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

2.6.2 Electrolytic capacitor considerations

Electrolytic capacitors is less noisy because they don’t vibrate the PCB due to their structure and packaging, however, they have higher resistance and inductance components, and can slow down LED current rise time and enable delay. Figure 10 is an example of Green LED with 4.7µF ceramic load in parallel, 10A.

Figure 10. LED Waveform with 4.7 µF Ceramic CapacitorsTIDA-080008 Waveform_1.gif

Figure 11 is an example of GREEN LED with 4.7µF electrolytic load in parallel, 10A.

Figure 11. LED Waveform with 4.7 µF Electrolytic CapacitorsTIDA-080008 Waveform_2.gif

Table 7 is an example of timing differences between Ceramic and Electrolytic Cap.

Table 7. Driver Performance between Ceramic and Electrolytic Capacitors

COLOR CAP VALUE (µF) CAPACITOR TYPE ENABLE DELAY (µS) RISE TIME (µS) ENABLE DELAY + RISE TIME (µS) RIPPLE PEAK TO PEAK (A)
Green 4.70 Ceramic 9.20 3.00 12.20 1.20
Green 4.70 Electrolytic 28.00 28.50 56.50 0.40
Green 3.30 Ceramic 7.00 3.00 10.00 1.00
Green 3.30 Electrolytic 7.80 12.00 19.80 0.40
Green 2.20 Ceramic 2.70 2.70 9.20 0.60
Green 2.20 Electrolytic 10/80 10.80 15.20 0.60