TIDUF52 December   2023 MSPM0L1303 , MSPM0L1304 , MSPM0L1305 , MSPM0L1306 , MSPM0L1343 , MSPM0L1344 , MSPM0L1345 , MSPM0L1346

 

  1.   1
  2.   Description
  3.   Resources
  4.   Features
  5.   Applications
  6.   6
  7. 1System Description
    1. 1.1 Key System Specifications
  8. 2System Overview
    1. 2.1 Block Diagram
    2. 2.2 Design Considerations
      1. 2.2.1 Photoelectric Smoke Detector Background – DC-Based Signal Chain
      2. 2.2.2 Modulation-Based Smoke Detection Signal Chain
      3. 2.2.3 Optical Sensing AFE Design
        1. 2.2.3.1 TIA
        2. 2.2.3.2 BPF
        3. 2.2.3.3 Demodulator and Integrator
        4. 2.2.3.4 LED Driver
      4. 2.2.4 Optical and Mechanical Design
    3. 2.3 Highlighted Products
      1. 2.3.1 MSPM0L1306
      2. 2.3.2 TLV9062S
      3. 2.3.3 TPS7A24
      4. 2.3.4 TS5A623157
      5. 2.3.5 SN74LVC1G66
      6. 2.3.6 HDC2010
  9. 3Hardware, Software, Testing Requirements, and Test Results
    1. 3.1 Hardware Requirements
      1. 3.1.1 Power
      2. 3.1.2 Communication Interface
      3. 3.1.3 Headers
    2. 3.2 Software Requirements
      1. 3.2.1 Getting Started Firmware
      2. 3.2.2 Measurements and Smoke Detection
      3. 3.2.3 Additional Demonstration Functionality
      4. 3.2.4 Smoke Detector GUI
    3. 3.3 Test Setup
      1. 3.3.1 UL217 Smoke Box and Fire Testing Setup
      2. 3.3.2 Ambient Light Testing Setup
      3. 3.3.3 Air-Quality Sensing Test Setup
    4. 3.4 Test Results
      1. 3.4.1 UL217 Testing Results
      2. 3.4.2 Ambient Light Testing Results
      3. 3.4.3 Air-Quality Sensing Test Results
      4. 3.4.4 Power Testing Results
      5. 3.4.5 Fire Room Smoke Testing
  10. 4Design and Documentation Support
    1. 4.1 Design Files
      1. 4.1.1 Schematics
      2. 4.1.2 BOM
      3. 4.1.3 CAD Files
    2. 4.2 Tools and Software
    3. 4.3 Documentation Support
    4. 4.4 Support Resources
    5. 4.5 Trademarks
  11. 5About the Author

2.2.3.4 LED Driver

Figure 2-12 shows the schematic of the LED drive. The transistors are controlled by the modulation signals LED_BL_MOD and LED_IR_MOD to turn the LEDs on and off. The limiting resistors R_BL and R_IR are designed to have nominal LED current as:

Equation 9. ILED,IR=VDD,LED-VF,IRR_IR=5-1.3538.3=95.3 mA,  ILED,BL=VDD,LED-VF,BLR_BL=5-3100=20 mA

The IR and BLUE LEDs are selected as TSAL6100 and C503B-BAN, respectively. The typical forward voltage, VF, in the respective data sheets is used in Equation 9 to calculate nominal LED current. The supply voltage, VDD,LED is a regulated output of 5 V, derived from the battery by TPS7A2405, which helps maintain a consistent LED current and smoke sensitivity consequently. If a different LED current is desired, the current-limiting resistors can be replaced accordingly.

As the LED current is not regulated from a constant current source, the output power from the blue and IR LEDs varies across temperature. This results in a signal chain gain variation across temperature. This variation can be addressed by temperature compensation in digital post-processing of the signal chain output by monitoring the ambient temperature using either or both of the onboard temperature sensors of the M0L MCU and the HDC2010.

GUID-20231020-SS0I-1SWT-XMGT-RGM9TMJKHS2L-low.svgFigure 2-11 LED Driver Schematic