LM3481-Q1: LM3481-Q1

Muhammed Shajih

Part Number: LM3481-Q1
Other Parts Discussed in Thread: CSD19532Q5B, LM5119, LM3481

I have implemented a Webench design using LM3481-Q1 for SEPIC 3V-36V input into 9V output. The circuit is working fine above 4V input voltage, but draws current when input voltage reduced below 4V without any load. Also it heats up the MOSFET (M1). Please give me suggestion to improve my design as my typical input will be around 3.5V.

Attaching Webench design link.

https://webench.ti.com/power-designer/switching-regulator/customize/33

over 6 years ago

0 EricLee over 6 years ago

TI__Guru 58861 points

Hi
The responsible engineer is out of office now. He will reply by 4/23
I think your MOSFET selection is wrong, please make it sure that your MOSFET fully turns on when input is ~ 3.5V. Select low gate threshold MOSFET
Regards,
EL

0 Muhammed Shajih over 6 years ago in reply to EricLee

Prodigy 145 points

I am using MOSFET (Part number: CSD19532Q5B). I observed MOSFET getting turned ON when input voltage is reduced below 4V, whereas the MOSFET remains OFF when voltage is above 4V. Is this way it should work? Waiting for reply.

0 Youhao Xi over 6 years ago in reply to Muhammed Shajih

TI__Guru* 78320 points

Hi Muhammed,

Your attached Webench design is an LM5119 circuit not the LM3481. Which device do you really use? If you are questioning about the LM5119, please re-post with the subject of LM5119. If you are talking about the LM3481, please attach your actual schematic.

Regarding the MOSFET, why do you use 100V for ~3Vin design? When you Vin can be that low, you should consider the logic level MOSFETs which can be fully turned on at about 2V.

Thanks,
Youhao Xi, Applications Engineering

0 Muhammed Shajih over 6 years ago in reply to Youhao Xi

Prodigy 145 points

Hi Youhau,

I have attached my schematic. Please have a look.dms_powerboard_v1_0_25_mar-pages-5.pdf

0 Youhao Xi over 6 years ago in reply to Muhammed Shajih

TI__Guru* 78320 points

Hi Muhammed,

Like Eric said earlier, you might choose a wrong MOSFETs. The 100V part that you selected may not be turned on at the gate voltage below 3V. You should change to the FET of lower gate threshold voltage, like the CSD18542.

Thanks,
Youhao

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LM3481-Q1: LM3481-Q1