• State Answer Suggested
  • Locked Locked
  • Replies 2 replies
  • Answers 1 answer
  • Subscribers 21 subscribers
  • Views 832 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

SN74LVC07A: What's the maximum data rate when working as level shift?

Wiky Liao
Intellectual 1940 points
Part Number: SN74LVC07A
Other Parts Discussed in Thread: SN74LVC1G07, SN74AHCT125, SN74LVC2G34

Hi Team,

We are using SN74LVC07A and configure as SPI level shift, schematic shows as below. VCC is 3.3V and using 5V pull up power at output side.

we set the data rate to 1MHz but find the waveform seems distortion, we remove all output components except pull up resistors but seems nothing change. Is it normal here?

I also notice datasheet section 9.2.2 mention Δt/ΔV but doesn't find any description in Recommended Operating Conditions, could you help to offer here? thanks.

Best Regards.

Wiky

  • 0
    TI__Expert 6680 points

    Hi Wiky,

    That's interesting, we should have that spec in the datasheet. I've went ahead and marked that to be changed in the next update. In the meantime, you can use the SN74LVC1G07's datasheet as a good reference point, as this is the 1 gate version of the SN74LVC07A.

    As for your waveform, is this an input or an output? Could you attach a waveform of both an input and an output? If the waveform is an output, you're likely not able to source current fast enough through a 4.7kΩ, and I would try using a 2kΩ resistor instead.

    Thanks!

    Chad Crosby

  • 0
    Guru 317060 points

    The Δt/ΔV specification does not apply to the outputs.

    The pull-up resistors, together with any parasitic capacitances in the circuit, form a low-pass RC filter. The waveform shows that the resistors are too large for 1 MHz signals. You can use smaller resistors, but this will increase power usage. For this reason, open-drain devices are usually not used for level shifting of fast signals.

    There is no single device that can handle all five of these signals well. To convert 3.3 V signals to 5 V signals, you can use any buffer with TTL-compatible inputs, e.g., SN74AHCT125. To convert 5 V signals to 3.3 V signals, you can use any buffer with overvoltage-tolerant inputs, e.g., SN74LVC2G34.