TIDUF59 March   2024

 

  1.   1
  2.   Description
  3.   Resources
  4.   Features
  5.   Applications
  6.   6
  7. 1System Description
    1. 1.1 Key System Specifications
  8. 2System Overview
    1. 2.1 Block Diagram
    2. 2.2 Design Considerations
      1. 2.2.1 PFC Inductance Design
      2. 2.2.2 Configuration of CS pin in LMG3622
      3. 2.2.3 AHB Topology and the VCC Design
      4. 2.2.4 LMG2610 for AHB Topology
    3. 2.3 Highlighted Products
      1. 2.3.1 UCC28056
      2. 2.3.2 LMG3622
      3. 2.3.3 LMG2610
  9. 3Hardware, Test Requirements, and Test Results
    1. 3.1 Hardware
    2. 3.2 Test Setup
    3. 3.3 Test Results
      1. 3.3.1 Switching Waveform
        1. 3.3.1.1 Switching Waveform on the PFC Stage
        2. 3.3.1.2 Switching Waveform on the AHB Stage
      2. 3.3.2 Efficiency Test Result
      3. 3.3.3 Thermal Test Result
  10. 4Design and Documentation Support
    1. 4.1 Design Files
      1. 4.1.1 Schematics
      2. 4.1.2 BOM
      3. 4.1.3 Layout Prints {Optional Section}
    2. 4.2 Tools
    3. 4.3 Documentation Support
    4. 4.4 Support Resources
    5. 4.5 Trademarks
  11. 5About the Author

2.2.2 Configuration of CS pin in LMG3622

For boost PFC design, a current shunt resistor is needed to detect the current for the system control and the over power protection.

LMG3622 integrates the current emulation function which supports a dependent current sourcing of IDS through the internal current mirror. The gain of the current emulation is GCS. With the very low value of CGS, RCS is designed with a high resistor value with a smaller package size which increases the efficiency and lowers the temperature stress on the PCB. The RCS resistor was set with Equation 7.

Equation 7. R C S = R S h u n t G C S

where

  • RSHUNT is the original current shunt resistor value.

The typical value of the GCS of LMG3622 is 0.691mA/A. In this application, RCS is designed as a 130Ω by 0603 package.

For most of the TM PFC, an AUX winding is needed to detect the ZVS condition and try to turn the device on at the valley for higher efficiency. To simplify the design, UCC28056 is designed by the resistors and capacitors divider to eliminate the AUX winding and combine the ZVS and CS in the same pin with SOT-23(6) package.

Instead of an AUX winding, the UCC28056 detects the ZVS with the capacitor and resistor divider. The sense capacitor induces high spike current during switching and converts the current to a high-voltage spike on the RCS resistor which leads to over stress on the CS pin of TI-GaN. Figure 2-2 shows voltage spike on the RCS resistor. The channel setting is:

  • Ch1 is VDS of LMG3622
  • Ch2 is the RCS voltage.
GUID-20231211-SS0I-2440-N930-DBMZF9DFSZXZ-low.svg Figure 2-2 High Spike Voltage was Found on the RCS When the Device Turns On and Off

One blocking diode (such as 1N4148) can be placed in series with the RCS which is shown in Figure 2-3 to prevent a high-voltage spike on the CS pin to damage TI GaN from overvoltage stress.

GUID-20231212-SS0I-QNZL-Q9JT-KVRXLGTK4W8C-low.svg Figure 2-3 Blocking Diode in Series with RCS to Prevent the Voltage Spike due to High Voltage Spike

Figure 2-4 shows the result on the CS pin with a blocking diode. The channel setting is:

  • Ch1 is VDS of LMG3622
  • Ch2 is CS voltage of LMG3622.
GUID-20231211-SS0I-MV05-ZTSM-D7NLKXLLMK52-low.svg Figure 2-4 LMG3622 CS Pin Voltage With Block Diode

The circuit with high voltage on RCS has to implement the blocking diode by using the LMG362x device.