Digital hybrid hysteretic controlled (HHC) LLC converter based on C2000 real-time MCUs
With the changing transient response requirements in the world of digital power, meeting stringent specs in applications like server power supply and other industrial ACDC power supplies has become challenging. This C2000 real-time MCU based digital hybrid hysteretic controlled (HHC) LLC converter design demonstrates how current mode control achieves better transient response compared to a traditional voltage mode control with least CPU resources yet achieving the needed performance.
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This is a two-stage reference design with PFC and DC-DC. One C2000 controller is used to control PFC and the other C2000 MCU is used to control half bridge LLC. The LLC stage utilize the current mode control to achieve better transient response compared with traditional voltage control. This design can be utilized in server PSU, telecom rectifier, and other industrial AC-DC power supply applications.
Recently the load transient response requirement has increased significantly due to higher power consumption and rapid power variation of power supply unit in data center servers. In the past the slew rate is 1 to 2 amps per microsecond. The requirement now is double and increased to be higher than 2.5 amps per microsecond or even 5 amps per microsecond.
With higher load slew rate it is more challenging to maintain the output voltage within the required range when the worse load transient condition occurs. This design a high transient response by using the hybrid hysteretic control converter, based on C2000 real-time microcontroller. It also helps to meet the building block of MCRPS spec.
Among different topologies the LLC is chosen for higher efficiency. Compared with traditional control, hysteretic control higher control load bandwidths and better transient response. C2000 MCU helps to implement hysteretic control with the least CPU resource and achieve higher switching frequency.
This design showcases very good voltage deviation and settling time. It also contains multiple features such as synchronous rectification, light load operation mode, and soft start. A running demo for LLC stage is shown here with high power DC source, high power DC load, and the reference design board. The switching frequency varies between 90 kilohertz and 250 kilohertz. And the frequency is around 160 kilohertz.
The scope shows the PWM output and the resonant capacitor voltage. hysteretic control demonstrates better transient response. This picture shows the comparison between HHC and VMC in terms of voltage deviation with a 60% load-step response. It also enables easy compensation design and better AC ripple rejection.
The C2000 MCU has the features to support high performance and easy implementation of hybrid hysteretic control of convertor. Flexible coupling of comparator, and PWM enables easy implementation. High computational power assists high frequency voltage control loop, which reduce the external loop latency. The configurable logic block helps to support flexible synchronous rectification.
In summary, high transient response requirement becomes a challenge for server PSU. To solve this challenge, hybrid hysteretic control is a good candidate. C2000 MCU empowers easy implementation of HHC LLC converter and also enables LLC converter with high switching frequency. For more information, please go to the Reference Design page. The user guide and the software can be downloaded from Digital Power SDK page. Thanks for watching.
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