What configuration is better to parallel two 5V SMPS

[Piet de Pad]

Dear readers,
I'm designing a small 5V SMPS which I want to use in a 5V parallel configuration. I want to use ORing Diodes but these give me a drop of 0,2..0.4 Volt. So I came up with and better solution, but I don't have experience with the solution I have in mind.

Below you see two buck converters. In SMPS[A] I have put the ORing diode in series with the output and in SMPS I have put the ORing diode before the FB resistor network. SMPS does not suffer from the 0.2..0.4 voltage drop. However in case the input voltage of B is zero the FB pin will have a voltage of around the FB voltage of 0.8V.

Assuming that both SMPS[A] and have input power the the combinations A-A A-B and B-B should work without a problem.

Assuming that SMPS[A] has input power SMPS has no power and is switched on after some time. The combinations A-A B-B will work but combination A-B I have my doubts about.

If B is powerless and has 0.8V at its feedback pin and ten starts up will that not generate trouble like latch up or some other issues I'm not aware of.

Now my question: does anyone have experience with this and can tell me if there are things I need to consider.

 

[BradtheRad]

Does your control IC have the ability to interleave two SMPS?

In other words does it have a pin which sends a second signal for switching a second buck converter On & Off? At opposite points in a cycle?

 

[cupoftea]

Use a Load share circuit....eg UCC2907. All it does , is measure output current of each stage...then has a bus between them, and on this bus, will go the output voltage of the current amplifier of the stage with the highest current.....the one with lower current will then up its game...
Ill send you a ltspice sim of it if you want.

Add a resistor in series with output divider, and make the error amp pull current through it as part of the sharing control.

 

[Piet de Pad]

Does your control IC have the ability to interleave two SMPS?

In other words does it have a pin which sends a second signal for switching a second buck converter On & Off? At opposite points in a cycle?

Hi Brad no unfortunatly not.

 

[Piet de Pad]

Use a Load share circuit....eg UCC2907. All it does , is measure output current of each stage...then has a bus between them, and on this bus, will go the output voltage of the current amplifier of the stage with the highest current.....the one with lower current will then up its game...
Ill send you a ltspice sim of it if you want.

Add a resistor in series with output divider, and make the error amp pull current through it as part of the sharing control.

Thanks I'll keep it in mind.

 

[cupoftea]

I can send you sim of it if you want?