STDA011 September   2025 UCC25661

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2Benefits of GaN In LLC Resonant Converter
    1. 2.1 Higher Efficiency
    2. 2.2 Faster Switching Speeds
    3. 2.3 Reduced Parasitic Capacitances
    4. 2.4 Improved Power Density
    5. 2.5 High Thermal Conductivity
    6. 2.6 Lower Junction Temperatures
  6. 3LLC Resonant Converter
    1. 3.1 The Relationship Between Output Voltage (VOUT) and Switching Frequency (fS) in an LLC Resonant Controller
      1. 3.1.1 The LLC Charging Challenge
      2. 3.1.2 A Wide VIN/VOUT Capable LLC
  7. 4Practical Application of LLC Converters for a Battery Charger Leveraging GaN Switches
    1. 4.1 Requirements and Scope
    2. 4.2 Charging Curve for Lithium-Ion Battery
    3. 4.3 How to Support Wide VOUT Range in an LLC Design for Battery Chargers
    4. 4.4 The Prototype Hardware
  8. 5Summary

4.2 Charging Curve for Lithium-Ion Battery

Lithium-ion batteries are charged using a specific algorithm to ensure safety, efficiency and longevity. The most common mode is called Constant Current /Constant Voltage (CC/CV) charging. This design incorporates the CC/CV algorithm.

Typical Li-Ion Battery Charging Profile Figure 4-1 Typical Li-Ion Battery Charging Profile
  • Trickle charge: Very low constant current phase, only used with deeply discharger battery (typically below 2.5-2.9V per cell). This phase secure the battery cells not are damaged.
  • Pre-charge: Low constant current phase brings the battery up to a safe level (current often 1/10th of normal ICHARGE).
  • Constant Current (CC): This is high current phase that rapidly deliver the bulk of the energy to the battery.
  • Constant Voltage (CV): Voltage is held constant when maximum battery voltage is reached (typically 4.2V per cell). When the battery is fully charger the internal resistance increases and lower ICHARGE to a defined termination level (ITERM , often around 2-5% of CC).