LTC1627 Monolithic Synchronous Step-Down Switching Regulator UFEATURESDESCRIPTIO ■ High Efficiency: Up to 96% The LTC®1627 is a monolithic current mode synchronous ■ Constant Frequency 350kHz Operation buck regulator using a fixed frequency architecture. The ■ 2.65V to 8.5V VIN Range operating supply range is from 8.5V down to 2.65V, making ■ VOUT from 0.8V to VIN, IOUT to 500mA it suitable for one or two lithium-ion battery-powered appli- ■ No Schottky Diode Required cations. Burst Mode operation provides high efficiency at ■ Synchronizable Up to 525kHz low load currents. 100% duty cycle provides low dropout ■ Selectable Burst Mode TM Operation operation, which extends operating time in battery-operated ■ Low Dropout Operation: 100% Duty Cycle systems. ■ Precision 2.5V Undervoltage Lockout ■ Secondary Winding Regulation The operating frequency is internally set at 350kHz, allowing ■ Current Mode Operation for Excellent Line and the use of small surface mount inductors. For switching noise Load Transient Response sensitive applications it can be externally synchronized up to ■ Low Quiescent Current: 200µA 525kHz. The SYNC/FCB control pin guarantees regulation of ■ Shutdown Mode Draws Only 15µA Supply Current secondary windings regardless of load on the main output by ■ ±1.5% Reference Accuracy forcing continuous operation. Burst Mode operation is inhib- ■ Available in 8-Lead SO Package ited during synchronization or when the SYNC/FCB pin is U pulled low to reduce noise and RF interference. Soft-start is APPLICATIO S provided by an external capacitor. ■ Cellular Telephones Optional bootstrapping enhances the internal switch drive for ■ Portable Instruments single lithium-ion cell applications. The internal synchronous ■ Wireless Modems switch increases efficiency and eliminates the need for an ■ RF Communications external Schottky diode, saving components and board ■ Distributed Power Systems space. The LTC1627 comes in an 8-lead SO package. ■ Scanners , LTC and LT are registered trademarks of Linear Technology Corporation. ■ Single and Dual Cell Lithium Burst Mode is a trademark of Linear Technology Corporation. UTYPICAL APPLICATIO 100 VOUT = 3.3V VIN = 3.6V 95 1 8 I SYNC/FCB V TH IN = 6V 47pF 90 2 7 C RUN/SS V SS DR 0.1µF LTC1627 VIN 3 6 85 VIN = 8.4V V V 2.8V* FB IN L1 15µH TO 8.5V 4 5 V + C EFFICIENCY (%) OUT IN 80 GND SW 22µF C 3.3V + OUT 16V 100µF 249k 75 6.3V 70 *V 1 10 100 1000 OUT CONNECTED TO VIN FOR 2.8V < VIN < 3.3V 80.6k OUTPUT CURRENT (mA) 1627 F01a 1627 F01b Figure 1a. High Efficiency Step-Down ConverterFigure 1b. Efficiency vs Output Load Current 1
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