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

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

17mm / 20mm MTN-MAXlp

22mm MTN-MAX

The first "torture" subject! Cool (earlier PCB revision).

22mm MTN-MAX

THIS POST IS A WORK IN PROGRESS!

I will continue filling it out as time permits.  Please feel free to ask questions.  

Special Thanks!

First off, I need to give special thanks to all of those who have helped along the way with this project and many others.  I have learned how to do most of this stuff through the examples, successes, failures, and other contributions of many others on this forum and elsewhere.  

What Is It?

low profile 17mm/20mm 22mm (20mm temporarily pulled) fully programmable buck driver, with a 4A maximum reliable output (with proper heatsinking and care) and low voltage protection.  This driver is meant to fit in shallow 17mm pills, such as a P60.  There is another version of this driver [upcoming] that is possibly good for 5A+, but requires more pill depth.  The higher profile driver will also be higher efficiency at lower currents, due to the possibility of a bigger inductor. 

What LEDs does it work with?

It is generally designed for a 3V LED (please see the note about maximum amperage, below), but it can also be used with 6V LEDs with some limitations. The driver is thermally limited with 6V LEDs since the wattage passing through the driver is higher than with a 3V LED.  

I have not tested the upper limit yet with 6V LEDs, but with the 17mm driver I am guessing that ~3A is the upper limit with 3S input.  I have only thoroughly tested 2A with 2S and 3S input.  The inductor chosen will ideally be different for a 6V LED, especially with 2S cells, since the input and output voltages are closer together.  

Does It Work?

Yes. While there's no guarantee that it will work in your particular setup, or with your particular components, this driver has been tested thoroughly at currents from 2A up to 3.8A to the LED.  Anything above 3A requires particularly good heatsinking to the pill.  

Specifications:

  • Low profile (only [mm] total height height, without a spring)
  • Configurable for 1A to 4A peak output, depending on the inductor and sense resistor combination
  • Can be configured for 2S-6S cells (5V-28V), depending on the inductor and capacitors used
    • Efficiency decreases and as the difference between the input and output voltage increases
  • Can be used with pretty much any emitter configuration, provided that the input voltage is greater than the output voltage
  • Not recommended for momentary use (high quiescent current drain)
How to Program the MCU?

You need a special programming board.  I have provided one here.

Components Needed 17mm/20mm:
 
