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TXS0102: Open drain vs Push pull mode

Vishnu Jayaraj
Intellectual 275 points
Part Number: TXS0102


Tool/software:

Hi,

TP109(MCU2 RX) is the output and TP111 (MCU1 TX) is the input.

MCU2 is in VCCB side and MCU1 is in VCCA side

output waveform is not square pulse.

Is this any limitation?

The UART baud rate is 1228800 (1.22Mhz)

The IC says this can be used for push pull and open drain config.

How this IC identifies whether I/O is push pull or open drain?

Regards

Vishnu

  • 0
    TI__Mastermind 45711 points

    Hi Vishnu,

    The waveforms are not very clear to me, did you mean that the OE waveform is the output behavior and the TP109 waveform is the input? If so, please note this knee on the logic high is common phenomenon if the output Cload is too high. It is generally recommended to keep traces/ parasitic capacitances below 70pF to ensure proper functioning of the internal one shot circuitry. This app note covers this further in detail: www.ti.com/.../scea135.pdf

    Regards,

    Jack 

  • 0 in reply to Jack Guan
    Intellectual 275 points

    OE is given directly from 3.3V.

    The Blue waveform (TP109) is output of buffer and pink waveform (TP111) is the input to buffer.

    Why the output waveform is not a clear square wave?

    Is there any mode through this IC detects whether the I/O are push pull or Open drain?

  • 0 in reply to Vishnu Jayaraj
    TI__Mastermind 45711 points

    Hi Vishnu,

    The TXS does not know if the inputs into the device are push pull or open drain drivers. It is a passive, switch based level shifter with open drain outputs with one-shot circuitry to help accelerate the rising edge. During an input logic low, the switch is closed and the input and output sides are directly connected. Note that the limitation for the data rate support is bottle-necked by the lack of the PMOS driver at the TXS inputs and not a limitation of the device itself. 

    Regards,

    Jack 

  • 0 in reply to Jack Guan
    Intellectual 275 points

    Hi Jack,

    Input to Buffer is clean as you can see in pink waveform (TP111).

    What could be the reason for output waveform getting distorted?

    Regards

    Vishnu

  • 0 in reply to Vishnu Jayaraj
    TI__Mastermind 45711 points

    Hi Vishnu,

    The slow rising edge of the waveform suggest that there is a heavy capacitive load at the output side, and will not allow the one-shot circuitry to function properly. Please reduce the Cload at the output side i.e trace lengths/ connector cables and retest-again. More information ono this topic is provided in the app note I shared in my first response. 

    Regards,

    Jack