LTC3549
250mA Low V
IN
Buck
Regulator in 2mm
×
3mm DFN
FEATURES
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DESCRIPTIO
■
■
■
■
■
■
■
■
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1.6V to 5.5V Input Voltage Range
Internal Soft-Start
Low Ripple Burst Mode
®
Operation
Output Ripple: <20mV
P-P
I
Q
: 50µA
2.25MHz Constant-Frequency Operation
High Efficiency: Up to 93%
250mA Output Current (V
IN
= 1.8V, V
OUT
= 1.2V)
450mA Peak Inductor Current
No Schottky Diode Required
Low Dropout Operation: 100% Duty Cycle
0.611V Reference Voltage
Stable with Ceramic Capacitors
Shutdown Mode Draws <1µA Supply Current
Current Mode Operation for Excellent Line and Load
Transient Response
Overtemperature Protection
Available in a Low Profile (0.75mm) 6-Lead
(2mm x 3mm) DFN Package
The LTC
®
3549 is a high efficiency, monolithic synchronous
buck regulator using a constant-frequency, current mode
architecture. The output voltage is adjusted via an external
resistor divider.
A fixed switching frequency of 2.25MHz is supported.
This switching frequency allows the use of small surface
mount inductors and capacitors, including ceramics.
Supply current during Burst Mode operation is only 50µA
dropping to < 1µA in shutdown. The 1.6V to 5.5V input
voltage range makes the LTC3549 ideally suited for single
cell Li-Ion, Li-Metal and 2-cell alkaline, NiCd or NiMH
battery-powered applications. 100% duty cycle capabil-
ity provides low dropout operation, extending battery
life in portable systems. Burst Mode operation can be
user-enabled, increasing efficiency at light loads, further
extending battery life.
The internal synchronous switch increases efficiency and
eliminates the need for an external Schottky diode. Internal
soft-start offers controlled output voltage rise time at start-
up without the need for external components.
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
Burst Mode is a registered trademark of Linear Technology Corporation. All other
trademarks are the property of their respective owners. Protected by U.S. Patents,
including 5481178, 6580258, 6304066, 6127815, 6498466, 6611131.
APPLICATIO S
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2 AA-Cell Applications
Cellular Phones
Digital Cameras
MP3 Players
TYPICAL APPLICATIO
Burst Mode Efficiency, V
OUT
= 1.5V
100
1
90
80
0.1
POWER LOSS (W)
High Efficiency Step-Down Converter
LTC3549
SW
4.7µF
CER
V
IN
RUN
MODE
V
FB
GND
*TDK VLF3012AT-3R3MR87
3549 TA01
3.3µH*
22pF
V
IN
1.8V TO
5.5V
EFFICIENCY (%)
V
OUT
1.5V
4.7µF
CER
70
60
50
40
30
20
10
0
0.1
137k 200k
U
0.01
V
IN
= 1.8V
0.001
V
IN
= 2.5V
V
IN
= 3.1V
POWER LOST
AT V
IN
= 2.5V
0.0001
10
100
1k
1
LOAD CURRENT (mA)
3549 TA02
3549f
U
U
1
LTC3549
ABSOLUTE
(Note 1)
AXI U RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW
MODE
RUN
V
FB
Input Supply Voltage ................................... –0.3V to 6V
RUN, V
FB
, MODE Voltages .............–0.3V to (V
IN
+ 0.3V)
SW Voltage < 100ns Pulse .............–0.3V to (V
IN
+ 0.3V)
Operating Temperature Range (Note 2) ... –40°C to 85°C
Junction Temperature (Note 3) ........................... 125°C
Storage Temperature Range.................. –65°C to 125°C
6
5
4
7
1
V
IN
2
GND
3
SW
DCB PACKAGE
6-LEAD (2mm
×
3mm) PLASTIC DFN
T
JMAX
= 125°C,
θ
JA
= 64°C/W
EXPOSED PAD (PIN 7) IS GND
MUST BE SOLDERED TO PCB
ORDER PART NUMBER
LTC3549EDCB
DCB PART MARKING
LBZR
Order Options
Tape and Reel: Add #TR
Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF
Lead Free Part Marking:
http://www.linear.com/leadfree/
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
SYMBOL
V
IN
V
RUN
I
RUN
V
MODE
I
MODE
V
FB
PARAMETER
Input Voltage Range
RUN Threshold
RUN Leakage Current
MODE Threshold
MODE Leakage Current
Regulated Feedback Voltage
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C, V
IN
= 2.2V.
