50-Step Shunt Attenuator Resistor Calculator - Neville Roberts
and choose 32 steps , then you calculate resistors in parallel to fit in 6 relay combination .
And at the end you will find my value !
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Yesterday I had an issue with PGA2310, want to post it here to check if someone may had similar thing. So, my PGA suddenly died. In the evening I turned off the device just usually (staying in standby, so the PGA and controller were on), and in the morning when I turned it on - it didn't work anymore.
On the PCB around the PGA traces of overheating are visible - the fiberglass even turned slightly brown, which means that for some reason the PGA just burned... Also, when I touched it (wasn't working already) it was still very hot.
Once I have met similar behaviour, when the PGA "hung-up" for some reason - the chip started heating up, but resetting it helped and that time it started working again. This time, obviously, I didn't detect the issue in time, so the chip went dead.
So, it seems to me, that it's a general design&manufacturing issue for the PGA2310 - when the chip looses communication (hangs) - the internal registers can set it to a random state, where some excessive current runs through the chip and it naturally burns. I think this issue needs to be addressed by TI's engineers, as if it happened to me - may happen to any customer. But in general, it spoiled a bit my impressions about this, otherwise fantastic chip. Just be aware.
I resoldered the chip and now everything works fine, but... How can I avoid this in the future? So far the best solution seems to me unpowering the device, which of course makes the standby mode useless...
Maybe worth adding an additional relay or two in parallel to the power relay, so it will turn off the power of PGA when the device is in standby? This would need at least 3 switching groups, to take down both digital and analog (+/-) power from the PGA...?
any thoughts?
On the PCB around the PGA traces of overheating are visible - the fiberglass even turned slightly brown, which means that for some reason the PGA just burned... Also, when I touched it (wasn't working already) it was still very hot.
Once I have met similar behaviour, when the PGA "hung-up" for some reason - the chip started heating up, but resetting it helped and that time it started working again. This time, obviously, I didn't detect the issue in time, so the chip went dead.
So, it seems to me, that it's a general design&manufacturing issue for the PGA2310 - when the chip looses communication (hangs) - the internal registers can set it to a random state, where some excessive current runs through the chip and it naturally burns. I think this issue needs to be addressed by TI's engineers, as if it happened to me - may happen to any customer. But in general, it spoiled a bit my impressions about this, otherwise fantastic chip. Just be aware.
I resoldered the chip and now everything works fine, but... How can I avoid this in the future? So far the best solution seems to me unpowering the device, which of course makes the standby mode useless...
Maybe worth adding an additional relay or two in parallel to the power relay, so it will turn off the power of PGA when the device is in standby? This would need at least 3 switching groups, to take down both digital and analog (+/-) power from the PGA...?
any thoughts?
Maybe you should try to find the actual cause of the overheating first. What I read in your post is speculation but there is no proof that the cause is what you think.
For exampe, when you 'turn off' the controller, in which state does it leave the PGA? Do you set it to mute? Do you have a relay on the output, and if so what state is it left?
jd
Pga2310
To avoid such result I modified Dan's volume control source code for M16, in my firmware version I deleted poweron/off function from M16. In my amplifire ATTiny2313 does it. And PGA2310 swetched off with amplifire power is off and PGA2310 is on when amplifire power is on.
P.S.: From the very beginning I thought that its bad idea to make PGA2310 allways be ON with +5v. Thats why I changed danzup source code first.
To avoid such result I modified Dan's volume control source code for M16, in my firmware version I deleted poweron/off function from M16. In my amplifire ATTiny2313 does it. And PGA2310 swetched off with amplifire power is off and PGA2310 is on when amplifire power is on.
P.S.: From the very beginning I thought that its bad idea to make PGA2310 allways be ON with +5v. Thats why I changed danzup source code first.
Hi , in 2 years of using this chip nevere faild !!
But if you forgot to connect digital gnd to the analog gnd then the PGA start burning !
I think you have a problems with GND traces .
The mute line is activated to the chip .
And there are not problems with that as PGA is working correctly if only all 3 tension are applied at the same time and removed at the same time .
When in stand-by my controller does not cut the power to the PGA !
Only to the power amplifier !!!
The atmega and PGA are always on a separate power source (separate transformer ) the so call stand-by transformer which can provide the +5V for digital section and the +- for analogue part !!!
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In the "off" state the PGA is set to mute and source selector relays are unpowered, only the power rails stay connected on. The output remains connected to the poweramp's input, which is also off.
As I mentioned before, I had a similar behaviour once - that time the sound went suddenly cranked (with a huge amount of "digitally sounding" distortion) and the PGA started heating up. Only powering the whole device off and on helped. The chip naturally "hung", and what I noticed - immediate and powerful overheating. So, my "speculation" comes out of a logical analysis, not just outta pointing my finger into the sealing...and the "actual cause of overheating" seats inside the chip's behaviour. If you have ever read the datasheet - it's mentioned inside, that the chip is basically a resistor ladder switched by digital switching network. It's more or less obvious for me, that once the data in chip's register for any reason get's wrong, there is a POSSIBLE STATE, where switches get open the way they are shorting power rails to the ground. This should not happen during the normal operation, of course, but the PROBLEM is that there is no protection within the chip against a mentioned uncontrolled condition.
Or have you got any better idea, not just speculation?
