1 Cell to 2 Cell, Low-Noise, High-Efficiency, Step-Up DC-DC Converter

The MAX1678 is a high-efficiency, low-voltage, synchronous-rectified, step-up DC-DC converter intended for use in devices powered by 1 to 3-cell alkaline, NiMH, or NiCd batteries or a 1-cell lithium battery. It guarantees a 0.87V start-up voltage and features a low 37µA quiescent supply current.

The device includes a 1Ω, N-channel MOSFET power switch, a synchronous rectifier that acts as the catch diode, a reference, pulse-frequency-modulation (PFM) control circuitry, and circuitry to reduce inductor ringing-all in an ultra-small, 1.1mm-high µMAX® package.

The output voltage is preset to 3.3V or can be adjusted from +2V to +5.5V using only two resistors. Efficiencies up to 90% are achieved for loads up to 50mA. The device also features an independent undervoltage comparator (PFI/PFO) and a logic-controlled 2µA shutdown mode.

Applications

* Pagers * Personal Medical Monitors * Pointing Devices * Remote Controls * Single-Cell Battery-Powered Devices

* 0.87V Guaranteed Start-Up

* Up to 90% Efficiency

* Built-In Synchronous Rectifier (no external diode)

* Ultra-Small µMAX Package, 1.1mm High

* 37µA Quiescent Current (85µA from 1.5V battery)

* 2µA Logic-Controlled Shutdown

* Power-Fail Detector

* Dual Mode™ Output: Fixed 3.3V

* Dual Mode Adjustable 2V to 5.5V

* 45mA Output Current at 3.3V for 1-Cell Input

* 90mA Output Current at 3.3V for 2-Cell Input

* Inductor-Damping Switch Suppresses EMI