CONDITIONS
●
●
MIN
1.6
0.3
0.3
0.599
0.597
0.596
40
●
TYP
0.7
0.01
0.65
0.01
0.611
0.611
0.611
60
0.04
0.04
MAX
5.5
1.1
1
1.1
1
0.623
0.623
0.626
±30
80
0.4
0.4
0.6
UNITS
V
V
µA
V
µA
V
V
V
nA
mV
%/V
%/V
A
%
V
RUN
= 0 or 2.2V
●
V
MODE
= 0 or 2.2V
T
A
= 25°C (Note 4)
0°C ≤ T
A
≤ 85°C (Note 4)
–40°C ≤ T
A
≤ 85°C (Note 4)
ΔV
OVL
=
ΔV
FBOVL
– V
FB
(Note 6)
1.6V < V
IN
< 5.5V (Note 4)
I
OUT
= 100mA, 1.6V < V
IN
< 5.5V (Note 7)
V
FB
= 0.5V or V
OUT
= 90%
Pulse Skip Mode, V
OUT
= 1.2V,
50mA < I
LOAD
< 250mA (Note 7)
0.3
●
I
VFB
ΔV
OVL
ΔV
FB
ΔV
OUT
I
PK
V
LOADREG
Feedback Current
ΔV
FBOVL
Overvoltage Lockout
Reference Voltage Line Regulation
Output Voltage Line Regulation
Peak Inductor Current
Output Voltage Load Regulation
●
0.45
0.5
2
U
3549f
W
U
U
W W
W
LTC3549
ELECTRICAL CHARACTERISTICS
SYMBOL
I
S
PARAMETER
Input DC Bias Current
Active Mode
Sleep Mode
Shutdown
Nominal Oscillator Frequency
Soft-Start Period
R
DS(ON)
of P-Channel FET
R
DS(ON)
of N-Channel FET
SW Leakage
RUN↑
I
SW
= 100mA, Wafer Level
I
SW
= 100mA, DD Package (Note 7)
I
SW
= 100mA, Wafer Level
I
SW
= 100mA, DD Package (Note 7)
V
RUN
= 0V, V
SW
= 0V or 5.5V, V
IN
= 5.5V
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C, V
IN
= 2.2V.
CONDITIONS
(Note 5)
V
OUT
= 90%, I
LOAD
= 0A
V
OUT
= 103%, I
LOAD
= 0A
V
RUN
= 0V, V
IN
= 5.5V
●
MIN
TYP
300
50
0.1
MAX
475
95
5
2.7
UNITS
µA
µA
µA
MHz
ms
Ω
Ω
Ω
Ω
f
OSC
t
SS
R
PFET
R
NFET
I
LSW
1.8
2.25
1
0.5
0.56
0.35
0.4
±0.1
±1
µA
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. Voltage on any pin may not exceed 6V.
Note 2:
The LTC3549E 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.
Note 3:
T
J
is calculated from the ambient temperature T
A
and power
dissipation P
D
according to the following formula:
LTC3549: T
J
= T
A
+ (P
D
)(64°C/W)
This IC includes overtemperature protection that is intended to protect the
device during momentary overload conditions. Overtemperature protection
becomes active at a junction temperature greater than the maximum
operating junction temperature. Continuous operation above the specified
maximum operating junction temperature may impair device reliability.
