POWER LOSS (mW)
LTC3851A
Synchronous
Step-Down Switching
Regulator Controller
Fea T Descrip T
n
Wide V Range: 4V to 38V Operation The LTC 3851A is a high performance synchronous
IN
n
R or DCR Current Sensing step-down switching regulator controller that drives
SENSE
n
1% Output Voltage Accuracy an all N-channel synchronous power MOSFET stage. A
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Phase-Lockable Fixed Frequency: 250kHz to 750kHz constant frequency current mode ar chitecture allows a
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Dual N-Channel MOSFET Synchronous Drive phase-lockable frequency of up to 750kHz.
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Very Low Dropout Operation: 99% Duty Cycle
OPTI-LOOP compensation allows the transient response
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Adjustable Output Voltage Soft-Start or Tracking
to be optimized over a wide range of output capacitance
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Output Current Foldback Limiting
and ESR values. The LTC3851A features a precision 0.8V
n
Output Overvoltage Protection
reference that is compatible with a wide 4V to 38V input
n
5V Internal Regulator
supply range.
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OPTI-LOOP Compensation Minimizes C
OUT
n
The TK/SS pin ramps the output voltage during start-up.
Selectable Continuous, Pulse-Skipping or
Current foldback limits MOSFET heat dissipation during
Burst Mode Operation at Light Loads
n
short-circuit conditions. The MODE/PLLIN pin selects
Low Shutdown I : 20A
Q
n
among Burst Mode operation, pulse-skipping mode or
V Range: 0.8V to 5.5V
OUT
n
continuous inductor current mode at light loads and al-
Thermally Enhanced 16-Lead MSOP, 16-Lead Narrow
lows the IC to be synchronized to an external clock. The
SSOP or 3mm 3mm QFN Package
LTC3851A contains an improved PLL compared to the
a T
LTC3851.
n
Automotive Systems
The LTC3851A-1 is a version with a power good output
n
Telecom Systems
signal instead of adjustable current limit.
n
Industrial Equipment L, LT, LTC, LTM, Burst Mode, OPTI-LOOP, Linear Technology and the Linear logo are registered
trademarks and No R , UltraFast are trademarks of Linear Technology Corporation. All other
SENSE
n
Distributed DC Power Systems
trademarks are the property of their respective owners. Protected by U.S. Patents including
5408150, 5481178, 5705919, 5929620, 6304066, 6498466, 6580258, 6611131.
Typical a T
High Efficiency Synchronous Step-Down Converter Efficiency and Power Loss
vs Load Current
V
IN
I V
LIM IN 100 10000
4.5V TO 36V
22F
V = 12V
IN
FREQ/PLLFLTR TG
95
V = 3.3V
OUT
0.68H
V
OUT
0.1F
82.5k
RUN SW 3.3V 90
EFFICIENCY
LTC3851A 0.1F 15A
85
TK/SS BOOST
1000
330F
0.1F
3.01k
80
2
75
POWER LOSS
INTV
CC
2200pF
4.7F
70
BG
I
TH
100
65
GND
330pF
15k
60
+
SENSE
55
MODE/PLLIN 0.047F 30.1k
154k
50 10
SENSE
10 100 1000 10000 100000
V
FB
LOAD CURRENT (mA)
48.7k
3851A TA01b
3851A TA01a
3851afa
1
EFFICIENCY (%)
ion pplica
ions pplica
ion uresLTC3851A
a Te Maxi Mu M r a T (Note 1)
Input Supply Voltage (V ) ......................... 40V to 0.3V INTV Peak Output Current ..................................50mA
IN CC
Topside Driver Voltage (BOOST) ................ 46V to 0.3V Operating Junction Temperature Range (Notes 2, 3)
Switch Voltage (SW) .....................................40V to 5V E-Grade, I-Grade ................................ 40C to 125C
INTV , (BOOST SW), RUN ...................... 6V to 0.3V H-Grade ............................................. 40C to 150C
CC
TK/SS, I ...........................................INTV to 0.3V MP-Grade .......................................... 55C to 150C
LIM CC
+
SENSE , SENSE .......................................... 6V to 0.3V Storage Temperature Range ..................65C to 150C
MODE/PLLIN, FREQ/PLLFLTR ..............INTV to 0.3V Lead Temperature (Soldering, 10 sec)
CC
I , V Voltages .......................................... 3V to 0.3V GN/MSE ............................................................300C
TH FB
p in c F T
TOP VIEW
TOP VIEW
MODE/PLLIN 1 16 SW TOP VIEW
MODE/PLLIN 1 16 SW
FREQ/PLLFLTR 2 15 TG
16 15 14 13
FREQ/PLLFLTR 2 15 TG
RUN 3 14 BOOST RUN 3 14 BOOST
RUN 1 12 BOOST
TK/SS 4 17 13 V
IN
TK/SS 4 13 V TK/SS 2 11 V
IN I 5 12 INTV 17 IN
GND
TH CC
FB 6 11 BG GND
I 3 10 INTV
I 5 12 INTV
TH CC
TH CC
SENSE 7 10 GND
+
FB BG
SENSE 8 9 I 4 9
FB 6 11 BG LIM
5 6 7 8
MSE PACKAGE
SENSE 7 10 GND
16-LEAD PLASTIC MSOP
+
SENSE 8 9 I
LIM
T = 125C, = 35C/W TO 40C/W
JMAX JA
EXPOSED PAD (PIN 17) IS GND,
GN PACKAGE
UD PACKAGE
MUST BE SOLDERED TO PCB
16-LEAD PLASTIC SSOP NARROW
16-LEAD (3mm 3mm) PLASTIC QFN
T = 125C, = 110C/W
JMAX JA
T = 125C, = 68C/W, = 4.2C/W
JMAX JA JC
EXPOSED PAD (PIN 17) IS GND,
MUST BE SOLDERED TO PCB
o r Der i n F Ma T
LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE
LTC3851AEGN#PBF LTC3851AEGN#TRPBF 3851A 16-Lead Plastic SSOP 40C to 125C
LTC3851AIGN#PBF LTC3851AIGN#TRPBF 3851A 16-Lead Plastic SSOP 40C to 125C
LTC3851AEMSE#PBF LTC3851AEMSE#TRPBF 3851A 16-Lead Plastic MSOP 40C to 125C
LTC3851AIMSE#PBF LTC3851AIMSE#TRPBF 3851A 16-Lead Plastic MSOP 40C to 125C
LTC3851AHMSE#PBF LTC3851AHMSE#TRPBF 3851A 16-Lead Plastic MSOP 40C to 150C
LTC3851AMPMSE#PBF LTC3851AMPMSE#TRPBF 3851A 16-Lead Plastic MSOP 55C to 150C
LTC3851AEUD#PBF LTC3851AEUD#TRPBF LFPZ 16-Lead (3mm 3mm) Plastic QFN 40C to 125C
LTC3851AIUD#PBF LTC3851AIUD#TRPBF LFPZ 16-Lead (3mm 3mm) Plastic QFN 40C to 125C
Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
Consult LTC Marketing for information on non-standard lead based finish parts.
For more information on lead free part marking, go to: