LM5149: LM5149 99% Duty

Noah Li

Part Number: LM5149

Hi Ti,

I want to use the function of Vout tracks Vin if the Vin is lower, whether it's mean the Pin18 PWM/SYNC can not connect to GND? I designed a LM5149 demo-- 48V convert 24V, connected the PWM/SYNC to GND, but when I take 24V Vin, and the output voltage only is 0V.

4 months ago

0 David Baba 4 months ago

TI__Mastermind 31190 points

Hello Noah,

please can you fill out design calculator of your design and also share your schematic, thank you. Output not coming up usually means there is an error in the design, or on the board. Thanks.

David,

0 Noah Li 4 months ago

Prodigy 10 points

Hi David

Thank you for your support! Here are my design and design calculator, and you can refer to the test in the ppt. LM5149 Test.pptx LM5149.pdf 6470.LM5149-LM25149 Quickstart Calculator_rev3.xlsm

Noah,

0 David Baba 4 months ago in reply to Noah Li

TI__Mastermind 31190 points

Hello Noah,

I check your design and the thing that stood out to me as an issue is the miller platueu voltage on the MOSFETs you have selected. The LM5149 requires logic level FETs.

See section 8.3.15 in datasheet.

Suggest swapping out MOSFETs for suitable MOSFETs and rechecking.

Thanks.

David.

0 Noah Li 4 months ago in reply to David Baba

Prodigy 10 points

Hi David,

The IAUC90N10S5N062 I used that Vth rang is 2.2V~3.8V, I want to know if the logic-level FET means Vth need to less than 2V? Could you have some suggestions for high and low side FETs in proply?

Thanks a lot!

Noah.

0 David Baba 4 months ago in reply to Noah Li

TI__Mastermind 31190 points

Hello Noah,

It's not the VGSth its the Miller Plateau you need to consider to fully enhance the MOSFET.

Please refer to the LM5149 User guide and use same/similar FETs as seen therein.

LM5149-Q1 Buck Controller Evalulation Module User's Guide

hope this helps.

David.

0 Noah Li 4 months ago in reply to David Baba

Prodigy 10 points

Hi David,

My board is working with changing a new logic-level FETs, thank you very much!

Noah.

Power management

Power management forum

LM5149: LM5149 99% Duty