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SN74AVC4T774: Asking for the SN74AVC4T774 driving capability support

SHH
Mastermind 32646 points

Part Number: SN74AVC4T774
Other Parts Discussed in Thread: SN74HC244, SN74LVC1G34

Hi Team,
My customer would like to evaluate to use SN74AVC4T774 for 1.8v to 3.3V level translator.
The SPI mater to slave trace length is 18 inch.

Please help for the two questions.
1.does SN74AVC4T774 has the capability to drive 18" inch length?

2.Can SN74AVC4T774 accept the VCCA and VCCB are the same voltage without voltage translator?


Thanks,
SHH

  • 0
    TI__Guru 64170 points
    Hi SHH ,

    The sn74AVC4T774 is built to support SPI communication with individual direction control for each of 4 channels.
    The AVC family has 12ma of drive strength per channel which is good, but ability to drive 18" is question of the parasitic cap which needs to be overcome.
    Vcca and Vccb are configurable to operate over full voltage range independently.
  • 0 in reply to ShreyasRao
    TI__Intellectual 2810 points
    My customer would also like to use this device on a SPI bus in a Notebook PC application. Can you comment the max trace length? Are there any "SPI redriver" type of devices in our portfolio?
  • 0 in reply to Andrew Kling
    TI__Guru* 97676 points
    Hi Andrew,
    Since SPI has only unidirectional signals and is relatively slow, there are many devices in our portfolio that can be used as a redriver -- basically any buffer (examples include SN74LVC244, SN74HC244, SN74LVC1G34, etc).

    Maximum trace length isn't something we can specify since it doesn't tell us anything about the electrical characteristics of the system. Typically, an 18" trace (as mentioned in the OP) is going to have significant inductance and capacitance, so you will see some overshoot and ringing at the distant end. The amount will depend on the geometry and materials of the pcb.
  • 0 in reply to Emrys Maier
    TI__Intellectual 2810 points

    Customer has 10” motherboard trace and 8” cable.  

  • 0 in reply to Andrew Kling
    TI__Guru 64170 points
    Hi Andrew ,

    Estimation of the cable and trace capacitance is difficult as mentioned by Emrys before. I would estimate that the trace capacitance would be about 20-30pF assuming 2-3pf/inch and the cable will add additional capacitance.
    While SN74AVC4T774 has 12mA of drive per channel, the LVC buffer devices have 32mA of drive strength. The advantage of AVC4T774 is that the same device can be configured for SPI communication from Master to/from Slave for the 4 signals( Clk, CMD, MOSI,MISO).
  • 0 in reply to ShreyasRao
    TI__Mastermind 32646 points
    Hi Shreyas,

    What is the max capacitor spec on the trace that SN74AVCT774 can support?


    Thanks,
    SHH
  • 0 in reply to SHH
    TI__Guru 64170 points
    We do not spec the max capacitor a device can support. The device can support any cap load but higher cap leads to larger rise / fall time and hence larger prop delay.