Author Topic: Diagnosing Power rail faults/ LTC1435 switching regulator  (Read 2343 times)

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Offline johndon2000Topic starter

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Diagnosing Power rail faults/ LTC1435 switching regulator
« on: July 03, 2013, 08:17:44 am »
Hi, I'm looking for a simple way to determine if a switching regulator is faulty (specifically the LTC1435)... there aren't clearly defined inputs & outputs as there is a lot of feedback, so comparing inputs & outputs with a KTBG device doesn't seem to help.

Basically, a 3.3V rail is showing as 2.9V and I suspect the LTC1435... obviously I can just swap it out but is there a more technical method for determining faulty devices for future reference?

Many thanks,

John.
 

Offline Paul Price

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Re: Diagnosing Power rail faults/ LTC1435 switching regulator
« Reply #1 on: July 03, 2013, 11:50:24 am »
From what you are describing, and while you are not offering a schematic to clarify your situation, I would not suspect the regulator IC as the cause of the low 2.9V rail reading.   Rather I would expect some filter capacitor feeding the voltage to be regulated by the switcher chip has developed ESR or has opened up and needs replacing.
 

Offline digsys

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Re: Diagnosing Power rail faults/ LTC1435 switching regulator
« Reply #2 on: July 03, 2013, 12:05:56 pm »
If it's part of a system, you'd first assume it's been designed ok (in most cases), so all that leaves you with is a good ol' DSO (or CRO).
Check V_level coming in and noise, check V_level going out and noise and finally current, which you can do with a current probe.
Hello <tap> <tap> .. is this thing on?
 

Offline dfmischler

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Re: Diagnosing Power rail faults/ LTC1435 switching regulator
« Reply #3 on: July 03, 2013, 12:19:12 pm »
Do you have a schematic?
 

Offline johndon2000Topic starter

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Re: Diagnosing Power rail faults/ LTC1435 switching regulator
« Reply #4 on: July 03, 2013, 02:38:50 pm »

No schematic but I'll upload a "typical application" diagram from the pdf... :)

 

Offline Paul Price

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Re: Diagnosing Power rail faults/ LTC1435 switching regulator
« Reply #5 on: July 03, 2013, 02:45:50 pm »
Have you scoped Vin to see if it is a clean D.C. >4.5V ?
 

Offline johndon2000Topic starter

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Re: Diagnosing Power rail faults/ LTC1435 switching regulator
« Reply #6 on: July 05, 2013, 07:13:33 am »
Yes, looks like a good level approx 5V.
 

Offline Paul Price

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Re: Diagnosing Power rail faults/ LTC1435 switching regulator
« Reply #7 on: July 05, 2013, 08:21:18 am »
Can you take a look with your scope at the "Switch" pin on the control IC and just a take a picture of what  you see on your scope with your cellphone or else just hand sketch a picture of a single pulse interval. The pulses should be periodic. And show with voltage levels by penning them on the picture. You can scan your hand-drawn or transfer your cellphone picture into your computer and post it as a .jpg file here. I can tell from a picture that is looking at this point and tell you what is wrong if your picture shows the upper and lower voltage levels of the pulse with your help, if necessary.

As far a advice goes, a picture is worth a thousand nerds.
 


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