If you know what you're doing, you can substitute these parts for many others.  These are simply what I have used and know works, so if you want to venture outside of these specifications you are on your own!
  • RSENSE: Sense Resistor 
    • 17mm: 2010; 1W or Higher  
    • 20mm: 2512; 1W or Higher
    • Formula: 0.2/R=I
      • An Additional Word of Caution Regarding Maximum Amperage.  The MAX16820 is a hysteretic converter with a 10% current ripple, meaning that from the center, or average, current set point, the LED will momentarily experience an additional 5% current over the average set current.  This means that if you have an LED that can only handle 6A, you need to set the sense resistor at least 5% below that number.  
        • Example: 6.1A maximum LED, 0.033 Ohm resistor.  If all of the components were ideal and perfect, the 0.033 Ohm resistor should give us 6.06A average current.  This sounds safe, but it's not.  The LED will see peak currents of up to 6.36A, which will blow our theoretical 6.1A maximum LED.
      • You also need to take into account the precision of your sense resistor, temperature variances, and several other factors.
      • Summary: don't specify a sense resistor that is on the ragged edge of what the LED string can handle.  
    • ~2A = 0.1 Ohm
    • ~3A = 0.068 Ohm
    • ~3.4A = 0.058 Ohm
    • ~4A = 0.05 Ohm
  • CIN: Input Capacitor
    • 2S-3S cells: 1206, 10uF, 16V (or higher), X7R
    • 4S-5S cells: 1206, 10uF, 25V (or higher), X5R or better
  • CMAX: Buck IC Bypass Capacitor
    • 2S-3S cells: 0805, 10uF, 16V (or higher), X6S or better
    • 4S-5S cells: 0805, 10uF, 25V (or higher), X6S or better
  • C_OUT: Output Capacitor
    • Optional, can slightly lower ripple.
    • 0805, 1uF, 10V (or higher if needed for higher output voltage), X7R
  • CVCC; CMCU: LDO Output/MCU Bypass
    • 0603, 10uF, 10V (or higher), X5R or higher
  • OTC: Off-time Capacitor
    • 0805, 1uF, 10V (or higher), X7R
  • MCU: MCU attiny13a-MMU
  • MAX:  Buck IC
    • Maxim Integrated MAX16820
  • FET: Main Switch N-Channel MOSFET
    • NXP PSMN2R4-YLDX LFPAK33
  • D1: Flyback/Freewheel Diode
    • 17mm: Diodes Inc. SBR3U40P1-7
    • 20mm: Diodes Inc. PowerDI-5
  • L1: Inductor.
    • INDUCTOR CHOICE DEPENDS ON SEVERAL FACTORS
      • Difference between input and output voltage
      • Target switching speed (must stay within ~0.3MHz and ~1.5MHz, but as switching speed increases, switching losses also increase, decreasing efficiency)
      • Resistance vs. inductance vs. size (you can usually only have two of these, so you have to prioritize based on the application and size restraints)
      • Inductor must be able to handle the peak inductor current without saturating
    • MAXIMUM SIZE= ~6mm x 6mm.  Pads are designed to allow many different inductors to fit and work.  I have tested this driver with over 10 different inductors with different pad layouts.
    • RECOMMENDED INDUCTORS:
      • Coilcraft XAL series inductors are the best performance for their size, but they are also the most expensive, at around $2.50 each, plus shipping.  The XAL6060 series work great!
      • Other inductors from Abracon, Bourns, and others will also work, but generally have more on resistance for a given inductance and size
      • 2S Cells:
        • 1A: 15uH-22uH
        • 2A: 8.2uH-11uH
        • 3A: 6.8uH-8.2uH
        • 4A: 4.7uH-6.8uH
      • 3S Cells:
        • 1A: 18uH-22uH
        • 2A: 8.2uH-15uH
        • 3A: 6.8uH-10uH
        • 4A: 4.7uH-8.2uH
  • R1: 36K 0603 1% (or better)
  • R2: 
    • 2S-3S: 4.7K 0603 1% (or better)
    • 4S-5S: 2K 0603 1% (or better)
  • RDIM: 100/200 ohm 0603
  • PLDN: 19.1K 0603 (helps with mode switch timing; can also use 4.7K if faster switching is desired)
Components Needed 22mm:
 
