SN74LVCH8T245 unused pins

Hello Doran,

You connect both un-used ports to ground or their respective Vcc.  GND is the usual connection due to ease of implementation.

-Francis Houde

Hello Francis,

Is it OK to connect the un-used B outputs to GND ?

Thanks,

Doron

Hello Doran,
Connect all unused ports to GND. For example, say you don't intend on using port 1 then connect A1 to GND and B1 to GND.
-Francis Houde

Hello Doran,
In fact, you only need to connect the input pin to GND because that will cause the output pin to be grounded. The important thing is that the input is grounded and not left floating.
-Francis Houde

Hi Francis,

Is the connection of Inputs to GND need be done through resistors ?

Doron

Hi Doron

If you are using SN74LVC8T245 (non "H" version), please follow Fancis recommendation and tie the unused inputs to GND. It is recommend to pull down through a 1K resistor.

If you are using SN74LVCH8T245, as your title says, do not use pull-ups or pull down. These parts have bus-hold circuitry. As stated on page 2 of the datasheet "

"Active bus-hold circuitry holds unused or undriven inputs at a valid logic state. Use of pullup or pulldown resistors with the bus-hold circuitry is not recommended."

Generally, pullup and pulldown resistors should not be used on the inputs of devices with bus hold. In applications that require pullup or pulldown resistors to hold the inputs at a specific logic level, the bus-hold current maximum specification should be considered.

The resistor value should be chosen to overcome bus hold under worst-case conditions. The resistor must supply enough current so that the input is pulled through the threshold to the desired logic level. If the current supplied is too weak, the input node could be held near the threshold, causing a high ICC that could damage the part.

Hope this helps.

 

Thanks