• State TI Thinks Resolved
  • Locked Locked
  • Replies 3 replies
  • Answers 1 answer
  • Subscribers 33 subscribers
  • Views 134 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.

SN74LXC8T245-Q1: Interface Voltage translation between Ethernet Phy transceiver and Microcontroller

Sajid Afaque
Prodigy 30 points
Part Number: SN74LXC8T245-Q1
Other Parts Discussed in Thread: SN74LVC2T45-Q1, PCA9306-Q1, TCA39306-Q1

Tool/software:

Hello Team,

I have an Ethernet Phy to be interfaced to Microcontroller.
Maximum supply of my Ethernet Phy is 3.3V. I am using the RMII mode of communication.

On, the other hand my Microcontroller is supplied with 5V and i am unable to use the 3v3 flex pins of microcontroller.
So i need a voltage translator between Ethernet Phy and Microcontroller.

Can you suggest me which voltage translator would be best.

According to my small research i am planning to use

  • SN74LXC8T245-Q1 → RMII bus (7 lines -> TXD[1:0], TX_EN, RXD[1:0], CRS_DV, REF_CLK).

  • SN74LVC2T45-Q1 → MDC + RESET_N.

  • PCA9306-Q1 → MDIO (+ optionally INT_N).

  • 0
    TI__Mastermind 28040 points

    Hello Sajid,

    1) For RMII, TXD and RXD will have opposite signal directions which means one single LXC8T245 cannot be used to support all RMII bus lines. Unfortunately, we don't have any 4-channel LXC devices so you could use 2x LXC8T245-Q1 or 4x LXC2T45-Q1. 

    2) SN74LVC2T45-Q1 would work for MDC and RESET

    3) PCA9306-Q1 or the updated version TCA39306-Q1 would work for MDIO and INT_N

    Regards

    Josh 

  • 0 in reply to Joshua Salinas
    Prodigy 30 points

    Hello Joshua,

    Thanks for the clarification.

    1. Shouldn't I be concerned with the timing if I use multiple voltage translators?

    2. So, SN74LXC8T245-Q1 is unidirectional? (that's why we need separate IC for RX and TX)

    3. what is the difference between SN74LXC8T245-Q1 and SN74LVC8T245-Q1? (Which one do you think is best suited for my application?)

    4. I have to use 2x LXC8T245-Q1 or 4x LXC2T45-Q1. Or there exist another IC for my application that I am unaware of?

  • 0 in reply to Sajid Afaque
    TI__Mastermind 28040 points

    Hello Sajid,

    1. That's correct. If you are using multiple devices, timing between both parts will have some impact. However, from my understanding of RMII, as long as you are below a 20ns period, part-to-part skew shouldn't be an issue.

    2. Yes, the LXC8T245-Q1 is uni-directional

    3. LXC is the updated version of LVC. It has a more robust power sequence circuitry, offers dynamic pull-down resistors and has Schmitt-Trigger inputs. Either part is suitable for your application.

    4. In addition to the parts you mentioned, you can look at the TXU0104-Q1, This part should meet your requirements and offer a compact solution.

    Regards,

    Josh