17mm/22mm MTN-MAXlp - Low-Profile 1A-4A Programmable Buck Driver + 22mm MTN-MAX

227 posts / 0 new
Last post
Flintrock
Offline
Last seen: 3 years 9 months ago
Joined: 09/10/2016 - 20:29
Posts: 1544

Thanks.  I asked because of this:

http://budgetlightforum.com/node/49462#comment-1004493

 

An idea to use a Ti IC (that I think you recommended) for analog buck control. Better discuss there I guess to not split conversation.

The_Driver
The_Driver's picture
Offline
Last seen: 1 month 3 weeks ago
Joined: 10/20/2016 - 05:51
Posts: 1462
Location: Germany

Is there any way to make the high-power version run above 6A?
I would prefer 7A for a big light with XP-L which I have.

RMM
RMM's picture
Offline
Last seen: 1 year 7 months ago
Joined: 07/23/2013 - 13:47
Posts: 4006
Location: USA

The_Driver wrote:
Is there any way to make the high-power version run above 6A? I would prefer 7A for a big light with XP-L which I have.

I haven't tried it...it may or may not work.  I think that 6A is already pushing it pretty hard, but 7A may be possible.  Remember, that 7A will be the average current and that the peak current seen by the LED will be a bit higher than that, so keep that in mind (this is all assuming that the driver maintains stability at 7A, which it may not).  

Mountain Electronics : batteries, Noctigon, and much more! What's new? 

Flintrock
Offline
Last seen: 3 years 9 months ago
Joined: 09/10/2016 - 20:29
Posts: 1544

This 10% ripple thing is something I'm pretty curious about.  I don't know about your circuit but the application diagram for the MAX16820 shows no output cap, ie no cap in parallel with the load.  I get that the current sense/switch-control is histeretic, and that means just like a constant off time setup, it needs to sense real time fluctuations in the inductor current (difference is constant off time only triggers on the up pulse not up and down).  But an output cap shouldn't have a big effect on the inductor ripple current, and that sense resistor, while on the other side of the load in that diagram, should still effectively see the inductor ripple I think, not the load ripple if there's a cap.   (The cap probably has some effect on inductor ripple as the usual simple inductor ripple current equations assume a constant output voltage, but the fact we're driving diodes still keeps a reasonably close approximation to that anyway.)  It's certainly possible to get big inductor ripple current (which I suspect the histeretic circuit needs) and a low output ripple current at the same time anyway, in worst case might require a bit smaller inductor value or a bit lower switching frequency.

 

Not trying to redesign the driver here though.  What I'm wondering though is what happens if one were to wire a 10 or 20uF cap across the led's without modifying anything else?  Does it break your buck?  Might be worth a try for someone who really just has to squeeze the last drop out of their diode, but they still better have spare diodes to kill I guess.

 

RMM
RMM's picture
Offline
Last seen: 1 year 7 months ago
Joined: 07/23/2013 - 13:47
Posts: 4006
Location: USA

If you read the entire datasheet you'll see that they do indeed talk about an output capacitor to reduce output ripple, and I have implemented one into the design.  That said, you severely limit your moonlight capability if you go much bigger than 1uF, and if you go way too big you can compromise stability.  I can measure a reduction in output ripple up to 10uF, but more than that doesn't seem to help (at least not with the non-ideal capacitor size and PCB location).  

But remember that 10% ripple?  Yeah, that's if everything was running perfect, with an ideal PCB layout and ideal components; in the real world as you start to push things sometimes that ideal 10% grows far beyond 10%, so I always say 10% with the capacitor to give some safety margin.  This PCB layout is far from ideal, but here we have to work within the constraints of a 17mm PCB with pre-defined ground and battery input points, limited heatsinking---a far cry from the demo circuit.

Mountain Electronics : batteries, Noctigon, and much more! What's new? 

Flintrock
Offline
Last seen: 3 years 9 months ago
Joined: 09/10/2016 - 20:29
Posts: 1544

Ok, thanks.  Yeah, I'm definitely learning these bucks are complicated, and indeed when pushed hard one approximation breaks down and the rest all become nonsense too and the simple hopes of any hand calculations may be moot.

 

I guess this stability issue at high capacitance may be related to the histereitc feedback, or maybe I just hope.  The numbers I've crunched for the texas buck look optimistic that we'll be able to get low ripple, but I'm also well aware that there are tons of demons hiding in the corners of these bucks, so we'll just have to see.  Really while that IC is probably nicer, there are things I still don't like about it too, oh and predictions now are based on components we could fit on a 49mm board, not a 17mm or whatever board.

Flintrock
Offline
Last seen: 3 years 9 months ago
Joined: 09/10/2016 - 20:29
Posts: 1544

Oh that moonlight thing is a really good point too.  We're thinking on the LM3409 of ramping down to low current and then adding PWM to go super low from there.  It might be easier because the PWM won't have to take it as far, but still better think it through, or maybe just find out.  Thanks again for the detailed reply.

RMM
RMM's picture
Offline
Last seen: 1 year 7 months ago
Joined: 07/23/2013 - 13:47
Posts: 4006
Location: USA

I look back at my earlier efforts (like these drivers) and I realize how many mistakes I had to make to get to where I am now.  These work well enough, make no mistake, but if I had the time or patience I would do a complete redesign on these, but right now I lack both of those!

