Other Parts Discussed in Thread: ULN2003A,
Tool/software:
Hi all,
We currently use the TI TPL7407LAPWR as an open-drain inverting buffer array to isolate our GPIO pins from customer-exposed I/O, and we have seen an abnormal failure rate with this part in the field as of late, ~10% as a rough estimate. At this point, we have recorded about 80 PCB's, and still increasing, with non-functioning chips.
The issue we are observing is the outputs not responding to changes at the inputs; regardless of any one input state, its output will either be stuck on or off, but usually it fails on (always stuck low, roughly 10mV to 30mV measured, and won't pull up), though I did observe a few (less than 5) stuck in the off-state (always pulled up, won't switch low). I have seen this failure both functionally within our design, and electrically with a DMM and a physical output pullup to 3.3V on a bench supply to rule out an issue with the GPIO internal pullups. I even de-soldered one failed chip from a PCB and tested it completely out of circuit (powered through bodge wires with the same pullup setup on the outputs) and verified the outputs do not switch. The de-soldered part in particular had all 7 channels not working, and I have observed several other instances with multiple channels not working, but I cannot confirm if all instances were multiple channel failures, or if some were only a single channel.
Another note is we have seen this steadily over the last 12 months, and from 2 different PCB vendors, so I am inclined to believe it is an issue with the component rather than the PCB assembly process, and also that it wasn't just a bad lot of parts.
All that being said, my questions are twofold:
1) Is there a known issue in the semiconductor manufacturing process for this part, or could we be missing something in our schematic/design implementation that is causing the part to enter this state?
2) Are there any recommended alternative parts that would just drop-in? All my searching has revealed we have minimal options and would require a PCB change to accommodate a new part, which we would like to avoid. Our requirements are:
a) Must take 12VDC as voltage supply
b) BJT or FET drivers are fine
c) Must be 16-TSSOP
d) 7 channels with identical pinout
e) Channel inputs must be able to survive 14VDC
f) Inverting is preferred, but non-inverting is not a dealbreaker
g) Output current source/sink capability is up in the air; the highest load we drive is a single optocoupler emitter input at about 50mA (not continuously, this is a serial com line), and the rest are GPIO inputs.
h) We do not need an output clamp diode
The TI SN74LS07DR is a noninverting chip we also use that has not had any issues, so we would accept something similar to that if it took 12VDC at the supply pin.
Any insight or guidance is a great help, thank you in advance and happy Thanksgiving.
Thomas