As I mentioned before, I had a similar behaviour once - that time the sound went suddenly cranked (with a huge amount of "digitally sounding" distortion) and the PGA started heating up. Only powering the whole device off and on helped. The chip naturally "hung", and what I noticed - immediate and powerful overheating. So, my "speculation" comes out of a logical analysis, not just outta pointing my finger into the sealing...and the "actual cause of overheating" seats inside the chip's behaviour. If you have ever read the datasheet - it's mentioned inside, that the chip is basically a resistor ladder switched by digital switching network. It's more or less obvious for me, that once the data in chip's register for any reason get's wrong, there is a POSSIBLE STATE, where switches get open the way they are shorting power rails to the ground. This should not happen during the normal operation, of course, but the PROBLEM is that there is no protection within the chip against a mentioned uncontrolled condition.
Or have you got any better idea, not just speculation?
Ok : this is something that must be investigate very carefully !In the "off" state the PGA is set to mute and source selector relays are unpowered, only the power rails stay connected on. The output remains connected to the poweramp's input, which is also off.
As I mentioned before, I had a similar behaviour once - that time the sound went suddenly cranked (with a huge amount of "digitally sounding" distortion) and the PGA started heating up. Only powering the whole device off and on helped. The chip naturally "hung", and what I noticed - immediate and powerful overheating. So, my "speculation" comes out of a logical analysis, not just outta pointing my finger into the sealing...and the "actual cause of overheating" seats inside the chip's behaviour. If you have ever read the datasheet - it's mentioned inside, that the chip is basically a resistor ladder switched by digital switching network. It's more or less obvious for me, that once the data in chip's register for any reason get's wrong, there is a POSSIBLE STATE, where switches get open the way they are shorting power rails to the ground. This should not happen during the normal operation, of course, but the PROBLEM is that there is no protection within the chip against a mentioned uncontrolled condition.
Or have you got any better idea, not just speculation?
Maybe you discovered a bug or a flaw in TI design !!!
Or maybe not .....
Time and investigation will tell us .
Dan, your assumptions are wrong. The AGND and DGND polygons are connected beneath the PCB in a single point through a ferrite bead inductor. This is hardwired, no chance they aren't connected.
Moreover, the device was working quite fine for more than a month, delivering me a big amount of pleasure, until yesterday
Is it possible that the input is left unterminated and that the chip oscilates because of that?
Anyway, the 'obvious' thing is not obvious to me as the switches are NOT connected to the power lines - so how can they short the power lines??
[snip]Or have you got any better idea, not just speculation?
No I'm still thinking loud, but I don't think you should start to point to TI engineers before you really know what's going on. Just to be fair.
The mentioned ground issue is also a possibility imho.
jd
Dan, your assumptions are wrong. The AGND and DGND polygons are connected beneath the PCB in a single point through a ferrite bead inductor. This is hardwired, no chance they aren't connected.
Moreover, the device was working quite fine for more than a month, delivering me a big amount of pleasure, until yesterday
Ok , here one thing to do : use a relay that is connected in parallel with the power relay to short the input of PGA to ground when in stand-by .
Possible oscillation as suggested by @janneman can destroy the PGA .
Or you can attached a 100k resistor on input of PGA to the ground for left and right input .
And tell us if there are more problems .
Okay, then mute doesn't mean anything? Shouldn't it be CONSIDERED BY DESIGNERS, that for a VOLUME CONTROLLER IC such a state can, and will most probably happen? WHY this did not happen before? Also, your assumption simply ignores my previous experience I just described...
Any switch is just a MOSFET which has to be fed by power, isn't it? What happens if they get ALL suddenly open? Normally they shouldn't...
Okay, just to be fair - your'e right. But also, just to remain fair enough I'll go back to study the datasheet more precisely. Worth to add, I'm NOT POINTING TI's engineers (really I don't understand why you take this in such an offensive-resisting manner... I am also an engineer, since about 15 years...) - but I am raising a definitely existing problem, which could be caused by POTENTIAL DESIGN ISSUE, this may at least be taken into attention by TI. As I mentioned before, the PGA is a volume controller IC - and such "unforeseen" cases should be foreseen by designers, imho.
Indeed, this is just your imho, because it's not the case, sorry.
This can be done easily, as the input selector relays are DPDT. So, if I connect the unused position (of any selector relay) to the ground - it will short the input of PGA to the ground, when the device is off.
But again, out of MY EXPERIENCE, this happened already with input's ON - see my previous posts, so I still don't think oscillation is the case.
I said it's a possibility, I didn't say it is the case. And a possibility it is.
The point I'm trying to make is that nobody has an idea what is going on. I only wanted to add some possibilities. Doesn't anybody measure and test anymore these days??
In your earlier post, without any information on what caused the problem, you immediately pointed to TI engineers. If we all are engineers, we should do what engineers do: measure, test, collect information, THEN conclude what the problem is and solve it.
jd
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Your'e right, I wasn't precise enough. Just to add - I didn't have an intention to blame anyone, especially not TI's engineers - rather I wanted to highlight a possible problem. Honestly, I didn't think the subject will cause such amount of feedback, therefore I didn't struggle too much to share all the prerequisites of my conclusions.
Again, I would be happy if I'm wrong and something went wrong due to my specific mistake, but, based on "test, collect&conclude" I had to conclude, that everything's fine with my design, the reason is somewhere behind.