POWER LOSS (mW)
LTC3808
TM
No R , Low EMI,
SENSE
Synchronous DC/DC Controller
with Output Tracking
FEATURES
DESCRIPTIO
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 V sensing eliminates the need for a current sense
DS
Wide V Range: 2.75V to 9.8V resistor and improves efficiency.
IN
Wide V Range: 0.6V to V
OUT IN
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)
The switching frequency can be programmed up to 750kHz,
Selectable Burst Mode /Pulse Skipping/Forced
allowing the use of small surface mount inductors and
Continuous Operation
capacitors. For noise sensitive applications, the LTC3808
Auxiliary Winding Regulation
can be externally synchronized from 250kHz to 750kHz.
Internal Soft-Start Circuitry
Burst Mode is inhibited during synchronization or when
Power Good Output Voltage Monitor
the SYNC/MODE pin is pulled low to reduce noise and RF
Output Overvoltage Protection
interference. To further reduce EMI, the LTC3808 incorpo-
Micropower Shutdown: I = 9A
Q
rates a novel spread spectrum frequency modulation
Tiny Thermally Enhanced Leadless (4mm 3mm)
technique.
DFN or 16-lead SSOP Package
U
The LTC3808 is available in the tiny footprint thermally
APPLICATIO S
enhanced DFN package or 16-lead SSOP package.
, LTC and LT are registered trademarks of Linear Technology Corporation. Burst Mode
One or Two Cell Lithium-Ion Powered Devices
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
Notebook and Palmtop Computers, PDAs
owners. Protected by U.S. Patents including 5481178, 5929620, 6580258, 6304066,
5847554, 6611131, 6498466. Other Patents pending.
Portable Instruments
Distributed DC Power Systems
Efficiency and Power Loss vs Load Current
TYPICAL APPLICATIO
100 10k
EFFICIENCY
High Efficiency, 550kHz Step-Down Converter
V = 3.3V
IN
V
90 1k
IN
2.75V TO 9.8V
V = 4.2V
10F V = 5V IN
IN
1M LTC3808
V
IN
80 100
PLLLPF +
SENSE
SYNC/MODE
TYPICAL POWER
TG
70 10
LOSS (V = 4.2V)
59k PGOOD IN
2.2H
V
OUT
V SW 2.5V
FB
15k +
2A
60 1
I BG
TH
47F
187k
FIGURE 11 CIRCUIT
RUN IPRG
220pF
V = 2.5V
OUT
GND
50 0.1
1 10 100 1k 10k
3808 TA01 LOAD CURRENT (mA)
3808 TA01b
3808f
1
EFFICIENCY (%)
U
ULTC3808
ABSOLUTE MAXIMUM RATINGS (Note 1)
Input Supply Voltage (V )........................ 0.3V to 10V TG, BG Peak Output Current (<10s)........................ 1A
IN
PLLLPF, RUN, SYNC/MODE, TRACK/SS, Operating Temperature Range (Note 2)... 40C to 85C
+
SENSE , IPRG Voltages ............ 0.3V to (V + 0.3V) Storage Ambient Temperature Range ... 65C to 125C
IN
V , I Voltages...................................... 0.3V to 2.4V Junction Temperature (Note 3)............................ 125C
FB TH
SW, SENSE Voltages......... 2V to V + 1V (10V Max) Lead Temperature (Soldering, 10 sec)
IN
PGOOD ..................................................... 0.3V to 10V GN16 Package .................................................. 300C
PACKAGE/ORDER INFORMATION
TOP VIEW
TOP VIEW ORDER PART ORDER PART
NUMBER NUMBER
1
GND 16 SW
PLLLPF 1 14 SW
2
PLLLPF 15 SENSE
SYNC/MODE 2 13 SENSE
LTC3808EDE LTC3808EGN
TRACK/SS 3 12 V 3
SYNC/MODE 14 V
IN
IN
+
+
PGOOD 4 15 11 SENSE
4
TRACK/SS 13 SENSE
V 5 10 TG
FB
5
PGOOD 12 TG
I 6 9 BG
TH
6
V 11 BG
FB
DE PART
RUN 7 8 IPRG
7
I 10 IPRG
TH
MARKING
DE PACKAGE 8
RUN 9 GND
14-LEAD (4mm 3mm) PLASTIC DFN
3808
GN PACKAGE
T = 125C, = 37C/W
JMAX JA
16-LEAD PLASTIC SSOP
EXPOSED PAD (PIN 15) IS GND
(MUST BE SOLDERED TO PCB) T = 125C, = 130C/W
JMAX JA
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
The indicates specifications which apply over the full operating
temperature range, otherwise specifications are at T = 25C. V = 4.2V unless otherwise noted.
A IN
PARAMETER CONDITIONS MIN TYP MAX UNITS
Main Control Loops
Input DC Supply Current (Note 4)
Normal Operation 350 500 A
Sleep Mode 105 150 A
Shutdown RUN = 0V 9 20 A
UVLO V = UVLO Threshold 200mV 9 20 A
IN
Undervoltage Lockout Threshold V Falling 1.95 2.25 2.55 V
IN
V Rising 2.15 2.45 2.75 V
IN
Shutdown Threshold of RUN Pin 0.8 1.1 1.4 V
Start-Up Current Source TRACK/SS = 0V 0.65 1 1.35 A
Regulated Feedback Voltage (Note 5) 0.591 0.6 0.609 V
Output Voltage Line Regulation 2.75V < V < 9.8V (Note 5) 0.01 0.04 %/V
IN
Output Voltage Load Regulation I = 0.9V (Note 5) 0.1 0.5 %
TH
I = 1.7V 0.1 0.5 %
TH
V Input Current (Note 5) 9 50 nA
FB
Overvoltage Protect Threshold Measured at V 0.66 0.68 0.7 V
FB
3808f
2
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