RS422 AM26LV32E Output (Y) Status When Unpowered

If G or G_bar is active then it will be high. If not, then it will be high impedance.

Hi Andrew, Please note: the AM26LV32E is "unpowered" ! i.e. no VCC and its G, G_bar must be inactive. Can you re-consider your answer? Thanks Sheng

Hello Sheng,

If the device is unpowered then every node will be indeterminate.

Thanks,
Andrew

Hi Andrew,

Thanks for your quick reply. If you don't mind, and if it is possible, I want to hear a second opinion from other TI engineers because I believe "indeterminate" is not the right anser.

Thanks
Sheng

Hello Sheng,

If there is no supply on the part. How can the part provide a high output. Maybe high impedance is a better way of wording it.

Does that make more sense to you?

Hi Andrew,

The reason I asked my orignial question here is becaue I plan to use a FPGA which does not support Cold Sparing. It means if the FPGA's I/O pins are driven (to High or half-High) when the FPGA is unpowered, the voltage applied to the I/Os will power up some part or whole of the FPGA (e.g. in ths case, FPGA pins may not stay in tri-state.). So, I have to know if there is any feedback power via AM26LV32E's output Y to the FPGA if the AM26LV32E's A and B pins are driven normally while AM26LV32E itself is unpowered.

Come back to your answer/question.  when unpowered, "the AM26LV32E's output Y is high impedance or carrys some energy" should depends on the chip internal design. In my opinion, some manufactor chips may be low-impedance to ground when unpowered, some may stay in high-impedanec, some may be stay in some voltage level, say 1.1V.  

Can you double-check your answer with your team?

Thanks

Sheng

 

 

 

 

 

 

Thanks Andrew, I saw the schematic on page 3 (datasheet verion JUly 2013). That is good.

As you know, for my case, it is crucial to know impedance value on output 1Y when unpowered. Would you mind to do me a favour to measure the impedance between Y/Vcc and Y/GND when the device is unpowered and its pin 1A and 1B are driven as "high"?

If you would, no rush, and take your time.

Thanks a lot in advance
Sheng

Hello Sheng,

There is no fixed impedance, as while the device is unpowered the gates of the output transistor will be floating and unknown. Hence, as transistor being gate controlled output impedance devices, the output impedance of the resistor will never be consistent.

So, if you were to measure the output impedance of 10 devices, all of them would be diferent.

THanks,
Andrew

OK, in this case, I have no more questions, Andrew. We can close the case. Thanks for your time and support.