I've had these around since they were introduced, finally came into a situation where it would have been good to employ -- but.....
Here's Z for 10V / 100mA a.c. current is 50mA
Here's Zout when the "Lower Set Resistor" option is chosen -- 499R/49.9K/10K per the figure in the datasheet:
Bypassing the with 47nF/100R at the 10K junction:
Bypassing with 470nF:
Bypassing with 4.7uF:
Here's Z for 10V / 100mA a.c. current is 50mA
An externally hosted image should be here but it was not working when we last tested it.
Here's Zout when the "Lower Set Resistor" option is chosen -- 499R/49.9K/10K per the figure in the datasheet:
An externally hosted image should be here but it was not working when we last tested it.
Bypassing the with 47nF/100R at the 10K junction:
An externally hosted image should be here but it was not working when we last tested it.
Bypassing with 470nF:
An externally hosted image should be here but it was not working when we last tested it.
Bypassing with 4.7uF:
An externally hosted image should be here but it was not working when we last tested it.
That's really interesting jack. There are clearly a lot of parameters that can affect the output impedance and noise of an IC regulator, not least of which is output current draw which you haven't investigated yet. TNT Audio did a few atricles on a similar topic.
Have you compared this one to the old 317 workhorse at the same Iout?
It's clear that just following the data sheet may not bring the best out of a regulator. Could be the start of a major thread here to optimise regulators.
Have you compared this one to the old 317 workhorse at the same Iout?
It's clear that just following the data sheet may not bring the best out of a regulator. Could be the start of a major thread here to optimise regulators.
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I disagree, the LT1963A, LT1764A, LT3032 and LT1763 all perform quite well and the LT1083 1084 1085/1033 LDO 3 pins are drop in lm317/337 with somewhat better performance as well as lower dropout
you just have to remember that many of them function very much as part of a system and their dynamic performance is a function of the output capacitance
you just have to remember that many of them function very much as part of a system and their dynamic performance is a function of the output capacitance
With a Kelvin connection (as I'm sure jackinnj is using) the resistance of the wire shouldn't matter.
I am currently using the LT3080 in a high voltage regulator application and have performed extensive simulation on it. The sims correlate well with lab measurements as can be seen in This Thread. I'm seeing the same 60-ish mOhm output impedance across the audio band.
It seems the regulator was optimized for operating with just Rset to ground.
That said, I have to take issue with 60 mOhm being "crappy performance", though. By the time the regulator is connected to the load, the PCB traces and/or wiring will add up to several times that. This is why remote sensing was introduced. Unfortunately, I don't think it's possible to do remote sensing with a floating regulator.
If you don't mind switching regulators, I suggest looking at the LM2267x-series from National Semiconductor (now TI). I use one in my Universal Filament Regulator. Its performance is rock solid with about 1.5 mOhm output impedance. You can take the feedback voltage at the load (remote sensing) for minimum output impedance. That's a topic for a different thread, though.
But all in all, I find the LT3080 to be a quite rocking regulator. I challenge anyone to beat its ripple rejection! In my high-voltage setup, I ran it with 50 Vpp (16 V RMS) ripple on the input, and measured 20 uV RMS AC on the output.
It also seems to jive quite well with the simulation results obtained in LTspice.
~Tom
PSRR in the data sheet is ~-80dB @10Hz with a 2.2uF ceramic cap. The best I've seen in a low voltage regulator is -130dB.
I initially looked to make the measurements analogous to those Jung did for his 1995 articles -- "Regulators for High Performance Audio" -- 13.7V or 15V out into a 100R load. For Z-Out I use 50mA which he also used. The articles are available on his website.
I'm awaiting some TO-220 devices since the MSSOPs are sweating a bit at greater Vin-Vout.
I use Mueller Kelvin clips and some I made with micro-grippers. With this setup I can measure below a micro-Ohm.
I initially looked to make the measurements analogous to those Jung did for his 1995 articles -- "Regulators for High Performance Audio" -- 13.7V or 15V out into a 100R load. For Z-Out I use 50mA which he also used. The articles are available on his website.
I'm awaiting some TO-220 devices since the MSSOPs are sweating a bit at greater Vin-Vout.
I use Mueller Kelvin clips and some I made with micro-grippers. With this setup I can measure below a micro-Ohm.
Jack
I seem to recall in Errol Dietz's article that the LM317 o/p Z falls rapidly with Iout from around 5uH at 10mA to 1uH at about 300mA or thereabouts (I don't have the actual graph to hand) then it levels off at a constant 1uH thereafter.
Wouldn't 300mA be a better value to run at since you can be sure of Zout when chosing values for any output cap and snubber?
You also mentioned remote sensing the load. Can you explain how that is actually done for a reg powering an op-amp say and is it really an improvement if the reg is right next to the op-amp?
I seem to recall in Errol Dietz's article that the LM317 o/p Z falls rapidly with Iout from around 5uH at 10mA to 1uH at about 300mA or thereabouts (I don't have the actual graph to hand) then it levels off at a constant 1uH thereafter.
Wouldn't 300mA be a better value to run at since you can be sure of Zout when chosing values for any output cap and snubber?
You also mentioned remote sensing the load. Can you explain how that is actually done for a reg powering an op-amp say and is it really an improvement if the reg is right next to the op-amp?
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Hi
This seems to be an old threat but I can't find anything more relevant for this question about the LT3080 reg. I am wondering if using a low noise Vref at the SET pin would be significatly better than a resistor. This is my impression when reading the datasheet. It seems to say that Noise viltage increase with resistor value. By using a good Vref the noise at the output can be much lower. Do I misunderstand it?
Cheers
This seems to be an old threat but I can't find anything more relevant for this question about the LT3080 reg. I am wondering if using a low noise Vref at the SET pin would be significatly better than a resistor. This is my impression when reading the datasheet. It seems to say that Noise viltage increase with resistor value. By using a good Vref the noise at the output can be much lower. Do I misunderstand it?
Cheers
You can bypass the Rset with an electrolytic cap which will knock down the noise. The current source in the LT3080 can also be "tricked" by using another resistor on the OUT pin -- see the datasheet.
Thanks for asking the question, I think the LT3080 is a really neat device.
Now obviously this is a very old post, however this reminds me of something I seem to notice a lot on here - people getting caught up in graphs and numbers without knowing exactly what will happen in application.
Hi dreadnoughtstrength,
-Chris
I'm not sure what you mean by that. This member put the part on the bench and compared it to the simulator results. Sounds like he knows exactly what will happen in an application. I often do similar things to regulators injecting noise, ripple and HF upstream of the regulator for the same reasons.
-Chris
'Poor performance' on paper. Excellent performance in application.
Thanks, jackinnj. Do you have any recommendation on value of the capacitor. I have used 100nF film cap as in datasheet but I don't have any instrument to measure noise. As you mention electrolytic I would guess the value would be much larger than 100nF. How about low ESR electrolytic?
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