down switching DC/DC controller that drives an all N-
channel synchronous power MOSFET stage.
The LTC3854 features a 400kHz constant frequency current
mode architecture. The LTC3854 operates from a 4.5V to
38V (40V absolute maximum) input voltage range and
regulates the output voltage from 0.8V to 5.5V.
The RUN/SS pin provides both soft-start and enable
features. OPTI-LOOP compensation allows the transient
response to be optimized over a wide range of output ca-
pacitance and ESR values. Current foldback limits MOSFET
dissipation during short circuit conditions. Current foldback
functions are disabled during soft-start.
The LTC3854 has a minimum on-time at 75ns, making it
well suited for high step-down ratios. The strong onboard
MOSFET drivers allow the use of high power external
MOSFETs to produce output currents up to 20A.
L,
LT, LTC, LTM, Linear Technology, the Linear logo 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 5705919, 6498466, 5408150, 6222231.
n
n
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Wide Operating V
IN
Range: 4.5V to 38V
R
SENSE
or DCR Current Sensing
±1% 0.8V Reference Accuracy Over Temperature
400kHz Switching Frequency
Dual N-channel MOSFET Synchronous Drive
Very Low Dropout Operation: 97% Duty Cycle
Starts Up Into Pre-Biased Output
Adjustable Output Voltage Soft-Start
Output Current Foldback Limiting
(Disabled During Soft-Start)
Output Overvoltage Protection
5V LDO for External Gate Drive
OPTI-LOOP
®
Compensation Minimizes C
OUT
Low Shutdown I
Q
: 15µA
Tiny Thermally Enhanced 12-Pin 2mm
×
3mm DFN
and MSOP Packages
APPLICATIONS
n
n
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Automotive Systems
Telecom Systems
Industrial Equipment
Distributed DC Power Systems
TYPICAL APPLICATION
High Efficiency Synchronous Step-Down Converter
V
IN
TG
0.1µF
LTC3854
RUN/SS
2200pF
10k
8.06k
FB
42.2k
SENSE
–
SENSE
+
GND
BG
100pF
INTV
CC
4.7µF
4.99k
92
1
2
3
4
5
LOAD CURRENT (A)
5.49k
0.22µF
ITH
BOOST
SW
4.7µH
AT 8.2mΩ DCR
V
OUT
5V
7A
150µF
93
V
IN
= 12V
6
7
3854 TA01b
Efficiency and Power Loss
vs Load Current
97
EFFICIENCY
2.0
47µF
50V
0.1µF
V
IN
6V TO 38V
96
EFFICIENCY (%)
1.6
POWER LOSS (W)
95
1.2
+
94
POWER LOSS
0.8
0.4
0
3854 TA01
3854fb
1
LTC3854
ABSOLUTE MAXIMUM RATINGS
(Note 1)
Input Supply Voltage (V
IN
) ........................ 40V to –0.3V
Top Side Driver Voltage (BOOST)............... 46V to –0.3V
Switch Voltage (SW) .................................. 40V to –5.0V
INTV
CC
, BOOST-SW .................................... 6V to –0.3V
SENSE
+
, SENSE
–
......................................... 6V to –0.3V
RUN/SS........................................................ 6V to –0.3V
ITH, FB Voltages ....................................... 2.7V to –0.3V
INTV
CC
Peak Output Current (Note 8) ....................40mA
Operating Temperature Range
(Notes 2, 3) ..........................................–40°C to 85°C
Maximum Junction Temperature ...................... 125°C
Storage Temperature Range .................. –65°C to 125°C
PIN CONFIGURATION
TOP VIEW
FB 1
ITH 2
RUN/SS 3
BOOST 4
TG 5
SW 6
13
12 SENSE
+
11 SENSE
–
10 V
IN
9 INTV
CC
8 BG
7 GND
FB
ITH
RUN/SS
BOOST
TG
SW
1
2
3
4
5
6
TOP VIEW
12
11
10
9
8
7
SENSE
+
SENSE
–
V
IN
INTV
CC
BG
GND
13
DDB PACKAGE
12-LEAD (3mm
×
2mm) PLASTIC DFN
T
JMAX
= 125°C,
θ
JA
= 76°C/W,
θ
JC
= 10°C/W
EXPOSED PAD (PIN 13) IS GND, MUST BE SOLDERED TO PCB
MSE PACKAGE
12-LEAD PLASTIC MSOP
T
JMAX
= 125°C,
θ
JA
= 40°C/W,
θ
JC
= 16°C/W
EXPOSED PAD (PIN 13) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
LTC3854EDDB#PBF
LTC3854IDDB#PBF
LTC3854EMSE#PBF
LTC3854IMSE#PBF
TAPE AND REEL
LTC3854EDDB#TRPBF
LTC3854IDDB#TRPBF
LTC3854EMSE#TRPBF
LTC3854IMSE#TRPBF
PART MARKING*
LDPC
LDPC
3854
3854
PACKAGE DESCRIPTION
12-Lead (3mm
×
2mm) Plastic DFN
12-Lead (3mm
×
2mm) Plastic DFN
12-Lead Plastic MSOP
12-Lead Plastic MSOP
TEMPERATURE RANGE
–40°C to 85°C
–40°C to 85°C
–40°C to 85°C
–40°C to 85°C
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:
