nRF51822, what is the input current/impedance

[Veronica]

I am sure I missed this in the docs - thanks.

[Petter Myhre]

The input impedance for a digital input pin is close to infinity when it's configured as an input, and to zero when it's configured as an output.

The analog input pins belong to the ADC, and the prescaler setting will affect their input impedance.

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EDIT 2016.03.29: New values can be found in the nRF51 Reference Manual V3.0, Chapter 31.1.3:

• Prescaling 1/1: Mean impedance 129.7 kΩ Standard deviation 2.74 kΩ
• Prescaling 2/3: Mean impedance 194.6 kΩ Standard deviation 4.1 kΩ
• Prescaling 1/3: Mean impedance 389.2 kΩ Standard deviation 8.2 kΩ

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The inputs also have some capacitance, 3-4pf.

[Russ Mirov]

Hi Petter. For my application I do need more information I'm afraid. "close to infinity" is difficult to design with. Is the input leakage current for a GPIO configured as a digital input (and with no pullups/pulldowns enabled) xx uA, nA, fA ? Often it can depend on DC bias as well as temperature. Is any of that information available ?

Thanks.

[Petter Myhre]

Hi

The leakage current of the GPIOs should be in the order of a few nA.

I don't have any more information, but I can try to aquire some, if you could be a bit more specific on what you need.

[Ronnie Bajwa]

Hi, can you comment on the expected variation for the 1/3 prescaling case. Would it be within 10% of 550 kohm?

[thorXI]

The impedances given above for the ADC pins are not consistent with the white paper available elsewhere on Nordic Dev Zone: http://tinyurl.com/hzeayvz --- Which of the two sources has the correct answer?