SLAT163 July   2024 AFE43902-Q1 , AFE439A2 , AFE53902-Q1 , AFE539A4 , AFE539F1-Q1 , AFE639D2 , DAC43204 , DAC43401 , DAC43401-Q1 , DAC43701 , DAC43701-Q1 , DAC43901-Q1 , DAC43902-Q1 , DAC53001 , DAC53002 , DAC53004 , DAC53004W , DAC53202 , DAC53204 , DAC53204-Q1 , DAC53204W , DAC53401 , DAC53401-Q1 , DAC53701-Q1 , DAC539E4W , DAC539G2-Q1 , DAC63001 , DAC63002 , DAC63004 , DAC63004W , DAC63202 , DAC63202W , DAC63204 , DAC63204-Q1 , DAC63204W

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1What is a Smart DAC?
  5. 2What is a Smart Analog Front End (AFE)?
  6. 3Smart DAC selection guide
  7. 4Smart AFE Selection Guide
  8. 5Applications
    1. 5.1 Lightning
      1. 5.1.1 Light Emitting Diode (LED) Biasing and Linear Fade-In Fade-Out
      2. 5.1.2 LED Biasing With LED Driver
      3. 5.1.3 Analog Thermal Foldback
        1. 5.1.3.1 Single Slope Thermal Foldback
        2. 5.1.3.2 Multi-Slope Thermal Foldback
      4. 5.1.4 Logarithmic Fade-In/Fade-Out
      5. 5.1.5 LED Sequencing
    2. 5.2 Control
      1. 5.2.1 Voltage Margining and Scaling With Voltage Output Smart DAC
      2. 5.2.2 Thermoelectric Cooling (TEC) Control
        1. 5.2.2.1 TEC Control Using DC/DC Driver
        2. 5.2.2.2 TEC control using h-Bridge driver
      3. 5.2.3 Analog Power Control (APC) of a Laser
      4. 5.2.4 Constant Power Control
    3. 5.3 Microcontroller Independent Fault Management and Communication
      1. 5.3.1 Programmable Comparator Using Smart DAC
      2. 5.3.2 GPI-to-PWM
      3. 5.3.3 If-Then-Else Logic
    4. 5.4 Driver
      1. 5.4.1 Lens Positioning Control for Camera Module Auto-Focus and Image Stabilization
      2. 5.4.2 Laser Drive
    5. 5.5 Miscellaneous Smart DAC Applications
      1. 5.5.1 Software-less Medical Alarm Generation
      2. 5.5.2 555 Timer

5.1.3.2 Multi-Slope Thermal Foldback

To maintain that the LED is lit up at the same luminosity throughout safe temperature ranges, the current through LED needs to be increased progressively by higher margin and at some point, when the temperature reaches a critical level, completely shut off the current and the LED. Usually software is required for such operation to process the temperature and adjust the slope of the current.

AFE53902-Q1 is the device that can implement thermal foldback with no need for software. This device has an integrated ADC which senses the temperature from an analog temperature sensor or a simple NTC. The input is then compared to the look-up table which is entirely customizable by the user. The LUT outputs in the operating region of the LED the current temperature is, and what the biasing current in such region needs to be. Using this information, the internal state machine adjusts the PWM duty cycle based on the temperature range and the desired LED output. All configurations including the look-up table can be stored in the non-volatile memory to remove the need for run-time software. Alternatively, if the PWM signal is required to stay constant, voltage output of the AFE can be used. The voltage controls current adjustment setting of the LED driver.

Table 5-4 Design Implementation
Hardware Block DiagramFigure 5-4 Hardware Block Diagram

Design Benefits

Suggested device

  • Processor-less multislope thermal foldback
  • Look-up table to program foldback points and slopes
  • Sensing and control in one chip
  • PWM or voltage output options
  • NVM to store all configurations to remove the need for run-time software
End EquipmentDesign help