LTC3808 Datasheet, PDF (1/28 Pages) Linear Technology – No RSENSE TM, Low EMI, Synchronous DC/DC Controller with Output Tracking

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