• State Resolved
  • Locked Locked
  • Replies 3 replies
  • Subscribers 19 subscribers
  • Views 308 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

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.

Original question:

SN74LVCC3245A: ViL, ViH, VoH,VoL

SN74LVCC3245A: Can B port support both 5V and 3.3V input signal when VCCB=5V and VCCA=3.3?

Dylan Zheng
Intellectual 1695 points
Part Number: SN74LVCC3245A
Other Parts Discussed in Thread: SN74CB3T3245, SN74LVC245A, , SN74LVC244A

Dear expert,

As shown in the datasheet 6.3 section. When VCCA=3.3V and VCCB=5.5V, the high-level voltage VIHB(min)=3.85.

I want do confirm whether B port can support both 5V and 3.3V input signal when VCCB=5V and VCCA=3.3?

What is the input threshold level when VCCB=5V and VCCA=3.3?

Best regards,

Dylan Zheng

  • 0
    Guru 267960 points

    The datasheet lists VCCB = 5.5 V as a test condition because that is the worst case of a nominal 5 V ± 10 % power supply.

    You should apply the specified VIHB value to your 5 V circuit, because your actual power supply will not be accurate. In any case, even if you assume that the threshold moves with the supply voltage, the worst-case VIHB at exactly 5 V would be 3.85 V − 0.5 V = 3.35 V, which would still be too high.

    To summarize: 5 V LVC inputs do not accept 3.3 V signals.

    (What is the actual problem you're trying to solve? LVC has overvoltage-tolerant inputs, so it might be possible to run with VCCB = 3.3 V.)

  • 0 in reply to Clemens Ladisch
    TI__Intellectual 1695 points

    Thanks. It is very clear. I want find a suitable level shift device to cover 5-V/3.3-V input and 3.3-V output.  And what do you think of the SN74CB3T3245?

  • 0 in reply to Dylan Zheng
    Guru 267960 points

    The CB3T can shift down from 5 V to 3.3 V. But it uses passive switches and does not have any drive strength; this might or might not be what you want.

    As I said, LVC family devices have overvoltage-tolerant inputs, so you can replace the SN74LVCC3245A with a plain transceiver like the SN74LVC245A running at 3.3 V, or, if you are using only one direction, a plain driver like the SN74LVC244A.