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max load for the PGA280

Ahmed Shaaban
Prodigy 60 points
Other Parts Discussed in Thread: PGA280

I will connect the PGA280 to PULSAR SAR from Analog device AD7684 which has input impedence 600 ohm durring the acquisition .

Can I connect pga280 directly to it without buffer ?

  • 0
    TI__Prodigy 100 points

    Short: you probably don't need a buffer if you have an appropriate RC filter (Fig 48 of the PGA280 datasheet) and provide enough time for the sampling phase. 

    Longer answer (not knowing the specifics of PULSAR): typically a SAR ADC has a sample and hold switch and a capacitor at its input. The cap size should be specified in the datasheet.  At end of the previous acquisition the capacitor contains some (usually unknown) charge.  When the S/H switch closes this capacitor gets connected to the input driver (in this case the PGA280) and the sampling phase starts.  The driver has to charge and settle this capacitor within 1LSB of the target voltage before the sampling phase ends (the S/H switch opens again at the beginning of the next conversion).  The key when driving a SAR ADC is to allow the driver to settle its output. This depends on the GBW and other parameters of the driver.  The PGA280 GBW is specified at 6MHz.

    You can find more details in this application note.

    Regards,

    Misha