Hello, I am using a SN74AVC1T45DRLR device in below configuration and I am having an issue when the SN74AVC1T45DRLR is in a partial power down condition. Can you please help me understand the issue better?
1. SN74AVC1T45DRLR is used on a signal that needs to reach the TIVA microcontroller from TI.
2. There can be 2 drivers for this signal reaching the TIVA microcontroller (a) SN74AVC1T45DRLR device (b) a debug connector which will be used only in the lab environment
3. VCCA is connected to the same power supply as the TIVA microcontroller.
4. VCCB is connected to 1.8V from a different source. In the scenario that I am facing this issue 1.8V is designed to be OFF and hence VCCB is at 0V
5. DIR pin is pulled down.
6. 1.8V level signal is connected to the B pin & 3.3V signal is connected to the A pin towards the TIVA microcontroller
In the above scenario, when VCCB is OFF, we try to drive the signal through the debug connector ( option {b} in point 2 above) and we see that we are not able to drive this signal. If during partial power down condition, the output A is tristated, then my understanding was that I could still drive the signal from the debug connector. However, this is not happening. We have tried the below 2 test cases to see if SN74AVC1T45DRLR is not functioning as per our expectation
1. We have a 0 Ohm resistor at the A pin. When this is removed, we are able to drive the signal from the debug connector. This hints that when A pin is isolated from the path, we are able to drive the signal from the debug connector
2. We change the DIR pin from a pull down to a pull Up, in which case the direction becomes A to B as per the specs. The 0 Ohm on the A pin is re-installed. In this case also, we are able to drive the signal from the debug connector. This also hints that when the direction is chosen as B to A and SN74AVC1T45DRLR is in partial power down condition, A pin might not be really tristated.
Can anyone please help understand this better?
Thanks,
SN
