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CCS/TMS320F28379D: TMS320F28379D

Shivashankar C
Intellectual 380 points

Part Number: TMS320F28379D

Tool/software: Code Composer Studio

I am using TMS320F28379D Launchpad XL V2.0  on board Level shifter TXB0106PWR which is giving an output of 3.8V for logic low and 4.8V for logic high while measuring the output with voltmeter. On board it is pulled up with 1K resistor.

  • 0
    TI__Mastermind 45606 points

    Hi Shivashankar,

    Can you further explain how you are using this level shifter? Typically the EQEP signals on the left are meant to be 5V outputs from an incremental encoder, level shifted to 3.3V MCU inputs on the right.

    Best,

    Kevin

  • 0 in reply to Kevin Allen18
    Intellectual 380 points

    Hi Kevin,

    I am measuring the output across the pin J15(A) with respect to GND. where there is a 1K pull up resistor used in the board. I was able to measure only 3.8v During logic low by setting the  respective GPIO55 as low.

    I have also tried by removing 1K resistor and I was able to see the voltage ~0v for logic Low and 4.8v for logic high. As in the data sheet of the the TXB0106PWR mentioned not to use pull up resistor if there is need then have to use over 50K where as in the board it is provided with 1K is there any specific reason for it.  

  • 0 in reply to Shivashankar C
    TI__Mastermind 45606 points

    Hi Shivashankar,

    Shivashankar C said:
    I have also tried by removing 1K resistor and I was able to see the voltage ~0v for logic Low and 4.8v for logic high. As in the data sheet of the the TXB0106PWR mentioned not to use pull up resistor if there is need then have to use over 50K where as in the board it is provided with 1K is there any specific reason for it.  

    This is a good question and I don't have a good answer right now. I'll need to get back to you on why 1k pull-ups are used. For the time being removing the pull-ups like you did should do the trick for 0-5V input/output as pull-ups are optional for TXB0106PWR.

    With the 1k resistors, ~4.0V is the expected V_OL like you are seeing, based on the equations from the TXB0106PWR datasheet below:

    Best,

    Kevin

  • 0 in reply to Kevin Allen18
    TI__Mastermind 45606 points

    Hi Shivashankar,

    Following up on the reason behind using 1K pull-up resistors. I believe 1K, or something close to it, are the kind of pull-ups needed for open-collector type of incremental encoders to have a chance of keeping up with the edge rates at decently high rpm rates. A stronger pull-up is needed than what's recommended in the TXB0106PWR datasheet.

    Now whether the TXB0106PWR is the best choice for this purpose I'm not certain about and would need to be evaluated further.

    Best,

    Kevin

  • 0 in reply to Kevin Allen18
    Intellectual 380 points

    Hi Kevin,

    Thank you for your follow up, I don't think  1K pull-up resister is the right value it has to be a greater value or or need to open that is what I have understood from reading the TXB0106PWR datasheet. I have removed the 1K resistor and the able to get expected output by doing this.