MAX1844

High-Speed Step-Down Controller with Accurate Current Limit for Notebook Computers


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Description

The MAX1844 pulse-width modulation (PWM) controller provides high efficiency, excellent transient response, and high DC output accuracy needed for stepping down high-voltage batteries to generate low-voltage CPU core or chipset/RAM supplies in notebook computers.

Maxim's proprietary Quick-PWM™ quick-response, constant-on-time PWM control scheme handles wide input/output voltage ratios with ease and provides 100ns “instant-on” response to load transients while maintaining a relatively constant switching frequency. Efficiency is enhanced by an ability to drive very large synchronous-rectifier MOSFETs. Accurate current sensing to ensure reliable overload protection is available using an external current-sense resistor in series with the synchronous rectifier. Alternatively, the synchronous rectifier itself can be used for less accurate current sensing at the lowest possible power dissipation.

Single-stage buck conversion allows the MAX1844 to directly step down high-voltage batteries for the highest possible efficiency. Alternatively, two-stage conversion (stepping down the 5V system supply instead of the battery) at a higher switching frequency allows the minimum possible physical size.

The MAX1844 is intended for CPU core, chipset, DRAM, or other low-voltage supplies as low as 1V. It is available in 20-pin QSOP, and QFN packages and includes both adjustable overvoltage and undervoltage protection.

For a dual step-down PWM controller with accurate current limit, refer to the MAX1845. The MAX1714/ MAX1715 single/dual PWM controllers are similar to the MAX1844/MAX1845 but do not use current-sense resistors.
MAX1844: Functional Diagram MAX1844: Functional Diagram Enlarge+

Key Features

  • Ultra-High Efficiency
  • Accurate Current-Limit Option
  • Quick-PWM with 100ns Load-Step Response
  • 1% VOUT Accuracy Over Line and Load
  • 1.8V/2.5V Fixed or 1V to 5.5V Adjustable Output Range
  • 2V to 28V Battery Input Range
  • 200/300/450/600kHz Switching Frequency
  • Adjustable Overvoltage Protection
  • Adjustable Undervoltage Protection
  • 1.7ms Digital Soft-Start
  • Drives Large Synchronous-Rectifier FETs
  • 2V ±1% Reference Output
  • Power-Good Window Comparator

Applications/Uses

  • 1.8V and 2.5V Supplies
  • Chipset/RAM Supplies as Low as 1V
  • CPU Core Supplies
  • Notebook Computers

Technical Documents

App Note 1845 Choosing the Right DC-DC Converter for Automotive Applications

Quality and Environmental Data

Request Reliability Report for: MAX1844 
Lead-Free Package Tin (Sn) Whisker Reports
Device   Fab Process   Technology   Sample size   Rejects   FIT at 25°C   FIT at 55°C  

Note : The failure rates are summarized by technology and mapped to the associated material part numbers. The failure rates are highly dependent on the number of units tested.

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