monolithic step-down regulator. The regulator features
a single resistor programmable output voltage, internal
compensation and high efficiencies over a wide V
OUT
range.
The step-down regulator operates from an input voltage
range of 3.1V to 60V and provides an adjustable rail-to-rail
output range from (V
IN
– 0.5V) to ground while delivering
up to 4A of output current. The switching frequency is
also adjusted with an external resistor. A user-selectable
mode input is provided to allow the user to trade off ripple
noise for efficiency at light loads; Burst Mode operation
provides the highest efficiency at light loads, while forced
continuous mode provides low output ripple. The MODE/
SYNC pin can also be used to allow the user to synchronize
the switching frequency to an external clock.
The LTC3649 operates with a peak current mode architec-
ture that allows for fast transient response with inherent
cycle-to-cycle current limit protection. It also features
programmable output current limit, current monitoring
and input voltage regulation.
L,
LT, LTC, LTM, Linear Technology, the Linear logo, Burst Mode and OPTI-LOOP are
registered trademarks of Analog Devices, Inc. All other trademarks are the property of their
respective owners. Protected by U.S. Patents, including 5481178, 5705919, 5847554, 6580258.
n
n
n
n
n
n
n
n
n
n
n
n
n
Wide V
IN
Range: 3.1V to 60V
Wide V
OUT
Range: 0V to (V
IN
– 0.5V)
Single Resistor V
OUT
Programming
Integrated 110mΩ Top N-Channel/50mΩ Bottom
N-Channel MOSFETs
95% Efficiency with 12V
IN
and 5V
OUT
Regulated I
Q
: 440µA, Shutdown I
Q
: 18µA
Accurate Current Monitoring (±4%) without Sense
Resistor
Accurate Resistor Programmable Frequency
(300kHz to 3MHz) with ±50% Frequency Sync Range
Accurate Programmable Output Current
Input Voltage Regulation for MPPT Applications
±0.8% Output Voltage Accuracy
Peak Current Mode Operation
Programmable Wire Drop Compensation
Burst Mode
®
Operation, Forced Continuous Mode
Internal Compensation and Programmable Soft-Start
Overtemperature Protection
Available in Thermally Enhanced 28-Lead (4mm ×
5mm) QFN and TSSOP Packages
APPLICATIONS
n
n
Industrial Applications
Automotive Applications
TYPICAL APPLICATION
24V to 5V
OUT
Burst Mode Operation
0.1µF
6.8µH
RUN
22µF
ITH
V
INREG
INTV
CC
2.2µF
ISET
100k
f
SW
= 500kHz
10nF
LTC3649
V
OUT
EXTV
CC
MODE/SYNC
SGND
PGND
R
T
200k
IMON
10k
10nF
3649 TA01a
Efficiency with V
OUT
= 5V
100
98
96
V
OUT
5V
4A
EFFICIENCY (%)
V
IN
= 12V
V
IN
= 24V
V
IN
5.5V TO 60V
V
IN
BOOST SW
47µF
×2
94
92
90
88
86
84
82
80
0
0.5
1
1.5
2
I
OUT
(A)
2.5
3
3.5
4
3649 TA01b
3649fb
For more information
www.linear.com/LTC3649
1
LTC3649
ABSOLUTE MAXIMUM RATINGS
(Notes 1, 2)
V
IN
Voltage (Note 3) .................................. 64V to –0.3V
ISET, OUT Voltage ..................................... 64V to –0.3V
RUN Voltage............................................... 64V to –0.3V
MODE/SYNC Voltage .................................. 6V to –0.3V
PGDFB, R
T ...........................................
