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LTC3851EGN#PBF

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LTC3851
1
3851fb
TYPICAL APPLICATION
FEATURES
APPLICATIONS
DESCRIPTION
Synchronous
Step-Down Switching
Regulator Controller
The LTC
®
3851 is a high performance synchronous
step-down switching regulator controller that drives
an all N-channel synchronous power MOSFET stage. A
con stant frequency current mode architecture allows a
phase-lockable frequency of up to 750kHz.
OPTI-LOOP compensation allows the transient response
to be optimized over a wide range of output capacitance
and ESR values. The LTC3851 features a precision 0.8V
reference that is compatible with a wide 4V to 38V input
supply range.
The TK/SS pin ramps the output voltage during start-up.
Current foldback limits MOSFET heat dissipation during
short-circuit conditions. The MODE/PLLIN pin selects
among Burst Mode operation, pulse skipping mode or
continuous inductor current mode at light loads and allows
the IC to be synchronized to an external clock.
The LTC3851-1 is a version with a power good output
signal instead of adjustable current limit.
High Effi ciency Synchronous Step-Down Converter
n
Wide V
IN
Range: 4V to 38V Operation
n
R
SENSE
or DCR Current Sensing
n
±1% Output Voltage Accuracy
n
Phase-Lockable Fixed Frequency: 250kHz to 750kHz
n
Dual N-Channel MOSFET Synchronous Drive
n
Very Low Dropout Operation: 99% Duty Cycle
n
Adjustable Output Voltage Soft-Start or Tracking
n
Output Current Foldback Limiting
n
Output Overvoltage Protection
n
5V Internal Regulator
n
OPTI-LOOP
®
Compensation Minimizes C
OUT
n
Selectable Continuous, Pulse-Skipping or
Burst Mode
®
Operation at Light Loads
n
Low Shutdown I
Q
: 20µA
n
V
OUT
Range: 0.8V to 5.5V
n
Thermally Enhanced 16-Lead MSOP, 16-Lead Narrow
SSOP or 3mm × 3mm QFN Package
n
Automotive Systems
n
Telecom Systems
n
Industrial Equipment
n
Distributed DC Power Systems
Effi ciency and Power Loss
vs Load Current
L, LT, LTC, LTM, Burst Mode and OPTI-LOOP are registered trademarks of Linear Technology
Corporation. All other trademarks are the property of their respective owners. Protected by
U.S. Patents including 5408150, 5481178, 5705919, 5929620, 6304066, 6498466, 6580258,
6611131.
I
LIM
RUN
TK/SS
I
TH
FREQ/PLLFLTR
V
IN
TG
SW
INTV
CC
MODE/PLLIN
BG
SENSE
+
SENSE
–
V
FB
GND
0.1µF
0.047µF
3.01k
LTC3851
22µF
V
IN
4.5V TO 36V
V
OUT
3.3V
15A
3851 TA01a
0.68µH
30.1k
330pF
2200pF
0.1µF
330µF
s2
BOOST
15k
154k
48.7k
82.5k
0.1µF
4.7µF
LOAD CURRENT (mA)
10
70
EFFICIENCY (%)
POWER LOSS (mW)
75
80
85
90
100 1000 10000 100000
3851TA01b
65
60
55
50
95
100
1000
100
10
10000
V
IN
= 12V
V
OUT
= 3.3V
EFFICIENCY
POWER LOSS
LTC3851
2
3851fb
ABSOLUTE MAXIMUM RATINGS
Input Supply Voltage (V
IN
) .........................40V to –0.3V
Topside Driver Voltage (BOOST) ................ 46V to –0.3V
Switch Voltage (SW) ..................................... 40V to –5V
INTV
CC
, (BOOST – SW), RUN ......................6V to –0.3V
TK/SS, I
LIM
............................................ INTV
CC
to –0.3V
SENSE
+
, SENSE
–
.......................................... 6V to –0.3V
MODE/PLLIN, FREQ/PLLFLTR ............... INTV
CC
to –0.3V
(Note 1)
GN PACKAGE
16-LEAD PLASTIC SSOP NARROW
1
2
3
4
5
6
7
8
TOP VIEW
16
15
14
13
12
11
10
9
MODE/PLLIN
FREQ/PLLFLTR
RUN
TK/SS
I
TH
FB
SENSE
–
SENSE
+
SW
TG
BOOST
V
IN
INTV
CC
BG
GND
I
LIM
T
JMAX
= 125°C, θ
JA
= 110°C/W
1
2
3
4
5
6
7
8
MODE/PLLIN
FREQ/PLLFLTR
RUN
TK/SS
I
TH
FB
SENSE
–
SENSE
+
16
15
14
13
12
11
10
9
SW
TG
BOOST
V
IN
INTV
CC
BG
GND
I
LIM
TOP VIEW
MSE PACKAGE
16-LEAD PLASTIC MSOP
17
T
JMAX
= 125°C, θ
JA
= 35°C/W TO 40°C/W
EXPOSED PAD (PIN 17) IS GND,
MUST BE SOLDERED TO PCB
16 15 14 13
5 6 7 8
TOP VIEW
17
UD PACKAGE
16-LEAD (3mm s 3mm) PLASTIC QFN
9
10
11
12
4
3
2
1RUN
TK/SS
I
TH
FB
BOOST
V
IN
INTV
CC
BG
FREQ/PLLFLTR
MODE/PLLIN
SW
TG
SENSE
–
SENSE
+
I
LIM
GND
T
JMAX
= 125°C, θ
JA
= 68°C/W, θ
JC
= 4.2°C/W
EXPOSED PAD (PIN 17) IS GND,
MUST BE SOLDERED TO PCB
PIN CONFIGURATION
ORDER INFORMATION
LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE
LTC3851EGN#PBF LTC3851EGN#TRPBF 3851 16-Lead Plastic SSOP –40°C to 85°C
LTC3851IGN#PBF LTC3851IGN#TRPBF 3851 16-Lead Plastic SSOP –40°C to 125°C
LTC3851EMSE#PBF LTC3851EMSE#TRPBF 3851 16-Lead Plastic MSOP –40°C to 85°C
LTC3851IMSE#PBF LTC3851IMSE#TRPBF 3851 16-Lead Plastic MSOP –40°C to 125°C
LTC3851EUD#PBF LTC3851EUD#TRPBF LCXN
16-Lead (3mm × 3mm) Plastic QFN
–40°C to 85°C
LTC3851IUD#PBF LTC3851IUD#TRPBF LCXN
16-Lead (3mm × 3mm) Plastic QFN
–40°C to 125°C
Consult LTC Marketing for parts specifi ed with wider operating temperature ranges. *The temperature grade is identifi ed by a label on the shipping container.
