17mm buck-boost driver (TPS63020 and LT6106)

[AnthoT]

So I haven't ordered anything yet, I go with the 0603 6.3V caps like the original ones?

 

[foulmist]

So I haven't ordered anything yet, I go with the 0603 6.3V caps like the original ones?

yeah go with the 22uF 0603V 6.3V caps

 

[AnthoT]

yeah go with the 22uF 0603V 6.3V caps

Alright :thanks:

 

[laserluke]

Hi AnthoT and foulmist,
i have prepared a simulation file for the driver that you can download here.
The file is for TINA-TI (a free spice simulator from TI). You can download it here.
The values i used for R5 and C7 are 5K, 2.2nF.
If you put a small inductor (100nH, for example the model SRP1235-R10M from Bourns) in series with the laser diode, the current ripple is dramatically reduced but it should be tried with TINA spice at several output current values.

EDIT: the source voltage model is changed

 

[foulmist]

aah that would be very nice thanks luke, I will look into it today :beer:

 

[foulmist]

I solved the issue with the voltage spike on startup! WOHOO!

It was just as I thought in the beginning!

See results:

vs.

 

[AnthoT]

Hi AnthoT and foulmist,
i have prepared a simulation file for the driver that you can download here.
The file is for TINA-TI (a free spice simulator from TI). You can download it here.
The values i used for R5 and C7 are 5K, 2.2nF.
If you put a small inductor (100nH, for example the model SRP1235-R10M from Bourns) in series with the laser diode, the current ripple is dramatically reduced but it should be tried with TINA spice at several output current values.

Thanks for making this :beer:

 

[laserluke]

Many thanks anthot and foulmist
i have found that there must be something wrong with the voltage source model... if you monitor the input voltage you'll find that is about 8V.
Please foulmist make a check...
...also you must not connect the supply voltage of the lt6106 to the battery because in the datasheet is stated that the V+ and V- inputs MUST not exceed supply voltage (the battery voltage is about 3.5-3.7V and the diode exceed 4.5V). The simulator cannot simulate a device fault...

 

[laserluke]

The source voltage model was wrong because the output voltage was 8V.
I have changed the schematic using a voltage source with 3.7V and 0.075 ohm internal resistance. The simulation is now correct.
The feedback network is now 470ohm and 10nF and the driver is stable over all the currents range with no self-oscillations (i have tryed it from 50mA to 2A).
The start overcurrent spike ends within 0.1ms.
The new file is here.
Foulmist, please try with this new one.

 

[foulmist]

Many thanks anthot and foulmist
i have found that there must be something wrong with the voltage source model... if you monitor the input voltage you'll find that is about 8V.
Please foulmist make a check...
...also you must not connect the supply voltage of the lt6106 to the battery because in the datasheet is stated that the V+ and V- inputs MUST not exceed supply voltage (the battery voltage is about 3.5-3.7V and the diode exceed 4.5V). The simulator cannot simulate a device fault...

ah damn. I though I solved it ok then I will try some other approach. Thanks for noting that Luke :beer:

 

[laserluke]

ah damn. I though I solved it ok then I will try some other approach. Thanks for noting that Luke :beer:

I have modified the schematic with the correct voltage source and new values for the feedback network.
Please read the previous post and use this new file for your simulations.

 

[foulmist]

EDIT: Output ripple decreased with replacing all the 22uF output caps with 47uF caps.
That will increase the bom cost and the design have to get some changes. The 47uF should be 1206 package. Check the pic.

Luke,

so far I got this:

adjustment of the R5 and C7 values only gave me an increased current ripple. (bummer) or no change at all. And I have tried over 100 different ones so far and I am not counting

I managed to FIX the overcurrent spike on startup by connecting all the output capacitors after the sense resistor instead of two before and one after as in the schem. Now the output rises smoothly BUT! that gives the output an increase in the current ripple! Not by much but it's worse than before

I am struggling to decrease that but I still have no luck I did this all DAY! haha will write back soon whether I give up or I found the solution. :beer:

here is a pic of no current spike on startup with increased ripple.

3x22uF after sense resistor.

3x47uF after sense resistor.

and just for reference: - low side current monitoring (THIS IS HOW THE OUTPUT SHOULD LOOK LIKE )

 

[laserluke]

EDIT: Output ripple decreased with replacing all the 22uF output caps with 47uF caps.
That will increase the bom cost and the design have to get some changes. The 47uF should be 1206 package. Check the pic.

Luke,

so far I got this:

adjustment of the R5 and C7 values only gave me an increased current ripple. (bummer) or no change at all. And I have tried over 100 different ones so far and I am not counting

I managed to FIX the overcurrent spike on startup by connecting all the output capacitors after the sense resistor instead of two before and one after as in the schem. Now the output rises smoothly BUT! that gives the output an increase in the current ripple! Not by much but it's worse than before

I am struggling to decrease that but I still have no luck I did this all DAY! haha will write back soon whether I give up or I found the solution. :beer:

here is a pic of no current spike on startup with increased ripple.

3x22uF after sense resistor.

3x47uF after sense resistor.

and just for reference: - low side current monitoring (THIS IS HOW THE OUTPUT SHOULD LOOK LIKE )

Tom,
many thanks for your efforts :wave:
A simpler way to reduce the ripple without pcb changes and increased costs, is to use the original schematic and connect a 100uF capacitor in parallel with the diode directly into the aixiz module.
Here is the results:

with an expanded scale...

As you can see the peak-to-peak ripple is less than 10mA, so we have a final result better of 0.55% (the best switching power supply in the market has usually 1%).
With the "low side current sensing" you loose much efficiency because you dissipates 0.9W in the shunt resistor versus 0.0324W with the "high side current sensing" (28 times less). So the battery discharges faster and we loose also the flexibility of a trimmer to regulate the current.
So it seems that, at the simulation level, we have the driver and any further trial is an unnecessary overkill.
I think that now we must only wait the anthot's boards

 

[foulmist]

yeah I know,

I was trying to eliminate the need to connect an additional capacitor to the diode. I tried with additional 150uF cap and the ripple was reduced very well but I was trying to avoid that

But did you move the caps that were before the sense resistor after it.. in the test or did you leave them there? Cuz the current spike is gone as I see? You must have moved them all after the sense resistor, right?

The original schematic was 2 before 1 after the Rsense. :thinking:

I know the low-side is a more unefficient method, I posted it for reference that the output is better.

 

[laserluke]

yeah I know,

I was trying to eliminate the need to connect an additional capacitor to the diode. I tried with additional 150uF cap and the ripple was reduced very well but I was trying to avoid that

But did you move the caps that were before the sense resistor after it.. in the test or did you leave them there? Cuz the current spike is gone as I see? You must have moved them all after the sense resistor, right?

The original schematic was 2 before 1 after the Rsense. :thinking:

I know the low-side is a more unefficient method, I posted it for reference that the output is better.

No, i have used the original schematic and simply placed a 100uF at the output.


I have modified the board to accept a bigger output capacitor (package 1206). The files in my first post at the top of this thread are now updated.


.

 

[laserluke]

Thanks for making this :beer:

Hi AnthoT,
do you have any new about the pcbs...