SN10501: Any experience with SN10501/SN10502/SN10503 as unity-gain voltage buffer?

Braulio Cancino

Part Number: SN10501
Other Parts Discussed in Thread: SN10502, , SN10503, OPA846

Hi everyone,

I'm currently designing a circuit that uses the SN10501/SN10502/SN10503 and I would like to know if someone has used it before as uniti-gain voltage buffer. The reason for my question is because in the market there are many opamps that in their datasheets say that they are stable in unity-gain configuration, but in reality they present oscillations or are unstable.

I hope you can help me.

Regards!

over 8 years ago

0 Samir Cherian over 8 years ago

TI__Genius 12631 points

Hello Braulio,
Looking at the open-loop gain and phase curve (Figure 23, page 8) of the datasheet, at unity gain crossover the phase margin looks to be only around 20-30 degrees which is typically not enough to guarantee stability across temperature and process corners. I wouldn't use the amplifier in unity gain configuration without playing some tricks with noise gain shaping, so that I can get closer to 50 degrees of phase margin.

0 Loren Siebert 1 over 8 years ago

TI__Genius 13935 points

Hello Braulio,

I do not have first hand experience with these amplifiers.

In the SN10501 datasheet there is a gain of 1 plot that shows a stable frequency response with only 0.5dB of peaking. Usually, if an amplifier is going to be unstable in unity gain there will be 6dB or more of peaking in the frequency response.

If you are concerned with stability make sure to follow the datasheet recommendations for bypass capacitors and board layout.

Regards,
Loren

0 Braulio Cancino over 8 years ago in reply to Samir Cherian

Prodigy 40 points

The problem is that I have not found an amplifier of these characteristics in the market that serves me as voltage buffer. Can you recommend an alternative amplifier?

Also I would like you to refer me some documents of the "noise-shaping tricks" of which you speak to me.

Thanks again.

0 Samir Cherian over 8 years ago in reply to Braulio Cancino

TI__Genius 12631 points

Braulio,
Please see Page 13 and 14 of the OPA846 datasheet, section titled "Noninverting Low-Gain Compensation" to see how a decompensated amplifier may be made stable at lower gains.

-Samir

0 Braulio Cancino over 8 years ago in reply to Samir Cherian

Prodigy 40 points

Thanks for the help. I also found this interesting forum discussion (electronics.stackexchange.com/.../what-is-noise-gain-really-and-how-is-it-determined-in-the-general-case , see "So what is "forcing the noise gain" and why does it work").

I will do the math to verify these results.

Thanks again!

PS: Do you suggest closing this topic ?. I will not have a concrete answer until I try the circuit.

0 Samir Cherian over 8 years ago in reply to Braulio Cancino

TI__Genius 12631 points

Braulio,
That is a nice article explaining noise gain vs signal gain. I concur with the author as well, i.e. in cases where there are weird multiple feedback paths it is always easier to actually calculate Beta rather than noise gain (remember to short all the external voltage sources when doing this math).

-Samir

PS - please go ahead an close this for now. If you have further questions in the future we can start a new thread and link back to this one.

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SN10501: Any experience with SN10501/SN10502/SN10503 as unity-gain voltage buffer?