Hi
I have inherited a design - please see attached schematic extract. Most of the time, the relay switches properly and I measure Voh = 2.62V and Vol = 0.118V.
Occasionally, the relay gets into a mode where it does not switch properly and I measure Voh = 1.8V Vol = 0.4V.
Having read the datasheet and application notes for the part, I am confused how this part is working and why this problem is occurring. I would like to understand this part better and know why this circuit sometimes fails.
It is already in production and if there is a simple mod that I can do to fix it.
From what I understand:
1) the driver device sinks/sources the current (ie. TXS108E is a passive switch in simple terms)
2) when Vi fall below 1.6V, the internal switch turns on and Vi is approximately equal to Vo. In this case, there is a 40k internal pull up. Required current at Vo is sourced from the driver?
3) when Vi is above 1.6V, the internal switch turns off and Vo has 4k pull-up to 3.3V. In this case, am I correct in understanding that the base current is sourced through this 4k pull up. So for example, lets say the base current is 1mA, that means that the there will be a voltage drop of Vdrop = IR = 1mA * 4k = 4V? Which means that output will never go high?
Please help me understand why this works most of the time and other times not.
Thank you kindly
