a possible new source for drivers/DAC's

i was at a customers place today just BS'ing and he brought up this company when he saw my ddl driver.

Linear Technology - Linear Home Page

they have buck/boost, linear, and DAC's. it is too technical for me to read and see if it is useful here but hopefully one of you guys can.... also if it is good source of DAC's then please post link in the laser shows section.

michael

I got some samples from them, but most all of there stuff is voltage regulation and is in hard to solder packages.

I would like some more "professional" input though, a linear distribution office is around 20 miles from where I live. I was talking to them about a 10A driver for the red LED from the projector but I don't think it would work so good. The driver has a maximum current of 16A and I think that would leave way too much room for thermal runaway.

Any opinions, electronics pros?

The LT3477 looks interesting ... its a buck-boost converter with a built-in current sense amp and can go up to 3A. TSSOPs and QFNs are not as bad as you think to solder, you just need good flux on the pads and they will suck the solder blob right off you iron. Clean up any bridged pins with solder wick. The hard part is keeping it lined up on the pads until you get the first pin soldered.

jib77 said:

The LT3477 looks interesting ... its a buck-boost converter with a built-in current sense amp and can go up to 3A. TSSOPs and QFNs are not as bad as you think to solder, you just need good flux on the pads and they will suck the solder blob right off you iron. Clean up any bridged pins with solder wick. The hard part is keeping it lined up on the pads until you get the first pin soldered.

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I don't know how I missed that one, I'll have to ask the guy I'm talking to about it.

Im planning on getting some samples ... Ill start on a schematic & layout tonight.

UPDATE:

I guess this part is too new to be in any of the EaglePCB libs ... had to create my own part ... fun fun fun.

I finally got around to looking at the LT3477 datasheet and App Notes closely and ... Boooo! ... it requires LD- to be connected to Vin in Buck-Boost mode. No bueno for red diodes, but it would still make a good efficient boost drive for blue/violet diodes.

I'm having trouble understanding why that would be an issue, could you explain a little please?

They aren't connected to Vin in this diagram.



I think it just depends on the polarity of the devices your driving.

One thing I wonder is how clean the output of these is. LD's need much cleaner power than LED's, after all.

Pontiacg5 said:

I'm having trouble understanding why that would be an issue, could you explain a little please?

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Because on red diodes the LD- is not isolated from the case like 445 and BR.

qumefox said:

They aren't connected to Vin in this diagram.

I think it just depends on the polarity of the devices your driving.

One thing I wonder is how clean the output of these is. LD's need much cleaner power than LED's, after all.

Click to expand...

That schem is for boost only mode not buck-boost. In that mode you loose the ability to drive anything lower than your input voltage.

I see some of you dont know that almost all voltage regulators work as current regulators too.

I made my first Switching driver out of an voltage regultator, the LT3400.
Linear Technology - LTC3400 - 600mA, 1.2MHz Micropower Synchronous Boost Converters in ThinSOT






It worked pretty well but one day accidentally I powered it up from a lithium battery, and its now dead, anyway it worked pretty well.

The porblem with these drivers is that you have to isolate the aixiz from the rest of the case. Otherwise you set the FB pin at 0V wich means infinite current to the diode, consequently, dead diode.

LT3477 needs one big coil, and as jib said its only boost.

Btw if you want to drive one, for example, PHR, wich works at about 4.5V and 100mA from a AAA Ni-MH, you have to use some SOLID, I mean, SOLID contacs to the battery. It needs an intensity spike to start, and this means you need a GOOD tailcap switch.

There are WAY better regulator than LT3477.

So if you have not requested samples yet you may want to use another IC. I can post my schematics and PCB board for the LT3400 driver. It gives up to 600mA, not bad, huh?

Have a nice day.

And BTW PLEASE, DO NOT request samples if you don't need them.

Linear technology is a VERY well known company that produces very well known integrated circuits that perform really good.

I have quite some experience designing switching drivers and most of them have used integrated circuits from Linear.

Why would I discard LT3477?
Well it's a pretty good IC with some interesting features but...

1º Has a bipolar switch. Those are pretty good for handling high voltages at fairly large currents, but not so good at handling relatively low voltages at large currents. Power FET's are better for that.

2º Requires too many external components.

What I would recomend from linear is:
For reddies:
Linear Technology - LTC3490 - Single Cell 350mA LED Driver
For 445's:
Linear Technology - LTC3454 - 1A Synchronous Buck-Boost High Current LED Driver
For low powered blu-rays (up to 180mA or so):
Linear Technology - LT1930 - 1A, 1.2MHz/2.2MHz, Step-Up DC/DC Converters in ThinSOT
For high powered blu-rays:
LM3410 - 525kHz/1.6MHz, Constant Current Boost and SEPIC LED Driver with Internal Compensation
(that is from national)
For driving PHR's with a single AA cell:
MAX1722, MAX1723, MAX1724 1.5µA IQ, Step-Up DC-DC Converters in Thin SOT23-5
(the MAX1723)


All those IC's require very few external components and are very reliable.
There are more IC's out there, some of them with very interesting features, but those are the ones I love more.

Oh, just in case, current ratings for some IC's don't mean you can get that current from the IC under the conditions you're going to use them. That doesn't apply to LT3490 and LT3454. LT3490 is PROVEN to give 350mA's to a reddie from a single AA, and LT3454 is proven to give almost a full stable ampere to a 445 during about half of the discharge period of a lithium cell, and 800mA's during the whole cycle.

I just wonder what the world is like in 2045.

Well I just got word my prototype boards for a TPS63000 based driver have shipped. Well see how that pans out. It is slightly modified version of this: link

^Dont you etch your own boards?

Rafa said:

^Dont you etch your own boards?

Click to expand...

Nah ... I use Sunstone ValueProto service.