SLUA778A June   2016  – July 2016 UCC21520 , UCC21520-Q1 , UCC21540

 

  1.   UCC21520: A Universal Isolated Gate Driver with Fast Dynamic Response
    1.     Trademarks
    2. 1 Introduction
    3. 2 Internal Shoot-Through with Mismatched Propagation Delay
    4. 3 UCC21520 Dynamic Characteristics
    5. 4 Parallel UCC21520 Output Channels
      1. 4.1 UCC21520 Efficiently Drives Heavy Capacitive Loads by Paralleling its Output Channels
      2. 4.2 Schematic and PCB Layout Recommendations when Paralleling Output Channels
    6. 5 UCC21520 Driving Different Power Topologies
    7. 6 Summary
  2.   Revision History

2 Internal Shoot-Through with Mismatched Propagation Delay

The propagation delay mismatch will introduce internal shoot-through if the two output channels are paralleled. Figure 2 shows the simplified circuit diagram with UCC21520 two output channels in parallel driving a heavy load. In this example, it is assumed that the channel A turn-on happens earlier than channel B, or channel A turn-off later than channel B. The red dotted line shows the shoot-through path which shorts VDD to ground with very small impedance, which is typically 1.5 Ω combining pull-up and pull-down resistance. Therefore, there will be large current flow through the gate driver device, and will result in additional internal heat. The estimated loss per cycle can be calculated by:

Equation 1. FORM.gif

    where

  • PST: Shoot-through introduced extra loss;
  • VDD: Supply voltage on VDDA and VDDB;
  • IST: Shoot-through current, decided by the pull-up and pull-down circuit design;
  • tDM_Rise: Propagation delay matching at rising edge;
  • tDM_Fall: Propagation delay matching at falling edge;
  • fSW: switching frequency;

To make sure UCC21520 two channels can be used in parallel, it is essential to quantify the delay matching data at different VDD voltage and temperature.

FIG_TWO.gifFigure 2. Internal Shoot-Through with Mismatched Propagation Delay Between Output Channels