Customer has seen two parts fail in their system i.e. bubble on top. We are wondering if there is a power initiation sequence that should happen because of the dual rails. Is there any other thing you think could cause this?
One other thing to look out for is the max ratings of the device. I saw on a separate email trail that the digital or analog inputs may be powered while the device is unpowered? If so, the max ratings are being exceeded and this could trigger a latchup event once the power supplies start to come up.
The recommendation from Klaus to add ~1k series resistors on the VDD/VSS lines would help limit the power supply current and possibly avoid a latchup situation. The other option for additional robustness is the ADG5408 which is a latchup immune version of the ADG1408, albeit with slightly higher RON.
I would still have concerns about the max ratings being exceeded on the analog and digital inputs, but if the current through the ESD diodes is limited to <30mA the ESD diodes should survive ok. If the power supply is grounded when it's off then the ESD diodes will just run the additional current. If the power supply is floating, there's a risk the VDD/VSS rails will become powered by the analog/digital inputs through the ESD diodes and power other devices downstream on the same VDD/VSS rail.
Another option for additional robustness is a fault protected part like the ADG5404F where the analog and digital pins can be powered while the device is unpowered. However, this would require a redesign of the board as it's not pin compatible and is only a 4:1 mux.
No sequencing required.
The supplies can't reverse polarity relative to ground.
The inputs need to stay within the supply voltage range.
You will have to show the surrounding circuitry to get a meaningful answer as to why they might have blown up.
Please see attached customer comments and pics. I advised customer that there is no power sequencing needed, so please see the
partial schematic and pic of failed device:
"A little more information. As you can see from the attached picture, there is evidence that a high level of current flowed between pins 2 (tied to VDD) and pin 3 (tied to VSS). There is also evidence of damage to the power supply powering VSS. It is interesting that both parts on the same board fail at the same time in the same way. I have about 400 boards in the field with a total of 800 ADG1408 in service. This is the first I have seen of this but the nature of the application is such that a failure can result in many
I suspect some sort of power supply sequencing issue. I feel I need to add reverse bias protection diodes to the VSS and VDD inputs. I will also add TVS diodes to the analog inputs although the signals are sensitive to leakage current. So that bring up a couple of questions.
The schematic did not originally attach, here it is...
still no attachment to your post.
Did you use the insert image button or how did you do it?
The advanced editor is what I originally used. If I use the process you advise, it tells me the files are great than 2MG to attach.
It shows on my end it is attached. Can I send them via email?
I'm pretty sure you are having polarity reversal on your supply.
You could easily fix this locally with a few low power components since the ADG1408 draw very little power.
The diodes could be a single SOT323 BAT30SFILM.
The series resistors value is a trade-off of worst case power consumption and normal operation voltage drop, but should be in the 100 Ohm to 1k range.
Of course you could also fix this at the supply itself, if that's under your control.
Thanks very much for the feedback.
Customer advised that he is adding reverse bias protection diodes to the supply lines, that should eliminate the problem. Please see the attachment AD1408_Change.pptx. Do you see any issues with this?
Ok, the diodes should help to block any current through the internal ESD diodes back to the supplies. Is there anything else hanging off the same VDD/VSS rails that could provide another current path? If the power supplies are floating while the digital input pins are high, the device itself and anything connected on the same power supply rails could be powered via the digital input pins through the ESD diodes.
If there proves to be no issue with the digital input pins then I'd suggest to continue to investigate the suggestions from Klaus.
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