Opamp as a Buffer for driving high capacitive load ( appx. 100nF & 10 Ohm resistor)

bijeta chakraborty

Prodigy 20 points

Other Parts Discussed in Thread: THS4271, LM8261, TINA-TI, LM7322, LM8272, LM7121, LM8262, LM7321

Hi,

Could someone please suggest a suitable opamp which can be used as a unit gain (buffer) configuration?.

This opamp should be able to drive a load with capacitance of 100nF(Appx.) & 10 Ohm resistance;

the O/P current sourcing capability should be >200 mA and Bandwidth of atleast 50MHz.

I was looking at THS4271 but could not find anything related to its capability of driving Capacitive load.

Please let me know your thoughts/inputs.

Regards

Bijeta C

over 10 years ago

0 Loren Siebert 1 over 10 years ago

TI__Genius 13935 points

Hi Bijeta,

Have you looked at the LM8261? It does not have the bandwidth that you requested, however, with a 100nF load the signal bandwidth of any amplifier will be very limited.

The following article may be helpful:

http://www.eetimes.com/document.asp?doc_id=1272424

Loren

0 bijeta chakraborty over 10 years ago in reply to Loren Siebert 1

Prodigy 20 points

Hi Loren,

Thanks for your quick reply!

I simulated THS4271 in TINA TI and could observe that it can work with 100nF load uptil 50 MHz. Have ordered for an EVM to try this out.

Do you think its a good idea to try this out?.

let me know your thoughts.

Regards

Bijeta C

0 Hooman Hashemi over 10 years ago in reply to bijeta chakraborty

TI__Mastermind 22825 points

Hello Bijeta,

If I may jump in here:

I would not put too much faith in the TINA-TI simulation of capacitive load response. You may have to search within the datasheets for this information and / or do some bench evaluation to be sure.

One thing that helps is if you operate a higher gain than unity (Av=+1) to improve stability with cap load.

Here is a list of TI parts that I know are qualified as "unlimited cap load", for your information:

LM8261, LM8262, LM8272, LM7321, LM7322, LM7121

Here is an E2E post of mine which may also be helpful:

http://e2e.ti.com/blogs_/b/analogwire/archive/2013/07/12/what-is-this-quot-unlimited-cap-load-quot-stuff-anyway.aspx

Regards,

Hooman

0 Hooman Hashemi over 10 years ago in reply to Hooman Hashemi

TI__Mastermind 22825 points

Hello again Bijeta,

Here is an E2E post which deals with stabilizing an amplifier with heavy cap load using output resistor isolation (Riso) and dual feedback, that I wanted to share:

http://e2e.ti.com/support/amplifiers/precision_amplifiers/f/14/p/296391/1087025.aspx#1087025

Regards,

Hooman

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Opamp as a Buffer for driving high capacitive load ( appx. 100nF & 10 Ohm resistor)