LM5156: Power management forum

Gil Schloss

Prodigy 30 points

Part Number: LM5156

Tool/software:

Hello Technical Support,

For designed and manufactured DC To DC up converter 10.5v to 28v:

Tested 90 MHz/ 2v ripple at output and Gate FET transistor.

Is there a way to debug or fix such significant ripple ?
Is there a way to improve ripple ?

Attached schematic, BOM and layout.

2112.BOM.xlsx 10.5v to 28v:

over 1 year ago

0 Moritz over 1 year ago

TI__Mastermind 18205 points

Hi Gil,

Thanks for reaching out.

Can you please send the schematic as a PDF? It is hard to see in the small picture.

Also can you please send some scopeshots of the behavior? I would like to see Vin, Vout, switchnode and COMP pin.

Best regards

Moritz

0 Gil Schloss over 1 year ago in reply to Moritz

Prodigy 30 points

Hi Moritz,

Attached schematic as a PDF and scopeshots.

I am available for more information.

Thanks.voltage booster regulator odu.pdf

0 Moritz over 1 year ago in reply to Gil Schloss

TI__Mastermind 18205 points

Hi Gil,

Thanks for the scopeshots.

It seems that you have much ringing and overshoots at the switchnode.

You can try to place an RC snubber across the MOSFET and use a gate resistor for the FET.

Did you check your circuit using our quickstart calculator? https://www.ti.com/tool/download/SNVC224

Especially to check the compensation network.

Best regards

Moritz

0 Gil Schloss over 1 year ago in reply to Moritz

Prodigy 30 points

Hi Moritz,

Please advise regard how to implement:

Regard Gate resistor to the FET- serial or parallel from gate to GND ? what value? ( for exist layout there is no room for serial).
Regard RC snubber : how to connect ? - from Drain to GND ? , or parallel to the diode ? what value to R,C ?
How to check the compensation network, how to modify ?

While the design I used the quick start calculator.

0 Moritz over 1 year ago in reply to Gil Schloss

TI__Mastermind 18205 points

Hi Gil,

the gate resistor has to be in series from the gate output to the gate (range 1 to 5 Ohms).

The RC snubber should be across the the MOSFET from Drain to GND. Please find a description here : https://www.omicron-lab.com/fileadmin/assets/Training_and_Events/Power_Analysis_and_Design-Symposium/2022/Presentation_BirichaDigital.pdf

The compensation network is calculated in the lower part of the quickstart calculator. It recommends values for Rcomp Ccomp and CHF. The goal is to achieve a phase margin of at least 60 degrees.

Best regards

Moritz