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PDF LTC3852 Data sheet ( Hoja de datos )
| Número de pieza | LTC3852 | |
| Descripción | Synchronous Step-Down DC/DC Controller | |
| Fabricantes | Linear | |
| Logotipo |  |
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FEATURES
n Charge Pump Input Range: 2.7V to 5.5V
n Controller Input Range: 4V to 38V
n Integrated Charge Pump Provides 5V Gate Drive to
Logic Level MOSFETs
n RSENSE or DCR Current Sensing
n ±1.25% Output Voltage Accuracy Over Temperature
n Phase-Lockable Fixed Frequency: 250kHz to 750kHz
n Power Good Output Voltage Monitor
n Adjustable Soft-Start Voltage Ramping
n Current Foldback Disabled During Start-Up
n No Reverse Current During Soft-Start
n Selectable Constant Frequency, Pulse-Skipping, or
Burst Mode Operation
n Output Overvoltage Protection
n Very Low Dropout Operation: 99% Duty Cycle
n Available in a 24-Lead (3mm ¥ 5mm) QFN Package
APPLICATIONS
n General Purpose 3.3V Systems
n Lithium-Ion Powered Devices
n Distributed DC Power Systems
LTC3852
Low Input Voltage,
Synchronous Step-Down
DC/DC Controller
DESCRIPTION
The LTC®3852 is a constant frequency, current mode
step-down DC/DC controller which can be powered by an
onboard charge pump. Input supplies as low as 2.7V, when
doubled by the charge pump, provide 5V to the LTC3852’s
control logic and gate drives, supporting a wide selection
of logic-level N-channel power MOSFETs.
The constant-frequency current mode architecture allows for
a phase-lockable fixed frequency of up to 750kHz. The RUN
pin provides a precision enable threshold while the TRACK/SS
pin combines tracking and adjustable soft-start features.
The MODE/PLLIN pin selects among Burst Mode® oper-
ation, pulse-skipping mode, and continuous current mode.
Current foldback limits MOSFET power dissipation during
short-circuit conditions. Reverse current and current
foldback functions are disabled during soft-start. A power
good output pin indicates when the output is within ±10%
of its designed set point.
L, LT, LTC, LTM, Linear Technology, Burst Mode and the Linear logo are registered trademarks
and 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 5408150, 5481178,
5705919, 6498466, 6580258, 6611131.
TYPICAL APPLICATION
High Efficiency Synchronous Step-Down Converter
100k
INTVCC
PGO0D
VIN1
MODE/PLLIN TG
FREQ/PLLFLTR SW
95.3k
1nF
BOOST
TRACK/SS
0.1μF
VIN2
INTVCC
ITH LTC3852 BG
12.1k
100pF
GND2
RUN SENSE+
OFF ON
CHARGE PUMP
2.2μF
SHDN
SENSE–
C+ VFB
C– GND1 VPUMP
3852 TA01
0.1μF
4.7μF
0.36μH
2.1k
22μF
VIN
2.7V TO 5.5V
VOUT
1.2V
+
20A
470μF
×2
0.1μF
20k
1%
40.2k
1%
Efficiency and Power Loss
vs Load Current
100
90
80
70
60
50
40
30
20
10
0
1
5
EFFICIENCY
4.5
4
3.5
3
2.5
2
POWER LOSS
1.5
1
0.5
10
LOAD CURRENT (A)
0
20
3852 TA01a
3852f
1
1 page  
TYPICAL PERFORMANCE CHARACTERISTICS
LTC3852
Efficiency vs Output Current
and Mode
100
Burst Mode OPERATION
80
Load Step
ILOAD
10A/DIV
5A TO 15A
60
40
20
0
0.01
IL
10A/DIV
CCM
PULSE-SKIPPING
FIGURE 16 CIRCUIT
VOUT
100mV/DIV
AC-COUPLED
VOUT = 1.5V
50μs/DIV
VIN1 = 3.3V
FIGURE 16 CIRCUIT
0.1 1 10
LOAD CURRENT (A)
100
3852 G02
Load Step
(Forced Continuous Mode)
ILOAD
10A/DIV
1A TO 12A
Load Step
(Pulse-Skipping Mode)
ILOAD
10A/DIV
1A TO 12A
IL
10A/DIV
VOUT
100mV/DIV
AC-
COUPLED
VOUT = 1.2V
20μs/DIV
VIN1 = 3.3V
FIGURE 17 CIRCUIT
IL
10A/DIV
3852 G06
VOUT
100mV/DIV
AC-
COUPLED
VOUT = 1.2V
20μs/DIV
VIN1 = 3.3V
FIGURE 17 CIRCUIT
Load Step
(Burst Mode Operation)
ILOAD
10A/DIV
1A TO 12A
IL
10A/DIV
VOUT
100mV/DIV
AC-COUPLED
3852 G04
VOUT = 1.2V
20μs/DIV
VIN1 = 3.3V
FIGURE 17 CIRCUIT
3852 G05
Inductor Current at Light Load
FORCED
CONTINOUS
MODE
5A/DIV
Burst Mode
OPERATION
5A/DIV
PULSE-
SKIPPING
MODE 5A/DIV
3852 G07
VOUT = 1.5V
1μs/DIV
VIN2 = 3.3V
ILOAD = 500mA
FIGURE 17 CIRCUIT
3852 G08
Start-Up with Prebiased Output
at 0.5V
VOUT
1V/DIV
TRACK/SS
0.5V/DIV
VFB
0.5V/DIV
0V
20ms/DIV
FIGURE 16 CIRCUIT
3852 G09
Coincident Tracking with Master
Supply
VMASTER
0.5V/DIV
VOUT
2A LOAD
0.5V/DIV
0V
100ms/DIV
FIGURE 16 CIRCUIT
3852 G10
Ratiometric Tracking with Master
Supply
VMASTER
0.5V/DIV
VOUT
2A LOAD
0.5V/DIV
0V
10ms/DIV
FIGURE 16 CIRCUIT
3852 G11
3852f
5
5 Page 
LTC3852
FUNCTIONAL DIAGRAM
FREQ/
PLLFLTR
MODE/PLLIN
100k
MODE/SYNC
DETECT
PLL-SYNC
BUCK REGULATOR
0.8V
–+
5V REG
OSC S
BURSTEN
RQ
PULSE SKIP
+
ICMP
–
5k
–
IREV
+
ON SWITCH
LOGIC
AND
ANTI-
SHOOT
THROUGH
RUN
SLOPE COMPENSATION
OV
1
100k
ITHB
INTVCC
UVLO
VIN2 SLEEP
0.8V
REF
–
+
0.4V
EA
FAULT
LOGIC
– SS +
0.64V
– RUN +
1.25V
1μA
+
UV
–
+
OV
–
VIN2
BOOST
CB
TG
SW
SENSE+ DB
SENSE–
VIN
38V MAX
M1
L1
INTVCC
BG
CINTVCC
GND2
PGOOD
M2
0.72V
R2
VFB
R1
0.88V
2μA
RUN
VOUT
+
COUT
ITH
RC
CC1
TRACK/SS
CSS
CPUMP
VPUMP
SOFT-START
AND
SWITCH CONTROL
SHDN
ON/OFF
1.2MHz
OSCILLATOR
VIN1
2.7V to 5.5V
VIN1
CIN
CHARGE PUMP
CHARGE
PUMP
C+
CFLY
C–
GND1
3852 FD
3852f
11
11 Page | ||
| Páginas | Total 30 Páginas | |
| PDF Descargar | [ Datasheet LTC3852.PDF ] | |
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