SLAU723A October 2017 – October 2018 MSP432E401Y , MSP432E411Y
The structure of the internal reference is shown in Figure 12-3. The internal reference is controlled by a single configuration register (ACREFCTL).
NOTE
In the figure above, N × R represents a multiple of the R value that produces the results specified in Table 12-1.
The internal reference can be programmed in one of two modes (low range or high range) depending on the RNG bit in the ACREFCTL register. When RNG is clear, the internal reference is in high-range mode, and when RNG is set the internal reference is in low-range mode.
In each range, the internal reference, VIREF, has 16 preprogrammed thresholds or step values. The threshold to be used to compare the external input voltage against is selected using the VREF field in the ACREFCTL register.
In the high-range mode, the VIREF threshold voltages start at the ideal high-range starting voltage of VDDA / 4.2 and increase in ideal constant voltage steps of VDDA / 29.4.
In the low-range mode, the VIREF threshold voltages start at 0 V and increase in ideal constant voltage steps of VDDA / 22.12. Table 12-1 summarizes the ideal VIREF step voltages for each mode and their dependence on the RNG and VREF fields.
ACREFCTL Register | Output Reference Voltage Based on VREF Field Value | |
---|---|---|
EN Bit Value | RNG Bit Value | |
EN = 0 |
RNG = X |
0 V (GND) for any value of VREF. It is recommended that RNG = 1 and VREF = 0 to minimize noise on the reference ground. |
EN = 1 |
RNG = 0 |
VIREF High Range: 16 voltage threshold values indexed by VREF = 0x0.. 0xF Ideal starting voltage (VREF =0): VDDA / 4.2 Ideal step size: VDDA/ 29.4 Ideal VIREF threshold values: VIREF (VREF) = VDDA / 4.2 + VREF × (VDDA / 29.4), for VREF = 0x0.. 0xF For minimum and maximum VIREF threshold values, seeTable 12-2. |
RNG = 1 |
VIREF Low Range: 16 voltage threshold values indexed by VREF = 0x0.. 0xF Ideal starting voltage (VREF =0): 0 V Ideal step size: VDDA / 22.12 Ideal VIREF threshold values: VIREF (VREF) = VREF × (VDDA / 22.12), for VREF = 0x0.. 0xF For minimum and maximum VIREF threshold values, seeTable 12-3. |
Note that the values shown in Table 12-1 are the ideal values of the VIREF thresholds. These values actually vary between minimum and maximum values for each threshold step, depending on process and temperature. The minimum and maximum values for each step are given by:
Examples of minimum and maximum VIREFvalues for VDDA = 3.3 V for high and low ranges, are shown inTable 12-2 and Table 12-3. Note that these examples are only valid for VDDA = 3.3 V; values scale up and down with VDDA.
VREF Value | VIREFMin | Ideal VIREF | VIREFMax | Unit |
---|---|---|---|---|
0x0 | 0.731 | 0.786 | 0.841 | V |
0x1 | 0.843 | 0.898 | 0.953 | V |
0x2 | 0.955 | 1.010 | 1.065 | V |
0x3 | 1.067 | 1.122 | 1.178 | V |
0x4 | 1.180 | 1.235 | 1.290 | V |
0x5 | 1.292 | 1.347 | 1.402 | V |
0x6 | 1.404 | 1.459 | 1.514 | V |
0x7 | 1.516 | 1.571 | 1.627 | V |
0x8 | 1.629 | 1.684 | 1.739 | V |
0x9 | 1.741 | 1.796 | 1.851 | V |
0xA | 1.853 | 1.908 | 1.963 | V |
0xB | 1.965 | 2.020 | 2.076 | V |
0xC | 2.078 | 2.133 | 2.188 | V |
0xD | 2.190 | 2.245 | 2.300 | V |
0xE | 2.302 | 2.357 | 2.412 | V |
0xF | 2.414 | 2.469 | 2.525 | V |
VREF Value | VIREFMin | Ideal VIREF | VIREFMax | Unit |
---|---|---|---|---|
0x0 | 0.000 | 0.000 | 0.074 | V |
0x1 | 0.076 | 0.149 | 0.223 | V |
0x2 | 0.225 | 0.298 | 0.372 | V |
0x3 | 0.374 | 0.448 | 0.521 | V |
0x4 | 0.523 | 0.597 | 0.670 | V |
0x5 | 0.672 | 0.746 | 0.820 | V |
0x6 | 0.822 | 0.895 | 0.969 | V |
0x7 | 0.971 | 1.044 | 1.118 | V |
0x8 | 1.120 | 1.193 | 1.267 | V |
0x9 | 1.269 | 1.343 | 1.416 | V |
0xA | 1.418 | 1.492 | 1.565 | V |
0xB | 1.567 | 1.641 | 1.715 | V |
0xC | 1.717 | 1.790 | 1.864 | V |
0xD | 1.866 | 1.939 | 2.013 | V |
0xE | 2.015 | 2.089 | 2.162 | V |
0xF | 2.164 | 2.238 | 2.311 | V |