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TXS0108E-Q1: Use TXS0108E-Q1 to tranfer 5V to 3.3V and 3.3V to 5V for driving ADC TLV2553 with spi

user5888983
Prodigy 60 points
Part Number: TXS0108E-Q1
Other Parts Discussed in Thread: TLV2553, , SN74LVC2T45, SN74LVC1T45

Hello

I use TXS0108E-Q1 to finish spi communication between 3.3V and 5 V for driving ADC TLV2553

THis is my Schematic：

I have read the reference book :the maximum data rates up to 110Mbps when it is push pull

                                                          the maximum data rates up to 1.2Mbps when it is open drain

I use it in push pull mode .But i make some test , it can not arrive the maximum data referenced in the book

This is  some Oscilloscope wave i take:

this pic is at 280k data rates in the side of  VCCA

 

this pic is at 280k data rates in the side of  VCCB

this pic is at 2.5M data rates in the side of  VCCA

this pic is at 2.5M data rates in the side of  VCCB

I must use data rates to 10M ,how can i resolve this problem.

And is TXS0108E-Q1 is suitable for spi?

Sorry my English is not well.

Thank you very much

Sincerely

Xiaowei

  • 0
    Prodigy 110 points

    Hi Xiaowei,

    First, I would always recommend taking a scope shot of both the input and the output -- on the same screen.  Without this, it is not possible to tell exactly what is happening from a timing perspective.

    From the scope shots you have, it looks like you have a relatively large capacitive load on the output of the TXS0108E-Q1.

    What do you have connected on the 5V side?

  • 0 in reply to Rigor
    Prodigy 60 points

    Hi Rigor

    Thank you for reply

    I directly use  TXS0108E-Q1 5v side connect to adc tlv2553 just like this pic

    And i tke a another scope shot of both the input and the output  at 280k-- on the same screen the blue is out the yellow is input.

    Look forward your reply

    Thanks

    Xiaowei

  • 0 in reply to user5888983
    TI__Guru 58990 points

    Hi Xiaowei,

    It definitely seems to me that the line capacitance is causing the slow output transition time. The TXS devices are passive translation devices with no active drivers(apart from oneshot accelerators for momentary AC drive). It is recommended to have very low capacitance on the line to achieve higher speeds. The datasheet has data rate measured at 15pF.

    Would changing to SN74LVC2T45/SN74LVC1T45 an option? These devices have active driver circuitry which can overdrive the line capacitance and achieve >10Mbps.

  • 0 in reply to ShreyasRao
    Prodigy 60 points
    Hi Shreyas

    Thank you very much.

    I will try another device.

    Xiaowei