Good day all.
At now, we are facing that THVD1450 failure issue.
Our product has RS-485 I/F between product and host PC system.
In production line, failure products shows low RS-485 signal amplitude.
To detect this failure in other process, we added special check process.
At that station, we measure a resistance value between RS-485 terminals and GND.
In this process, failure products were found as low resistance value.
(NG ratio is less than 1%)
Detail of failure symptom
Resistance value between differential signal output pin and GND is very low.
(about 10 ohm)
As the result, RS-485 output signal level is reduced.
Based on TI’s failure analysis, output pin(#7) and GND are shorted.
We suspect that ESD protection cell in THV1450 is broken by any reason.
As countermeasure for this issue, we applied below items.
1)Connect GND between host PC and product in apparel to RS-485.
We have a doubt ESD or GND line noise based on voltage gap between them.
(Power is supplied from host PC system, so we made them common.)
2)To avoid IC broken by hot swap, added discharge resister between RS-485 signal lines and GND.
3)Confirm all frame GNDs are connected to earth.
But still now, same failure never gone away.
Is there any possibility that cause like this issue?
Any idea is appreciated.