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Maxim > Design Support > Technical Documents > Application Notes > Power-Supply Circuits > APP 3939
Keywords: Average Current-Mode, ACMC, Multimedia,Telematics
APPLICATION NOTE 3939
DC-DC Controllers Use Average-Current-Mode
Control for Infotainment Applications
Nov 22, 2006
Abstract: Auto infotainment products (multimedia and telematics) are demanding more power and
challenging a vehicle's power-management systems. This application note explains average-current-
mode control (ACMC) technology for power management. The article demonstrates that this technology
minimizes several power-management problems, including efficiency, size, EMI, transient response,
design complexity, and overall cost. The MAX5060/MAX5061 will serve as examples of the technique.
Introduction
As high-performance microprocessors demand more power in auto multimedia and telematics, (e.g.,
infotainment products), so do some of the well-known design problems like noise susceptibility, EMI, and
loop compensation. Average-current-mode control (ACMC) helps to relieve these problems, especially in
auto infotainment applications. This application note describes ACMC and explains its benefits over a
current-mode control design for infotainment applications. The MAX5060/MAX5061 illustrate ACMC, and
the information presented here supplements the basic narrative in the product data sheet.
Define the Design Goals
Each auto infotainment application presents a unique set of technical and commercial requirements for
power management. The most important design considerations are efficiency, size, EMI, transient
response, design complexity, and cost. All of these parameters are indirectly related to the power-supply
switching frequency, an important parameter which is chosen to balance all these requirements.
Advantage of ACMC
For converters with relatively high output currents (5A to 25A), lowering the value of the current-sense
resistor in current-mode control (CMC) techniques helps boost efficiency. In this article, CMC implies
constant-frequency with peak current-sensing. There is, however, a drawback to this approach: CMC
makes the converter increasingly susceptible to noise. In extreme high-current cases, even the best PCB
layout cannot adequately suppress noise superimposed on the current-sense signal. One way to
circumvent this problem is by using voltage-mode control, VMC, an old but proven technique. VMC
improves noise immunity and efficiency, but requires a certain amount of loop compensation design to
achieve acceptable performance.
ACMC Design Basics
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