SBAA549 April   2022 AMC23C11 , AMC23C12 , AMC23C14

 

  1.   Trademarks
  2. 1Background
  3. 2Overcurrent Protection on DC+
  4. 3DC+ Power Supply Solution
    1. 3.1 Selection of Charge Pump Capacitor
    2. 3.2 Simulation in PSpice for TI
    3. 3.3 Hardware Test
    4. 3.4 Low-Cost Power Supply Solution
  5. 4Power-On Short-Circuit Risk and Solution
  6. 5Reference

4 Power-On Short-Circuit Risk and Solution

Since the bootstrap circuit and charge pump need to wait for one cycle of half-bridge operation before they power the isolated comparator. After VDD1 has powered up to greater than 3 V, the capacitor on the reference pin must charge to the threshold voltage before the isolated comparator is functional. Figure 4-1 shows that output of isolated comparator is valid when reference voltage is within 1% of the set value.

Figure 4-1 Output Behavior for Long Settling Times of the Reference Voltage (AMC23C11)

Therefore, the boot strap charge pump solution is not able to provide OC protection during the initial start-up of the motor drive. This risk can be reduced by adding DC– OC protection and pre-turn on the three low-side IGBTs.



Figure 4-2 Add DC– Short-Circuit Protection

The added DC– protection can share power with the low-side driver, so there is always protection on the DC–. The DC– protection protects against both shoot-through fault (blue) and phase-to-phase short fault (yellow). However, the DC+ ground fault (red) cannot be protected directly through the DC–. Turn on the three lower IGBTs before the IGBT module starts working to detect whether there is a short to ground, and also to charge the bootstrap capacitor.