SBAA586 October   2023 AMC23C11 , UCC23513

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2System Challenge on Isolated Gate Drivers With Integrated DESAT
  6. 3System Approach With UCC23513 and AMC23C11
    1. 3.1 System Overview and Key Specification
    2. 3.2 Schematic Design
      1. 3.2.1 Circuit Schematic
      2. 3.2.2 Configure VCE(DESAT) Threshold and DESAT Bias Current
      3. 3.2.3 DESAT Blanking Time
      4. 3.2.4 DESAT Deglitch Filter
    3. 3.3 Reference PCB Layout
  7. 4Simulation and Test Results
    1. 4.1 Simulation Circuit and Results
      1. 4.1.1 Simulation Circuit
      2. 4.1.2 Simulation Results
    2. 4.2 Test Results With 3-Phase IGBT Inverter
      1. 4.2.1 Brake IGBT Test
      2. 4.2.2 Test Results on a 3-Phase Inverter With Phase to Phase Short
  8. 5Summary
  9. 6References
  10. 7Revision History

3.2.2 Configure VCE(DESAT) Threshold and DESAT Bias Current

Resistors R9 to R14 can be used to adjust the VCE(DESAT) threshold and the DESAT bias current iBIAS(DESAT). The following equations are simplified for a quick estimation on their values for different DESAT threshold and DESAT bias current configurations.

The isolated comparator AMC23C11 has a reference voltage VREF which is set by an internal 100 μA current source and the external resistor R9. The value of R9 is calculated per Equation 1 to set the VREF to 1.5 V in this design. Here 1.5 V is chosen to make the AMC23C11 to operate in the high-hysteresis mode[1].

Equation 1. R9=VREF100 μA=15 kΩ 

R10 and R11 determine the DESAT bias current and are calculated per Equation 2:

Equation 2. R10=R11=2×VDD-VCEDESAT-VFWD1-R12×iBIAS(DESAT)iBIAS(DESAT)+iR13R14(DESAT)

Here:

  • VDD is the UCC23513's supply voltage; 15 V in this case for IGBT driving;

  • VCE(DESAT) is the desired DESAT threshold; 8 V by default in this design;

  • VFW(D1) is the forward voltage of the high-voltage diode D1; assumed to be 0.5 V;

  • R12 is set to 100 Ω as a common practice[9];

  • iR13R14(DESAT) is the current through R13 and R14. Set to 0.5 mA. Lower setting may reduce noise immunity.

  • iBIAS(DESAT) is DESAT bias current when the IGBT's VCE reaches VCE(DESAT). Set to 5.5 mA in this design.

So R10 and R11 could be calculated at 2 kΩ for this design.

The power rating of R10 and R11 needs to be selected for normal IGBT operation, where the VCE(DESAT) is significantly smaller. Assuming R12 << R10, the simplified maximum power losses are per Equation 3:

Equation 3. PR10,  MAX=PR11,  MAX=(VDD - VFWD1 - R12 × iBIAS(DESAT) - VCE(SAT))2R10×PWMDUTY,  MAX

With the default settings in table 3-1 and a typical VCE(SAT) of 1.5V, the maximum power losses of PR10(MAX) and PR11(MAX) are around 69.8 mW even at 1000% PWM duty cycle.

R13 and R14 are calculated per Equation 4 and Equation 5:

Equation 4. R13=VREFiR13R14(DESAT)
Equation 5. R14=VDD-(iBIASDESAT+iR13R14DESAT)×R10÷2iR13R14(DESAT)-R13

Applying the parameters' values, we can get R13 of 3 kΩ and R14 of 15 kΩ.