WEBENCH® Tools/LM5122: not sure if this chip will provide enough output current

Hi Brittany,

Thanks for your interest in LM5122.

Please note that the peak HO sink current is different from the load current. So which one are you talking about?

Thanks,

Yinsong

Where on the datasheet does it show the continuous max output current (ie load current) of the LM5122? 

Hi Brittany,

The output current/power limit is on the power stage instead of the controller. For higher power, synchronous rectifier is usually used instead of diode. This requires a synchronous controller like LM5122 instead of LM5155. The controller itself does not have the load limitation.

Please let me know if you have any questions.

Thanks,

Yinsong

So that makes sense to some extent. but I am then confused by the webench operation. like I said I put in the parameters below 

where my understanding was the output was a 15A peak but I am not sure if that is correct. and then I look at the generated schematic which shows 2 different Iout, where I assume I1 is the peak current and I2 is the load current (is that correct?)

How do I set the Webench based on the load current and not the peak current? 

Hi Brittany,

Could you re-upload the graphs? They failed. Please try "inserting file" instead of dragging in.

Conceptually, the peak current is the current on the inductor which should include the inductor current ripple.

Thanks,

Yinsong

Ah sorry about that yes. let me reupload.

I put in the parameters below 

where my understanding was the output was a 15A peak but I am not sure if that is correct. and then I look at the generated schematic which shows 2 different Iout, where I assume I1 is the peak current and I2 is the load current (is that correct?)

Hi Brittany,

Thanks for the information.

Let me explain it. The output current is already filtered by the LC and is treated as a constant current. Hence, there is no peak/valley for this current. But if you are thinking about peak current as maximum current, then you are right. The place you input the parameters are for the maximum load current.

Regarding the I1 and I2 shown in the schematic, it gives you the load transient, which means the load current pulses between I1 and I2 (which is why it has the pulse symbol on the Iout sink). This is more related to the loop response than the power stage design.

Thanks,

Yinsong

So what is the output current from the parameters I set in the previous message? the simulation shows the current going from the spike of 15A to what appears to be a steady-state current of 3.75A . So I am still confused then on what the steady-state current that this design can output, and how to change it if you are saying the 3.75A is part of the pulse.

Hi Brittany,

Could you share with me the link for your Webench?

The 15A is the maximum output current per definition. You can try set I2 to be 15A as well. That might give you the steady state at 15A output.

Thanks,

Yinsong

sure, but i don't think the link will work. also you just needed to put in those parameters I sent to simulate the same webench . i also don't see where I can change I2. 

Hi Brittany,

Please see the screenshot I got.

Please check the "steady state" instead of "load transient" in the selection list on the left hand side circled in red. And then click start below to run again.

Thanks,

Yinsong