• State TI Thinks Resolved
  • Locked Locked
  • Replies 1 reply
  • Answers 1 answer
  • Subscribers 35 subscribers
  • Views 514 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.

THVD1552: Enable signal connection for different supply voltages

cafain
Mastermind 6785 points

Part Number: THVD1552
Other Parts Discussed in Thread: SN74LVC2G125, SN74LVC1G08, THVD1452

Hi, staff

Enable signal connection for different supply voltages

Q1:
Drive the THVD1552 RE(2) with SN74LVC2G125 2Y-OUT(3).
The Vcc of the SN74LVC2G125 is 3.3V.
The THVD1552 VCC is 5V.

The THVD125 RE-pin is internally pulled up to Vcc (5 V).
(RE terminal leakage current is 5V/2MΩ=2.5uA)

The SN74LVC2G125 2Y-OUTPUT outputs High-Level at Vcc(3.3 V), but the RE pin is pulled up at 5V.
It is possible that current reverses from 5V to 3.3V (RE-pin → 2YOUT-pin).
Is the problem of connecting different signal lines with different Vcc?

Q2:
Drive DE(3) of THVD1552 with SN74LVC1G08 Y(4)OUT.
The Vcc of SN74LVC1G08 is 3.3V.
The THVD1552 VCC is 5V.
The THVD125 DE pin is internally pulled down to GND.
The Y output of the SN74LVC1G08 is
VOH: Vcc-0.15V (3.15V)
VOL: 0.1V
The THVD125 DE terminal is
VIH: 2V
VOL: 0.8V
SN74LVC1G08 Y-pin (4) TH THVD1552 DE (3) does not seem to be a problem.

Please tell me the problem above.

best regards
cafain

  • 0
    TI__Mastermind 25705 points

    cafain,

    It's possible that current flows into SN74LVC2G125 from THVD1552 Vcc through REB. But since the internal pull up resistor is big, the current should be small. If you're interested, you may take a look at THVD1452 that works with 3.3V supply. If you have to keep the design and want to prevent this happening, you can refer to this app note.

    2068.3V MCU to 5V XCVR Interface.pdf

    Please let me know if you have more questions.

    Regards,

    Hao