POWER LOSS (mW)
LTC3851-1
Synchronous
Step-Down Switching
Regulator Controller
FEATURES DESCRIPTION
n
Wide V Range: 4V to 38V Operation
The LTC 3851-1 is a high performance synchronous
IN
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R or DCR Current Sensing
step-down switching regulator controller that drives
SENSE
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1% Output Voltage Accuracy
an all N-channel synchronous power MOSFET stage. A
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Power Good Output Voltage Monitor
con stant frequency current mode architecture allows a
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Phase-Lockable Fixed Frequency: 250kHz to 750kHz
phase-lockable frequency of up to 750kHz.
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Dual N-Channel MOSFET Synchronous Drive
OPTI-LOOP compensation allows the transient response
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Very Low Dropout Operation: 99% Duty Cycle
to be optimized over a wide range of output capacitance
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Adjustable Output Voltage Soft-Start or Tracking
and ESR values. The LTC3851-1 features a precision 0.8V
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Output Current Foldback Limiting
reference and a power good indicator. A wide 4V to 38V (40V
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Output Overvoltage Protection
absolute maximum) input supply range encompasses most
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OPTI-LOOP Compensation Minimizes C
OUT
battery con gurations and intermediate bus voltages.
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Selectable Continuous, Pulse-Skipping or
The TK/SS pin ramps the output voltage during start-up
Burst Mode Operation at Light Loads
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and shutdown with coincident or ratiometric tracking.
Low Shutdown I : 20A
Q
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Current foldback limits MOSFET heat dissipation during
V Range: 0.8V to 5.5V
OUT
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short-circuit conditions. The MODE/PLLIN pin selects
Thermally Enhanced 16-Lead MSOP
among Burst Mode operation, pulse skipping mode or
or 3mm 3mm QFN Package
continuous inductor current mode at light loads and allows
APPLICATIONS
the IC to be synchronized to an external clock.
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Automotive Systems The LTC3851-1 is identical to the LTC3851 except that the
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Telecom Systems I pin is replaced by PGOOD.
LIM
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Industrial Equipment
L, LT, LTC, LTM, Burst Mode and OPTI-LOOP are registered trademarks of Linear Technology
n Corporation. All other trademarks are the property of their respective owners.
Distributed DC Power Systems
Protected by U.S. Patents including 5408150, 5481178, 5705919, 5929620, 6304066,
6498466, 6580258, 6611131.
TYPICAL APPLICATION
High Ef ciency Synchronous Step-Down Converter Ef ciency and Power Loss
vs Load Current
100k
V
IN
INTV PGO0D V
CC IN
4.5V TO 38V
100 10000
22F
TG V = 12V
FREQ/PLLFLTR IN
0.68H
V 95
OUT V = 3.3V
0.1F OUT
82.5k
RUN SW 3.3V
EFFICIENCY
90
LTC3851-1 0.1F 15A
TK/SS BOOST
330F 85
1000
0.1F
3.01k s 2
80
POWER LOSS
INTV
CC
75
2200pF
4.7F
BG
I
70
TH
100
GND
65
15k 330pF
+
60
SENSE
MODE/PLLIN 0.047F 30.1k
55
154k
SENSE
50 10
V
FB 10 100 1000 10000 100000
LOAD CURRENT (mA)
48.7k
38511TA01b
38511 TA01a
38511fa
1
EFFICIENCY (%)LTC3851-1
ABSOLUTE MAXIMUM RATINGS (Note 1)
Input Supply Voltage (V ) ......................... 40V to 0.3V I , V Voltages .......................................... 3V to 0.3V
IN TH FB
Topside Driver Voltage (BOOST) ................ 46V to 0.3V INTV Peak Output Current ..................................50mA
CC
Switch Voltage (SW) ..................................... 40V to 5V Operating Junction Temperature Range
INTV , (BOOST SW), RUN, PGOOD ........ 6V to 0.3V (Notes 2, 3) ............................................40C to 125C
CC
TK/SS .................................................... INTV to 0.3V Storage Temperature Range ...................65C to 150C
CC
+
SENSE , SENSE .......................................... 6V to 0.3V Lead Temperature (Soldering, 10 sec)
MODE/PLLIN, FREQ/PLLFLTR ............... INTV to 0.3V MSE ..................................................................300C
CC
PIN CONFIGURATION
TOP VIEW
TOP VIEW
MODE/PLLIN 1 16 SW
16 15 14 13
FREQ/PLLFLTR 2 15 TG
RUN 3 14 BOOST
RUN 1 12 BOOST
4
TK/SS 13 V
IN
17
TK/SS 2 11 V
I 5 12 INTV IN
TH CC
17
6
FB 11 BG
I 3 10 INTV
TH CC
SENSE 7 10 GND
+
8
SENSE 9 PGOOD FB 4 9 BG
MSE PACKAGE 5 6 7 8
16-LEAD PLASTIC MSOP
T = 125C, = 35C/W TO 40C/W
JMAX JA
EXPOSED PAD (PIN 17) IS GND, MUST BE SOLDERED TO PCB
UD PACKAGE
16-LEAD (3mm s 3mm) PLASTIC QFN
T = 125C, = 68C/W, = 4.2C/W
JMAX JA JC
EXPOSED PAD (PIN 17) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE
LTC3851EMSE-1#PBF LTC3851EMSE-1#TRPBF 38511 16-Lead Plastic MSOP 40C to 85C
LTC3851IMSE-1#PBF LTC3851IMSE-1#TRPBF 38511 16-Lead Plastic MSOP 40C to 125C
LTC3851EUD-1#PBF LTC3851EUD-1#TRPBF LDNT 40C to 85C
16-Lead (3mm 3mm) Plastic QFN
LTC3851IUD-1#PBF LTC3851IUD-1#TRPBF LDNT 16-Lead (3mm 3mm) Plastic QFN 40C to 125C
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.
Consult LTC Marketing for information on non-standard lead based nish parts.
For more information on lead free part marking, go to: