LTC3736 Dual 2-Phase, No R TM SENSE , Synchronous Controller with Output Tracking UFEATURESDESCRIPTIO ■ No Current Sense Resistors Required The LTC®3736 is a 2-phase dual synchronous step-down ■ Out-of-Phase Controllers Reduce Required switching regulator controller with tracking that drives Input Capacitance external complementary power MOSFETs using few exter- ■ Tracking Function nal components. The constant frequency current mode ■ Wide VIN Range: 2.75V to 9.8V architecture with MOSFET VDS sensing eliminates the ■ Constant Frequency Current Mode Operation need for sense resistors and improves efficiency. Power ■ 0.6V ±1.5% Voltage Reference loss and noise due to the ESR of the input capacitance are ■ Low Dropout Operation: 100% Duty Cycle minimized by operating the two controllers out of phase. ■ True PLL for Frequency Locking or Adjustment Burst Mode operation provides high efficiency at light loads. ■ Selectable Burst Mode®/Forced Continuous Operation 100% duty cycle capability provides low dropout operation, ■ Auxiliary Winding Regulation extending operating time in battery-powered systems. ■ Internal Soft-Start Circuitry ■ Power Good Output Voltage Monitor The switching frequency can be programmed up to 750kHz, ■ Output Overvoltage Protection allowing the use of small surface mount inductors and ca- ■ Micropower Shutdown: I pacitors. For noise sensitive applications, the LTC3736 Q = 9µA ■ Tiny Low Profile (4mm × 4mm) QFN and Narrow switching frequency can be externally synchronized from SSOP Packages 250kHz to 850kHz. Burst Mode operation is inhibited dur- ing synchronization or when the SYNC/FCB pin is pulled low UAPPLICATIO S in order to reduce noise and RF interference. Automatic soft- start is internally controlled. ■ One or Two Lithium-Ion Powered Devices ■ The LTC3736 is available in the tiny thermally enhanced Notebook and Palmtop Computers, PDAs ■ (4mm Portable Instruments × 4mm) QFN package or 24-lead SSOP narrow ■ package. Distributed DC Power Systems , LTC and LT are registered trademarks of Linear Technology Corporation. Burst Mode is a registered trademark of Linear Technology Corporation. No RSENSE is a trademark of Linear Technology Corporation. All other trademarks are the property of their respective owners. Protected by U.S. Patents including 5481178, 5929620, 6144194, 6580258, 6304066, 6611131, 6498466. UTYPICAL APPLICATIOHigh Efficiency, 2-Phase, Dual Synchronous DC/DC Step-Down ConverterEfficiency vs Load Current VIN 100 2.75V TO 9.8V 95 V 10µF IN V ×2 IN = 3.3V 90 SENSE1+ SENSE2+ 85 V TG1 TG2 IN = 4.2V 80 2.2µH SW1 SW2 2.2µH VIN = 5V LTC3736 75 BG1 BG2 70 EFFICIENCY (%) PGND PGND 65 187k 118k VOUT1 V V OUT2 FB1 VFB2 60 2.5V 1.8V I FIGURE 16 CIRCUIT TH1 ITH2 55 220pF SGND 220pF VOUT = 2.5V 47µF 47µF 50 1 10 100 1000 10000 59k 15k 15k 59k LOAD CURRENT (mA) 3736 TA01b 3736 TA01a 3736fa 1
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