Datasheet LTC3808 (Analog Devices)

LTC3808 No R TM SENSE , Low EMI, Synchronous DC/DC Controller with Output Tracking
U FEATURES DESCRIPTIO
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Programmable Output Voltage Tracking
The LTC®3808 is a synchronous step-down switching ■
Sense Resistor Optional
regulator controller that drives external complementary ■
Spread Spectrum Modulation for Low Noise
power MOSFETs using few external components. The ■ Constant Frequency Current Mode Operation for constant frequency current mode architecture with MOSFET Excellent Line and Load Transient Response VDS sensing eliminates the need for a current sense ■ Wide VIN Range: 2.75V to 9.8V resistor and improves efficiency. ■ Wide VOUT Range: 0.6V to VIN Burst Mode operation provides high efficiency operation ■ 0.6V ±1.5% Reference at light loads. 100% duty cycle provides low dropout ■ Low Dropout Operation: 100% Duty Cycle operation, extending operating time in battery-powered ■ True PLL for Frequency Locking or Adjustment systems. (Frequency Range: 250kHz to 750kHz) ■ Selectable Burst Mode®/Pulse Skipping/Forced The switching frequency can be programmed up to 750kHz, Continuous Operation allowing the use of small surface mount inductors and ■ Auxiliary Winding Regulation capacitors. For noise sensitive applications, the LTC3808 ■ Internal Soft-Start Circuitry can be externally synchronized from 250kHz to 750kHz. ■ Power Good Output Voltage Monitor Burst Mode is inhibited during synchronization or when ■ Output Overvoltage Protection the SYNC/MODE pin is pulled low to reduce noise and RF ■ Micropower Shutdown: I interference. To further reduce EMI, the LTC3808 incorpo- Q = 9µA ■ Tiny Thermally Enhanced Leadless (4mm × 3mm) rates a novel spread spectrum frequency modulation DFN or 16-lead SSOP Package technique.
U
The LTC3808 is available in the tiny footprint thermally
APPLICATIO S
enhanced DFN package or 16-lead SSOP package. ■ One or Two Cell Lithium-Ion Powered Devices , 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 ■ Notebook and Palmtop Computers, PDAs Linear Technology Corporation. All other trademarks are the property of their respective owners. Protected by U.S. Patents including 5481178, 5929620, 6580258, 6304066, ■ Portable Instruments 5847554, 6611131, 6498466. Other Patents pending. ■ Distributed DC Power Systems
U TYPICAL APPLICATIO Efficiency and Power Loss vs Load Current
100 10k EFFICIENCY
High Efficiency, 550kHz Step-Down Converter
VIN = 3.3V VIN 90 1k 2.75V TO 9.8V POWER LOSS (mW) 1M V LTC3808 10µF IN = 5V VIN = 4.2V VIN PLLLPF 80 100 SENSE+ SYNC/MODE TG TYPICAL POWER 70 10 59k PGOOD LOSS (V 2.2µH V IN = 4.2V) OUT EFFICIENCY (%) VFB SW 2.5V 15k + 2A I 60 1 TH BG 187k 47µF FIGURE 11 CIRCUIT 220pF RUN IPRG VOUT = 2.5V GND 50 0.1 1 10 100 1k 10k 3808 TA01 LOAD CURRENT (mA) 3808 TA01b 3808f 1