I haven't looked over at the Texas Buck yet at all, but I wish you luck.  TI has the best datasheets and the LM3409 is actually designed to handle some power and is much more versatile, which is why I recommended it to him.  I hope you waste less time and money because of the good datasheet and some of the work that has already been done.  

Mountain Electronics : batteries, Noctigon, and much more! What's new? 

Lopan
Offline
Last seen: 1 month 1 day ago
Joined: 08/02/2014 - 22:23
Posts: 77
Location: Germany
RMM wrote:

OK, finally got time to get the new 4L 17mm and 2L 22mm uploaded and shared.  Should I keep everything in this thread and just update the OP, or should I start something newer and tidier?  


17mm 4L v1.1 w/ ISP Programming (of course, more details to come)


 


22mm 2L v1.12



You will notice that besides the ISP on the 4L, there is a new part on the board.  I also need to update some of my component recommendations, especially those regarding inductors.

Have I missed the updated component recommendations or has it never happend because a lack of time?
I’m looking for a buck driver for my Convoy L2 and I think the MTN-MAX is still the best there is or have I missed something apart from having to either grind down the 22mm driver or build an adaptor for the 17mm driver with good heat transfer.

RMM
RMM's picture
Offline
Last seen: 1 year 7 months ago
Joined: 07/23/2013 - 13:47
Posts: 4006
Location: USA

Lopan wrote:
RMM wrote:

OK, finally got time to get the new 4L 17mm and 2L 22mm uploaded and shared.  Should I keep everything in this thread and just update the OP, or should I start something newer and tidier?  

17mm 4L v1.1 w/ ISP Programming (of course, more details to come)

 

22mm 2L v1.12

You will notice that besides the ISP on the 4L, there is a new part on the board.  I also need to update some of my component recommendations, especially those regarding inductors.

Have I missed the updated component recommendations or has it never happend because a lack of time? I'm looking for a buck driver for my Convoy L2 and I think the MTN-MAX is still the best there is or have I missed something apart from having to either grind down the 22mm driver or build an adaptor for the 17mm driver with good heat transfer.

Sorry, I never got around to updating the component list.  I really need to redo the entire main post since there have been so many changes over the years.  

There is also a 20mm driver again, but 4-layer this time and much better than the old 20mm design.  

Mountain Electronics : batteries, Noctigon, and much more! What's new? 

giorgoskok
giorgoskok's picture
Offline
Last seen: 6 days 21 hours ago
Joined: 11/13/2015 - 10:46
Posts: 2671
Location: Greece

Starting a new thread would be cool Smile Is this driver much more difficult to build than a fet/fet+1 etc driver ?

RMM
RMM's picture
Offline
Last seen: 1 year 7 months ago
Joined: 07/23/2013 - 13:47
Posts: 4006
Location: USA

giorgoskok wrote:
Starting a new thread would be cool Smile Is this driver much more difficult to build than a fet/fet+1 etc driver ?

I think that a new thread is in order at this point.  I've been so busy though lately that it has been hard to find time to do it.  

I would consider these to be much more difficult than a standard FET driver due to the small pin pitch no-lead components, number of components, and the fact that the 20mm and smaller are double sided.  

Mountain Electronics : batteries, Noctigon, and much more! What's new? 

giorgoskok
giorgoskok's picture
Offline
Last seen: 6 days 21 hours ago
Joined: 11/13/2015 - 10:46
Posts: 2671
Location: Greece

Thanks Richard . Take your time , i think we all can wait Smile

Lopan
Offline
Last seen: 1 month 1 day ago
Joined: 08/02/2014 - 22:23
Posts: 77
Location: Germany
RMM wrote:

There is also a 20mm driver again, but 4-layer this time and much better than the old 20mm design.  

A 20mm driver is just too good to be true. Great news.

I agree with giorgoskok, take your time, at least I can wait. Thanks for all the effort you put in these drivers.

Lexel
Lexel's picture
Offline
Last seen: 11 months 1 week ago
Joined: 11/01/2016 - 08:00
Posts: 5895
Location: Germany

As this driver is not longer available I stepped into it and designed my own 17mm Driver

I completely went from scratch just taking the same Max16820/16819 Chip,
Attiny13A MLF10 went to MLF25 Attiny 25/85 for more features and programming space
6mm spring pad to fit common BLF springs, where the MTN had 5mm

I also found that on many cases the 16819 is far better to get a relative low switching frequency
The 16820 is designed for 2Mhz the 16819 has with same values only 666kHz

Using the formulas from the data sheet to optimize part values on 3 examples

I have made here a BLF topic
It is an interest list to see how much parts I order from mouser beside from prototype ones

The design is with 2/4 Input capacitors and 1/2 3A fly back diodes depending on the output current

Tom E
Tom E's picture
Offline
Last seen: 7 hours 22 min ago
Joined: 08/19/2012 - 08:23
Posts: 14684
Location: LI NY

Dang, would have been great if you could get 2S 6 amps for the flat white W1. Can you do a little better than the 4.5 amps?

Pages