TIDUEW9 April   2020

 

  1.    Description
  2.    Resources
  3.    Features
  4.    Applications
  5.    Design Images
  6. 1System Overview
    1. 1.1 Key System Specifications
    2. 1.2 Block Diagram
    3. 1.3 Top Side Pump
    4. 1.4 LED Driver Input Signals
    5. 1.5 LED Driver SDIM/UDIM Settings
    6. 1.6 TPS92641 Board Description
    7. 1.7 Setting the LED Current and Analog Dimming
    8. 1.8 PWM Dimming
  7. 2LED Driver Key Parameters
    1. 2.1 Enable and Disable Delay
    2. 2.2 Rise and Fall Time
    3. 2.3 Ripple
    4. 2.4 Performance Parameters
    5. 2.5 LED Load Capacitor for Rise/Fall Time
    6. 2.6 LED Load Capacitor And Audible Noise
      1. 2.6.1 Layout Considerations
      2. 2.6.2 Electrolytic capacitor considerations
      3. 2.6.3 Standoff Capacitors
    7. 2.7 LED Driver Calculator Tool
  8. 3Layout
  9. 4Related Documentation
    1. 4.1 Trademarks
    2. 4.2 Third-Party Products Disclaimer

2.5 LED Load Capacitor for Rise/Fall Time

Choosing LED capacitor is very important when it comes to rise times, delay times, and current ripple. Here is a table what capacitor measurements that we made to help choose proper capacitor based on rise time and current ripple requirements. Capacitor choice might be different for Blue vs. Green LEDs. Green and top side pump are placed in parallel and are a larger load to the driver compared to just a Blue LED by itself.

Table 6. Load Capacitor effect on performance

COLOR CAP (UF) ENABLE DELAY (US) RISE TIME (US) ENABLE DELAY + RISE TIME RIPPLE PEAK TO PEAK (A)
Green 6.60 16.70 4.30 21.00 0.60
Green 4.40 12.40 4.40 16.80 0.80
Green 3.30 7.00 3.00 10.00 1.00
Green 2.20 6.50 2.70 9.20 0.60
Blue 10.0 11.20 3.60 14.80 0.64
Blue 6.60 11.50 4.80 16.30 0.56
Blue 4.40 8.70 3.40 12.10 0.72
Blue 3.30 5.50 3.30 8.80 0.60
Blue 2.20 4.00 1.90 5.90 0.56