LM1085: Fixed 3.3V output gives 0.6V

SndrS

Part Number: LM1085
Other Parts Discussed in Thread: LM1086

Dear all!

Trying to get a LDO LM1085 fixed 3.3V 3A (LM1085ISX3.3 NOPB, DDPAK/TO-263) running. But somehow I get a fixed output of 0.6V. I supply the part with a 6V (from voltage switching regulator).

My PCB setup:
- Input cap 10µF (C1), next to Vin and IC.
- output cap 10µF (tantalum) also very close.

I suspect, when turning on, the LM1085 is too fast... but not sure. See my output (1=LM1085, 2=Vin):

I have also tried so far:
- Several loads, same output (adding pull down resistor to OUT), same output
- Another LM1086 fixed 3.3V (1.5A, LM1086CSX3.3NOPB), but that gives the same output
- Connect the LM1085 directly to my bench power supply, same output

Did I miss something? Thanks a lot!

9 months ago

0 Hannah Grace 9 months ago

TI__Genius 12145 points

Hello,

Thank you for your question.

I will be working on your thread in the coming days.

Best Regards,

Hannah

0 Hannah Grace 9 months ago

TI__Genius 12145 points

Hello,

Do you have an additional LM1085 to run this same test again? This setup seems okay and should not be giving problems. I would like to verify that the previous test was not run on a broken part.

Please let me know when you have a moment.

Best Regards,

Hannah

0 SndrS 9 months ago in reply to Hannah Grace

Prodigy 50 points

Hi Hannah,

Thanks for your quick reply. I have already swapped it to a LM1086 before.

Yes, we got several more LM1085 (the same reel, batch) here.

After long checking, we have been figuring out what was wrong. Related to a faulty part and a design error in our footprint (actually the other way around). We managed to replace the part and correct footprint placement and it works perfectly nice!

Thanks!

0 Hannah Grace 9 months ago in reply to SndrS

TI__Genius 12145 points

I am glad to hear everything has been fixed.

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LM1085: Fixed 3.3V output gives 0.6V