LM5018: Problem with the LM5018 in design

Jean Bailly

Part Number: LM5018

Hi,

I need, for a new design (a big production shall be following) , to use the LM5018MR/NOPB. Vin min:14V ; Vin max:60V ; Vout:12V ; Iout max: 250mA.

I've tried the shematic in the datasheet, with and without the diode, (it's bad with the diode), so i've tried with Webench.

I've done my design with the recommandations, and with the values gave in the shematic.

When i have no load, the Vout is correct ( about 12V)

But when i load with Iout = 50ma or more, the Vout decrease (6.6V), and the LM5018 become hot !

i don't understand

Please help me, i need to find a solution for this project, my Customer waiting my prototype and i'm blocked only there.

Best regards

M.Bailly

over 5 years ago

0 Brani Dubocanin over 5 years ago

TI__Expert 4100 points

Hello,
Can you please post schematic of your design?
Regards
Brani

0 Jean Bailly over 5 years ago in reply to Brani Dubocanin

Prodigy 50 points

Hello M. Brani

Thanks, for your reply. See in attached files, Webench, my PCB design and schematic.

Best regards.

M. Bailly

Webench Simulation :

My schematic :

My pcb design bottom view with components :

Top layers view :

Bottom layers view :

0 Brani Dubocanin over 5 years ago in reply to Jean Bailly

TI__Expert 4100 points

Hello,
Your schematic looks OK, nothing is obviously wrong.
Also layout is acceptable.
As first step i would suggest to verify all components are placed correctly, device exposed pad is soldered to PCB, and your power supply is current limited.
From your description i would suggest that you change R23 value to 10-12Ohm resistor value and test circuit functionality.
This should help.
For component calculation there is circuit calculator available for this device. It can be found here
www.ti.com/.../lm5018quick-calc

Please let me know any updates.
Best regards
Brani

0 Brani Dubocanin over 5 years ago in reply to Brani Dubocanin

TI__Expert 4100 points

Hello,
Since there is no activity on this post i will go ahead and close it.
Regards
Brani

0 Jean Bailly over 5 years ago in reply to Brani Dubocanin

Prodigy 50 points

Hello,

Sorry for the delay, i was on an other project.
I've tried you solution but it doesn't work, R23 isn't for the current output ripple ?
I've looked again my pcb design, i've tried to enlarge solder layer but the result is the same !
i've need a quick solution, i think i gonna change of regulator, sorry.
Is it possible to send me the demonstration PCB, to try with the values of my projet before the change of regulator ?

Best regards
Jean

0 Brani Dubocanin over 5 years ago in reply to Jean Bailly

TI__Expert 4100 points

Hello,
The evaluation board for this device is available.
Unfortunately i don't have any on hand available, so please order from TI website or from Digikey.
See link here
www.ti.com/.../lm5018eval

Regards
Brani

0 Jean Bailly over 5 years ago in reply to Brani Dubocanin

Prodigy 50 points

Hi,

To earn any time, i've tried to make the eval PCB myself, with the example give on webench.

I've put the values and, surprise (for me), it work well ! with or without load !

So i thnk the problem is on my design. i gonna look again my design pcb and i'll try to do the same think for the copper layer and the distance between the components.

I'll give you news as soon as possible.

Best regards

M. Bailly

0 Brani Dubocanin over 5 years ago in reply to Jean Bailly

TI__Expert 4100 points

Hello Jean,
If no other questions, please click 'resolved" , so i can close this post.
Thanks!
Brani

0 Jean Bailly over 5 years ago in reply to Brani Dubocanin

Prodigy 50 points

Hi every body !
I know where i did a mistake !!
I reversed BST ad SW PIN on my design !
Sorry and thank again for your help.
Regards, Jean

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LM5018: Problem with the LM5018 in design