Hello,
I'm using a sn74lvc2t45 voltage translator to translate two 3.3V signals coming from a SPI device into 5V. The behavior of the translator doesn't however look right:
- 3.3V inputs and supply are connected to the B side of the chip (pins 6,7,8) and 5V inputs and supply to the A side (pins 3,2,1); DIR (pin 8) is connected to ground, as the traslating direction is from B (3V3) to A (5V). In an other section of the circuit, 3V3 is generated by 5V and therefore always comes up not earlier than 5V.
- When the IC is powered and either input line is left unconnected (pins 6 or 7 open), I read 5V on the corresponding output (outputs are left open as well).
- When the IC is powered and either input line is shorted to ground, I read 3.8V on the corresponding output (open, not connected to anything).
- When the IC is not powered, and all input and output lines are disconnected, I read a resistance of approximately 877Ohm between pin 2 abd GND, 877 Ohm between pin 3 and GND, 1500 Ohm between pin 2 and pin 1 and infinity between pin 3 and pin 1.
Since the board is a prototype, I considered the possibility that the IC was mounted inverted (with pin 1 in the position of pin 5). Looking however at both the documentation and at the chip's markings, I was not able to recognize pin 1. The only distintive marking is a white stripe (similar to the one reported on SMD capacitors): I guess it indicates the pin-1/pin-8 side. If so, the chip is installed correctly.
Could you please confirm that the above behavior is an indication of a faulty chip ? Is it possible that the chip was installed inverted ?
Thank you for any help !
