SPRADQ1 February   2025 TMS320F2800133 , TMS320F2800135 , TMS320F2800137 , TMS320F2800155 , TMS320F2800157 , TMS320F280025C , TMS320F280037C-Q1 , TMS320F280039C , TMS320F280039C-Q1 , TMS320F280045 , TMS320F280049 , TMS320F280049C , TMS320F28P559SJ-Q1

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2Potential Risks with Traditional PWM Configuration
  6. 3PWM Configurations for Robust Control
    1. 3.1 Create Additional Delay for the Sync Event for the PWM Counter
    2. 3.2 Configure a ZCD Signal as a T1 Event
  7. 4How to Capture the Phase Difference and Period of Multiphase Totem Pole PFCs
  8. 5How to Eliminate the External ZCD Circuits with TI GaN
  9. 6Summary
  10. 7References

5 How to Eliminate the External ZCD Circuits with TI GaN

Figure 3-3 shows a common external ZCD circuits for a TCM totem pole PFC. Generally, this consists of a shunt resistor, a high-bandwidth operational amplifier, and a high speed comparator. When designing a high power system with high switching frequency, it is challenging to balance the detection speed and the noise immunity for the ZCD circuits. Additionally, the shunt resistor causes power loss and affects efficiency.

External ZCD Circuits Figure 5-1 External ZCD Circuits

TI released an intelligent GaN (LMG3427R030), which integrates a ZCD signal to simplify the system design, as Figure 5-2 shows.

GaN with Integrated ZCD for Totem Pole PFC Figure 5-2 GaN with Integrated ZCD for Totem Pole PFC

The device integrates a ZCD circuit that provides a digital feedback signal when the drain-to-source current direction changes from negative to positive, which is different from traditional ZCD signals. To better illustrate how to leverage the ZCD signals from both high side and low side GaN, Figure 5-3 shows the ZCD signal behaviors during a positive cycle and a negative cycle and the corresponding PWM logic. Therefore, different from the usage of traditional single ZCD signals, it is required to switch the source for the ZCD signal in the PWM configurations, since the high side GaN provides the effective ZCD signal for the control during the positive cycle and the low side GaN provides the ZCD signal during the negative cycle. This can be done by changing the GPIO source in the settings of the input XBAR.

GaN ZCD Signal Behaviors During Positive and Negative Cycles Figure 5-3 GaN ZCD Signal Behaviors During Positive and Negative Cycles