2.1 General Purpose Mode

Figure 4 shows the configuration of SAC general-purpose mode. In this mode, OAx+ and OAx- are dedicated signal inputs. As the red highlighted part in Figure 4 shows, the internal DAC and feedback resistance ladder are not used. There is no limitation when using the SAC in general-purpose mode, it is the same as using external single-supply operational amplifier. You can use the SAC and external component to compose kinds of different circuits such as an inverting amplifier, noninverting amplifier, filter, and so on. Biasing and a feedback resistor usually must be added. External components and connections determine the circuit type. It is convenient to migrate from an external amplifier circuit to the integrated SAC in general-purpose mode. Compared to an external amplifier, the SAC can have the same circuit type while saving BOM cost and PCB size. When the SAC is not in use, it can be disabled by the control register in the MSP430 MCU to save power. SAC-L1 supports only general-purpose mode and does not include the DAC or the feedback resistance ladder.

To configure the SAC for general-purpose mode, the SACEN, OAEN, PMUXEN, and NMUXEN bits must be set in the SAC OA control register SACxOA. The PSEL and NSEL bits are also in SACxOA register, and they are configured to select external pins as the OA inputs by default. The OAPM bit is used to select high-speed or low-speed mode. The high-speed mode enables higher gain bandwidth and slew rate at the cost of higher power consumption. Example 1 shows one code sequence of configuring SAC into general-purpose mode with driver library API functions. The pin function must be selected as SAC function before SAC module configuration, although this example code does not include the pin function setting. Different MSP430 MCUs have different pin definitions (see the data sheets for details).