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