Note 4:
The LTC3549 is tested in a proprietary test mode that connects V
FB
to the output of the error amplifier.
Note 5:
Dynamic supply current is higher due to the gate charge being
delivered at the switching frequency.
Note 6:
ΔV
OVL
is the amount V
FB
must exceed the regulated feedback
voltage.
Note 7:
Determined by design, not production tested.
3549f
3
LTC3549
TYPICAL PERFOR A CE CHARACTERISTICS
(From Typical Application on the front page, except for the resistive divider resistor values)
Efficiency/Power Loss vs Load
Current, V
OUT
= 1.5V, Burst Mode
100
90
80
70
EFFICIENCY (%)
60
50
40
30
20
10
0
0.1
1
10
100
LOAD CURRENT (mA)
POWER LOSS
V
IN
= 1.8V
V
IN
= 2.5V
V
IN
= 3.1V
0.0001
1000
3549 G01a
EFFICIENCY (%)
60
50
40
30
20
10
0
0.1
EFFICIENCY
POWER LOSS
V
IN
= 1.8V
V
IN
= 1.8V
V
IN
= 2.5V
V
IN
= 2.5V
V
IN
= 3.1V
V
IN
= 3.1V
1
10
100
LOAD CURRENT (mA)
0.01
EFFICIENCY (%)
EFFICIENCY
V
IN
= 1.8V
V
IN
= 2.5V
V
IN
= 3.1V
Efficiency vs Input Voltage
V
OUT
= 1.2V, Pulse Skip
100
90
80
70
EFFICIENCY (%)
EFFICIENCY (%)
60
50
40
30
20
10
0
1.5
I
OUT
:
0.1mA
1mA
2.5
3.5
4.5
INPUT VOLTAGE (V)
10mA
100mA
5.5
3549 G03
EFFICIENCY (%)
Efficiency vs Load Current
V
OUT
= 1.2V, Burst Mode
100
90
80
EFFICIENCY (%)
EFFICIENCY (%)
70
60
50
40
30
20
10
0
0.1
V
IN
= 1.6V
V
IN
= 2.5V
V
IN
= 3.1V
1
10
100
LOAD CURRENT (mA)
1000
3549 G05a
70
60
50
40
30
20
10
0
0.1
1
10
100
LOAD CURRENT (mA)
1000
3549 G05b
REFERENCE VOLTAGE (V)
4
U W
1
300mA
Efficiency/Power Loss vs Load
Current, V
OUT
= 1.5V, Pulse Skip
100
90
0.1
POWER LOSS (W)
80
70
0.1
POWER LOSS (W)
1
100
90
80
70
60
50
40
30
20
10
Efficiency vs Input Voltage
V
OUT
= 1.2V, Burst Mode Operation
0.01
I
OUT
:
0.1mA
1mA
10mA
100mA
300mA
2.5
3.5
4.5
INPUT VOLTAGE (V)
5.5
3549 G02
0.001
0.001
0.0001
1000
0
1.5
3549 G01b
Efficiency vs Load Current
V
OUT
= 1.8V, Burst Mode
100
90
80
70
60
50
40
30
20
10
0
0.1
1
0.01
L = 4.7µH
1
100
90
80
0.1
POWER LOSS (W)
70
60
50
40
30
20
10
Efficiency vs Load Current
V
OUT
= 1.8V, Pulse Skip
L = 4.7µH
EFFICIENCY
V
IN
= 2.5V
V
IN
= 3.6V 0.001
V
IN
= 4.2V
POWER LOSS
V
IN
= 3.6V
10
100
LOAD CURRENT (mA)
0.0001
1000
0
0.1
EFFICIENCY
V
IN
= 2.5V
V
IN
= 3.6V
V
IN
= 4.2V
1
10
100
LOAD CURRENT (mA)
1000
