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ADS1251 Power-up sequence

Vincent50285
Prodigy 20 points
Other Parts Discussed in Thread: ADS1251

Hi,

I´ve made a prototype with an ADS1251 with 2 differents voltage sources (5V for digital and 5.0V for analog) starting simultaniously.
A scheme is enclosed.
However, it could be, that the 5V digital source turns on very shortly before the analog one
and your notice says (page 9), that the digital supply should start first.

Do the 2 x 10kohms resistors at the digital input protect sufficiently the ADS device to avoid damage in time ?
Actually, the prototype board works correctly.

Thank you in advance for your answer.

  • 0
    TI__Guru* 94285 points

    Vincent,

     

    The resistors should prevent any damage to the ADS1251. The pins should be able to take 10mA continuous input, and the resistors limit the current to 0.5mA.

    I would say that the open-drain drive may be a bit slow and you could replace the resistors with some voltage level translators. Also, you have to make sure that the microcontroller input for DOUT is 5V tolerant. Other than those concerns, it should work.

     

    Joseph Wu

  • 0 in reply to Joseph Wu
    Prodigy 20 points

    Joseph,

    Thank you for your answer.

    The open-drain output are fast enough for my application and the 3 pins I use to communicate with the ads1251 are 5V tolerant.

    Can you please find the maximal current that the DOUT pin can source and leakage current values for digital inputs? (In ADS1251 datasheet current (max and leakage) and capacitance specifications for digital Inputs and outputs are missing )


    Thanks,

    Vincent

  • 0 in reply to Vincent50285
    TI__Guru* 94285 points

    Vincent,

     

    I'll look for more, but there isn't much documentation in that regard. The datasheet says that it the pins will source 500uA to +4.5V and sink 500uA to +0.4V. Based on similar parts on the same process, I'm sure it can drive 1mA similarly, but I don't have any data for that.

    As for the capacitance and the leakage, there isn't much more information. I imagine that the capacitance is about 5pF or less. On similar parts, the leakage was specified to 10uA max, but I believe that was an effort to reduce test time (it takes longer to measure smaller currents). The typical leakage is certainly under 10nA. Inputs only see the input of the logic gate and any leakage from ESD protection diodes.

     

    Joseph Wu