SN74LVCH16T245-EP: SN74LVCH16T245: Question about the input voltage drop of ports

Prodigy 160 points

Replies: 2

Views: 55

Part Number: SN74LVCH16T245-EP

Hi, there.

I am using SN74LVCH16T245-EP in one of my project. Here I am driving 16 IO's of SN74LVCH16T245 from B port to A port. A port is referenced to 3.3V and B port is referenced to 5V.

A and B ports of SN74LVCH16T245-EP do not have external pull-up or pull-down resistors in my system. 

(I know that external pull-up resistor is not required because  the device has a built-in bus hold function.)

Also, I applied a 5V signal to the B ports and kept the ~OE signal 'HIGH'(3.3V).

In this environment, the voltage level at B ports is 1.2V, not 5V. 

why is the 1.2V voltage measured at B Ports?

(I know that the B ports stay 'Hi-Z' when the OE signal is 'HIGH'. Also, if 5V signal is supplied to B port in 'Hi-Z' state, I think it should keep 5V.)

Please answer in my question. 

I will wait your answer. 

Thanks. 

2 Replies

  • When you are applying a 5 V signal to a B port pin, it should not be possible for the voltage at the pin to be anything but 5 V.

    Where does that 5 V signal come from? Can you check whether a current flows?

  • Can you provide a schematic and scope shot of your issue?  This will help make sure to understand your issue completely.

    A schematic with annotated voltages would be helpful if you do not have scope shots.

    Regards,

    Wade