The MAX8744A/MAX8745A 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 MAX8744A/MAX8745A 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 can 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 MAX8744A/MAX8745A feature output undervoltage and thermal-fault protection. The MAX8744A also includes output overvoltage-fault protection. The MAX8744A/MAX8745A 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.
Feature
- 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 (MAX8744A 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
- 2 to 4 Li+ Cell Battery-Powered Devices
- Main Power Supplies
- Notebook and Subnotebook Computers
- PDAs and Mobile Communicators
