What is AECM control?

There are many types of control topologies addressing specific design challenges for non-isolated switching DC/DC converters and controllers [1], including peak current-mode control (PCM), voltage-mode control, constant on-time (COT) control, D-CAP2™ control topology and all of their derivatives. In accordance with the implementation of duty cycle, it is possible to separate these control topologies into two categories: the pulse-width modulation (PWM) technique and the pulse-frequency modulation (PFM) technique.

The PWM technique is common in DC/DC converters used to power communications, audio and automotive equipment. It has a fixed and predictable switching frequency, which is convenient when designing the output filter for low electromagnetic interference (EMI).

The PFM technique is common in DC/DC converters used to power digital applications such as graphic engines, memory, digital signal processors and field-programmable gate arrays because of its fast load-transient response. Control topologies do affect DC/DC converter design and may vary based on system-level requirements such as ripple, solution size, load-transient response, fixed frequency and light load efficiency. No single control topology is a good fit for all applications.

In this white paper, a constant frequency and inductor current-based control topology is introduced with smart loop-bandwidth control called advanced emulated current mode (AECM). This new control topology combines the benefits of PFM and PWM techniques, showing a fast load-transient response with a true fixed switching frequency operation. AECM can help enhance the performance of applications currently using both the PCM and PFM techniques.