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TXS0202: TXS0202

user1075061
Prodigy 80 points
Part Number: TXS0202
Other Parts Discussed in Thread: LSF0102

There is a usage of TXS0202 for voltage translation between an external USB host ( PC) and an embedded microcontroller that is running at 1.8V,but somthing abnormal happened.

1.There is a 30Mhz or 80Mhz waveform like a sine when the usb insert to the PC ,  PC could recorgnize the USB device insert ,but communication with  microcontroller was fail;

2. Input a signal(8Mhz) from the signal generator to the A port or B port of the TXS0202 ,the signal could pass the TXS0202 successfully.

Q:

1.The usage of TXS0202 for voltage translation between PC and microcontroller is right?

2.why there is a high frequence  waveform when no signal input to the TXS0202?

Best regards.

 

  • 0
    TI__Genius 16735 points

    Hello luke,

    For me to help you find an answer for your problem I will need to see a schematic as well as some scope plots of these waveforms. If not designed properly the TXS devices will not behave as per the datasheet.

    Here is an app note about the operation of the TXS devices.


    Here is an app note on effects of pull up resistors on TXS devices.


    Here is a training series that talks about using our LSF devices for translation. These are very similar to the TXS family, except the TXS family has internal pull up resistors and one shots. 

    Differences between the auto directional translation familes:

    [FAQ] What is the difference between TXS TXB and LSF devices? - Logic forum - Logic - TI E2E support...

    e2e.ti.com
    FAQ: Logic and Voltage Translation > Voltage Translators >> Current FAQ

    Thanks!

    -Karan

  • 0
    Guru 294890 points
    The TXS0202 is designed for IC-USB (Interchip USB). A PC uses 'normal' USB, and normal USB signals are never level shifted.

    What interface does your microcontroller use? Doesn't it have a pin for VBUS (5 V)?
  • 0 in reply to Karan Kotadia
    Prodigy 80 points

    Hi, Karan

     Thanks for your reply.  Below is the schematic for the TXS0202 applied.

    B port is connected to the MCU powered by 1.8V , A port is connected to the PC through a USB cable. This SCH just like the type application on the datasheet.

  • 0 in reply to user1075061
    Guru 294890 points
    Which MCU are you using? What happens with the VBUS signal from the USB cable?
  • 0 in reply to Clemens Ladisch
    Prodigy 80 points

    Dear Clemens

     The MCU is STM32F429II  .   

    The  signal from the USB cable may be a 80Mhz waveform like sine, this signal may be generated by plugging the USB cable into the PC.

    Waveform just like as below:

     

    I wanna know  using the TXS0202 between the PC and the MCU to perform a level shifter  is all right ?

    Best regards,

    Luke

  • 0 in reply to user1075061
    TI__Genius 16735 points
    Hi Luke,

    The TXS0202 has a max data rate of 15Mbps if you are trying to create a 80 MHz waveform on it, it will not work.
    You might try the LSF0102 for such high speed waveforms. LSF 0102 supports up to 100 MHz up translation and greater than 100 MHz down translation at ≤ 30pF cap load and up to 40 MHz Up/Down translation at 50 pF cap load. This device however will require external pullups.

    Thanks!
    -Karan
  • 0 in reply to user1075061
    Guru 294890 points

    The STM datasheet says:

    It is not necessary to use a level shifter; the USB pins are 5V tolerant and designed for USB; they can be connected directly.

    And as I said above, the TXS0202 is designed for IC-USB, which is different from USB. The STM does not support IC-USB, so you must not use the TXS0202.

  • 0 in reply to Clemens Ladisch
    Prodigy 80 points

    Hi,Clemens 

    Maybe  you neglect   the range of VDD for stm32f4xx  is from 2V~3.6V when connect to the USB.

    Mine is run in 1.8V , so I must use a level shifter .

  • 0 in reply to user1075061
    Guru 294890 points
    Sorry, I did not read that part of the datasheet.

    Between 2.7 V and 3.0 V, the STM's full-speed transceiver has degraded electrical characteristics, so a redriver might help. But at 1.8 V, there are no guarantees whatsoever. There are not even any specified characteristics that would make it possible to design a level shifter.

    The USB signals are not designed to allow level shifting. (IC-USB is different because it use logic voltage levels.) The only way to get USB to work at 1.8 V is to connect an external 1.8 V ULPI transceiver.