If you know what you're doing, you can substitute these parts for many others.  These are simply what I have used and know works, so if you want to venture outside of these specifications you are on your own!
  • RSENSE: Sense Resistor 
    • 22mm: 2512; 1W or Higher
    • Formula: 0.2/R=I
      • An Additional Word of Caution Regarding Maximum Amperage.  The MAX16820 is a hysteretic converter with a 10% current ripple, meaning that from the center, or average, current set point, the LED will momentarily experience an additional 5% current over the average set current.  This means that if you have an LED that can only handle 6A, you need to set the sense resistor at least 5% below that number.  
        • Example: 6.1A maximum LED, 0.033 Ohm resistor.  If all of the components were ideal and perfect, the 0.033 Ohm resistor should give us 6.06A averagecurrent.  This sounds safe, but it's not.  The LED will see peak currents of up to 6.36A, which will blow our theoretical 6.1A maximum LED.
      • You also need to take into account the precision of your sense resistor, temperature variances, and several other factors.
      • Summary: don't specify a sense resistor that is on the ragged edge of what the LED string can handle.  
    • ~2A = 0.1 Ohm
    • ~3A = 0.068 Ohm
    • ~3.4A = 0.058 Ohm
    • ~4A = 0.05 Ohm
    • ~5A = 0.04 Ohm
    • ~5.5A = 0.036 Ohm
    • ~6A = 0.033 Ohm
  • C1: Input Capacitor
    • 2S-3S cells: 1206, 10uF, 16V (or higher), X7R
    • 4S-5S cells: 1206, 10uF, 25V (or higher), X5R or better
  • C2: Input Capacitor (optional)
    • 2S-3S cells: 0805, 1uF, 16V (or higher), X7R
    • 4S-5S cells: 0805, 1uF, 25V (or higher), X5R or better
  • CMAX: Buck IC Bypass Capacitor
    • 2S-3S cells: 0805, 10uF, 16V (or higher), X6S or better
    • 4S-5S cells: 0805, 10uF, 25V (or higher), X6S or better
  • C_OUT: Output Capacitor
    • Optional, can slightly lower ripple.
    • 1206, 1uF, 10V (or higher if needed for higher output voltage), X7R
  • CVCC: LDO Output
    • 0805, 10uF, 10V (or higher), X5R or higher
  • CTINY: MCU Bypass
    • 0805, 10uF 10V (or higher), X5R or higher
  • OTC: Off-time Capacitor
    • 0603, 1uF, 10V (or higher), X7R
  • MCU: MCU attiny13a-MMU
  • MAX:  Buck IC
    • Maxim Integrated MAX16820
  • FET: Main Switch N-Channel MOSFET
    • NXP PSMN2R4-YLDX LFPAK33
  • D1: Flyback/Freewheel Diode
    • 22mm: Diodes Inc. POWERDI-5
  • L1: Inductor. 
    • INDUCTOR CHOICE DEPENDS ON SEVERAL FACTORS
      • Difference between input and output voltage
      • Target switching speed (must stay within ~0.3MHz and ~1.5MHz, but as switching speed increases, switching losses also increase, decreasing efficiency)
      • Resistance vs. inductance vs. size (you can usually only have two of these, so you have to prioritize based on the application and size restraints)
      • Inductor must be able to handle the peak inductor current without saturating
    • MAXIMUM SIZE= ~6mm x 6mm. 
    • RECOMMENDED INDUCTORS:
      • Coilcraft XAL series inductors are the best performance for their size, but they are also the most expensive, at around $2.50 each, plus shipping.  The XAL6060 series work great!
      • Other inductors from Abracon, Bourns, and others will also work, but generally have more on resistance for a given inductance and size
      • External inductors also supported with through-hole vias
      • 2S Cells:
        • 1A: 15uH-22uH
        • 2A: 8.2uH-11uH
        • 3A: 6.8uH-8.2uH
        • 4A: 4.7uH-6.8uH
        • 5A: 4.7uH-6.8uH
        • 6A: 4.7uH-6.8uH
      • 3S Cells:
        • 1A: 18uH-22uH
        • 2A: 8.2uH-15uH
        • 3A: 6.8uH-10uH
        • 4A: 4.7uH-8.2uH
  • R1: 36K 0603 1% (or better)
  • R2: 
    • 2S-3S: 4.7K 0603 1% (or better)
    • 4S-5S:2K 0603 1% (or better)
  • RDIM: 200-4.7K ohm 0603
  • PL: 19.1K 0603 (helps with mode switch timing; can also use 4.7K if faster switching is desired)
Firmware:

Use any attiny13a firmware, but one with low voltage protection is recommended.  Momentary use not recommended.

Oshpark PCB Link:
 
20mm - v1.01 (temporarily pulled --- need to change layout)
 
MTN PCB Link:
22mm - v1.01

Parts Shopping Cart Links:

17mm v1.01 Mouser - 2S-3S Cells - NO INDUCTOR OR SENSE RESISTOR

17mm v1.01 Mouser - 2S-5S Cells NO INDUCTOR OR SENSE RESISTOR

17mm v1.01 MTN Electronics - 2S-3S Cells

20mm v1.01 MTN Electronics - 2S-3S cells

 

 

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Edited by: RMM on 07/18/2015 - 17:35
zeremefico
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Sweet…
This fills the buck driver gap.

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Blazer296
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Sorry… got a little excited there.
Been waiting for this one.

May just have to try my hand at building a driver soon.

Jim

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subscribed and waiting on the higher amperage one too! Good work Richard.

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Been waiting for something like this for years. Keep up the hard work! Did you ever consider going to school to be an EE?

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Richard, thanks.

Let us know when (we the build challanged) can buy this/these from your store?

I have three s7 hosts which I want to get drivers for along with incidentals.

