On AM65x silicon revision 1.0, ADC input leakage current may be higher than expected at worst case Process/Voltage/Temperature (PVT) conditions, where process variation and operating temperature are the major contributors. Leakage current is larger for strong process devices operating at elevated temperatures.

There is also a dependency on the potential applied to an ADC input. Leakage current flows out of the ADC when applying a potential equal to VSS, flows into the ADC when applying a potential equal to VDDA_ADC_MCU, and the direction change occurs at approximately 42% of VDDA_ADC_MCU. Magnitude of leakage current has a non-linear function to the applied potential, where it increases exponentially as the applied potential approached VSS or VDDA_ADC_MCU.

Significant error can be introduced in ADC measurements when high impedance sources are connected to inputs with high leakage. This occurs because the input leakage current introduces a voltage drop across the source impedance. For example, the ADC would measure a potential of 1.45 V when measuring a 1.5 V source with 1 kΩ output impedance that is connected to an ADC input with 50 µA of leakage flowing into the ADC input. The error of this measurement would be 50 mV, which is 3.3% lower than the expected value. Reducing the source impedance from 1 kΩ to 100 Ω in this example would reduce the measurement error to 0.33%.

There are design techniques that can be used to minimize the impact of input leakage.

Reduce impedance of sources connected to ADC inputs. For example, it may be necessary to buffer outputs of a high impedance sources with voltage-follower operational amplifier circuits.

Design static DC sources to apply a nominal potential of approximately 42% of VDDA_ADC_MCU. For example, this approach can be used to minimize leakage when monitoring a DC power source via a resistor voltage divider.