Yeah, but still, doesn't change the fact it's highly succeptable to rf. Or am i missing something?
I have been using AD797 for some 20 years.
In phono preamps, as well as in measurement amps.
Never had any problems with RF pickup.
https://www.diyaudio.com/community/...sfet-relay-for-loudspeaker-protection.370678/
The Jung / Didden regulator is very picky on opamps because the way it is powered (from the output of the same opamp).
But it can be easily cured.
And for this particular circuit, Fran has mutiple working examples. Also no problems.
Cheers,
Patrick
In phono preamps, as well as in measurement amps.
Never had any problems with RF pickup.
https://www.diyaudio.com/community/...sfet-relay-for-loudspeaker-protection.370678/
The Jung / Didden regulator is very picky on opamps because the way it is powered (from the output of the same opamp).
But it can be easily cured.
And for this particular circuit, Fran has mutiple working examples. Also no problems.
Cheers,
Patrick
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AD797 is, for decades, widely used not only in hobby electronics, but more importantly in industrial applications.
Just that some hobbyists made some remarks out of context does not make it a faulty product.
The above-linked measurement was done by Jan Didden himself.
Both he and I understand why the "super regulator" tends to oscillate with some cap / opamp combinations.
Patrick
Just that some hobbyists made some remarks out of context does not make it a faulty product.
The above-linked measurement was done by Jan Didden himself.
Both he and I understand why the "super regulator" tends to oscillate with some cap / opamp combinations.
Patrick
Someone also mentioned that the AD797 might get hot.
It is a fair comment, since it draws ~8mA and hence will dissipate ~200mW.
And in this layout, it is facing down.
LT1028, and even AD8429 that Fran tried earlier are all about the same.
OPA627 is also 7mA, not much better.
A drop of thermal grease between the case and PCB before soldering will surely help.
The TI low-noise opamps such as OPA1611 or OPA211 will have much less, drawing 3.6mA instead.
Patrick
It is a fair comment, since it draws ~8mA and hence will dissipate ~200mW.
And in this layout, it is facing down.
LT1028, and even AD8429 that Fran tried earlier are all about the same.
OPA627 is also 7mA, not much better.
A drop of thermal grease between the case and PCB before soldering will surely help.
The TI low-noise opamps such as OPA1611 or OPA211 will have much less, drawing 3.6mA instead.
Patrick
Supplement to the above :
SOIC8 thermal resistance is typically ~200°C/W junction to ambient.
Assuming 200mW and worst worst case 40°C ambient, junction temperature (not case temperature) is 90°C, so still save.
But junction to case is much improved at 40°C/W. So dT for 200mW is 8°C.
if we thermally couple the case to the PCB, even if the PCB is at 40°C, junction temperature is well below 60°C.
Which is very very safe.
🤓
Patrick
SOIC8 thermal resistance is typically ~200°C/W junction to ambient.
Assuming 200mW and worst worst case 40°C ambient, junction temperature (not case temperature) is 90°C, so still save.
But junction to case is much improved at 40°C/W. So dT for 200mW is 8°C.
if we thermally couple the case to the PCB, even if the PCB is at 40°C, junction temperature is well below 60°C.
Which is very very safe.
🤓
Patrick
AD claimed 120°C/W for AD797, so things are much better.
Inside a closed case, it may be higher, but not significantly.
200°C/W is quoted by some TI technical documents.
Die size and thickness does have a direct influence.
My Class A power amp is 60°C inside.
I do not think a DAC will ever get to that.
So even assume 60°C ambient, 200mW and 120°C/W Rthja for AD797.
Junction temperature is still only 84°C.
😉
Patrick
Die size and thickness does have a direct influence.
My Class A power amp is 60°C inside.
I do not think a DAC will ever get to that.
So even assume 60°C ambient, 200mW and 120°C/W Rthja for AD797.
Junction temperature is still only 84°C.
😉
Patrick
"some" 🙂
Checked some, for soic8:
TLV6002 - 138,
OPA140 - 160
OPA1688 - 166
OPA1656 - 119
OPA1632 - 200.
Semiconductor and IC Package Thermal Metrics
TI Application Report SPRA953C–December 2003–Revised April 2016
https://www.ti.com/lit/an/spra953c/spra953c.pdf?ts=1679131050082
Please refer to detailed test conditions.
And for thermal management, I don't mind being too pessimistic.
Cheers,
Patrick
TI Application Report SPRA953C–December 2003–Revised April 2016
https://www.ti.com/lit/an/spra953c/spra953c.pdf?ts=1679131050082
Please refer to detailed test conditions.
And for thermal management, I don't mind being too pessimistic.
Cheers,
Patrick
Maybe something changes since 2016.
OPA1632, which was developed in 2002, have 200 C/W
But developed in 2018 OPA1656, have ~120.
Alex.
OPA1632, which was developed in 2002, have 200 C/W
But developed in 2018 OPA1656, have ~120.
Agree, but for the starting point I prefer to use the numbers of the specific device and not "general".
Alex.
Latest OPA1632 datasheet (rev D) gives 126.3 C/W for SOIC8 but older rev C datasheet only 114.5 C/W.
You're right, maybe the packaging technology has changed. I'm looking at revision B (Jan2010). It was 200.
You confirmed what I told in the past 🤣 "do not buy the SMD versions of the PCM1702 and PCM1704 from china, because it is desoldered from e-waste and is damaged by heat, they use a heatgun without temperature control" ... DIP chips are a little more prone to damage, and some could be pulled out from the socket without damage 😉