NRF52811-QCAA-R datasheet(265/444 Pages) NORDIC

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Peripherals

Output

Input

RESP = Pulldown

RESP = Pullup

Figure 108: Resistor ladder for positive input (negative input is equivalent, using RESN instead of RESP)

6.17.8 Reference

The ADC can use two different references, controlled in the REFSEL field of the CH[n].CONFIG register.

These are:

• Internal reference

• VDD as reference

The internal reference results in an input range of ±0.6 V on the ADC core. VDD as reference results in an

input range of ±VDD/4 on the ADC core. The gain block can be used to change the effective input range of

the ADC.

Input range = (+- 0.6 V or +-VDD/4)/Gain

For example, choosing VDD as reference, single ended input (grounded negative input), and a gain of 1/4

the input range will be:

Input range = (VDD/4)/(1/4) = VDD

With internal reference, single ended input (grounded negative input), and a gain of 1/6 the input range

will be:

Input range = (0.6 V)/(1/6) = 3.6 V

The AIN0-AIN7 inputs cannot exceed VDD, or be lower than VSS.

6.17.9 Acquisition time

To sample the input voltage, the ADC connects a capacitor to the input.

For illustration, see Simplified ADC sample network on page 266. The acquisition time indicates how

long the capacitor is connected, see TACQ field in CH[n].CONFIG register. The required acquisition time

depends on the source (Rsource) resistance. For high source resistance the acquisition time should be

increased, see Acquisition time on page 266.

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