  1. a triple using the XP-E 660nm Photo Red emitters (probably a different driver)
  2. a MT-G2 with 2× 18350 (this driver)
  3. a (other)

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things would be a lot more complicated than they already are.”
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Ronin42 wrote:
Richard, thanks.

Let us know when (we the build challanged) can buy this/these from your store?

I have three s7 hosts which I want to get drivers for along with incidentals.

  1. a triple using the XP-E 660nm Photo Red emitters (probably a different driver)
  2. a MT-G2 with 2× 18350 (this driver)
  3. a (other)

You shouldn’t need this buck driver for #2. MT-G2 runs off 6V which you have with the 2 18350 batteries. Any of the Zener modded drivers should suffice for that. This buck is going to drop the voltage of multiple cells down to 3v so that you could run something like a XM-L2 off multiple cells in series.

Three tomatoes are walking down the street- a poppa tomato, a momma tomato, and a little baby tomato. Baby tomato starts lagging behind. Poppa tomato gets angry, goes over to the baby tomato, and smooches him… and says, Catch up.

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I’ve been waiting this for too long! Thanks for bringing this 17mm high current capable buck driver to us Richard! Beer

I am waiting for the release of the 6A version for my 1405… and nope, I’m not gonna build this driver by myself but I will order one from mtnelectronics directly. I hope you will offer them as a complete driver in the future Richard. Smile

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Ordered, along with one of those mmu programming boards.

Still looking forward to your other versions. This is good stuff Richard.

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Major Projects:  Illuminated Tailcap, TripleDown/TripleStack Driver

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n10sivern wrote:
Ronin42 wrote:
Richard, thanks.

Let us know when (we the build challanged) can buy this/these from your store?

I have three s7 hosts which I want to get drivers for along with incidentals.

  1. a triple using the XP-E 660nm Photo Red emitters (probably a different driver)
  2. a MT-G2 with 2× 18350 (this driver)
  3. a (other)

You shouldn’t need this buck driver for #2. MT-G2 runs off 6V which you have with the 2 18350 batteries. Any of the Zener modded drivers should suffice for that. This buck is going to drop the voltage of multiple cells down to 3v so that you could run something like a XM-L2 off multiple cells in series.

Richard does sell a 20mm 6 volt 3 amp buck driver. I bought one to try on a XHP50 upgrade on one of my lights that can’t take the heat of a fet driver. Also I was too lazy to zener mod a 105E driver. :bigsmile:
LD-2D 2 or 3 Cell Driver – 20mm – For 6V LEDs – 3A

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Slim Pickens wrote:
Did you ever consider going to school to be an EE?

At this point in my life I think I'm about ready to be done with school!  I have a biology degree where I did learn a little bit about basic electronics in physics, and now I'm finishing up law school.  I did consider going back afterwards to get an EE degree or CS degree because those are very desirable in the patent law field, but after I decided not to pursue patent law I decided not to go back.

Besides, I just do this stuff mainly because I enjoy doing it.  I don't know if I'd enjoy it as much if it were a "real job".  I'm sure that a real EE would just laugh at some of my attempts, because these drivers are really simple compared to some of the products we use every day.  I design these drivers at lunch time and when I get a few spare minutes, so I usually move pretty slow.

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crap! we need an EU warehouse!!!!!

Mooooooo

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thanks Richard. I appreciate you putting this out there for the BLF community. Ordered the boards and the MMU breakout board that pilotdog reminded me of!! Beer

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n10sivern wrote:
subscribed and waiting on the higher amperage one too! Good work Richard.

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OSH spamers Big Smile

 

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subscribed and waiting on the higher amperage one also! Kudos to Richard for this fantastic resource. Wonderful vendor.

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cant wait for other versions! twenty and 22 mm versions would be cool

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nickzom wrote:
cant wait for other versions! twenty and 22 mm versions would be cool

For 20~22mm size we already have the LD-29 (about 21mm) which is capable to handle and deliver high current.
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Or you could plant this on a 22 mm contact board

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i need more than 3a though. 6a would be good. or more

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Rufusbduck wrote:
Or you could plant this on a "22 mm contact board":https://oshpark.com/shared_projects/vDNmPf9B[/quote]

I wouldn't recommend using this with a contact board, as it relies on having a direct thermal path between the ground ring and the pill, either by use of a retaining ring or solder to transfer the heat from the driver.  Any intermediate piece, especially another PCB, will limit the transfer to some extent. 

