power Supply IC

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LTC3531-3.3 - Mouser Product page is at

 

https://www.mouser.com/ProductDe...

 

Attributes:

    Buck-boost, 1.8V to 5.5V in, 3.3V out up to 200mA (200mA only with Vin > 3V) Will work with LiIon, Alkaline, and NiMH batteries.

    ThinSOT23-6. Almost anyone can solder.

    Three external parts - 10uH inductor, 10uF or more output cap, 2.2uF or more input cap.

    Pretty good efficiency. Works well at very low load currents. Good transient response for intermittent high current loads.

    Easy to lay out for DIY board creators.

    Cost for IC is $5.04 USD from Mouser. A bit expensive! Available from DigiKey, Mouser, and others.

 

Given everything it does, I am not too dismayed by the price. If you just have to have one on a breakout board, I will have one or two extras by about March 1, 2020. PCB will fit on a standard spring proto board. Contact me via PM if you want info. Board layout is also available free on OSH Park (boards cost, of course, but less that $1 USD per board); contact me via PM for info about board layout & BOM.

 

Jim

 

Until Black Lives Matter, we do not have "All Lives Matter"!

 

 

Last Edited: Wed. Feb 12, 2020 - 08:08 PM
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I don't know... I think that I would rather go with a all-in-one $4 eBay special like this one:

 

It's got the two USB connectors, an adjust pot, mode push-switch, a 7-segment display for goodness sakes, a terminal connector, and might even use an IC of the same family.  I suppose that the LTC3531 solution uses much less space when the power supply is on a custom PCB.

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For battery powered applications, I don't think that would help all that much.

 

Jim

 

Until Black Lives Matter, we do not have "All Lives Matter"!

 

 

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Jim,

 

there are more manufacturers that have regulators like that. TI has a whole range. IIRC Maxim has a couple.

 

what I am curious about is what the output voltage will do when your input supply voltage gets close to or even is on the output voltage.

In the past we tested a couple ( that is a number of years ago ) and back then when the input and output got really close to eachother the output voltage would get a lot of noise on it as the regulators struggled to keep the voltage .

Back then we decided to put a second LDO behind the switcher to ensure our supplies were clean. So curious if that issue is solved in the mean time.

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On this device, there are 3 operating modes, buck, boost, and "close to output" which AD refers to as "4 switch mode". The circuit description addresses this situation. That was one  of the reasons I like it - operation is unambiguous when input is near output. Noise may be a bit higher there, but it does not seem extreme; with a load of 200ma, the spec sheet shows about 100mv pk-pk noise; at 100ma, it drops to about 50mv and about 30mV at 20ma. Four switch mode operates from Vout-400mV to Vout+800mV.

 

Jim

 

Until Black Lives Matter, we do not have "All Lives Matter"!

 

 

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That is indeed a nice part.  Thanks for sharing.

 

In fact you've inspired me to share a couple of nice switchers too.  Namely LT8650S and LT8609S.

 

Both are from Linear Tech's (Analog Devices') line of Silent Switchers (2nd Gen).  These have some built in goodness making it easy to comply with EMI standards.

What blows my mind is the current handling capacity.  The LT8650S is a dual buck converter with each channel capable of delivering 6A individually or 4A simultaneously.  And its in a 4mm x 3mm QFP package!  What's more is the 2 channels switch 180 degs out of phase allowing for the 2 outputs to be combined for a single 8A output, and further, a 90 deg sync signal allows 2 devices to be used as a single 4-phase 16A output!

 

Maybe a bit more power than you need Jim but then it does have a nice low (battery suitable) Iq of ~6uA to boot.

 

Cheers

Steve

Last Edited: Thu. Feb 13, 2020 - 06:35 AM
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ok, thanks, got them marked, if we ever need something like this I will go and get me some samples to play with :D

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Nice part! Run your gadget from an 18650 cell.

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