POWER LOSS (W)
LTC3852
Low Input Voltage,
Synchronous Step-Down
DC/DC Controller
FEATURES DESCRIPTION
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Charge Pump Input Range: 2.7V to 5.5V
The LTC 3852 is a constant frequency, current mode
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Controller Input Range: 4V to 38V
step-down DC/DC controller which can be powered by an
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Integrated Charge Pump Provides 5V Gate Drive to
onboard charge pump. Input supplies as low as 2.7V, when
Logic Level MOSFETs
doubled by the charge pump, provide 5V to the LTC3852s
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R or DCR Current Sensing
control logic and gate drives, supporting a wide selection
SENSE
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1.25% Output Voltage Accuracy Over Temperature
of logic-level N-channel power MOSFETs.
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Phase-Lockable Fixed Frequency: 250kHz to 750kHz
The constant-frequency current mode architecture allows for
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Power Good Output Voltage Monitor
a phase-lockable xed frequency of up to 750kHz. The RUN
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Adjustable Soft-Start Voltage Ramping
pin provides a precision enable threshold while the TRACK/SS
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Current Foldback Disabled During Start-Up
pin combines tracking and adjustable soft-start features.
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No Reverse Current During Soft-Start
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The MODE/PLLIN pin selects among Burst Mode oper-
Selectable Constant Frequency, Pulse-Skipping, or
ation, pulse-skipping mode, and continuous current mode.
Burst Mode Operation
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Current foldback limits MOSFET power dissipation during
Output Overvoltage Protection
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short-circuit conditions. Reverse current and current
Very Low Dropout Operation: 99% Duty Cycle
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foldback functions are disabled during soft-start. A power
Available in a 24-Lead (3mm 5mm) QFN Package
good output pin indicates when the output is within 10%
APPLICATIONS
of its designed set point.
L, LT, LTC, LTM, Linear Technology, Burst Mode and the Linear logo are registered trademarks
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General Purpose 3.3V Systems
and No R is a trademark of Linear Technology Corporation. All other trademarks are the
SENSE
property of their respective owners. Protected by U.S. Patents including 5408150, 5481178,
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Lithium-Ion Powered Devices
5705919, 6498466, 6580258, 6611131.
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Distributed DC Power Systems
TYPICAL APPLICATION
High Ef ciency Synchronous Step-Down Converter
Ef ciency and Power Loss
vs Load Current
100k
V
IN
PGO0D
INTV V
CC IN1
2.7V TO 5.5V
100 5
22F
TG
MODE/PLLIN
90
0.36H 4.5
V
OUT
EFFICIENCY
FREQ/PLLFLTR SW
1.2V
80
4
0.1F 20A
95.3k
BOOST
70 3.5
470F
TRACK/SS
2.1k
V 2
IN2
60
3
0.1F
INTV
1nF CC 50 2.5
4.7F
LTC3852
I
BG 40
TH 2
GND2
30
1.5
12.1k 100pF
POWER LOSS
+
20k 20 1
RUN SENSE
1%
0.1F
OFF ON 10 0.5
SHDN
SENSE
+ 0 0
CHARGE PUMP V
C FB
12100
2.2F
40.2k
V
C
PUMP
GND1
LOAD CURRENT (A)
1%
3852 TA01
3852 TA01a
3852f
1
EFFICIENCY (%)
+LTC3852
ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION
(Note 1)
TOP VIEW
Input Supply Voltage (V ) .........................6V to 0.3V
IN1
Top Side Driver Voltage (BOOST) ...............46V to 0.3V
Switch Voltage (SW) ..................................40V to 0.3V
24 23 22 21
V .......................................................5.5V to 0.3V
PUMP
SHDN, RUN ..................................................6V to 0.3V
SENSE 1 20 FREQ/PLLFLTR
+
V Short-Circuit Duration .......................... Inde nite
PUMP SENSE 2 19 MODE/PLLIN
V ............................................................40V to 0.3V
PGOOD 3 18 SW
IN2
INTV , (BOOST-SW), RUN, PGOOD ...........6V to 0.3V GND2 4 17 TG
CC
25
GND
BG BOOST
5 16
INTV , Peak Output Current .................................50mA
CC
+
NC 6 15 V
IN2
SENSE , SENSE ..........................................6V to 0.3V
+
C 7 14 INTV
CC
MODE/PLLIN, TRACK/SS .....................INTV to 0.3V
CC
C 8 13 V
PUMP
FREQ/PLLFLTR .....................................INTV to 0.3V
CC
I , V ........................................................3V to 0.3V
TH FB 910 11 12
Operating Junction Temperature (Note 2) ............. 125C
Storage Temperature Range .................. 65C to 125C
UDD PACKAGE
24-LEAD (3mm s 5mm ) PLASTIC QFN
T = 125C, q = 38C/W
JMAX JA
EXPOSED PAD (PIN 25) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE
LTC3852EUDD#PBF LTC3852EUDD#TRPBF LFRJ 40C to 125C
24-Lead (3mm 5mm) Plastic QFN
LTC3852IUDD#PBF LTC3852IUDD#TRPBF LFRJ 40C to 125C
24-Lead (3mm 5mm) Plastic QFN
Consult LTC Marketing for parts speci ed with wider operating temperature ranges. *The temperature grade is identi ed by a label on the shipping container.
For more information on lead free part marking, go to: