Searching for 3.3V low quiescent current regulator.

photomankc

I'm working on a Propeller based parallel to my Basic Stamp USB battery pack.· The basic idea is that it runs on 6 AA and provides the USB charging specs of 5VDC @ 500mA.· The·Stamp is there to monitor the battery pack voltage, display charge level when requested,·and cut the load before it's allowed to completely drain the batteries.· It also allows a user-configuable timeout that allows you to walk away and not have the·device under charge go into 'plugged-in' mode and drain the pack dry.··It works pretty well.· Only thing is that this is built on my homework board and a real design would include the nearly $50 for the stamp.

I also have a propeller breadboarded and I've been tinkering on it and have the basic battery monitor features working and I'll be adding the user interface in soon.· Thing is I have 3 of these chips and they cost all of $8 so I'm thinking it would be nice to get this working using the Prop.· What's killing me is that the whole idea was to be able to kill the battery-draining linear regulator I'm using for convieince and sleep at very low current.· The Stamp can do this with it's onboard regulator and thus it can stay awake and ready to turn back from sleep with input.· The propeller needs a 3.3V regulator and all the simple ones I can find draw around 2.5 to 3mA just to idle.· That's about 5 to 6 times above what I'd like to make sure that I get plenty of time to·replace the batteries before total exhaustion and polarity reversal and such.·

I have found a few switchers that idle at 500uA without asserting a shutdown line but they are surface mount so no way for me to work with them minus a PC board which I won't have.· Wondering if anyone has any suggestions on a through-hole type switcher that runs quiescent under 1mA.· I'm wondering if maybe a couple of boost switchers·might not be better and go with 3 AA series instead.· Then I run into the problem that 3 cells is too much for 3.3v boosters and 2 cells is not enough for multiple charges of USB powered devices.· My 6AA charger can charge the IPod Touch about 3 times and smaller devices even more and has enough voltage to stay above LDO requirements over the full range of discharge.· 2AA won't usually even get you 1 full charge of an iTouch.

My search has been frustrating so far.· Without that, I'm stuck with the Basic Stamp since it can sleep with very little power draw and no extra regulator is needed.· It's still helping me to learn with the Prop though even if I don't get a real·prototype going with it.

photomankc

Well I see someone just asked almost the same question.· The DigiKey search is the ticket.· LT wouldn't let me start with package options.· The LTC1174CN8 looks like the ticket if I can find some in stock where I don't have to order 500 of them.

Tracy Allen

You can order direct from www.linear.com in quantity of 2 or more at the 25 unit price. Just search for the part and click on the buy link.

I don't see right off why you don't use a linear regulator like the one on the Stamp (LT1121A), if the current demand is generally low for the application.

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Tracy Allen
www.emesystems.com

photomankc

Cause I didn't know about it in the TO92 package!··· 30uA operating Iq is very nice.··I thnk the 150mA limit would work.· Not much is going to riding the 3.3V side of the circuit.

sam_sam_sam

·I do not know if this is what you are looking for or not

This dose come in a 3.3 volt version

http://www.national.com/ds/LM/LM2676.pdf

I have use these regulator in two of my Projects and so far they work very well

Nuts and Volt Store has a project kit use this regulator but with a ADJ version but you can change it to a fixed 3.3 volt one

the only change is to leave out the ADJ pot and jumper two of the three pins

all of the parts come in the kit

I think these are nice little boards for the money one note they use LM2675 instead of LM2676

Here is the data sheet for the http://www.national.com/ds/LM/LM2675.pdf

Here is where you can buy one at··Digikey··· in search put·· LM2575T-3.3-ND or LM2675N-3.3-ND

Here is a site that you can buy a board with a 5 volt board and you could change the IC to a 3.3 volt one for· $ 6.97 board

http://www.futurlec.com/Mini_Power.shtml


I have use the 5 volt and the ADJ type I have 3.3 volt one but have not used it yet

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··Thanks for any··that you may have and all of your time finding them

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Sam

Post Edited (sam_sam_sam) : 8/7/2009 1:42:29 AM GMT

BradC

sam_sam_sam said...
I do not know if this is what you are looking for or not

This dose come in a 3.3 volt version

http://www.national.com/ds/LM/LM2676.pdf

I have use these regulator in two of my Projects and so far they work very well

They are hardly "low quiescent current" regulators. They consume at least a few mA by themselves when they are running.

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lt's not particularly silly, is it?

photomankc

Just a quick word of thanks for the nudge to the 1121A which·led me to the 1529-5 for the 5 volt USB line.· My project will work out well now.· Measured current with the Prop in RCSLOW waiting for a wake-up and the SHUTDOWN on the 1529 pulled low is 34 microAmps.· At that level it can run for weeks on a small reserve of the battery capacity.· Both regulators are darn good when running too, adding up to just about 3mA waste even with the device pulling 300 to 400mA.· I was giddy with that performance.· The total draw for·the prop and regs is about 16mA with the prop running at 40Mhz.· Not to bad at 5 to 7% waste at typical charging loads.· The 1529 also eliminated the need for extra shutdown circuitry and it's quiesent running current is about 40 microAmps so having it on and unloaded is a non-issue compared to the Prop now.

I just wish I could get rid of the 6AA's I require·and get to 4 but to do that I need a buck/boost 5V regulator and all the assorted bits to make it work.· For now I'm ok with using 1 1/2 AA's to feed the regulator.· If I decide to do anything more with it I think I'll have to get it down to 4 and go with a buck/boost type supply.

The prop stomps all over the Basic Stamp for idle current with RCSLOW but the·Stamp is·a couple percent·better at active running since it's·draw is around 5mA·vs 14 for the·Prop.· This has been a fun project to et working.· Now i need to solder it up and find an enclosure... a chore in it's own right.

Thanks for the help!·