Achieving Fast Load-Transient Response and Low EMI With the AECM DC/DC Control Topology
At a glance
 1 What is AECM control? | AECM is a control topology based on a fixed-frequency modulation with
emulated current information for the loop control. |
| 2 PCM | PCM is a popular fixed-frequency control topology for DC/DC converters given
its overload protection, accuracy and ease of compensation. |
| 3 D-CAP2 control scheme | The D-CAP2 control scheme is a variation of adaptive COT control with an
emulated ramp-generator circuit integrated inside the IC. |
| 4 AECM control benefits | AECM control topology can help engineers simplify EMI filter design with
fixed frequency and supports wide- output, large-duty-cycle applications
with good load-transient performance |
| 5 How AECM control works | AECM control offers mode-detection block to identify whether the DC/DC
converter is in PWM mode or PFM mode. Its integrated oscillator generates
the fixed clock in PWM mode, enables on-time generator and adjusts DC gain
to achieve high bandwidth. |
Authors
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.