Consult LTC Marketing for information on non-standard lead based fi nish parts.
For more information on lead free part marking, go to: http://www.linear.com/leadfree/
For more information on tape and reel specifi cations, go to: http://www.linear.com/tapeandreel/
I
TH
, V
FB
Voltages .......................................... 3V to –0.3V
INTV
CC
Peak Output Current ..................................50mA
Operating Temperature Range (Note 2)..–40°C to 125°C
Junction Temperature (Note 3) ............................. 125°C
Storage Temperature Range ...................–65°C to 150°C
Lead Temperature (Soldering, 10 sec)
GN/MSE ............................................................ 300°C
LTC3851
3
3851fb
ELECTRICAL CHARACTERISTICS
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
Main Control Loops
V
IN
Operating Input Voltage Range
l
438V
V
FB
Regulated Feedback Voltage I
TH
= 1.2V (Note 4)
l
0.792 0.800 0.808 V
I
FB
Feedback Current (Note 4) –10 –50 nA
V
REFLNREG
Reference Voltage Line Regulation V
IN
= 6V to 38V (Note 4) 0.002 0.02 %/V
V
LOADREG
Output Voltage Load Regulation (Note 4)
Measured in Servo Loop,
∆I
TH
= 1.2V to 0.7V
l
0.01 0.1 %
(Note 4)
Measured in Servo Loop,
∆I
TH
= 1.2V to 1.6V
l
–0.01 –0.1 %
g
m
Transconductance Amplifi er g
m
I
TH
= 1.2V, Sink/Source = 5µA (Note 4) 2 mmho
g
m
GBW Transconductance Amp Gain Bandwidth I
TH
= 1.2V 3 MHz
I
Q
Input DC Supply Current
Normal Mode
Shutdown
(Note 5)
V
RUN
= 5V
V
RUN
= 0V
1.2
20 35
mA
µA
UVLO Undervoltage Lockout on INTV
CC
V
INTVCC
Ramping Down 3.25 V
UVLO Hys UVLO Hysteresis 0.4 V
V
OVL
Feedback Overvoltage Lockout Measured at V
FB
l
0.86 0.88 0.90 V
I
SENSE
SENSE Pins Current ±1 ±2 µA
I
TK/SS
Soft-Start Charge Current V
TK/SS
= 0V 0.6 1 2 µA
V
RUN
RUN Pin On Threshold V
RUN
Rising
l
1.10 1.25 1.35 V
V
RUNHYS
RUN Pin On Hysteresis 130 mV
V
SENSE(MAX)
Maximum Current Sense Threshold V
FB
= 0.7V, V
SENSE
= 3.3V, I
LIM
= 0V
V
FB
= 0.7V, V
SENSE
= 3.3V, I
LIM
= Float
V
FB
= 0.7V, V
SENSE
= 3.3V, I
LIM
= INTV
CC
l
l
l
20
40
65
30
50
75
40
65
90
mV
mV
mV
TG R
UP
TG Driver Pull-Up On-Resistance TG High 2.6
TG R
DOWN
TG Driver Pull-Down On-Resistance TG Low 1.5
BG R
UP
BG Driver Pull-Up On-Resistance BG High 2.4
BG R
DOWN
BG Driver Pull-Down On-Resistance BG Low 1.1
TG t
r
TG t
f
TG Transition Time
Rise Time
Fall Time
(Note 6)
C
LOAD
= 3300pF
C
LOAD
= 3300pF
25
25
ns
ns
BG tr
BG tf
BG Transition Time
Rise Time
Fall Time
(Note 6)
C
LOAD
= 3300pF
C
LOAD
= 3300pF
25
25
ns
ns
TG/BG t
1D
Top Gate Off to Bottom Gate On Delay
Bottom Switch-On Delay Time
C
LOAD
= 3300pF Each Driver
(Note 6)
30 ns
BG/TG t
2D
Bottom Gate Off to Top Gate On Delay
Top Switch-On Delay Time
C
LOAD
= 3300pF Each Driver
(Note 6)
30 ns
t
ON(MIN)
Minimum On-Time (Note 7) 90 ns
INTV
CC
Linear Regulator
V
INTVCC
Internal V
CC
Voltage 6V < V
IN
< 38V 4.8 5 5.2 V
V
LDO
INT INTV
CC
Load Regulation I
CC
= 0mA to 50mA 0.5 2 %
The l denotes the specifi cations which apply over the full operating
temperature range, otherwise specifi cations are at T
A
= 25°C. V
IN
= 15V, V
RUN
= 5V unless otherwise noted.
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LTC3851EGN#PBF

Mfr. #:
Buy LTC3851EGN#PBF
Manufacturer:
Analog Devices / Linear Technology
Description:
Switching Voltage Regulators Sync Buck Sw Reg Cntr
Lifecycle:
New from this manufacturer.
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