SLAA833A May   2018  – October 2019 MSP430FR2353 , MSP430FR2355

 

  1.   How to Use the Smart Analog Combo in MSP430™ MCUs
    1.     Trademarks
    2. 1 Introduction
      1. 1.1 Smart Analog Combo (SAC) Concept
      2. 1.2 Single-Supply Amplifier Design Consideration
      3. 1.3 Smart Analog Combo Driver Library
    3. 2 Smart Analog Combo Operation Modes
      1. 2.1 General Purpose Mode
        1.       Example 1. Code Example for Smart Analog Combo General-Purpose Mode
      2. 2.2 Buffer Mode
        1.       Example 2. Code Example for Smart Analog Combo Buffer Mode
      3. 2.3 Noninverting PGA Mode
        1.       Example 3. Code Example for Smart Analog Combo Noninverting PGA Mode
      4. 2.4 Inverting PGA Mode
        1.       Example 4. Code Example for Smart Analog Combo Inverting PGA Mode
      5. 2.5 DAC Mode
        1.       Example 5. Code Example for Smart Analog Combo DAC Mode
    4. 3 Smart Analog Combo Interconnection Configuration
      1. 3.1 Smart Analog Combo Cascading
      2. 3.2 Smart Analog Combo Interconnection With Other Peripherals
    5. 4 Smart Analog Combo Use Cases in Sensing Applications
      1. 4.1 Use Smart Analog Combo in Smoke Detector
      2. 4.2 Use Smart Analog Combo in Current Loop
    6. 5 References
  2.   Revision History

2.4 Inverting PGA Mode

Figure 7 shows the SAC Inverting PGA mode. In this mode, signal can be amplified with inverting. As negative voltage is not allowed in SAC usage, biasing is must have for SAC inverting PGA mode. Bias voltage can be generated by external circuit or internal 12-bit DAC. The red highlighted part in Figure 7 shows the use case that using internal DAC to generate bias voltage at OA positive input. Usually bias voltage is half of the power supply voltage. The signal input is from external pin OAx- or internal paired OA.

SLAU445_SAC_INV.gifFigure 7. Smart Analog Combo Inverting PGA Mode

To configure SAC into inverting PGA mode, The PGA MSEL selects OAx- (MSEL = 00b) or a paired OA (MSEL = 11b) as the source, and the OA negative port must select PGA input (NSEL = 01b). The OA positive port can select from the external pin OAx+ or the 12-bit DAC. SAC gain is configured by GAIN bits in SACxPGA control register. Example 4 shows one code sequence of configuring SAC into inverting PGA mode with driver library API functions.