combine DC current for the same voltage (3.3V)

[michcfr]

Hello,
I want to use the following power management system that has 4 synchronous Buck DC-DC converters: http://www.x-powers.com/en.php/Info/product_detail/article_id/61

Three of the 4 converters can convert to 3.3V with DC-DC1:3.3V/1A, DC-DC3:3.3V/1.2A, DC-DC4/3.3V/1.2A
Can we combine the current outputs of the three DC-DC synchronous converters to get 3.3V output at 3.4A (1A+1.2A+1.2A)?
If yes, advices on any precaution to take (diodes...)?

Thank you for your help,
Michel

 

[KlausST]

Hi,

I´d say it does ot work.

Why:
* Each power supply has it´s own regulation loop. It tries to maintain stable output voltage by adjusting output current.
* but each has it´s own setpoint. Although all say 3.3V, each has it´s individual tolerance, individual drift per time, per temperature and drawn current.
* no one knows what happens when all three are hard connected in parallel. Usually one will deliver the very most current, while the others are lazy. And for sure the one that delivers the most current will first go into overcurrent shutdown ... causing a domino effect.
* no one knows whether they are stable and during power up (1) and during normal operation.
* adding with diodes, may improve stability, but then the ouput is more 2.8V than 3.3V.
* adding with resistors, may also improve stability, but the power up problem still exist, and the voltage drop problem. Also one can not guarantee the current distribution to 1.0A and 1.2A..

(1) Some details to "paralleled power up situation"
I had a DCDC controller (expensive and very good brand) that did not like when the output voltage was normal (3.3V in your case), while the input was shut down for a short time. If I remember rigt, then this had to do with soft start, which was active at low output voltages. Since here the output voltage is not guaranteed to be close to zero (because the other supplies) the soft start never was activated ... causing an explosion of the SMPS IC.
This IC was not suitable for big capacitors at the output, or goldcaps, batteries, paralleled supplies.

Klaus

 

[danadakk]

There are specific featured power solutions that can sense buss
conditions and share. Usually found in open frame like supplies.
That usually involves at least one additional pin for sensing. A
review of this datasheet does not mention paralleling.

They have a application doc but my browser would not let me
look at it.

Regards, Dana.

 

[michcfr]

Thank you Klaus, Thank you Dana
My conclusion is that it is very tricky and uncertain to do such a thing.
I'll try to do it in a different way

thank you again