WEBENCH® Tools/LOWPASSFILTER-CALC: Amplifier selection error in WEBENCH

Firman Sasongko

Tool/software: WEBENCH® Design Tools

Hello,

I was trying to design a low pass filter (5th order Butterworth using Sallen-Key at cut-off frequency of 500 kHz) in WEBENCH designer, and I want to develop the real circuit and create the BOM based on the output. However, I always get the following message:

"Amplifier bandwidth requirements are higher than available amplifiers. Ideal has been assigned to allow Spice simulations."

The highest required gain bandwidth stated in schematic section is actually only 81 MHz which is not the problem at all (as you can see in the following figure).

Thank you for your support.

Best regards,

Firman

over 5 years ago

0 Praveen Badiger over 5 years ago

TI__Expert 8365 points

Hi Firman,

We will soon get back to you on this query.

Thanks & Regards,
Praveen B

0 Alfred Chong over 5 years ago in reply to Praveen Badiger

TI__Expert 3482 points

Firman,

The calculated min GBW is 80.911 MHz. However, to achieve 1% accuracy the tool added 100X margin and this made the GBW requirement to be 8000.911

MHz. Currently, the highest GBW of our amplifiers is 8000MHz and this would not meet the requirement to achieve 1% accuracy.

We are currently developing an HTML5 Filter Design Tool that will allow user to specify the margin by compromising the accuracy. In this case, if you really need

to operate at this frequency, you can lower the margin to get an amplifier by sacrifying the accuracy.

Regards,

Alfred

0 Firman Sasongko over 5 years ago in reply to Alfred Chong

Prodigy 60 points

Hi Alfred,

thanks for the detailed answer.

Regards,

Firman

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WEBENCH® Tools/LOWPASSFILTER-CALC: Amplifier selection error in WEBENCH