http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to:
http://www.linear.com/tapeandreel/
3854fb
2
LTC3854
ELECTRICAL CHARACTERISTICS
SYMBOL
V
IN
V
FB
I
FB
V
REFLNREG
V
LOADREG
PARAMETER
Operating Input Voltage Range
Regulated Feedback Voltage
Feedback Current
Reference Voltage Line Regulation
Output Voltage Load Regulation
(Note 4); ITH Voltage = 1.2V
(Note 4)
V
IN
= 6V to 38V (Note 4)
(Note 4) Measured in Servo Loop;
∆
ITH
Voltage = 0.7V to 1.2V
Measured in Servo Loop;
∆
ITH
Voltage = 1.2V to 2V
ITH = 1.2V; Sink/Source = 5µA (Note 4)
ITH = 1.2V; (Guaranteed by Design)
(Note 5)
RUN = 0V
V
IN
Ramping Down; Measured at INTV
CC
V
IN
Ramping Down then Up; Measured at INTV
CC
Measured at FB
V
SENSE
– = V
SENSE
+ = 3.3V
In Dropout
RUN/SS = 0V
RUN/SS Pin Must be Taken Below this Value to
Reset Part (or Put into Shutdown Mode)
Soft-Start Mode
FB = 0.7V, V
SENSE
– = 3.3V, V
IN
= 6V
TG High
TG Low
BG High
BG Low
(Note 6)
C
LOAD
= 3300pF
C
LOAD
= 3300pF
(Note 6)
C
LOAD
= 3300pF
C
LOAD
= 3300pF
C
LOAD
= 3300pF Each Driver
C
LOAD
= 3300pF Each Driver
(Note 7)
6V < V
IN
< 38V
I
CC
= 0 to 20mA
360
4.8
40
97
0.6
l
l
l
l
l
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 15V, V
RUN
= 5V, unless otherwise noted.
CONDITIONS
MIN
4.5
0.792
0.8
±5
0.002
0.1
–0.1
2.0
3
2
10
3.0
0.86
3.5
350
0.88
±0.5
98
1.25
0.4
1.2
50
2.5
2.1
2.5
1.2
25
25
25
25
30
30
75
5.0
0.2
400
5.2
1.0
440
65
2.0
0.90
±1
3
25
TYP
MAX
38
0.808
±50
0.02
0.5
–0.5
UNITS
V
V
nA
%/V
%
%
mmho
MHz
mA
µA
V
mV
V
µA
%
µA
V
V
mV
Ω
Ω
Ω
Ω
ns
ns
ns
ns
ns
ns
ns
V
%
kHz
Main Control Loop
gm
gm
GBW
I
Q
UVLO
UVLO
HYST
V
OVL
I
SENSE
DF
MAX
I
RUN/SS
V
RUN/SS_SD
V
RUN/SS_ON
V
SENSE(MAX)
TG R
UP
TG R
DOWN
BG R
UP
BG R
DOWN
TG t
r
TG t
f
BG t
r
BG t
f
TG/BG t
1D
BG/TG t
2D
t
ON(MIN)
V
INTVCC
V
LDO
INT
Oscillator
f
SW
Transconductance Amplifier gm
Transconductance Amplifier GBW
Input DC Supply Current
Normal Mode
Shutdown
Undervoltage Lockout
Undervoltage Lockout Hysteresis
Feedback Overvoltage Lockout
Sense Pins Source Current
Maximum Duty Factor
Soft-Start Charge Current
Shutdown Threshold
Soft-Start Threshold
Maximum Current Sense Threshold
TG Driver Pull-Up On Resistance
TG Driver Pull-Down On Resistance
BG Driver Pull-Up On Resistance
BG Driver Pull-down On Resistance
TG Transition Time:
Rise Time
Fall Time
BG Transition Time:
Rise Time
Fall Time
Top Gate Off to Bottom Gate On Delay
Synchronous Switch-On Delay Time
Bottom Gate Off to Top Gate On Delay
Top Switch-On Delay Time
Minimum On-Time
Internal V
CC
Voltage
INTV
CC
Load Regulation
Switching Frequency
INTV
CC
Linear Regulator
3854fb
3
LTC3854
ELECTRICAL CHARACTERISTICS
Note 1:
Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2:
The LTC3854E is guaranteed to meet performance specifications
from 0°C to 85°C. Specifications over the –40°C to 85°C operating
temperature range are assured by design, characterization and correlation
with statistical process controls. The LTC3854I is guaranteed to meet
performance specifications over the full –40°C to 85°C operating
temperature range.
Note 3:
T
J
is calculated from the ambient temperature T
A
and power
dissipation PD according to the following formulas:
LTC3854DDB: T
J
= T
A
+ (P
D
• 76°C/W)
LTC3854MSE: T
J
= T
A
+ (P
D
• 40°C/W)
Note 4:
The LTC3854 is tested in a feedback loop that servos V
ITH
to a
specified voltage and measures the resultant V
FB
.
Note 5:
Dynamic supply current is higher due to the gate charge being
delivered at the switching frequency. See Applications Information.
Note 6:
Rise and fall times are measured using 10% and 90% levels. Delay
times are measured using 50% levels. Not 100% tested in production.
Note 7:
The minimum on-time condition is specified for an inductor peak-
to-peak ripple current 40% of I
MAX
(see Minimum On-Time Considerations
in the Applications Information section).
Note 8:
The LTC3854 maximum LDO current specification assumes there
is no external DC load current being pulled from INTV
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