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SN74CBT3245C: Looking for 8 separate 1:2 SPDT for +5Vcc signals with minimal signal degradation

Christoph Hesse
Prodigy 150 points
Part Number: SN74CBT3245C
Other Parts Discussed in Thread: TS12A44515, TS12A44514, TS12A44513

Hello Community,

I have two different data communications that I need to interrupt in many places (hundreds) along their course with the least signal quality loss and least propagation speed loss possible at a reasonable price. (The interruptions are necessary to implement a re-routing to newly inserted bus segments via plugged-in modules. Those connections will be made through the plugs, no additional switching necessary for that)

One of the connections will either be I2C, CAN or a RS485 Bus running at their highest speeds, could be as high as 20 Mbps or even more (for RS-485)

The other one is a connection of daisy-chained WS2812b LED chips, where signals between 0.3us and 0.9 us duration are transferred with a timing tolerance of 150ns.

On one PCB, there will be between 8 and 16 of these interrupting switches. They are normally closed and need to be operated separately, one by one. Signal and supply voltage should be 5V (for now,could be lower in the future). 

As I understand, there are no Normally closed 1:1 SPST switches, so I have to use 1:2 SPDT switches instead, correct. I found 8 coupled channels all switched by one input (the part number is mentioned in this post's header), but I did not find any IC with 8 or more separate switches. Do you offer any?

Reading the digital bus switch selection guide, it seemed that the output signal voltage of the switch does not always equal the input voltage? I need a switch that does not alter the signal form, of course. I guess I understood it wrong though as this requirement is quite basic. My 5V signals should remain 5V on the output side.  

Can you recommend one or more of your bus switches for this task?

Is it necessary to use bus-specific signal regenerating ics to make up for any signal changes these switches might have?

Thanks and best regards

Christoph

  • 0
    TI__Mastermind 45370 points

    Christoph,

    What do you mean by "normally closed" ?  Solid state switch will either be ON creating a low impedance path or OFF creating a high impedance path?  All of our switches are either ON or OFF based on a logic high or logic low on the control pins.

    To find devices  with 8 or more separate switches you can use the "number of channels" filter on the selection tool.  This how many integrated switches there are in a package.  Unfortunately as you mentioned the "bus switches" ones with large number of channels are the SN74CBTXXXX devices that are single N-FET switches.  As you mentioned the single N-FET switch doesn't not pass a signal through the I/O path from 0 to Vcc but 0V to ~Vcc-1V due to the FET voltage threshold Vt needed to bias the gate of the FET.

    The closest match I could find is the TS12A44513, TS12A44514, or TS12A44515 devices.  Do you think using 2 of these will meet your needs?   

    Thank you,

    Adam

  • 0 in reply to Adam Torma
    Prodigy 150 points
    Hi Adam,
    2 x TS12A44515 will do I think. Thanks!
    Christoph