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TS3USB221E: /OE Input Threshold

hideyuki sakai
Mastermind 6250 points
Part Number: TS3USB221E

Dear, Sir.

My customer is considering to apply TS3USB221E under the condioon as ;

1) VCC is applied from external 3.0V.

2) /OE is controled by 1.8V bus line. It will be pulled up by 2.2kOHM resister.

3) During the start-up, 1.8V applied first, then 3.0V VCC will be applied.

I would like to make sure followings.

1. I would like to make sure /OE input threshold. I wonder VIH & VIL (defined on page4) would

    correspond to these?

2. Data sheet 9.2.1 Design Requirements is defined the recommendation /OE to be pulled up

    to VCC. Is it no problem that /OE will be pulled to another voltage source(1.8V) not VCC?

3. If above #2 was OK, Please recommend the proper value as pull-up resistor.

4. If you find the remarkable point on 1) to 3) condition especiaaly start-up, Please let us know.

Best Regards,

H. Sakai

   

  • 0
    TI__Guru* 76130 points
    Hello,
    It is OK to pull the control pins to 1.8V, use 4.7K pull-up.
    The device supports the control pins pulled up to 1.8V while VCC is off, however, this condition is not recommended because the value on S and /OE will be indeterminate, the recommendation is to apply VCC first or at the same time than the voltage rail of the control pins.
    Regards
  • 0 in reply to Elias Villegas M.
    Mastermind 6250 points
    Dear, Elias-san.
    Thank you for your advice.
    I would like to double-confirm about your comments.

    1. The device supports the control pins pulled up to 1.8V while VCC is off.
    Does it mean that the device will not get damage under this condition,
    but the correct input or output might not expected because to be indeterminate?

    2. S and /OE will be indeterminate.
    You explained as above. I suppose such indetermination will be caused by
    the VCC transient from zero to 3.0V. Correct?

    3. The recommendation is to apply VCC first or at the same time than the voltage rail of the control pins.
    It is impossible for the customer to realize the recommendation due to already fixed power supply & rail.
    Do you mean that you don't recommend to use TS3USB221E under the out of the recommendation?

    Best Regards,
    H. Sakai
  • 0 in reply to hideyuki sakai
    TI__Guru* 76130 points
    Hello,
    You are correct on your three assumptions.
    Regards