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

1 Introduction

In 3-phase inverters for motor drives, OCP and SCP are critical to protect the system from damage caused by abnormal operating conditions. Shunt-based system level OCP or SCP are often implemented by sensing the current through the negative DC bus or the three low-side switches; especially in many lower power, compact models, where form factor and system cost are critical. These protections are effective for the commonly seen fault patterns of arm shoot-through and phase-to-phase short. However, neither of them can detect an earth ground short when the fault current flows through a high-side switch, as shown in Figure 1-1. A DESAT function on the gate driver can help to protect the power switch against this fault. In fact, device level DESAT protection is effective to all these fault modes in a 3-phase inverter, thus has been widely used in many high power, high performance models.

GUID-20230821-SS0I-SQNN-C7KV-MRCLVC3WCPTT-low.svgFigure 1-1 Short Circuit Due to Earth Ground Fault in A 3-Phase Inverter

Many industrial motor drives also have a regeneration brake switch to shunt the current to the negative VDC- bus and discharge the bulk capacitor when the voltage goes too high during a regeneration brake operation. Often this brake resistor needs to be installed externally and then connected to the system by a specific terminal on the drive. If a user makes an error in connecting this resistor, or mistakenly used one with a very low resistance, an overcurrent fault can occur once a brake operation is started by the system controller, as shown in Figure 1-2. In this case, a DESAT function on the gate driver can detect the problem and protect the power switch in time.

GUID-20230821-SS0I-F2JG-RZ1Z-GBDNJDQ7CNGR-low.svgFigure 1-2 Short Circuit Due to Miswiring of External Brake Resistor Terminal

A typical approach to protect the system against these faults uses an isolated smart gate driver with DESAT function, like the UCC21750 reinforced isolated gate driver with CMOS input. As seen in Figure 1-3, a DESAT pin monitors the voltage drop of VCE when the IGBT is turned ON. Once this voltage drop goes up and reaches the set threshold, which means an over current or short circuit condition is happening, the output of the gate driver will be pulled to low at once and a fault output wii be activated to inform the system controller on the fault.

GUID-20230821-SS0I-73NJ-HZNP-SZKR7CHJRQLM-low.svg Figure 1-3 UCC21750 With Integrated DESAT Protection