FEATURES
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LTC3547
Dual Monolithic
300mA Synchronous
Step-Down Regulator
DESCRIPTIO
The LTC
®
3547 is a dual, 2.25MHz, constant-frequency,
synchronous step-down DC/DC converter in a tiny 3mm
×
2mm DFN package. 100% duty cycle provides low drop-
out operation, extending battery life in portable systems.
Low output voltages are supported with the 0.6V feed-
back reference voltage. Each regulator can supply 300mA
continuous output current.
The input voltage range is 2.5V to 5.5V, making it ideal for
Li-Ion and USB powered applications. Supply current dur-
ing operation is only 40µA and drops to < 1µA in shutdown.
Automatic Burst Mode
®
operation increases efficiency at
light loads, further extending battery life.
An internally set 2.25MHz switching frequency allows
the use of tiny surface mount inductors and capacitors.
Internal soft-start reduces inrush current during start-
up. All outputs are internally compensated to work with
ceramic capacitors. The LTC3547 is available in a low
profile (0.75mm) 3mm
×
2mm DFN package. The LTC3547
is also available in a fixed output voltage configuration,
eliminating the need for the external feedback networks
(see Table 2).
, 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 6580258, 5481178, 6304066, 6127815, 6498466, 6611131.
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High Efficiency Dual Step-Down Outputs: Up to 96%
300mA Output Current per Channel at V
IN
= 3V
Automatic Low Ripple Burst Mode Operation
(20mV
P-P
)
Only 40µA Quiescent Current During Operation
(Both Channels)
2.25MHz Constant-Frequency Operation
2.5V to 5.5V Input Voltage Range
Low Dropout Operation: 100% Duty Cycle
Internally Compensated for All Ceramic Capacitors
Independent Internal Soft-Start for Each Channel
Current Mode Operation for Excellent Line and Load
Transient Response
0.6V Reference Allows Low Output Voltages
Short-Circuit Protected
Ultralow Shutdown Current: I
Q
< 1µA
Low Profile (0.75mm) 8-Lead 3mm
×
2mm
DFN Package
APPLICATIO S
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Cellular Telephones
Digital Still Cameras
Wireless and DSL Modems
PDAs/Palmtop PCs
Portable Media Players
TYPICAL APPLICATIO
V
IN
2.5V TO 5.5V
Dual Monolithic Buck Regulator in 8-Lead 3mm × 2mm DFN
100
90
80
RUN2 V
IN
RUN1
V
OUT2
1.8V AT
300mA
L2
4.7µH
10pF
LTC3547
SW2
SW1
10pF
L1
4.7µH
V
OUT1
2.5V AT
300mA
EFFICIENCY (%)
4.7µF
70
60
50
40
30
20
V
FB2
V
IN
= 2.7V
V
IN
= 3.6V
V
IN
= 4.2V
1
10
100
OUTPUT CURRENT (mA)
4.7µF
475k
237k
GND
V
FB1
150k
475k
4.7µF
3547 TA01
10
0
0.1
U
U
U
Efficiency vs Output Current
for V
OUT
= 2.5V
1
0.1
POWER LOSS (W)
0.01
0.001
0.0001
1000
3547fa
3547 TA01b
1
LTC3547
ABSOLUTE
(Note 1)
AXI U RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW
V
FB1
1
RUN1 2
V
IN
3
SW1 4
9
8 V
FB2
7 RUN2
6 SW2
5 GND
V
IN
............................................................... –0.3V to 6V
V
FB1
, V
FB2
......................................... –0.3V to V
IN
+0.3V
RUN1, RUN2 ..................................... –0.3V to V
IN
+0.3V
SW1, SW2 (DC) ................................ –0.3V to V
IN
+0.3V
P-Channel Switch Source Current (DC) ...............500mA
N-Channel Switch Sink Current (DC) ...................500mA
Peak SW Sink and Source Current (Note 5) .........700mA
Ambient Operating Temperature Range ... –40°C to 85°C
Maximum Junction Temperature .......................... 125°C
Storage Temperature Range................... –65°C to 125°C
DDB PACKAGE
8-LEAD (3mm
×
2mm) PLASTIC DFN
T
JMAX
= 125°C,
θ
JA
= 76°C/W
EXPOSED PAD (PIN 9) IS GND MUST BE SOLDERED TO PCB
ORDER PART NUMBER
LTC3547EDDB
LTC3547EDDB-1
DDB PART MARKING
LCDP
LCPC
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
UV
I
FB
V
FBREG1
PARAMETER
V
IN
Operating Voltage
V
IN
Undervoltage Lockout
Feedback Pin Input Current
Regulated Feedback Voltage (V
FB1
)
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 3.6V, unless otherwise noted.
