WEBENCH® Tools/LM5175: LM5175 instability with Vin = 9-15Vdc, Vout = 12V, Iout = 10A

MANUEL MARQUES

Part Number: LM5175
Other Parts Discussed in Thread: LM5176

Tool/software: WEBENCH® Design Tools

We have designed in the Webench a DC-DC converter with Vin = 9 to 15Vdc, Vout = 12Vdc, Iout = 10A.

The controller LM5175 goes to instability at Vin < 10V or Iout > 4A.

I have found here in the forums three similar cases, but the solution suggested is the migration for the LM5176 controller.

Anyone have solved the problem only with the adjustment of the control components?

over 6 years ago

0 Garrett Roecker over 6 years ago

TI__Mastermind 21720 points

Hi Manuel,

Thanks for reaching out with your question.

Can you please post the schematic? This will allow us to see what component values need to be adjusted.

Thanks,

Garrett

0 MANUEL MARQUES over 6 years ago in reply to Garrett Roecker

Prodigy 120 points

The schematic is below,

Thanks

DC-UPS-P 1622C.pdf

0 MANUEL MARQUES over 6 years ago in reply to MANUEL MARQUES

Prodigy 120 points

And the components are below,

Cheers,

Manuel

Copy of 06 DC DC-12V Bill of Materials DC-DC converter with LM5175PWPR(T....xlsx

0 MANUEL MARQUES over 6 years ago in reply to MANUEL MARQUES

Prodigy 120 points

Hi Garrett,

Should be good idea:
1) increase the switching frequency to 400kHz (RT = 62kHz) which actually is 334kHz (Will extend the VIN voltage range operation)
2) increase the number of the input CBULCK capacitors (Will increase the value of the input ripple current capacity), and
3) Increment the value of the CSLOPE capacitor to 82pF, to lower the slope ripple to VCOMP(BUCK) = 1.44V and VCOMP(BOOST) = 2.10V. The actual CSLOPE = 68pF.

Regards,

Manuel

0 MANUEL MARQUES over 6 years ago in reply to Garrett Roecker

Prodigy 120 points

Good morning Garrett,

Just in case, this is the WEBENCH project.

Regards,

Manuel

2018-06-11_(My Designs ID 15)_DC-DC converter In 9-15Vdc Out 12Vdc 10A LM5175PWPR .pdf

0 Garrett Roecker over 6 years ago in reply to MANUEL MARQUES

TI__Mastermind 21720 points

Hi Manuel,

How much ripple is on the output? And when you say unstable is the LM5175 just hoping between the modes? (boost, buck-boost, buck)

The easiest way to improve this transition region behavior is to switch to the LM5176, as seen in the other threads. The LM5176 is the next generation of the LM5175 and has better transition region behavior.

Thanks,

Garrett

0 MANUEL MARQUES over 6 years ago in reply to Garrett Roecker

Prodigy 120 points

Hello, Garrett

We discover that problem is related with our schematic. The number of MOSFETS is wrong, should be the duplicate!

What happened was when we exported the files from webench simulator, the number of semiconductors isn't posted in the schematic, although it appears in the electrical BOM. Of course it's our fault, but in the future versions the webench should have the constraint improved. Perhaps there are more designers out there with the same faulty.

Anyway we decided to migrate for the LM5176 regulator. The new prototypes are in the way!

Thanks for your help!

Best Regards,

Manuel

Power management

Power management forum

WEBENCH® Tools/LM5175: LM5175 instability with Vin = 9-15Vdc, Vout = 12V, Iout = 10A