9.4.6.10.1 Input-Output Transfer Functions

The ADC can be configured to operate in the following input voltage modes:

• Single-Ended—ADC_CCR.DIFFx = 0 and ADC_PDR.PDIFFx = 0. This is the default mode after a reset.
• Differential—ADC_CCR.DIFFx = 1 and ADC_PDR.PDIFFx = 0 (see the figure below). In Differential mode, the ADC requires differential input signals having a VDD/2 common mode voltage (refer to the section “Electrical Characteristics”).
• • Pseudo-Differential—ADC_PDR.PDIFFx = 1. In Pseudo-Differential mode, one of the analog pins is used as the negative input of the ADC (see table Input Pins and Channel Numbers in Pseudo-Differential Mode). The ADC samples the other analog inputs with respect to this one. The common mode input range is 0 to VDD (refer to the section “Electrical Characteristics”).

The following equations provide the unsigned ADC input-output transfer function in each mode⁽¹⁾. With signed conversions (see field ADC_EMR.SIGNMODE), subtract 2047 from the ADC_LCDR.DATA value given below. Note that the Single-Ended mode introduces a x2 gain compared to the Pseudo-Differential mode.

In the formula, REFP = VREFP, REFN = VREFN.

Single-Ended mode:

Differential mode:

Pseudo-Differential mode:

If ADC_MR.ANACH is set, the ADC can manage both differential channels and single-ended channels. If ADC_MR.ANACH is cleared, the parameters defined in ADC_CCR are applied to all channels.

The following tables provide the internal positive and negative ADC inputs assignment with respect to the programmed mode (ADC_CCR.DIFFx and ADC_PDR.PDIFFx).

For example, if Differential mode is required on channel 0, input pins AD0 and AD1 are used. In this case, only channel 0 must be enabled by writing a 1 to ADC_CHER.CH0.

In Pseudo-Differential mode, inputs are managed by a 12/2:1-channel analog multiplexer. See the table below.