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Old 17th February 2013, 08:38 AM   #2421
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Originally Posted by qusp View Post
Ray, its misleading to say you can realistically input +36v for a +1.4v output and you have not even covered load current. this application of the TPS reg does not have much copper for heatsink, its designed for a low dropout voltage at 100-150ma in this application. the TPS gets best performance with ~1V dropout to work with.
As you previously have written -> It is in the data sheet

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a cap multiplier will negate or complicate the use of the load sense function, load regulation and transient response suffers, so not sure of the improvement
If you check the previous posts you may realize that I wrote "in front of the regulator" and not "after".
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Old 17th February 2013, 10:05 AM   #2422
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Ray thank you, at least somebody understands my questions! At times it seems we are talking different languages here! : )
That was the information I've been looking for, it didn't cross my mind I could look up this info in the data sheet. For some reason been carrying the impression around this is such a highly integrated circuit, that only the creator of it could answer me.

qusp, I've been reading the thread and associated ones back and fort, must have missed it, if it is there. You kind of interpret a bit more into my questions than necessary - for sure this was not a debate about batteries!

bkdog, ya, I was surprised by the improvement too, give it a try!
My questions were about Ian's regulators, I've only brought up the tridents, because Ian has them too, so it might be easier having a common ground.

Thank you guys ...
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Old 17th February 2013, 10:37 AM   #2423
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yes, everyone DOES have trouble, measuring 1ps phase noise is troublesome, no matter what equipment you have.
not really
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Old 17th February 2013, 11:05 AM   #2424
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Nazar,
we have a bit to learn.

Well, let me know the difference measuring a standard XO like the Crystek and a state of the art OCXO like the HCD.
Take a look at the attached image, maybe is easier measuring the state of the art device, since 1 Hz offset from the carrier is showed? Or simply Crystek choice to not display the result at 1 Hz offset? At the bottom of the phase noise analisys you can read: Start 10Hz. But such kind of Agilent measures below 1 Hz.
Well, now let me know the difference starting at 1 Hz or 10 Hz with an Agilent E50 or E55 series or an Aeroflex PN9000.
I'm very curious.

P.S. An useful link to convert phase noise into RMS jitter
http://www.raltron.com/cust/tools/osc2.asp
Attached Images
File Type: jpg HCD_Phase_Noise.jpg (56.4 KB, 293 views)
File Type: jpg Crystek_Phase_Noise.jpg (47.7 KB, 294 views)

Last edited by andrea_mori; 17th February 2013 at 11:07 AM.
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Old 17th February 2013, 11:21 AM   #2425
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Originally Posted by Nazar_lv View Post
not really
yet more contextual issues, but of course we know that your abilities dwarf that of those that do this sort of thing every day for work. you know, I almost made a recording with a date on it predicting that you, or some other person who likes to present as some sort of super human would say its easy. so I could play it back to show how predictable you guys are.
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Old 17th February 2013, 11:34 AM   #2426
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Just when someone said something wrong it would be easy to step back.
Keep in mind, I know the answer, HCD build the OCXO as a custom part for me, so I know how many time they spent to trace the phase noise...
again, if was not clear... WITH THE PROPER EQUIPMENT.
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Old 17th February 2013, 11:55 AM   #2427
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Originally Posted by RayCtech View Post
As you previously have written -> It is in the data sheet



If you check the previous posts you may realize that I wrote "in front of the regulator" and not "after".
no Ray not as you have understood it, I guess you havent worked with LDOs very much, especially with packages like this. with this area of copper, ie less than 2 square inches, we have best case ~50 degrees C/W temperature rise above ambient with 2oz copper (not sure if its 2oz or 1oz copper on this board) and the part thermally limits at 170c... just how much current do you think you could drive through this reg with a 34.6v voltage drop with that in mind?

PD = (Vin-Vout) x Load current
PD = (36v - 1.4v) x 125mA
PD = 34.6 x 125mA
PD = 4.325W


ambient 20c leaves 150c rise, at 50c/w thats about 3W if its 2oz and if its a perfect and direct connection between the die and the heatsink, which it isnt, for reliable operation its recommended to keep it at 125c, so 2W

so even without taking the interface from the package to the heatsink into account we have more than doubled the recommended current limit.

it may allow 36V input with 1.4v output, but its not a miracle reg, it still must obey thermo-dynamics

depending on the output caps, I wonder if it would even start under such conditions.

Last edited by qusp; 17th February 2013 at 12:01 PM.
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Old 17th February 2013, 12:09 PM   #2428
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Originally Posted by qusp View Post
no Ray not as you have understood it, I guess you havent worked with LDOs very much, especially with packages like this. with this area of copper, ie less than 2 square inches, we have best case ~50 degrees C/W temperature rise above ambient with 2oz copper (not sure if its 2oz or 1oz copper on this board) and the part thermally limits at 170c... just how much current do you think you could drive through this reg with a 34.6v voltage drop with that in mind?

PD = (Vin-Vout) x Load current
PD = (36v - 1.4v) x 125mA
PD = 34.6 x 125mA
PD = 4.325W


ambient 20c leaves 150c rise, at 50c/w thats about 3W if its 2oz and if its a perfect and direct connection between the die and the heatsink, which it isnt, for reliable operation its recommended to keep it at 125c, so 2W

so even without taking the interface from the package to the heatsink into account we have more than doubled the recommended current limit.

it may allow 36V input with 1.4v output, but its not a miracle reg, it still must obey thermo-dynamics

depending on the output caps, I wonder if it would even start under such conditions.
I use the TPS7A47 LDO voltage regulator - configured optimal for my designs.

I do not know what your intentions are, but I leave you to them alone.
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Old 17th February 2013, 12:13 PM   #2429
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hehe I dont care if you use it or not, you are bound by the same issues as with this design, to the thermal performance of the PCB as well as dropout and load current, you do not have a trick to avoid this. with that kind of dropout, you might squeeze 30-40mA max before it limits or ceases to give you anywhere near the stated performance.

do not give advice like that without considering the actual situation. larger copper area may mitigate, but not avoid the issue and remember this is a 1A device, its not even possible to make a PCB that will get 1A output with that much dropout.

Last edited by qusp; 17th February 2013 at 12:22 PM.
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Old 17th February 2013, 12:19 PM   #2430
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Quote:
Originally Posted by andrea_mori View Post
Just when someone said something wrong it would be easy to step back.
Keep in mind, I know the answer, HCD build the OCXO as a custom part for me, so I know how many time they spent to trace the phase noise...
again, if was not clear... WITH THE PROPER EQUIPMENT.
if I wasnt clear, even with the proper equipment, it still isnt a simple or quick issue. ask them how long it took them and how much their test fixture cost them where you bought the XO's. good chance they built and characterized a buffer and its performance is deducted from the measurement
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