SN74CBTLV3257: B side termination

Each "SW" box in the functional block diagram is one such switch:

Unused I/O pins can be left floating; see [FAQ] Frequently Asked Questions about signal switches and multiplexers.

Hi Yusuke,

Can you elaborate a little more of this:

"Can The xB1 pins terminate open at production mode(xA pins are always connected to B2, S=High)"

When S = High xB2 will be connected to xA , xB1 pins will effectively be Hi-Z in this state.  Any unused signal pins should be connected to ground through a 50 Ohm resistor. If I am misunderstanding your question, please let me know so I can help find your answer.

The Diagram that Clemens indicated shows the basic Multiplexer channel, while the switch you provided is what would go into each of the boxes labeled "SW". Each switch uses a transmission gate architecture, which is what you have attached to your question. This architecture allows the switch to pass analog signals with a lower Ron over the signal range than a normal N-FET switch. For digital signals it allows the capability to pass hard zeros and hard 1's because the switch utilizes both N and P Type MOSFET. 

For more information please see our video on switch architecture

Best,

Parker Dodson

Hi Dodson-san,

Customer is considering as below,

Test mode : they use xB1 for software update for MCU by UART signals at test process. xB1 will be not used in production.

The customer will change S pin to low, Then, MCU signal path will be change to dedicated test board. And, if Test is finished, this board will be removed connection.

So, The production mode is use only xB2. And xB1 pins will be open.

Customer want to terminate xB2 by open or pullup to Vcc. 

As you mentioned, should the xB2 be connect to ground through a 50 Ohm resistor at this situation?

Thanks

Muk

Termination of unused I/O pins would matter only in high-speed applications. For slow digital signals like UART, you can simply leave it open, without any measurable effect. (And 50 Ω termination would conflict with the test mode; if you are paranoid enough to add a resistor, a 10 kΩ pullup would be fine.)