I’m measuring the input leakage current in unbuffered mode. It is significantly higher than the value specified in the data sheet. Why is this?
Static leakage current is specified in the datasheet. The dynamic leakage current (the leakage current when the ADC is converting) is not specified.
If you put the ADC into unbuffered mode and measure the input current, you will observe a combination of leakage current and the dynamic current charging and discharging the sampling capacitor. If the dynamic charging current is likely to be a problem in your application, for example, if you have a high source impedance, you can use the on-chip buffer to isolate the input from these dynamic charging currents. However, this will result in reduced input common mode voltage. With the buffer enabled, the absolute voltage on the analog input pins is from GND + 250 mV to AVDD – 250 mV. With the buffer disabled, the absolute voltage on the analog input pins is from GND - 50 mV to AVDD + 50 mV.
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