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High-Efficiency, Quad Output, Main Power-Supply Controllers for Notebook Computers

Product Details

Key Features

Simplified Block Diagram

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Key Features

  • Fixed-Frequency, Current-Mode Control
  • 40/60 Optimal Interleaving
  • Internal BST Switches
  • Internal 5V, 100mA Linear Regulator
  • Auxiliary Linear-Regulator Driver (12V or Adjustable Down to 1V)
  • Dual Mode™ Feedback—3.3V/5V Fixed or Adjustable Output Voltages
  • 200kHz/300kHz/500kHz Switching Frequency
  • Undervoltage and Thermal-Fault Protection
  • Overvoltage-Fault Protection (MAX8744 Only)
  • 6V to 26V Input Range
  • 2V ±0.75% Reference Output
  • Independent Enable Inputs and Power-Good Outputs
  • Soft-Start and Soft-Shutdown (Voltage Ramp)
  • 8µA (typ) Shutdown Current

Applications/Uses

  • 2 to 4 Li+ Cell Battery-Powered Devices
  • Main Power Supplies
  • Notebook and Subnotebook Computers
  • PDAs and Mobile Communicators

Description

The MAX8744/MAX8745 are dual step-down, switch-mode, power-supply (SMPS) controllers with synchronous rectification, intended for main 5V/3.3V power generation in battery-powered systems. Fixed-frequency operation with optimal interleaving minimizes input ripple current from the lowest input voltages up to the 26V maximum input. Optimal 40/60 interleaving allows the input voltage to go down to 8.3V before duty-cycle overlap occurs, compared to 180° out-of-phase regulators where the duty-cycle overlap occurs when the input drops below 10V.

Output current sensing provides peak current-limit protection, using either an accurate sense resistor or using lossless inductor DCR current sensing. A low-noise mode maintains high light-load efficiency while keeping the switching frequency out of the audible range.

An internal, fixed 5V, 100mA linear regulator powers up the MAX8744/MAX8745 and their gate drivers, as well as external keep-alive loads. When the main PWM regulator is in regulation, an automatic bootstrap switch bypasses the internal linear regulator, providing current up to 200mA. An additional adjustable linear-regulator driver with an external pnp transistor may be used with a secondary winding to provide a 12V supply, or powered directly from the main outputs to generate low-voltage outputs as low as 1V.

Independent enable controls and power-good signals allow flexible power sequencing. Voltage soft-start gradually ramps up the output voltage and reduces inrush current, while soft-shutdown gradually ramps the output voltage down, preventing negative voltage dips. The MAX8744/MAX8745 feature output undervoltage and thermal-fault protection. The MAX8744 also includes output overvoltage-fault protection.

The MAX8744/MAX8745 are available in a 32-pin, 5mm x 5mm, thin QFN package. The exposed backside pad improves thermal characteristics for demanding linear keep-alive applications.

Simplified Block Diagram

MAX8744, MAX8745: Functional Diagram MAX8744, MAX8745: Functional Diagram Zoom icon

Technical Docs

Support & Training

Search our knowledge base for answers to your technical questions.

Filtered Search

Our dedicated team of Applications Engineers are also available to answer your technical questions. Visit our support portal .