LTC3543
600mA Synchronous Step
Down Buck Regulator with PLL,
Soft-Start and Spread Spectrum
FEATURES
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DESCRIPTION
The LTC
®
3543 is a high efficiency monolithic synchronous
current mode buck regulator.
The switching frequency is internally set at 2.25MHz,
allowing the use of small surface mount inductors and
capacitors. In PLL mode, the LTC3543 can acquire fre-
quencies between 1MHz and 3MHz. Also, the LTC3543
has spread spectrum capability providing a lower noise
regulated output, as well as low noise at the input.
In Burst Mode
®
operation, the supply current is only 45μA,
dropping to <1μA in shutdown. The 2.5V to 5.5V input
voltage range makes the LTC3543 ideally suited for single
Li-Ion battery-powered applications. The 100% duty cycle
provides a low dropout operation, extending the battery
life in portable systems. Burst Mode operation increases
efficiency at light loads, further extending battery life.
The internal synchronous switch increases efficiency and
eliminates the need for an external Schottky diode.
L,
LT, LTC, LTM, Linear Technology, Burst Mode and the Linear logo are registered trademarks
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.
600mA Output Current
2.5V to 5.5V Input Voltage Range
2.25MHz Constant-Frequency Operation, Spread
Spectrum or Synchronized PLL (1MHz to 3MHz)
High Efficiency: Up to 95%
1A Peak Inductor Current
Very Low Quiescent Current: Only 45μA During
Burst Mode Operation
No Schottky Diode Required
Low Dropout Operation: 100% Duty Cycle
Overtemperature Protected
Stable with Ceramic Capacitors
Shutdown Mode Draws <1μA Supply Current
±2%
Output Voltage Accuracy
Current Mode Operation for Excellent Line and Load
Transient Response
Soft-Start
Available in a Low Profile (0.75mm) 2mm
×
3mm
6-Lead DFN Package
APPLICATIONS
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Portable Instruments
Cellular Phones
TYPICAL APPLICATION
3.3μH
2.5V TO 5.5V
10μF
LTC3543
PWR_EN
MODE
RUN
V
FB
200k
V
IN
SW
300k
1.5V
10pF
10μF
V
OUT
1.5V
Efficiency and Power Loss vs Load Current
100
90
80
70
EFFICIENCY (%)
60
50
40
30
3543 TA01a
1000
V
IN
= 2.7V
V
IN
= 4.2V
100
POWER LOSS (mW)
MODE
CAP
GND
V
IN
= 3.6V
10
POWER LOSS
AT V
IN
= 3.6V
4nF
EXPOSED
PAD
MODE = V
IN
PULSE SKIP
MODE = V
FB
PULSE SKIP WITH SPREAD SPECTRUM
MODE = GND Burst Mode OPERATION
MODE = EXTERNAL CLOCK PLL
20
10
0
0.1
10
Burst Mode OPERATION ENABLED
1
10
100
LOAD CURRENT (mA)
0.1
1000
3543 TA01b
3543fa
1
LTC3543
ABSOLUTE MAXIMUM RATINGS
(Note 1)
PIN CONFIGURATION
TOP VIEW
SW
1
CAP
2
MODE
3
7
6
V
IN
5
RUN
4
VFB
V
IN
Voltage ................................................... –0.3V to 6V
RUN, V
FB
, MODE, CAP Voltages...................–0.3V to V
IN
SW Voltage ....................................–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
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 INFORMATION
LEAD FREE FINISH
LTC3543EDCB#PBF
TAPE AND REEL
LTC3543EDCB#TRPBF
PART MARKING
LCCK
PACKAGE DESCRIPTION
6-Lead (2mm
×
3mm) Plastic DFN
TEMPERATURE RANGE
–40°C to 85°C
Consult LTC Marketing for parts specified with wider operating temperature ranges.
