TIDUES6 August   2020  – MONTH 

 

  1.   Description
  2.   Resources
  3.   Features
  4.   Applications
  5.   5
  6. 1System Description
    1. 1.1 Key System Specifications
  7. 2System Overview
    1. 2.1 Block Diagram
    2. 2.2 Design Considerations
    3. 2.3 Highlighted Products
      1. 2.3.1 DRV8906-Q1
      2. 2.3.2 DRV8873-Q1
      3. 2.3.3 TPS1HB16-Q1
      4. 2.3.4 LM2904B-Q1
      5. 2.3.5 TLIN1028-Q1
    4. 2.4 System Design Theory
      1. 2.4.1 Mirror XY and LED Driver
      2. 2.4.2 Mirror Fold Driver
      3. 2.4.3 Mirror Heater Driver for Defogging and De-icing
      4. 2.4.4 Electrochromic Mirror Driver
        1. 2.4.4.1 Sallen-Key Low-Pass Filter
        2. 2.4.4.2 High-Current Buffer Amplifier
        3. 2.4.4.3 Buffer Amplifier Stability for Very-Large Capacitive Loads
        4. 2.4.4.4 Fast Discharge of Large Capacitive Load
      5. 2.4.5 SBC - LIN Communication Interface and System Supply
  8. 3Hardware, Software, Testing Requirements, and Test Results
    1. 3.1 Required Hardware and Software
      1. 3.1.1 Hardware
    2. 3.2 Testing and Results
      1. 3.2.1 Test Setup
      2. 3.2.2 Test Results
        1. 3.2.2.1 Reverse Battery Protection
        2. 3.2.2.2 X&Y Motors and LED Driver
        3. 3.2.2.3 Thermal Performance
  9. 4Design Files
    1. 4.1 Schematics
    2. 4.2 Bill of Materials
    3. 4.3 Altium Project
    4. 4.4 Gerber Files
    5. 4.5 Assembly Drawings
  10. 5Software Files
  11. 6Related Documentation
    1. 6.1 Trademarks
    2. 6.2 Third-Party Products Disclaimer
  12. 7Terminology

2.4.4.1 Sallen-Key Low-Pass Filter

A unity gain second order Sallen-Key low-pass filter is used to filter a PWM signal from the MSP430™ LaunchPad™ to a stable analog voltage value. The voltage value can range from 0 V to 3.3 V depending on the duty cycle of the PWM signal. This low-pass filter output voltage goes to a high-current buffer amplifier circuit which drives the electrochromic mirror.

The resistors and capacitors were chosen such that the cut-off frequency is set to roughly around 315 Hz and the Q factor to around 1/2. The low cut-off frequency allows only the DC component of the PWM signal to pass through the filter. The Q factor being close to 1/2 sets the system in a critically damped state which limits oscillations at the output and results in a faster response with minimum overshoot.