INTV
CC
+0.3V to –0.3V
EXTV
CC
Voltage ......................................... 28V to –0.3V
IMON, PGOOD Voltage ................................. 4V to –0.3V
V
INREG
, ITH Voltage ..................................... 4V to –0.3V
Operating Junction
Temperature Range (Notes 5, 7) ............ –40°C to 125°C
Storage Temperature Range .................. –65°C to 125°C
PIN CONFIGURATION
TOP VIEW
TOP VIEW
PGND
PGND
PGND
SW
SW
SW
PGND
PGND
PGND
22 SW
21 SW
20 SW
29
SGND
19 SW
18 BOOST
17 INTV
CC
16 EXTV
CC
15 ITH
9 10 11 12 13 14
V
INREG
IMON
V
OUT
R
T
PGDFB
ISET
PGND
PGND
V
IN
V
IN
RUN
SGND
1
2
3
4
5
6
7
8
9
29
SGND
28 SW
27 SW
26 SW
25 SW
24 SW
23 SW
22 SW
21 BOOST
20 INTV
CC
19 EXTV
CC
18 ITH
17 ISET
16 V
OUT
15 R
T
28 27 26 25 24 23
PGND 1
PGND 2
V
IN
3
V
IN
4
RUN 5
SGND 6
MODE/SYNC 7
PGOOD 8
MODE/SYNC 10
PGOOD 11
PGDFB 12
IMON 13
V
INREG
14
UFD PACKAGE
28-LEAD (4mm
×
5mm) PLASTIC QFN
T
JMAX
= 125°C,
θ
JA
= 43°C/W,
θ
JC
= 3.4°C/W
EXPOSED PAD (PIN 29) IS SGND, MUST BE SOLDERED TO PCB
FE PACKAGE
28-LEAD PLASTIC TSSOP
T
JMAX
= 125°C,
θ
JA
= 30°C/W,
θ
JC
= 5°C to 10°C/W
EXPOSED PAD (PIN 29) IS SGND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
LTC3649EUFD#PBF
LTC3649IUFD#PBF
LTC3649EFE#PBF
LTC3649IFE#PBF
TAPE AND REEL
LTC3649EUFD#TRPBF
LTC3649IUFD#TRPBF
LTC3649EFE#TRPBF
LTC3649IFE#TRPBF
http://www.linear.com/product/LTC3649#orderinfo
PART MARKING*
3649
3649
LTC3649
LTC3649
PACKAGE DESCRIPTION
28-Lead (4mm × 5mm) Plastic QFN
28-Lead (4mm × 5mm) Plastic QFN
28-Lead Plastic TSSOP
28-Lead Plastic TSSOP
TEMPERATURE RANGE
–40°C to 125°C
–40°C to 125°C
–40°C to 125°C
–40°C to 125°C
Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
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/.
Some packages are available in 500 unit reels through
designated sales channels with #TRMPBF suffix.
3649fb
2
For more information
www.linear.com/LTC3649
LTC3649
The
l
denotes the specifications which apply over the specified operating
junction temperature range, otherwise specifications are at T
J
= 25°C. (Note 5) V
IN
= 24V, V
EXTVCC
= 0V unless otherwise noted. (Notes 5, 7)
SYMBOL
V
IN
V
OUT
I
VIN
I
ISET
ΔV
OUT(LOAD+LINE)
V
EA(OFFSET)
g
m
(EA)
I
LSW
R
SW-GND
R
DS(ON)
D
MAX
t
ON(MIN)
V
RUN
I
RUN
V
MODE/SYNC
I
MODE/SYNC
I
LIM
V
UVLO
V
UVLO(HYS)
V
OVLO
V
OVLO(HYS)
f
OSC
f
SYNC
V
INTVCC
V
EXTVCC
R
VOUT
I
PGDFB
OV
PGDFB
UV
PGDFB
ΔV
PGDFB
R
PGOOD
I
PGOOD(LEAK)
t
PGOOD
A
IMON
I
IMON
V
IMON
V
VINREG
I
VINREG
PARAMETER
Input Supply Operating Voltage Range
Output Operating Voltage Range
Input Quiescent Current
CONDITIONS
(Note 4)
Shutdown Mode; V
RUN
= 0V
Burst Mode Operation
FC Mode (Note 6)
V
ISET
= 3.3V
l
l
ELECTRICAL CHARACTERISTICS
MIN
3.1
0.05
TYP
Reference Current
Output Voltage Load + Line Regulation
Error Amp Input Offset
Error Amplifier Transconductance
Topside NMOS Switch Leakage
SW Resistance to GND
Topside NMOS On-Resistance
Bottom Side NMOS On-Resistance
Maximum Duty Cycle
Minimum On-Time
RUN Input Rising
RUN Hysteresis
RUN Input Current
Burst Mode Operation
FC Mode
MODE/SYNC Input Current
Peak Current Limit
V
INTVCC
Undervoltage Lockout
V
INTVCC
Undervoltage Lockout Hysteresis
V
IN
Overvoltage Lockout Rising
V
IN
Overvoltage Lockout Hysteresis
Oscillator Frequency