CONDITIONS
●
MIN
2.5
●
●
●
●
●
●
●
TYP
2.0
3
MAX
5.5
2.5
30
6
0.610
0.612
1.830
1.836
0.610
0.612
1.220
1.224
0.5
UNITS
V
V
nA
µA
V
V
V
V
V
V
V
V
%/V
%
V
IN
Low to High
LTC3547, V
FB
= V
FBREG
LTC3547-1, V
FB
= V
FBREG
LTC3547, 0°C ≤ T
A
≤ 85°C
LTC3547, –40°C ≤ T
A
≤ 85°C
LTC3547-1, 0°C ≤ T
A
≤ 85°C
LTC3547-1, –40°C ≤ T
A
≤ 85°C
LTC3547, 0°C ≤ T
A
≤ 85°C
LTC3547, –40°C ≤ T
A
≤ 85°C
LTC3547-1, 0°C ≤ T
A
≤ 85°C
LTC3547-1, –40°C ≤ T
A
≤ 85°C
V
IN
= 2.5V to 5.5V
I
LOAD
= 0mA to 300mA
V
FB1
= V
FB2
= 0.95V
×
V
FBREG
V
FB1
= V
FB2
= 1.05V
×
V
FBREG
, V
IN
= 5.5V
RUN1 = RUN2 = 0V, V
IN
= 5.5V
V
FB
= 0.6V
V
IN
= 3V, V
FB
< V
FBREG
, Duty Cycle < 35%
0.590
0.588
1.770
1.764
0.590
0.588
1.180
1.176
0.600
0.600
1.800
1.800
0.600
0.600
1.200
1.200
0.3
0.5
450
40
0.1
V
FBREG2
Regulated Feedback Voltage (V
FB2
)
Δ
V
LINEREG
Δ
V
LOADREG
I
S
Reference Voltage Line Regulation
Output Voltage Load Regulation
Input DC Supply Current
Active Mode (Note 3)
Sleep Mode
Shutdown
Oscillator Frequency
Peak Switch Current Limit
Channel 1 (300mA)
Channel 2 (300mA)
700
60
1
2.7
f
OSC
I
LIM
●
1.8
400
400
2.25
550
550
3547fa
2
U
µA
µA
µA
MHz
mA
mA
W
U
U
W W
W
LTC3547
ELECTRICAL CHARACTERISTICS
SYMBOL
R
DS(ON)
PARAMETER
Channel 1 (Note 4)
Top Switch On-Resistance
Bottom Switch On-Resistance
Channel 2 (Note 4)
Top Switch On-Resistance
Bottom Switch On-Resistance
Switch Leakage Current
Soft-Start Time
RUN Threshold High
RUN Leakage Current
Output Ripple in Burst Mode Operation
V
OUT
= 1.5V, C
OUT
= 4.7µF
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
CC
= 3.6V, unless otherwise noted.
CONDITIONS
V
IN
= 3.6V, I
SW
= 100mA
V
IN
= 3.6V, I
SW
= 100mA
V
IN
= 3.6V, I
SW
= 100mA
V
IN
= 3.6V, I
SW
= 100mA
V
IN
= 5V, V
RUN
= 0V
V
FB
From 10% to 90% Full-Scale
●
●
MIN
TYP
0.8
0.75
0.8
0.75
0.01
MAX
1.05
1.05
1.05
1.05
1
0.850
1.2
1
UNITS
Ω
Ω
Ω
Ω
µA
ms
V
µA
mV
P-P
I
SW(LKG)
t
SOFTSTART
V
RUN
I
RUN
V
BURST
0.450
0.4
0.650
1
0.01
20
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 LTC3547E is guaranteed to meet specified performance
from 0°C to 85°C. Specifications over the –40°C and 85°C operating
temperature range are assured by design, characterization and correlation
with statistical process controls.
Note 3:
Dynamic supply current is higher due to the internal gate charge
being delivered at the switching frequency.
Note 4:
The DFN switch on-resistance is guaranteed by correlation to
wafer level measurements.
Note 5:
Guaranteed by long term current density limitations.
Note 6:
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
temperature may impair device reliability.