3549 G04b
3549 G04a
Efficiency vs Load Current
V
OUT
= 1.2V, Pulse Skip
100
90
80
0.6132
V
IN
= 1.6V
V
IN
= 2.5V
V
IN
= 3.1V
0.6111
Reference Voltage
vs Temperature
V
IN
= 1.6V
V
IN
= 2.2V
V
IN
= 4.2V
0.6090
0.6069
–50
–25
0
25
50
75
TEMPERATURE (ºC)
100
125
3549f
3549 G06
LTC3549
TYPICAL PERFOR A CE CHARACTERISTICS
(From Typical Application on the front page, except for the resistive divider resistor values)
Oscillator Frequency
vs Temperature
2.35
OSCILLATOR FREQUENCY SHIFT (%)
OSCILLATOR FREQUENCY (MHz)
2.30
2.25
2.20
2.15
2.10
2.05
–50
V
IN
= 2.7V
2.5
2.0
OUTPUT VOLTAGE (V)
1.5
1.0
0.5
0
–0.5
–1.0
–1.5
1.5
3.5
2.5
4.5
INPUT VOLTAGE (V)
5.5
3549 G08
V
IN
= 1.6V
V
IN
= 4.2V
–25
0
25
50
75
TEMPERATURE (°C)
R
DS(ON)
vs Input Voltage
0.9
0.8
0.7
0.6
R
DS(ON)
(Ω)
0.5
0.4
0.3
0.2
0.1
0
1.5
2.5
3.5
INPUT VOLTAGE (V)
4.5
5.5
3549 G10
DYNAMIC SUPPLY CURRENT—PULSE SKIP (µA)
MAIN SWITCH
R
DS(ON)
(Ω)
SYNCHRONOUS SWITCH
Dynamic Supply Current vs
Temperature, V
IN
= 3.6V,
V
OUT
= 1.5V, No Load
350
DYNAMIC SUPPLY CURRENT (µA)
300
250
200
150
100
50
0
–50
BURST
SWITCH LEAKAGE (nA)
250
SWITCH LEAKAGE (nA)
PULSE SKIP
–25
0
25
50
75
TEMPERATURE (°C)
U W
100
100
Oscillator Frequency Shift
vs Input Voltage
1.205
1.204
1.203
1.202
Output Voltage vs Load Current
V
IN
= 1.6V, V
OUT
= 1.2V
BURST
1.201
1.200
1.199
0
200
100
LOAD CURRENT (mA)
300
3549 G09
V
OUT
PULSE SKIP
125
3549 G07
R
DS(ON)
vs Temperature
0.95
0.85
0.75
0.65
0.55
0.45
0.35
0.25
0.15
–50
–25
0
25
50
75
TEMPERATURE (°C)
100
125
3549 G11
Dynamic Input Current
V
OUT
= 1.5V, 247k
Ω
Load
DYNAMIC SUPPLY CURRENT—BURST MODE (µA)
10000
Burst Mode
OPERATION
70
60
50
40
1000
30
PULSE SKIP MODE
20
10
0
100
1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0
INPUT VOLTAGE (V)
3549 G12
MAIN SWITCH
V
IN
= 1.6V
V
IN
= 2.7V
V
IN
= 4.2V
SYNCHRONOUS SWITCH
V
IN
= 1.6V
V
IN
= 2.7V
V
IN
= 4.2V
Switch Leakage vs Temperature
V
IN
= 5.5V
1.6
1.4
200
1.2
1.0
Switch Leakage vs Input Voltage
150
SYNCHRONOUS SWITCH
MAIN SWITCH
0.8
0.6
0.4
0.2
SYNCHRONOUS
SWITCH
0
4
2
INPUT VOLTAGE (V)
6
3549 G15
100
50
MAIN SWITCH
125
3549 G13
0
–50
0
–25
0
25
50
75
TEMPERATURE (°C)
100
125
3549 G14
3549f
5
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