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ES9038Q2M Board
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Old 14th July 2020, 06:56 AM   #5781
kimschips is offline kimschips  Denmark
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You could also look her��

Mr. Jung's ultra-low noise VREF - the GLED431
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Old 14th July 2020, 11:33 AM   #5782
Markw4 is online now Markw4  United States
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ESS recommends +3.3v +-5% for AVCC for each of the two AVCC supplies. They also specify low noise in order to minimize DAC distortion and noise.

As can probably be seen there are long discussions in the forum about all the different ways to design low noise references, and the various trade offs to consider. I don't think we should get sidetracked into that this early in the going. We are trying to focus on the bigger picture and not get deeper into the weeds than we have to.

Regarding Tom Jung's GLED431, here are Walt's later comments he appended to original article:
"Addendum of March 8, 2016:
The circuit originally shown with a LT6200 op amp was/is intended as a conceptual example of low noise reference voltage scaling, not a complete working regulator!
The LT6200, like many low noise op amp devices, also has a very high bandwidth. From that it follows that it can readily oscillate. There are past caveats here and elsewhere about using very high BW parts within regulators (AD797, etc). Always proceed with caution, and make good use of a scope to monitor the output."


If someone really wants to get into it and is equipped to do the design and testing for a +3.3v version with known good PSRR, stability, etc., then let me know and I will see about getting Walt's updated paper to you.
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Old 14th July 2020, 10:27 PM   #5783
eightdigitword is offline eightdigitword  Scotland
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What op amps were used in the 'OSB' word doc?

I have some AD797 spare and would be nice to use them. should i just use the ess 'Application_Note_Component_Selection_and_PCB_Layo ut.doc' as used on the reference board?
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Old 15th July 2020, 01:11 AM   #5784
Markw4 is online now Markw4  United States
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Regarding use of spare AD797, may I ask if they are new and therefore SMD? Old and possibly DIP? Assuming SMD, are you comfortable prototyping in SMD?

Probably best to make some updates to the original ESS recommendations, but they are a great start in multiple ways.

OSB.rtf circuit is laid out for dual opamps and DIP sockets, so it has been tried with opamps like LME49720 and OPA1612.
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Old 15th July 2020, 06:16 AM   #5785
kimschips is offline kimschips  Denmark
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What About max6126 anyone worked with that?
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Old 15th July 2020, 12:04 PM   #5786
Markw4 is online now Markw4  United States
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Don't know if they make 3.3v max6136 any more. Some other voltages are still in production.
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Old 16th July 2020, 10:56 AM   #5787
eightdigitword is offline eightdigitword  Scotland
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Quote:
Originally Posted by Markw4 View Post
Regarding use of spare AD797, may I ask if they are new and therefore SMD? Old and possibly DIP? Assuming SMD, are you comfortable prototyping in SMD?

Probably best to make some updates to the original ESS recommendations, but they are a great start in multiple ways.

OSB.rtf circuit is laid out for dual opamps and DIP sockets, so it has been tried with opamps like LME49720 and OPA1612.
Hi Marc,

chips are DIP, I'll follow the ESS recommendations with my 797's see how it measures up.

ta
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Old 16th July 2020, 11:57 AM   #5788
Markw4 is online now Markw4  United States
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Quote:
Originally Posted by eightdigitword View Post
I'll follow the ESS recommendations with my 797's see how it measures up.
Okay. You planning to do stereo 3-opamp output stages and stereo AVCC buffers with the AD797s?

Last edited by Markw4; 16th July 2020 at 12:07 PM.
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Old 16th July 2020, 01:59 PM   #5789
eightdigitword is offline eightdigitword  Scotland
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I am, yes.
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Old 16th July 2020, 03:34 PM   #5790
Markw4 is online now Markw4  United States
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Have you thought about taking control of the dac chip I2C registers with an MCU, maybe an Arduino?
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