Datasheet LTC3809 (Analog Devices)

ManufacturerAnalog Devices
DescriptionNo RSENSE , Low EMI, Synchronous DC/DC Controller
Pages / Page24 / 1 — FEATURES. DESCRIPTION. No Current Sense Resistor Required. Selectable …
File Format / SizePDF / 298 Kb
Document Languageenglish

FEATURES. DESCRIPTION. No Current Sense Resistor Required. Selectable Spread Spectrum Frequency Modulation

Datasheet LTC3809 Analog Devices

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LTC3809 No RSENSE™, Low EMI, Synchronous DC/DC Controller
FEATURES DESCRIPTION
n
No Current Sense Resistor Required
The LTC®3809 is a synchronous step-down switching regu- n
Selectable Spread Spectrum Frequency Modulation
lator controller that drives external complementary power
for Low Noise Operation
MOSFETs using few external components. The constant n
Constant Frequency Current Mode Operation for
frequency current mode architecture with MOSFET VDS
Excellent Line and Load Transient Response
sensing eliminates the need for a current sense resistor n True PLL for Frequency Locking or Adjustment and improves effi ciency. (Frequency Range: 250kHz to 750kHz) For noise sensitive applications, the LTC3809 can be exter- n Wide VIN Range: 2.75V to 9.8V nally synchronized from 250kHz to 750kHz. Burst Mode is n Wide VOUT Range: 0.6V to VIN inhibited during synchronization or when the SYNC/MODE n 0.6V ±1.5% Reference pin is pulled low to reduce noise and RF interference. To n Low Dropout Operation: 100% Duty Cycle further reduce EMI, the LTC3809 incorporates a novel n Selectable Burst Mode®/Pulse-Skipping/Forced spread spectrum frequency modulation technique. Continuous Operation n Auxiliary Winding Regulation Burst Mode operation provides high effi ciency operation n Internal Soft-Start Circuitry at light loads. 100% duty cycle provides low dropout n Output Overvoltage Protection operation, extending operating time in battery-powered n Micropower Shutdown: I systems. Q = 9μA n Tiny Thermally Enhanced Leadless (3mm × 3mm) The switching frequency can be programmed up to 750kHz, DFN and 10-lead MSOP Packages allowing the use of small surface mount inductors and capacitors.
APPLICATIONS
The LTC3809 is available in tiny footprint thermally enhanced DFN and 10-lead MSOP packages. n 1- or 2-Cell Lithium-Ion Powered Devices n Portable Instruments L, LT, LTC, LTM and Burst Mode are registered trademarks of Linear Technology Corporation. No R n Distributed DC Power Systems SENSE 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, 6580258, 6304066, 5847554, 6611131, 6498466. Other Patents pending.
TYPICAL APPLICATION Effi ciency and Power Loss vs Load Current
100 10k
High Effi ciency, 550kHz Step-Down Converter
EFFICIENCY VIN = 3.3V VIN 90 1k 2.75V TO 9.8V POWER LOSS (mW) V LTC3809 10μF IN = 5V VIN = 4.2V PLLLPF V 80 100 IN POWER LOSS SYNC/MODE TG 70 10 59k V 2.2μH IN = 4.2V VOUT EFFICIENCY (%) VFB SW 2.5V 15k 2A 60 1 ITH BG 187k 47μF FIGURE 10 CIRCUIT 470pF RUN IPRG VOUT = 2.5V GND 50 0.1 1 10 100 1000 10000 LOAD CURRENT (mA) 3809 TA01 3809 TA01b 3809fc 1
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