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TXS01018E Question

Jake Kim
Intellectual 680 points

Other Parts Discussed in Thread: TXS0108E, TXB0108, SN74AVC4T245

Hi TIer

TXS0108E has been used for RS-232 signal. On 1.8V side, We have only CPU. On 3.3V side, We have RS-232 Driver and another MCU. Problem is when CPU pulled signals to low,  VOL is 0.7V. So, We disconnected MCU and then preblem has been disappeared. We assume that it is caused by lack sink current. 

Would it  be right? Also, If you have a solution, please share with us.

Connection as below

VCCA=1.8V(CPU) - TXS0108E - VCCB=3.3V (MCU & RS232 Driver)

Thanks

  • 0
    TI__Expert 6430 points

    Hi,

    I am not sure the root cause. Could you please check the CPU output voltage. If CPU output voltage is  more than 0.3V, TXS0108E output could be 0.7V.

    If it is possible, could you try TXB0108. they are p2p compatible. If the greater driver is needed, please try SN74AVC4T245 fro RS232 interface.

    Thanks

     

  • 0 in reply to Wei Lang
    Intellectual 680 points

    Thank you for your answer.

    For my case I've also tested with A port connected to forced GND.

    But, result didn't changed. How much sink current TXS0108 can drive?

    And Shall I know what is your opinion on this knid of case?

    Thanks in advance.

  • 0 in reply to Jake Kim
    Intellectual 385 points

    You could connect the output to a potentiometer and Vcc and see how much output current you can sink before the output voltage starts coming up.

    If you look at the electrical characteristics section at Volb, the most it is specifying for a load current is 600 uA under the test conditions it lists.

  • 0 in reply to Jake Kim
    TI__Expert 6430 points

    Hi

    For TXS01XX serials, they are specific design for open-drain application. Thus, the circuits design is based on transmit gate architecture. When input is low, the transmit gate is on and logic low signal pass the transmit gate. There is a voltage drop between sides of the transmit gate. The value could be 100-200mV. Therefore, output voltage should be equal to input voltage + dropped voltage and output voltage also is reignited as low. For TXS018E, its sink current is less than 4mA for DC value.

    For your application, what i concern is  output load since the device is used to drive RS232 device by cable. If output load is greater, TXS0108E could not drive/sink enough current. Please check this point.

    Thanks

  • 0 in reply to Wei Lang
    Intellectual 680 points

    Thank you Wei lang.

    I need to look into the opposite devices.

    I appreciate your answer.

    Best wishes