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MAX1677：Compact, High-Efficiency, Dual-Output Step-Up and LCD Bias DC-DC Converter

Logic and LCD Supply with Only 35 µA Supply Current and Minimal External Components

The MAX1677 is a compact, high-efficiency, dual-output boost converter for portable devices needing two regulated supplies, typically for logic and liquid crystal displays (LCDs). Operation with inputs as low as 0.7V allows the MAX1677 to accept 1, 2, or 3-cell alkaline, NiCd, or NiMH batteries as well as 1-cell lithium-ion batteries. The device requires no external FETs and can maintain regulation while consuming only 20µA, making it ideal for hand-held pen-input and PDA devices operating with low-current "sleep" states. The MAX1677's primary regulator supplies up to 350mA at either a factory-preset 3.3V or an adjustable 2.5V to 5.5V output. On-chip synchronous rectification provides efficiencies up to 95%. 300kHz (or externally clocked) pulse-width-modulation (PWM) operation is particularly suitable for applications needing low noise, such as those with wireless features. The primary converter also features pin-selectable pulse-frequency-modulation (PFM) operation that consumes only 20µA. A 1µA shutdown state also minimizes battery drain. The MAX1677's secondary step-up converter supplies up to +28V or -28V for LCD bias, varactor tuning, or other high-voltage, low-current functions. Other MAX1677 features include precision reference, logic control inputs for both regulators, and an uncommitted comparator for low-battery detection or a reset function. The MAX1677 is supplied in Maxim's compact 16-pin QSOP package, which occupies no more space than a standard SO-8.

Key Features No External FETs Required Main Output Up to 350mA for Logic Supply Fixed 3.3V or Adjustable (2.5V to 5.5V) Synchronous Rectification for High Efficiency (up to 95%) 300kHz (200kHz to 400kHz Synchronizable) Fixed-Frequency PWM Operation Secondary Output Up to +28V or -28V for LCD Bias Programmable Current Limit 0.7V to 5.5V Input Voltage Range 20µA Quiescent Current 1µA Shutdown Current Low-Battery Comparator Small 16-Pin QSOP Package

MAX1677: Typical Operating Circuit Applications/Uses Handheld Terminals PDAs Portable Instrumentation Portable Phones

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Design kits & evaluation modules

• MAX1677EVKIT

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