LTC3809
No RSENSE™, Low EMI,
Synchronous DC/DC Controller
FEATURES
DESCRIPTION
TheLTC®3809isasynchronousstep-downswitchingregu-
latorcontrollerthatdrivesexternalcomplementarypower
MOSFETs using few external components. The constant
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No Current Sense Resistor Required
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Selectable Spread Spectrum Frequency Modulation
for Low Noise Operation
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Constant Frequency Current Mode Operation for
frequency current mode architecture with MOSFET V
DS
Excellent Line and Load Transient Response
sensing eliminates the need for a current sense resistor
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True PLL for Frequency Locking or Adjustment
and improves efficiency.
(Frequency Range: 250kHz to 750kHz)
Fornoisesensitiveapplications,theLTC3809canbeexter-
nallysynchronizedfrom250kHzto750kHz. BurstModeis
inhibitedduringsynchronizationorwhentheSYNC/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.
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Wide V Range: 2.75V to 9.8V
IN
OUT
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Wide V
Range: 0.6V to V
IN
0.6V 1.5% Reference
Low Dropout Operation: 100% Duty Cycle
Selectable Burst Mode®/Pulse-Skipping/Forced
Continuous Operation
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Burst Mode operation provides high efficiency operation
at light loads. 100% duty cycle provides low dropout
operation, extending operating time in battery-powered
systems.
Auxiliary Winding Regulation
Internal Soft-Start Circuitry
Output Overvoltage Protection
Micropower Shutdown: I = 9μA
Q
Tiny Thermally Enhanced Leadless (3mm × 3mm)
Theswitchingfrequencycanbeprogrammedupto750kHz,
allowing the use of small surface mount inductors and
capacitors.
DFN and 10-lead MSOP Packages
APPLICATIONS
The LTC3809 is available in tiny footprint thermally
enhanced DFN and 10-lead MSOP packages.
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1- or 2-Cell Lithium-Ion Powered Devices
Portable Instruments
L, LT, LTC, LTM and Burst Mode are registered trademarks of Linear Technology Corporation.
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No R
is a trademark of Linear Technology Corporation.
SENSE
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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.
Distributed DC Power Systems
TYPICAL APPLICATION
Efficiency and Power Loss vs Load Current
100
90
80
70
60
50
10k
EFFICIENCY
High Efficiency, 550kHz Step-Down Converter
V
IN
= 3.3V
1k
V
IN
2.75V TO 9.8V
V
IN
= 4.2V
V
IN
= 5V
10μF
LTC3809
100
10
V
IN
PLLLPF
POWER LOSS
= 4.2V
SYNC/MODE TG
V
IN
59k
2.2μH
47μF
V
2.5V
2A
OUT
V
SW
FB
15k
1
I
TH
BG
187k
FIGURE 10 CIRCUIT
RUN
IPRG
470pF
V
OUT
= 2.5V
GND
0.1
10000
1
10
100
1000
LOAD CURRENT (mA)
3809 TA01b
3809 TA01
3809fc
1