SLLA646 August   2024 ISO6520 , ISO6521

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
    1. 1.1 Where are Digital Isolators Commonly Used?
    2. 1.2 What is Functional Isolation?
    3. 1.3 Key Benefits of Functional Isolation
  5. 2Application Use Cases
    1. 2.1 Telecom Power Supplies
      1. 2.1.1 48V Isolated DC-DC
      2. 2.1.2 48V Non-Isolated DC-DC
    2. 2.2 Server Power Supply
      1. 2.2.1 Totem-Pole Power Factor Correction Stage
      2. 2.2.2 Half-Bridge LLC Stage
    3. 2.3 AC - DC Power Supply in Pluggable Wall-Chargers
      1. 2.3.1 Introduction
      2. 2.3.2 Topology Details
      3. 2.3.3 Using ISO65xx for Reliable PWM Signaling
    4. 2.4 Semiconductor Test and Measurement
  6. 3Conclusion
  7. 4References

2.1.1 48V Isolated DC-DC

A standard H-Bridge stage is commonly implemented for an isolated DC-DC power source as shown in Figure 2-1. Digital controller generating PWM signals for switching Power FETs can be referenced to either the isolated or the non-isolated side. In Figure 2-1, the digital controller is referenced to the isolated side.

Typical 48V Isolated DC-DC Implementation Using ISO65xx Figure 2-1 Typical 48V Isolated DC-DC Implementation Using ISO65xx

On the non-isolated side, high-side power FETs in the H-bridge require a level-shifted signal to enable FET switching. A blocking voltage of at least 100V would be necessary for this application along with immunity to high voltage switching noise (>100kV/us) across the barrier.

Functional isolation devices like ISO65xx are the right fit for this application, capable of VIOWM > 200Vrms voltage across the barrier. A similar implementation can be used on the isolated side, where the isolator is used for high-voltage blocking. Low-side FETs in these designs may also choose to use of ISO65xx to match the propagation delays between the high side and low side.

The 48V DC-DC isolation barrier may also require just functional isolation where an ISO65xx can be used. In case basic isolation is needed across the power stage, TI's digital isolator families like ISO6741 can be picked for PWM communication across the barrier.