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problem about power up sequence

bowen jing
Prodigy 125 points
Other Parts Discussed in Thread: ADS1298

hi

  i have a question about the power-up sequence.it is written on the datasheet that "Before device power-up, all digital and analog inputs must be low."i want know why . if i don't follow this practise,what gonna happen and whether it will cause any damage to the ads1298.

     thanks

  • 0
    TI__Guru**** 176541 points

    Hi Bowen,

    Welcome to the e2e Forum!  The ADS1298, like many other semiconductor devices, has ESD cells and other structures on the analog and digital inputs/outputs that can be enhanced if voltages exceeding the Analog and Digital power rails are applied to the input/output pins before power is applied to the device.  What can happen is that the chip can 'latch-up' and cause the device to simply not work correctly (erroneous conversion results, can't program the device registers, etc) or possibly cause permanent damage to the silicon. 

    If you review the Absolute Maximum Ratings table on page three of the ADS1298 data sheet, you will see that the analog and digital inputs/outputs are to remain within +/-300mV of the applied Analog/digital supply voltage.

  • 0 in reply to Tom Hendrick
    Prodigy 125 points

    hi Tom:

          thanks for your advice.but i m wondering what should i do to prevent the possible damage you mentioned above.

    should i use a Pull-down resistor wired between anolog/digital input/output and GND???

  • 0 in reply to bowen jing
    TI__Guru**** 176541 points

    Hi Bowen,

    On the digital side, usually its not too much of an issue assuming your digital rail for the ADS1298 tracks the digital rail for whatever controller you have driving the device.  Series R's and/or external over voltage diodes on the analog side are the usual means of protection if you cannot ensure the analog rail will be established before an input voltage source is applied to the inputs.