TYPICAL PERFOR A CE CHARACTERISTICS
Burst Mode Operation
100
SW, AC
COUPLED
5V/DIV
EFFICIENCY (%)
V
OUT
50mV/DIV
90
80
70
60
50
3547 G01
SUPPLY CURRENT (µA)
I
L
50mA/DIV
2.5µs/DIV
V
IN
= 3.6V
V
OUT
= 1.8V
I
LOAD
= 20mA
U W
Efficiency vs Input Voltage
V
OUT
= 1.8V
60
55
50
45
Supply Current vs Temperature
RUN1 = RUN2 = V
IN
I
LOAD
= 0A
V
IN
= 5.5V
40
35
30
25
V
IN
= 2.7V
40
30
2.5
I
OUT
= 0.1mA
I
OUT
= 1mA
I
OUT
= 10mA
I
OUT
= 100mA
I
OUT
= 300mA
3
3.5
4.5
4
V
IN
(V)
5
5.5
3547 G02
20
–50
–25
50
25
0
TEMPERATURE (ºC)
75
100
3547 G03
3547fa
3
LTC3547
TYPICAL PERFOR A CE CHARACTERISTICS
Oscillator Frequency
vs Temperature
2.6
2.5
LEAKAGE CURRENT (nA)
LEAKAGE CURRENT (pA)
2.4
FREQUENCY (MHz)
2.3
2.2
2.1
2.0
1.9
1.8
– 50 – 25
0
50
75
25
TEMPERATURE (°C)
100
125
0
– 50 – 25
0
V
IN
= 4.2V
V
IN
= 3.6V
V
IN
= 2.7V
40
400
50
Reference Voltage
vs Temperature
612
608
604
R
DS(ON)
(Ω)
V
FB
(mV)
600
596
592
588
– 50
1.0
R
DS(ON)
(Ω)
– 25
50
25
TEMPERATURE (°C)
0
Efficiency vs Load Current
100
90
80
70
EFFICIENCY (%)
EFFICIENCY (%)
60
50
40
30
20
10
0
0.1
V
IN
= 2.7V
V
IN
= 3.6V
V
IN
= 4.2V
1
10
100
OUTPUT CURRENT (mA)
1000
3547 G10
V
OUT
= 1.2V
EFFICIENCY (%)
4
U W
75
Switch Leakage vs Temperature
500
Switch Leakage vs Input Voltage
30
300
SYNCHRONOUS
SWITCH
200
20
SYNCHRONOUS
SWITCH
MAIN SWITCH
10
100
MAIN SWITCH
100
125
0
2.5
3
3.5
4.5
4
V
IN
(V)
5
5.5
6
50
75
25
TEMPERATURE (°C)
3547 G04
3547 G05
3547 G06
R
DS(ON)
vs Input Voltage
1.3
MAIN SWITCH
0.9
1.1
0.8
0.7
0.6
0.5
0.5
100
3547 G07
R
DS(ON)
vs Temperature
1.2
V
IN
= 2.7V
1.0
0.9
0.8
0.7
0.6
SYNCHRONOUS
SWITCH
V
IN
= 3.6V
V
IN
= 4.2V
0
0.4
2.5
3
3.5
4.5
4
V
IN
(V)
5
5.5
6
0.4
– 50 – 25
MAIN SWITCH
SYNCHRONOUS
SWITCH
100
125
50
75
25
TEMPERATURE (°C)
3547 G08
3547 G09
Efficiency vs Load Current
100
90
80
70
60
50
40
30
20
10
0
0.1
V
IN
= 2.7V
V
IN
= 3.6V
V
IN
= 4.2V
10
100
1
OUTPUT CURRENT (mA)
1000
3547 G11
Efficiency vs Load Current
100
90
80
70
60
50
40
30
20
10
0
0.1
V
IN
= 2.7V
V
IN
= 3.6V
V
IN
= 4.2V
1
10
100
OUTPUT CURRENT (mA)
1000
3547 G12
V
OUT
= 1.8V
V
OUT
= 2.5V
3547fa
LTC3547
TYPICAL PERFOR A CE CHARACTERISTICS
Load Regulation
1.2
1.O
0.8
0.6
0.4
0.2
0
–0.2
0
50
100
150 200 250
LOAD CURRENT (mA)
300
350
–0.4
–0.6
2.5
Burst Mode
OPERATION
V
OUT
= 1.2V
V
OUT
= 1.8V
V
OUT
= 2.5V
V
IN
= 3.6V
0.6
0.4
V
OUT
ERROR (%)
0.2
0
–0.2
V
OUT
ERROR (%)
Start-Up From Shutdown
RUN
2V/DIV
V
OUT
1V/DIV
RUN
2V/DIV
V
OUT
1V/DIV
I
L
100mA/DIV
3547 G15
250µs/DIV
V
IN
= 3.6V
V
OUT
= 1.8V
I
LOAD
= 0A
V
IN
= 3.6V
V
OUT
= 1.8V
I
LOAD
= 300mA
Load Step
V
OUT
, AC
COUPLED
100mV/DIV
V
OUT
, AC
COUPLED
100mV/DIV
I
L
200mA/DIV
I
LOAD
200mA/DIV
3547 G18
V
IN
= 3.6V
V
OUT
= 1.8V
I
LOAD
= 20mA TO 300mA
U W
Line Regulation
V
OUT
= 1.8V
I
LOAD
= 100mA
3
3.5
4
V
IN
(V)
4.5
5
5.5
3547 G14
3547 G13
Start-Up From Shutdown
V
OUT
, AC
COUPLED
100mV/DIV
Load Step
I
L
200mA/DIV
I
LOAD
200mA/DIV
3547 G16
3547 G17
I
L
200mA/DIV
200µs/DIV
10µs/DIV
V
IN
= 3.6V
V
OUT
= 1.8V
I
LOAD
= 0mA TO 300mA
Load Step
I
L
200mA/DIV
I
LOAD
200mA/DIV
3547 G19
10µs/DIV
10µs/DIV
V
IN
= 3.6V
V
OUT
= 1.8V
I
LOAD
= 50mA TO 300mA
3547fa
5
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