SYNC Capture Range
V
INTVCC
LDO Output Voltage
EXTV
CC
Switchover Voltage
V
OUT
Resistance to GND
PGDFB Leakage Current
Output Overvoltage PGOOD Upper Threshold
Output Undervoltage PGOOD Lower Threshold
PGOOD Hysteresis
PGOOD Pull-Down Resistance
PGOOD Leakage Current
PGOOD Delay
I
OUT
/I
IMON
IMON Pin Current
49.6
49.4
–5
400
0.5
18
440
1.4
50
50
0.1
550
0.1
1
110
50
95
60
1.2
120
0
V
ISET
= 3.3V
V
ITH
= 0.7V, V
OUT
= 3.3V
MAX
60
V
IN
30
600
2.5
50.4
50.6
0.5
5
700
1
1.5
V
ISET
= V
IN
(Note 4)
l
1.08
1.32
10
0.4
V
RUN
= 12V
1.2
–8
5.7
5.4
2.4
64
R
T
= 100kΩ
% of Programmed Frequency
V
IN
> 5.0V, V
EXTVCC
> 3.2V
l
l
V
MODE/SYNC
= 0V
l
V
IN
Rising
l
V
OUT
= 5V
V
PGDFB
= 0.6V
PGFB Rising
PGFB Falling
PGFB Returning
V
PGOOD
= 3.3V
PGOOD Low to High
PGOOD High to Low
Ratio of Output Current to I
IMON
l
Current
I
OUT
= 4A
l
l
l
0.92
50
3.25
2.85
3.1
3.25
80
0.63
0.54
–5
6
6
2.65
200
68
2
1.00
3.45
3.0
3.15
100
0
0.645
0.555
10
550
16
64
40
40
100
100
2.0
2.0
0
6.3
6.6
2.9
4
1.08
150
3.65
3.15
3.2
120
100
0.66
0.57
100
Regulated I
MON
Voltage Under Output Current Regulation
Input Voltage Regulation Voltage
V
INREG
Leakage Current
V
VINREG
= 3.3V
38.5
36
96
90
1.94
1.85
41.5
44
104
110
2.06
2.15
0.1
UNITS
V
V
µA
µA
mA
µA
µA
%
mV
µS
µA
MΩ
mΩ
mΩ
%
ns
V
mV
nA
V
V
µA
A
A
V
mV
V
V
MHz
%
V
V
V
V
kΩ
nA
V
V
mV
Ω
nA
Switch Cycles
Switch Cycles
k
k
µA
µA
V
V
µA
3649fb
For more information
www.linear.com/LTC3649
3
LTC3649
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:
All voltages are referred to V
SGND
/V
PGND
.
Note 3:
Transient absolute maximum voltages should not be applied for
more than 4% of the switching duty cycle.
Note 4:
V
OUT
can be programmed to V
IN
if the ISET pin is driven to that
voltage. If a resistor is used to program V
ISET
, the current into the ISET pin
will decrease as V
ISET
approaches V
IN
. Refer to the ISET current vs V
ISET
graph as an example and reference. Furthermore, during high I
OUT
and
high duty cycle operation, V
OUT
may be limited by the voltage drop across
the top switch. Refer to the High Duty Cycle/Dropout Operation section for
more details.
Note 5:
The LTC3649 is tested under pulsed load conditions such that
T
J
≈ T
A
. The LTC3649E is guaranteed to meet specifications from
0°C to 85°C junction temperature. Specifications over the –40°C to
125°C operating junction temperature range are assured by design,
characterization and correlation with statistical process controls. The
LTC3649I is guaranteed over the full –40°C to 125°C operating junction
temperature range. Note that the maximum ambient temperature
consistent with these specifications is determined by specific operating
conditions in conjunction with board layout, the rated package thermal
impedance and other environmental factors.
Note 6:
The quiescent current in FC mode does not include switching loss
of the power FETs.
Note 7:
This IC includes overtemperature protection that is intended
to protect the device during momentary overload conditions. Junction
temperature will exceed 125°C when overtemperature protection is active.
Continuous operation above the specified maximum operating junction
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