Hi,

I have found application note AN-257 from Analog Devices describing how to make almost any opamp amplifier unity gain stable. Article starts on the page 6 and it is named "Trick those op amps".

According the information here is my take on calculating the needed values, which are Rc and Cc. I am not sure if my calculations are right, thats why I post them.

I choose minimum stable gain for LM3886 to be 11 (according to the datasheet it is 10).

For this gain I have Rf=10k Ohm and Ri=1k Ohm. (But I think Ri doesn´t matter and Rf I can choose whatever I can? - If I understand the article correctly.)

Rc= Rf/10, so Rc=1k Ohm

Cc= 1/(2*Pi*Rc*(fc/10)), so I need fc now.

fc for gain 11 is = open loop BW/closed gain, so fc=8 MHz/11, fc=727,2 kHz

Cc= 2,2nF, Cc should be made 1000 times bigger to lower the overshoot,

so Cc= 2,2uF

Calculated results for unity gain stable LM3886 should be:

Rf= 10k Ohm

Rc= 1k Ohm

Cc= 2,2uF

Are these calculations right?

Thanks.

I have found application note AN-257 from Analog Devices describing how to make almost any opamp amplifier unity gain stable. Article starts on the page 6 and it is named "Trick those op amps".

According the information here is my take on calculating the needed values, which are Rc and Cc. I am not sure if my calculations are right, thats why I post them.

I choose minimum stable gain for LM3886 to be 11 (according to the datasheet it is 10).

For this gain I have Rf=10k Ohm and Ri=1k Ohm. (But I think Ri doesn´t matter and Rf I can choose whatever I can? - If I understand the article correctly.)

Rc= Rf/10, so Rc=1k Ohm

Cc= 1/(2*Pi*Rc*(fc/10)), so I need fc now.

fc for gain 11 is = open loop BW/closed gain, so fc=8 MHz/11, fc=727,2 kHz

Cc= 2,2nF, Cc should be made 1000 times bigger to lower the overshoot,

so Cc= 2,2uF

Calculated results for unity gain stable LM3886 should be:

Rf= 10k Ohm

Rc= 1k Ohm

Cc= 2,2uF

Are these calculations right?

Thanks.