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Looks great RMM.  You know much more about this stuff than me.  So I apologize if this is a dumb suggestion.  I find that the fly back diode to be a limiting factor in some buck drivers.  Maybe the inductor size you are limited to space wise is more of a bottleneck, but it looks like you have room to add a parallel to D1.

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ImA4Wheelr wrote:

Looks great RMM.  You know much more about this stuff than me.  So I apologize if this is a dumb suggestion.  I find that the fly back diode to be a limiting factor in some buck drivers.  Maybe the inductor size you are limited to space wise is more of a bottleneck, but it looks like you have room to add a parallel to D1.

Extreme high power isn't the point of this board.  An extremely low profile along with programmability and reliability was the design goal; the other board (still to be released) is for higher power.  

In a small SMD inductor there is a lot of resistance, and with that resistance comes a lot of heat at high currents.  You also have to deal with core saturation on a small inductor like this, although it would tolerate 5A-6A.  That is why there is two versions of the board: one for low-profile applications, and another that is for pills with a bit more room for an external inductor that can run more current due to its lower resistance and getting the heat away from the board (and also has a bigger diode).  I didn't stick a huge diode on here because it simply isn't needed for what my design goal was (3.5A-4A), is smaller, and is less than half the price of a bigger diode.  

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RMM wrote:

Rufusbduck wrote:
Or you could plant this on a 22 mm contact board wouldn’t recommend using this with a contact board, as it relies on having a direct thermal path between the ground ring and the pill, either by use of a retaining ring or solder to transfer the heat from the driver.  Any intermediate piece, especially another PCB, will limit the transfer to some extent. 

Would a copper ring soldered to the annular ring be ok?

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Scott

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Rufusbduck wrote:

Would a copper ring soldered to the annular ring be ok?[/quote]

I'm sure it would be.  That said, if you're patient you'll get a 20mm soon that can do 5A+ with a bigger inductor and diode on board.  It will also be slightly more efficient due to the slightly bigger inductor, so if you want to do 20mm I'd wait.  

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RMM wrote:
if you’re patient you’ll get a 20mm soon that can do 5A+ with a bigger inductor and diode on board.  It will also be slightly more efficient due to the slightly bigger inductor, so if you want to do 20mm I’d wait.  

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BTW, I am currently testing a few different 17mm revisions setup for more power, but I don't generally release anything that I haven't personally built and tested.  I don't have time to support and post on many "WIP" types of threads.  The general rule is that if I've shared it, it's actually been built and tested.  It doesn't mean it will be perfect, but that if properly built it will work.

If you want maximum performance and efficiency you really need a Coilcraft inductor (XAL series).  Their small inductors blow away everything else in similarly sized packages.  They are almost three times the price of an Abracon or Bourns, but if you really want a 5A+ 17mm driver with an SMD inductor, I think it's the only way to go.  

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I ordered from OshPark today so I threw three of these in my cart as well

Also placed an order with RMM today. Richard, please check my note and get back to me if there is a problem with the resistors I’m using.

Three tomatoes are walking down the street- a poppa tomato, a momma tomato, and a little baby tomato. Baby tomato starts lagging behind. Poppa tomato gets angry, goes over to the baby tomato, and smooches him… and says, Catch up.

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ill be waiting on a parts list so i no im ordering the right parts Smile

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RMM wrote:
I’m sure it would be.  That said, if you’re patient you’ll get a 20mm soon that can do 5A+ with a bigger inductor and diode on board.  It will also be slightly more efficient due to the slightly bigger inductor, so if you want to do 20mm I’d wait.  

Hi Richard, as I read your OP I thought you’re working on a 17mm buck driver which can deliver 5A+ current (with bigger inductor), instead of 20mm isn’t it?
pilotdog68
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I believe he’s doing both

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I believe he is designing 17mm low and high current drivers. It shouldn’t take much to extend the borders for the OshPark boards so he will probably release 20mm as well, but the goal is the 17mm boards as there is more of a need for them.

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