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SN74CB3Q3244: SN74CB3Q3244

Gus Martinez
Mastermind 29141 points
Part Number: SN74CB3Q3244
Other Parts Discussed in Thread: SN74LVC2G66, SN74CB3Q3245, SN74CBTLV3245A

Hello,

I'm considering the SN74CB3Q3244PWR for isolating JTAG & UART signals on my board design. I currently use SN74ALVC244PWR, but since I need to support bidirectional cJTAG signals, I need to move to an analog switch. I only need 6-channels, 2 of which are bidirectional. However, space on my board is limited hence I rather use this single 8-channel device vs a multiple devices. Is SN74CB3Q3244 a good fit for this application or is there a different part number to consider?

  • 0
    Guru 317280 points

    3× SN74LVC2G66 in DSBGA might be smaller.

    For 8-channel devices, consider SN74CB3Q3245, or SN74CBTLV3245A (less power and slightly cheaper, but lower bandwidth).

  • 0
    TI__Intellectual 2694 points

    HI Gus,

    Thank you for reaching out. Could you please provide  few more details on the use case.

    Based on the choice of device SN74CB3Q3244 and mentioned information above, seems like you are working on 6x 1:1 signals in the schematic. 

    - What is the expected supply and signal voltage?

    - What is the JTAG signal frequency?

    - Are you planning 4 channels for JTAG and 2 for UART?

    We can come up with a optimal size and cost effective solution.

    Thank you,

    Sandesh

  • 0 in reply to Sandesh Rawool
    TI__Mastermind 29141 points

    Hi Sandesh,

    Here are the details:

    • All data and I/O runs at 3.3V
    • JTAG runs at <10MHz.
    • 4 channels for JTAG (two of which are bidirectional in cJTAG submode) and 2 for UART
    • Need separate OE control for UART and JTAG pins

    Here is a screenshot of the current schematic which uses a buffer. The SN74CB3Q3244 device is attractive because it looks to be pin-to-pin compatible with the buffer we use now. The '3245 parts suggested before are not a good fit because they have a single OE. I would also rather not use BGA to simplify assembly.

  • 0 in reply to Gus Martinez
    TI__Intellectual 2694 points

    Hi Gus,

    Based on the schematic and details provided, the SN74CB3Q3244 is a good choice and will support both JTAG and UART requirements. It does have matching pins as the buffer device and will fit well using the existing control signals/logic and supply.

    If you want to further reduce the solution size there is a QFN option available SN74CB3Q3244RGYR and has a 0.5mm pin pitch. This is ~60% smaller footprint compared to the TSSOP. If you do that, please make sure to tie the thermal pad to the GND reference as a standard practice.

    Let us know if any further questions.

    Thank you,

    Sandesh