AD7484 REFOUT

  1. How much current can I draw from the internal reference (REFOUT)? With REFSEL floating with a 0.1uF cap to AGND, REFOUT drops to 1.9V volts with a 4.7K load (0.5ma). Table 10 says the REFOUT impedance is 1 ohm.
  2. Fig 10 in the data sheet indicates very flat temperature drift (approximately 2mv) but Table 1 says +/100mv. Please explain this difference. My tests here indicate it’s even worse than that. What typical temperature drift should I expect of the internal reference? Is the drift affected by the REFOUT load?
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  • 0
    •  Analog Employees 
    on Nov 7, 2016 11:53 PM

    Hi,

       The AD7484 has a typical spec of 220uA. This is usually the typical current to drive the ADC reference and this is also the typical current the internal reference is driving the ADC. Not enough current to drive the ADC will not have a good conversion result .

       The specs in Table 1 were gathered with the condition indicated on the upper portion on page 3, that is Vdrive = 2.5 to 5.25 and AVDD/DVDD = 5+/-5% and maximum throughput rate at 3MSPS across Tmin and Tmax. The result, with this conditions, will have a maximum reference error of +/-~100mV. Figure 10 of the datasheet shows 1 data plots at varying temperature, this means that it was gathered at specific condition across temperatures.

    Regards,

    Jonathan

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  • 0
    •  Analog Employees 
    on Nov 7, 2016 11:53 PM

    Hi,

       The AD7484 has a typical spec of 220uA. This is usually the typical current to drive the ADC reference and this is also the typical current the internal reference is driving the ADC. Not enough current to drive the ADC will not have a good conversion result .

       The specs in Table 1 were gathered with the condition indicated on the upper portion on page 3, that is Vdrive = 2.5 to 5.25 and AVDD/DVDD = 5+/-5% and maximum throughput rate at 3MSPS across Tmin and Tmax. The result, with this conditions, will have a maximum reference error of +/-~100mV. Figure 10 of the datasheet shows 1 data plots at varying temperature, this means that it was gathered at specific condition across temperatures.

    Regards,

    Jonathan

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