LM5146: Proper converter spec for peak currents of short durations

NIcolas Gallardo

Prodigy 50 points

Part Number: LM5146
Other Parts Discussed in Thread: LM61495, , LM61480, LM70880-Q1

Tool/software:

Hi Tim,

I submitted a question a couple of weeks ago about large currents with no load and we narrowed it down to 2 things:

1. Large inductor core loss

2. Switch losses

I have designed this converter using the webench tool with a max current of 8A although I only need this current for less than 1s, with several seconds in between the next peak.

Is the converter generated by webench therefore overspec'd for my application?

Do you have any advice for designing a converter that has a constant current spec along with a peak current spec?

My thought is that I can significantly downsize the inductor and fets, eliminating the core loss issue and significant heat generated by my current design.

Thank you,

Nico

over 1 year ago

0 EricLee over 1 year ago

TI__Guru 59001 points

Hello Nico

The responsible engineer is out of office now. I will respond until he returns back. Thank you for your patience.

Please consider LM61480, and LM61495 if the maximum input voltage is <=36V. If VIN>36V, then ypou may have to use controller devices like as LM5146.

TI will release new device (LM70880-Q1) in two weeks, whcih meets your electrical requirements. (I am sorry I cannot disclose more details of preRTM device. ) . Please check TI.COM later.

-EL

0 NIcolas Gallardo over 1 year ago in reply to EricLee

Prodigy 50 points

Hi Eric,

This is part of a series of questions I've been asking as I go through design, test, and validation.

Question 1: General design questions

https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/1348171/lm5146-wbench-power-designer-output-verification/5137550#5137550

Question 2: Question about heat dissipation and more detailed description of the circuit characteristics

https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/1369207/lm5146-no-load-current/5228328#5228328

Hopefully these links help to get us on the same page about my system. With this new information, do you have any information or advice on designing power converters for short pulse peak currents (8A for <1s), and much lower constant currents (<100mA)? Can I safely downsize my power components (L,C,FETs)?

Best,

Nico

0 EricLee over 1 year ago in reply to NIcolas Gallardo

TI__Guru 59001 points

Hello Nico

Since the maximum voltage is 58V. I think you have to consider controller devices like as LM5146.

If you can wait, please find LM70880-Q1 converter device on TI.COM later . this device can meet your electrical specifications.

-EL

0 NIcolas Gallardo over 1 year ago in reply to EricLee

Prodigy 50 points

Hi Eric,

I'm a bit confused about "I think you have to consider controller devices like as LM5146" - that is in fact the controller I am using. I am interested in the LM70880-Q1 but it that would have to be used in a future revision of the current design.

Do you have any answers to the specific questions I asked in the previous post?

0 EricLee over 1 year ago in reply to NIcolas Gallardo

TI__Guru 59001 points

Hello Nicolas

Would you please specify the questions/answers you are interest on?

Questions on 6/18 in this E2E post ?
Questions on 4/16 in LM5146: Bench power designer output verification E2E post ?
Questions on 5/31 in LM5146: No load current E2E post

- EL

0 NIcolas Gallardo over 1 year ago in reply to EricLee

Prodigy 50 points

Hi Eric,

In my previous to last post - "With this new information, do you have any information or advice on designing power converters for short pulse peak currents (8A for <1s), and much lower constant currents (<100mA)? Can I safely downsize my power components (L,C,FETs)?

0 EricLee over 1 year ago in reply to NIcolas Gallardo

TI__Guru 59001 points

Hello Nicolas

About the inductor, I think you still have to select the inductor whose saturation current rating is above the inductor peak current at 8A, but the RMS current rating can be less than 8A. For example, if the load is a pulse load with 8A/1sec during on-time on and 0A/7sec during-off time, you only need 1A RMS current. MOSFET selection is similar. MOSFETs need to handle only 1A load current considering the transient thermal impedance.

For more information about the Transient Thermal Impedance of the MOSFET, please contact NEXFET team.

-EL

Power management

Power management forum

LM5146: Proper converter spec for peak currents of short durations