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ADS8422: ADS8422 - how to tie together 32 BUSY signals (pin 36)

Fouad Brikci
Prodigy 70 points
Part Number: ADS8422
Other Parts Discussed in Thread: SN74LVC1G06,

I need to connect together 32 ADS84221 (pin 36 BUSY). I would like to have the exact specifications of this output.

These 32 pins will be connected together and connected to one pin of a FPGA Cyclone 5 (ALTERA).

The best will be to have some schematic recommendations to be able to connect all these pins and with one component be able to build ONLY one signal BUSY.

I have used a simple diode (anode to pin 36 and all cathodes are shorted) connected to each ADS84221 but I do not like this solution.

Any application note talking about this subject will be appreciated.

The signal BUSY is intended to be used by an FPGA CYCLONE 5 from ALTERA.

Thank you for your help.

  • 0
    TI__Mastermind 36390 points

    Hello Fouad,

    I am not aware of a single device with 32 inputs that can be used, other than a programmable logic device.  I suggest using an open drain inverter, and tie all outputs together with a single pull-up resistor.  The output will then only go high when all inputs are low, indicating that all ADS8422's are done converting the inputs.  The SN74LVC1G06 is available in a 0.64mm^2 package, and could be placed next to each ADS8422.

    I assume that all converters use the same /CONVST signal.  After /CONVST is pulled low, you could simply delay the maximum time of t-d2=225nS, and then read the data from each ADC.  All ADC's will complete the conversion and make data available in 225nS or less over all rated conditions.

    Regards,
    Keith Nicholas
    Precision ADC Applications

  • 0
    Prodigy 70 points

    Dear Keith.

    Thank you for your answer.

    You have solved my problem.

    Fouad Brikci