800mA, Low-Noise, Step-Up DC-DC Converter with 500mA Linear Regulator

The MAX1765 is a high-efficiency, low-noise, step-up DC-DC converter intended for use in battery-powered wireless applications. This device operates at a high 1MHz fixed frequency while maintaining an exceptionally low quiescent supply current (200µA). Its small external components and tiny package make this device an excellent choice for small hand-held applications that require the longest possible battery life.

The MAX1765 uses a synchronous-rectified pulse-width-modulation (PWM) boost topology to generate 2.5V to 5.5V outputs from a wide range of input sources, such as one to three alkaline or NiCd/NiMH cells or a single lithium-ion (Li+) cell. Maxim's proprietary architecture significantly improves efficiency at low load currents while automatically transitioning to fixed-frequency PWM operation at medium to high load currents to maintain excellent full-load efficiency. Forced-PWM mode is available for applications that require constant-frequency operation at all load currents, and the MAX1765 may also be synchronized to an external clock to protect sensitive frequency bands in communications equipment.

The MAX1765's low-dropout (LDO) linear regulator and DC-DC converter have separate shutdown control. The linear regulator's 250mΩ pass device maintains excellent dropout voltage at currents up to 500mA. The MAX1765 also features analog soft-start and current-limit functions to permit optimization of efficiency, external component size, and output voltage ripple.

The MAX1765 comes in a 16-pin QSOP package and a thermally enhanced 16-pin TSSOP-EP.

Applications

* Handheld Instruments (PDAs, Palmtops) * Palmtop Computers * PCS Phones * Personal Communicators * Portable Audio Players * Wireless Handsets

* High-Efficiency Step-Up Converter

* Up to 93% Efficiency

* Adjustable Output from +2.5V to +5.5V

* Up to 800mA Output

* PWM Synchronous-Rectified Topology

* 1MHz Operating Frequency (or Sync)

* LDO Linear Regulator

* 500mA LDO Linear Regulator

* 2.85V Linear Regulator Output or Adjustable (1.25V to 5V)

* Low 125mV Dropout at 500mA

* +0.7V to +5.5V Input Range

* 0.1µA Logic-Controlled Shutdown

* Adjustable Inductor Current Limit and Soft-Start

* Thermal Shutdown

* 1.5W, 16-Pin TSSOP-EP Package Available