LM3478 in boost configuration

Djordje Radivojevic

Other Parts Discussed in Thread: LM3478

Hi,

I have been using LM3478 chip in boost configuration in order to generate 50V from 3x1.5V battery as a supply. I have created circuit according to proposal from webench.ti.com:

http://webench.ti.com/webench5/power/webench5.cgi?VinMin=3.6&VinMax=4.5&O1V=50&O1I=.015&base_pn=LM3478&AppType=None&op_TA=30&lang_chosen=en_US&optfactor=3

As you can see from proposed schematic, in my application I don't need high current on output (~15mA).

Main problem with circuit is that for voltage lower than 4V, without load, my circuit doesn't work properly. In that case I have around 3.5 on output of boost converter. Can you please give me some explanation what can be possible reason for that,

and how can I resolve this issue?

Thank you in advance,

Djordje Radivojevic

over 10 years ago

0 Karl Wallinger over 10 years ago

TI__Genius 16410 points

Hello Djordje,

Let me move this to the non-isolated DCDC forum.

Regards,
Karl

0 John Bowie over 10 years ago

TI__Intellectual 890 points

Hi, I have placed an order for components to replicate this on the bench, are you looking at this with one of our EVMs?, I will get back to you as soon as possible.
regards
John

0 Djordje Radivojevic over 10 years ago in reply to John Bowie

Prodigy 100 points

Thank you very much John! I'm waiting for your answer.
Regards,
Djordje

0 John Bowie over 10 years ago in reply to Djordje Radivojevic

TI__Intellectual 890 points

Hi Djordje,

I checked our standard EVM with your battery set-up and it was ok at 24VOUT, we found the part number BSC265N wont fit our EVM so we are trying to source another with higher Voltage rating to withstand you desired output Voltage, will be in back in touch soon.

regards

John

0 Djordje Radivojevic over 10 years ago in reply to John Bowie

Prodigy 100 points

Thank you John! I'm still waiting for information from your side. Best regards, Djordje

0 Djordje Radivojevic over 10 years ago in reply to John Bowie

Prodigy 100 points

Hi John,

I have resolved problem. Thank you for your help.

Best regards,

Djordje

0 John Bowie over 10 years ago in reply to Djordje Radivojevic

TI__Intellectual 890 points

Hi Djordje,

I'm really glad to here you resolved this, just for my reference what was the problem, I would like to know in case other customer come across the same issue.

regards

John

0 Djordje Radivojevic over 10 years ago in reply to John Bowie

Prodigy 100 points

Hi John,

I didn't use proposed MOSFET and instead of it I took one in smaller casing because of limited place on PCB, but I did not pay attention on Vgs_threshold.

MOSFET that I have been using has higher threshold voltage, so switching didn't work for voltage lower than 4V.

Thank you for support from your side!

Best regards,

Djordje

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LM3478 in boost configuration