LM5141-Q1: Max current Iout of a buck controller

DARSHAN M M V

Part Number: LM5141-Q1
Other Parts Discussed in Thread: LM5141, LM25143-Q1, , LM5143A-Q1, LM25148-Q1, LM5148-Q1, LM25141-Q1, LM25149

Hello team,

I found the max current LM5141 can support is 30A in the Data sheet , but I have question w.r.t the Maximum current of LM5141,

all the load current will be delivered through the External High side and Low side MOSFET ,until and unless if my MOSFET is able to handle the required load current example 50A , is the buck controller iable to handle it or not.

If not please can you provide the technical justification , how the load current >30A is going to effect my buck controller , or what is the reason for limiting the current to 30A

3 months ago

0 Timothy Hegarty 3 months ago

TI__Guru 53312 points

Hi Darshan,

There is no real limitation on the max output current in terms of the controller. It really depends on the selected components for the power stage - MOSFETs, inductors and caps.

If your current is 50A, you may want to consider a 2-phase solution from a thermal performance standpoint. Take a look at the LM5143A-Q1 (65V) or LM25143-Q1 (42V) dual controller, which is the same family as the LM5141-Q1. We also have the LM(2)5148-Q1 that is a single channel controller but stackable to two phases if needed.

Regards,

Tim

0 Timothy Hegarty 3 months ago in reply to Timothy Hegarty

TI__Guru 53312 points

Btw, if automotive grade isn't required, just remove the "-Q1" from the part numbers above.

0 DARSHAN M M V 3 months ago in reply to Timothy Hegarty

Prodigy 150 points

Hello Timothy,

Thank you for the feedback.

referring to your answer I have few questions, If your current is 50A, you may want to consider a 2-phase solution from a thermal performance standpoint. - when you say thermal performance , is it related to buck controller or external MOSFET ?

My assumptions is , If my MOSFET is able to handle all the load current and power dissipation , then Iout Max does not depend

on Buck controller . Correct me if i am wrong

0 DARSHAN M M V 3 months ago in reply to Timothy Hegarty

Prodigy 150 points

I am using it for automotive application.

0 Timothy Hegarty 3 months ago in reply to DARSHAN M M V

TI__Guru 53312 points

Yes, correct, the controller should not be the bottleneck, as long as it can drive the FETs.

0 Timothy Hegarty 3 months ago in reply to Timothy Hegarty

TI__Guru 53312 points

Btw, the LM5148-Q1 (80V) and LM25148-Q1 (42V) are newer versions of this controller series, very similar to the LM5141-Q1 and LM25141-Q1. They have a few added features, including stackability for 2 phases, advanced spread spectrum for lower EMI, and lower shunt voltage drop (60mV vs. 75mV).

0 DARSHAN M M V 2 months ago in reply to Timothy Hegarty

Prodigy 150 points

Hello Timothy,

we have used LM5141 for converting 24V to 12V in our applications , when I am testing the output Voltage Vout is 7.4V which is not correct , I will attach my design screen shot please review it and provide the solution or debugging methods

if you are not able to view the file please share me your mail ID I can send the design PDF

0 Timothy Hegarty 2 months ago in reply to DARSHAN M M V

TI__Guru 53312 points

Hi Darshan,

I recommend filling out the quickstart calculator for the LM5141 (this helps to check component selection for stability, power losses, etc.)

Here are some comments:

The caps to GND on FB and COMP are too high. These are effectively poles causing phase lag.
No need for low-side FET gate resistors.
Remove caps on FET gate-source - these just increase the gate capacitance.
Use one cap on VDDA close to the pin. 470nF works here (no need for two caps).
RES cap at 10nF is low - 220nF is typical for a longer hiccup time.
SS cap at 10nF is also low. 47nF is typical.
Use 4 x 10nF for the input ceramic cap near the FETs (see BOM & layout for the LM25149 EVM as an example). No need for different value caps.

Regards,

Tim

0 DARSHAN M M V 2 months ago in reply to Timothy Hegarty

Prodigy 150 points

Hell Timothy,

Thanks for the solution , I am able to get the Vout =12V by making changes in the circuit as per your suggestion.

Kindly request you to guide me in understanding the importance of poles and zeros in deciding the stability of buck controller.

Please provide me some useful link or material to study and understand the bodeplot and stability of a system if available,

+1 Timothy Hegarty 2 months ago in reply to DARSHAN M M V

TI__Guru 53312 points

Hi Darshan,

Take a look at this article series regarding the stability for a current-mode control architecture:

http://www.how2power.com/pdf_view.php?url=newsletters/1406/articles/H2PToday1406_design_TexasInstruments.pdf

http://www.how2power.com/pdf_view.php?url=/newsletters/1407/articles/H2PToday1407_design_TexasInstruments.pdf

And for more generalized and in-depth theory, see this TI collateral:

https://www.ti.com/lit/an/snva555/snva555.pdf

Regards,

Tim

0 DARSHAN M M V 2 months ago in reply to Timothy Hegarty

Prodigy 150 points

Hello timothy,

Today I did rework to one of my new board (most of the boards are working fine ) as you suggested in the previous loop , initially Vout =12V which is expected , but after some time it stopped giving the Vout , when I started debugging the circuit , Vcc=5v on the pin was seen , but VDDA was giving 0V (internal LDO) and out put voltage also 0v ,Please can you suggest me to debug the circuit or do let me know what are the chances it could go wrong .

0 Timothy Hegarty 2 months ago in reply to DARSHAN M M V

TI__Guru 53312 points

Hi Darshan,

It's quite unusual for VCC to be up but not VDDA. I suspect you may have a damaged part that will need to be replaced. Note there should be no external load on VDDA except to pullup DEMB etc. if needed.

Regards,

Tim

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LM5141-Q1: Max current Iout of a buck controller