DAC121S101QML-SP: SPI while powered down

Ryan,

I realize this question is actually assigned the high-reliability folks, but we just recently looked at exactly this part in exactly this question in detail recently from the DAC side of things so I figured I'd chime in quickly and save everyone some time...

The absolute maximum ratings table for this part is actually quite robust. The main things to look at are the "Voltage on any input pin", "Input current at any pin", and footnote 3 from this table (on page 4).

From an official stand-point and what I would suggest they heed since this is an implied high-reliability application is to abide by what is in the table. So, if we're talking about an non-powered device and the potential for signaling on the digital lines they will obviously exceed VA+0.3V (abs max rating for voltage on any input pin) and therefore the current needs to be limited to less than 10mA. There is also some implication on the number of pins that exceed this voltage limit, as in total the datasheet states that there should be less than 20mA of violation.

However...

As I mentioned we recently looked into this and it turns out that the implication doesn't totally appear to be realized on the digital pins (which...oddly, are the only input pins on the part). Essentially there are not actually ESD cells between the input pins and the positive supply rails which we would ordinarily expected given the statements in the absolute maximum ratings table. So for the most part, you can survive this situation and not see any drooping on the power supply lines, drooping on the digital input pins, or damage to the device.

The context of this particular situation was just a prototype, though. So in the end we gave credence to this being mostly "okay" for functional / performance evaluation - but as I eluded to before I would strongly suggest that the customer abides the datasheet table on page 3 for their final design.

Ryan,

To add to Kevin's comments, the abs max voltages listed in the datasheet are incorrect.  The abs max for the input pins should be 6.5 V. This will be updated in the next rev. of the datasheet.  The protection circuit is shown in the diagram at the bottom of page 4.