SLUAAP2 March   2023 LMG2610 , UCC28782

 

  1.   Abstract
  2.   Trademarks
  3. 1Introduction
    1. 1.1 Design Requirement 1: Managing Thermals Induced by Power Losses
    2. 1.2 Design Requirement 2: Reducing Energy Storage Requirement by Switching at High Frequency
  4. 2A Brief Introduction to GaN's Value
  5. 3The Active Clamp Flyback
    1. 3.1 Power Loss Saving 1: Zero-Clamp Loss
    2. 3.2 Power Loss Saving 2: Zero-Voltage-Switching
  6. 4The Value of GaN in Active Clamp Flyback
  7. 5Leveraging Integrated GaN to Simplify ACF Stage
  8. 6Physical Design Implementations Using LMG2610 Integrated Half-Bridge and UCC28782 ACF Controller
    1. 6.1 UCC28782EVM-030
    2. 6.2 PMP23146
  9. 7Leverage Design Tools for ACF
  10. 8Summary
  11. 9References

5 Leveraging Integrated GaN to Simplify ACF Stage

This application note has analyzed how the GaN-based ACF can address the thermal and energy storage challenges to facilitate small-form-factor designs. However, the next challenge is managing a practical implementation with considerations for cost and integration. Figure 5-1 shows the main components that are required to support the power stage of this topology.

GUID-20230223-SS0I-PNQ5-GBNF-NSXJWFBVB20H-low.svg Figure 5-1 Practical Implementation of ACF

Aside from the controller, the semiconductor devices required in the primary side of the power stage are the high-side and low-side FETs, high-side and low-side gate drivers, high-side level shifter, and bootstrap diode. All the devices, together with biasing resistors and bypass capacitors, can add an undesirable increase in the cost, BOM count, and overall board space.

To address the complexity of all these devices, the LMG2610 simplifies the power stage by integrating all the devices into a single 7 mm × 9 mm package.

GUID-20230223-SS0I-TXMP-RDWF-QPFTMNM0R9MP-low.svgFigure 5-2 LMG2610 Block Diagram

As shown in Figure 5-2, LMG2610 integrates 170 mΩ/248 mΩ GaN half-bridge, gate drivers, level shifter, and bootstrap diode. This device can support ACF designs up to 75 W.

In addition to the integration, a key feature of LMG2610 that can further decrease power losses in ACF designs is the current sense emulation. All current-mode controllers sense the current through the low-side FET to control the on-time of the device. However, instead of having to sense the actual FET current through a traditional sense resistor, LMG2610 outputs a scaled-down replica (1 mA/A) of the low-side FET current through the CS pin. This replicated current signal is then fed into a resistor and produces the same voltage required by the controller that a traditional current sensing scheme produces. The difference here is that the power loss is a small fraction of the traditional sensing scheme as shown in Equation 6.

Equation 6. P s e n s e , e m u l a t i o n P s e n s e , t r a d i t i o n a l = . 001 I L S , a v g   × 1.5V a u x I L S , r m s 2 × R s e n s e

Using this feature in conjunction with ZVS and zero-clamp-loss enables the highest efficiency for ACF.

Pairing the LMG2610 Integrated GaN Half-Bridge with the UCC28782 ACF controller provides a simple, cost-effective solution compared to a discrete design. This combination allows for high frequency operation, high efficiency across all load levels, low standby power, and a reduced EMI signature at high input voltages. Compared to Figure 5-1, Figure 5-3 is much simpler due to the integration provided by LMG2610.

GUID-20230223-SS0I-DTL3-JDLJ-29NRR7NJPHJZ-low.svgFigure 5-3 ACF Power Stage with UCC28782 Controller and LMG2610 Integrated GaN Half-Bridge