LM25184: Adding Current Limiting to this part?

Hi Johny,

I deleted my post that was the answer, and it looks like it deleted your post.

I'll look into it.

Thanks,
Andrew

Hello,

This section talks about regular operation, and how the device will switch normally:

This section describes what happens if the output drops below the regulation level, and the device hits the peak output of the internal FET:

Does this answer your question?

Thanks,

Andrew

Would a current limiter on the secondary side confuse the regulator?

Can this regulator power multiple transformers, each supplying a separate galvanically isolated load?

If i put current limiters on each secondary, and the loads are drawing different amounts of current, will that confuse the SMPS?

Generally I don't think it's advisable to have 1 FETs powering multiple magnetics. I think what you might be looking for is the fly-buck topology, but one of the loads isn't galvanically isolated. Multiple sets of secondary windings is potentially more preferable.

Also The feedback resistor network isn't setting a voltage, but rather feeding a current (section 7.3.3). So, something like LMP8646 won't be helpful for this device. I'm not sure what you plan on using for a current limiter.

One way a colleague was suggesting using a current limiter and logic to switch the enable pin on and off as an alternative to the internal current limiter of the device.

 Thanks,
Andrew

Andrew Kutzler said:

I don't think it's advisable to have 1 FETs powering multiple magnetics

Why?

This arrangement on the LM25184 output was recommended by an EE. Tho i'm not sure these outputs are galvanically isolated from each other.
They appear to share grounds. 

Andrew Kutzler said:

fly-buck topology, but one of the loads isn't galvanically isolated

Which one?

Andrew Kutzler said:

Multiple sets of secondary windings is potentially more preferable.

Why?

Andrew Kutzler said:

not sure what you plan on using for a current limiter.

Could be an LDO, could be TL431, could be CLD.

www.bristolwatch.com/.../TL431A3.htm

https://www.centralsemi.com/files/manager/Engineering/Whitepapers/Boosting_the_CLD.pdf

Andrew Kutzler said:

current limiter and logic to switch the enable pin on and off

But that that would limit current of the regulator output, not individual secondaries, correct?

thx!

Hi Johny,

Here's the flybuck topology.

Here's a topology with multiple windings

johny radio said:

This arrangement on the LM25184 output was recommended by an EE. Tho i'm not sure these outputs are galvanically isolated from each other.
They appear to share grounds. 

Could you link the source on this for me to review?

I'll discuss with my team with the other points.

Thanks,

Andrew

Andrew Kutzler said:

Could you link the source on this for me to review?

I think to obtain galvanic iso between series trafos, we just need to remove those common ground connections.

EDIT: Yes, confirmed by the other EE. The secondary grounds should not be connected to ea other.

Andrew Kutzler said:

Here's the flybuck topology.

That looks similar to the LM2584 circuit. 

Hi Johny,

The main reason why I wouldn't mess around too much with topologies (2 transformers in series or parallel) other than the recommended ones is because the device is not optimized to have good control loop stability with them. I would triple check the spectrum analyzer bode plot when you verify your design. 

For this image is the LM25184 on the left or the right? It might theoretically be possible, but it's up to you to verify the design works.

johny radio said:

Could be an LDO, could be TL431, could be CLD.

I'm not sure how any of these will provide the on-the-fly current limiting you are requesting. Remember that you also have to level shift the control signal to galvanically isolated control topologies which will require additional circuitry. I'm not sure how this is advantageous over using 2 separate LM25184's for your loads and controlling them with the EN pin. That requires no level shifting or current limiting at the load.

Thanks,

Andrew