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TXB0104 OUTPUT LEVEL

Kamal Najmi
Expert 3435 points
Other Parts Discussed in Thread: TXB0104, TXS0104E, TXS0108E, SN74AVC4T774

hi,

I'm just about to check the functionality of a partial area of our circuit. We use the TXB0104 to SPI signals from 1.8V to 3.3V to shift your (unidirectional flow of data per pin).
The TXB0104 has indeed a One.Shot implementation to drive the edge as quickly as possible. Thereafter, the level is maintained over a 4k resistor, see Figure 1 in the data sheet. Unfortunately I could not figure out the variation of this resistor  (temperature and process accuracy).

on output A we have a pulled resistor with a nominal 20k to VCC going to an IC, ie if zero state is available in the direction of the IC, it will creates a voltage divider and the zero level rises. To ensure that safe zero level is not exceeded here, what will be your solution proposal.

  • 0
    TI__Expert 6430 points

    Hi,

    Your comment is right. For TXB0104, if there is external pull-up resistor, low logic voltage will be divided by external and internal resistor. It is hard to make output to be close to zero if external resistor is less than 50K.

    For your application, it is better to use TXS0104E. It also can be used for push-pull application.

    Thanks

    Wei

  • 0 in reply to Wei Lang
    TI__Expert 3435 points

    Thank you for the feedback, this is a short summary or our level shifter requirements:

    HD Audio

    Frequency 24 MHz

    Input 1.5V output 3.3V

    HDA_SDO (unidirectional)

    HDA_SDI (bidirectional)

    HDA_CLK (unidirectional)

    HDA_RST# (unidirectional)

    HDA_SYNC (unidirectional)

     

    SPI Interface

    Frequency up to 50 MHz

    Input 1.5V output 3.3V

    SPI_CLK (unidirectional)

    SPI_CS (unidirectional)

    SPI_MOSI (bidirectional)

    SPI_MISO (unidirectional)

     

    Could you please send us a level shifter proposal for the above interfaces.

  • 0 in reply to Kamal Najmi
    TI__Expert 6430 points

    Hi,

    For HD Audio interface, Please try TXS0108E which 8 channle bidrectional voltage level translator. It can support 24MHz when device VCCA=1,5 and VCCB=3.3V.

    For SPI interface, since its frequency is up to 50MHz and external pull-up resistor will be used in application, TXS0104E and TXB0104 can not used.

    But SPI_MOSI singal should be unidirectional in SPI standard interface. If MOSI is unidirectional, SN74AVC4T774 can be used in the application.

    Thanks

    Wei