LM25005: Incorrect resistor in Webench ? (Rramp )

Yuriy Stukalo

Prodigy 40 points

Part Number: LM25005

Hi,
I have issue with LM25005 design.
My pcb is working only when I removed Rramp resistor.

What is destination of this resistor in webench?
There is no such resistor in datasheet.
Regards

over 6 years ago

0 Samuel Jaffe over 6 years ago

TI__Mastermind 25590 points

Yuriy,

Rramp is discussed on pg 12 of the datasheet. It increases the ramp slope compensation to help reduce sub-harmonic oscillation. This will help high-VOUT, high-duty cycle applications. It is just there to improve operation of the circuit and is not necessary if the circuit works to your specs without it.

-Sam

0 Yuriy Stukalo over 6 years ago in reply to Samuel Jaffe

Prodigy 40 points

Sam,

many thanks for you response, I have read the sections about the Ramp and as I understand the resistors using only if output voltage more then 7.5V

Why I should put the resistors for - 6V output in design what I got from the Webench ?

Value for the RAMP resistor what I got is - 6.98 Ohm - using calculation of datasheet the value shouldbe about 280 kOhm, so valuse 6.98 Ohm is correct?

Link for my design here, please advice if the value 6.98 Ohm is correct. Thank you.

webench.ti.com/.../webench5.cgi

0 Samuel Jaffe over 6 years ago in reply to Yuriy Stukalo

TI__Mastermind 25590 points

Yuriy,

Your WEBENCH link did not take me to a specific design. I agree that 6.98 ohms seems way out of the ballpark for that resistor value. Please share your WEBENCH design using the "Share Design" button on the top-right of the page. Click "Share With Public" then "Get New Shareable Link."

-Sam

0 Yuriy Stukalo over 6 years ago in reply to Samuel Jaffe

Prodigy 40 points

Hi, try to use it:

https://webench.ti.com/appinfo/webench/scripts/SDP.cgi?ID=169793770E566AD0

Thank you !

0 Samuel Jaffe over 6 years ago in reply to Yuriy Stukalo

TI__Mastermind 25590 points

Yuriy,

That link works. Thanks!. That resistor definitely looks off to me. I'll ask around and see if there's something off with WEBENCH with this resistor. In the meantime, I'd suggest removing that resistor and continuing with your work.

-Sam