MAX1678

19-1381; Rev 0; 7/98 KIT ATION EVALU E L B AVAILA 1-Cell to 2-Cell, Low-Noise, High-Efficiency, Step-Up DC-DC Converter General Description Features o 0.87V Guaranteed Start-Up o Up to 90% Efficiency o Built-In Synchronous Rectifier (no external diode) o Ultra-Small µMAX Package, 1.1mm High o 37µA Quiescent Current (85µA from 1.5V battery) o 2µA Logic-Controlled Shutdown o Power-Fail Detector o Dual Mode™ Output: Fixed 3.3V Adjustable 2V to 5.5V o 45mA Output Current at 3.3V for 1-Cell Input o 90mA Output Current at 3.3V for 2-Cell Input o Inductor-Damping Switch Suppresses EMI MAX1678 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 Remote Controls Pointing Devices Personal Medi...