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SN74CB3T3257: I need a 2:1 high speed 4-channel mux, with each channel capable of level shifting 1.8V and 3.3V

Adam Torma
Mastermind 45485 points
Part Number: SN74CB3T3257

E2E, 

I'm looking for a mux that can also act as level translator.  A 2:1 high speed 4-channel mux, with each channel capable of working at different voltages. 

Typical application:

One Jtag connector with many chips on board. 

Jtag dongle works at 3.3V

out1 (Chip1) works at 3.3V

out2 (Chip2) works at 1.8V 

I was looking through the mux portfolio and I don’t see anything which supports different voltages on the output ports.

What does “output voltage translation tracks Vcc” mean?

I see this in the datasheet for:

Thank you,

Adam

  • 0
    TI__Genius 9132 points

    Hi Adam

    The “output voltage translation tracks Vcc”  means  how the output follows the input voltage based on Vcc value. 

    You can find more details in this app note here:

    This family can operate with a power-supply voltage range of 2.3 V to 3.6 V.

    • When VCC = 3.3 V, the device can translate from a 5-V input to a 3.3-V output. 
    • When VCC = 2.3 V the device can translate from 5-V or 3.3-V inputs to a 2.3-V output

    see the graphs below for Data Output Voltage vs Data Input Voltage at specific Vcc.

    What is the input signal range for your application?

    Can you explain how much down translation you are looking for?

    Thanks

    Saminah

  • 0 in reply to Saminah C
    TI__Genius 9305 points

    Hi Saminah

    The voltage level translation required is mentioned in the original post. The customer needs this for a JTAG use case where the JTAG signals on the dongle are at 3.3V. The requirement is to have the 2 outputs each at different voltage one at 3.3V and the other at 1.8V.

    It looks like in our device both outputs will track a single voltage so I assume this is not doable.

    Thanks!

  • 0 in reply to TIDR
    TI__Genius 9132 points

    Hi TIDR,

    Yes, the  SN74CB3T3257 will perform same level shifting for all output signals.

    You can use 2  SN74CB3T3257 for different (1.8V and 3.3V) level shifts.

    Thanks

    Saminah