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TXB0102 output oscillates at 40MHz - TX/RX 3.3V/5V level shifter

Tim Davis
Prodigy 225 points
Other Parts Discussed in Thread: TXB0102, SN74LV1T34, TXB0101, TXB0104, SN74LV4T125, SN74LV1T125, SN74AHCT1G125, SN74AHCT125, SN74AHCT367, SN74AHCT541, SN74AHCT16541, SN74AHCT16244, SN74AHC1G125, SN74LVC1G125, SN74LVC1G34, SN74LVC2G34, SN74LVC2G125, SN74AHC125, SN74LVC125A, SN74AHC367, SN74AHC541, SN74AHC244, SN74LVC541A, SN74LVC244A, SN74LVC827A, SN74AHC16244, SN74AHC16541, SN74LVC16244A, SN74AVC2T244

A TXB0102 is connected as a 3.3V to 5V level shifter between an Altera MAX10 (Dkey 544-3145-ND) and a FTDI TTL-232RG-VIP-WE (Dkey 768-1069-ND).  The signals are '232 TX and RX.

The RX side of the level shifter to the FTDI cable oscillates at 40MHz when the system is powered up.  Sometimes the oscillation waits to start after the first packet.

It is as if there is a contention, but there is no known contention.  Have other users of this level shifter seen this problem?  The TI IC is meant to auto-detect direction.   We don't know the IC details of the FTDI circuit receiving the oscillating output signal. The I/O on the Altera are set to 8mA I/O drive. 

CH2 light blue trace is the '02 oscillating output.  The CH2 light blue trace should be following as a 5V level shifted version of the 3.3V level on CH4 green trace.

  • 0
    Guru 317000 points

    In theory, the Altera's output should be string enough for the TXB. But it's possible that some pull-up resistor is too strong (see SCEA043).

    Anyway, you do not need an auto-direction sensing translator for unidirectional signals. Up translation can be done by any buffer with TTL-compatible inputs; down translation can be done by any buffer with 5 V tolerant inputs. The SN74LV1T34 has both.

  • 0 in reply to Clemens Ladisch
    Prodigy 225 points

    Clemens,

    Thanks for the reply.

    I reviewed the datasheet on the SN74LV1T34.  I haven't used this part, but will be now. 

    I just checked for the dual and the quad of this part, but haven't specifically found them.  The search was done from within the Dkey site.

    Do you happen to know a dual and quad with similar performance and specs to the SN74LV1T34.

    (we are trying to replace the TXB0101, TXB0102, TXB0104 series)  TXB0101 with SN74LV1T34

    Tim 

  • 0 in reply to Tim Davis
    TI__Mastermind 30575 points

    Hello Tim,

    Yes, I agree that you do not need an auto-direction translator. These translators are very sensitive to output capacitance especially at higher frequencies and I would assume the 1.8m cable exceeds the 70pF limit of the TXB0102.

    I think the LCV would meet your requirements. It is available in dual control packages but only in 16 bit configurations. I will notify an engineer who handles our other translator portfolio to see if they have anything that meets your needs.

  • 0 in reply to Tim Davis
    TI__Guru 62180 points
    Hi Tim ,

    we do not have dual version currently , however , SN74LV4T125 is a quad buffer you could consider .
  • 0 in reply to Tim Davis
    Guru 317000 points

    The following devices have TTL inputs, for up translation:

      LVxT AHCT
    1x SN74LV1T34, SN74LV1T125 SN74AHCT1G125
    4x SN74LV4T125 SN74AHCT125
    6x   SN74AHCT367
    8x   SN74AHCT541
    16x   SN74AHCT16244, SN74AHCT16541

    The following devices have 5V-tolerant inputs, for down translation:

      LVxT AHC LVC
    1x SN74LV1T34, SN74LV1T125 SN74AHC1G125 SN74LVC1G34, SN74LVC1G125
    2x     SN74LVC2G34, SN74LVC2G125
    4x SN74LV4T125 SN74AHC125 SN74LVC125A
    6x   SN74AHC367  
    8x   SN74AHC244, SN74AHC541 SN74LVC244A, SN74LVC541A
    10x     SN74LVC827A
    16x   SN74AHC16244, SN74AHC16541 SN74LVC16244A
    32x     SN74LVC32244

    The (2x) SN74AVC2T244 has two supplies for either up or down translation.

  • 0
    Prodigy 225 points
    Thanks to all who have replied.

    The following 3 TI parts are being purchased from a distributor.
    4 Channel, SN74LV4T125PWR
    2 Channel, SN74LVC2T45DCUR
    1 Channel, SN74LV1T34DBVR

    The most important electrical feature is to be able to level shift UP and level shift down.

    What is the most common application that requires the auto-sense I/O direction feature for the "TXB" series level shifters and requires a designer to insure a minimum (or reasonable) load capacitance?

    Tim
  • 0
    Prodigy 225 points

    What is the most common application that requires the auto-sense I/O direction feature for the "TXB" series level shifters and requires a designer to insure a minimum (or reasonable) load capacitance?

    Tim

  • 0 in reply to Tim Davis
    TI__Mastermind 30575 points
    Hello Tim,

    TXB translators are commonly used for small SPI buses, UART, interfacing MCUs and FPGAs to sensors/other peripherals, etc. Many of the applications they are used in do not actually require the auto-direction sensing feature.