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/
ELECTRICAL CHARACTERISTICS
SYMBOL
RUN
V
FB
I
VFB
I
PK
V
LOADREG
V
LINEREG
V
IN
I
S
PARAMETER
Run Threshold
Regulated Feedback Voltage
Feedback Pin Current
Peak Inductor Current
Output Voltage Load Regulation
Output Voltage Line Regulation
Input Voltage Range
Input DC Bias Current
Active Mode
Sleep Mode
Shutdown
Nominal Oscillator Frequency
R
DS(ON)
of P-Channel FET
R
DS(ON)
of N-Channel FET
SW Leakage
The
l
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
(Note 4)
V
IN
= 3.6V, V
FB
= 0V
(Note 4)
l
l
MIN
0.3
0.588
0.7
TYP
1
0.6
1
0.5
MAX
1.5
0.612
50
1.3
0.5
UNITS
V
V
nA
A
%/mA
%/V
V
μA
μA
μA
MHz
Ω
Ω
2.5
375
45
0.1
5.5
500
70
1
(Note 5)
V
OUT
= 90%, I
LOAD
= 0A
V
OUT
= 103%, I
LOAD
= 0A
V
RUN
= 0V, V
IN
= 5.5V
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OSC
R
PFET
R
NFET
I
SW
1.80
2.25
0.45
0.35
±1
I
SW
= 100mA
I
SW
= 100mA
V
RUN
= 0V, V
SW
= 0V or 5.5V, V
IN
= 5.5V
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.
Note 2:
The LTC3543E is guaranteed to meet performance specifications
from 0°C to 85°C. Specifications over the –40°C to 85°C operating
temperature ranges are assured by design, characterization and
correlation with statistical process controls.
3543fa
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LTC3543
ELECTRICAL CHARACTERISTICS
Note 3:
T
J
is calculated from the ambient temperature T
A
and power
dissipation P
D
according to the following formula: T
J
= T
A
+ (P
D
)(64°C/W)
Note 4:
The LTC3543 is tested in a proprietary test mode that connects
V
FB
to the output of the error amplifier. This test mode is equivalent to
continuous mode operation.
Note 5:
Dynamic supply current is higher due to the gate charge being
delivered at the switching frequency.
TYPICAL PERFORMANCE CHARACTERISTICS
Efficiency vs Input Voltage (V
IN
)
100
I
OUT
= 200mA
90
80
70
I
OUT
= 10mA
60
50
40
V
OUT
= 1.8V
2.5
3.0
3.5
4.0
4.5
INPUT VOLTAGE (V)
5.0
5.5
3543 G01
T
A
= 25°C unless otherwise noted. (From Figure 1a)
Efficiency vs Load Current
100
V
IN
= 2.7V
90 Burst Mode OPERATION
80 ENABLED
70
EFFICIENCY (%)
60
50
40
30
20
10
0
0.1
V
OUT
= 1.2V
1
10
100
LOAD CURRENT (mA)
1000
3543 G02
Efficiency vs Load Current
100
Burst Mode OPERATION
90 ENABLED
80
70
EFFICIENCY (%)
60
50
40
30
20
10
0
0.1
V
OUT
= 1.5V
1
10
100
LOAD CURRENT (mA)
1000
3543 G03
EFFICIENCY (%)
I
OUT
= 600mA
V
IN
= 4.2V
V
IN
= 4.2V
V
IN
= 3.6V
V
IN
= 3.6V
V
IN
= 2.7V
Power Loss vs Load Current
500
V
OUT
= 1.2V
V
OUT
= 1.5V
V
OUT
= 1.8V
V
OUT
= 2.5V
EFFICIENCY (%)
100
Efficiency vs Load Current
Burst Mode OPERATION
90 ENABLED
80
V
IN
= 4.2V
EFFICIENCY (%)
70
100
Efficiency vs Load Current
Burst Mode OPERATION
90 ENABLED
80
70
60
50
40
30
20
V
IN
= 4.2V
400
POWER LOSS (mW)
300
60
50
40
30
200
V
IN
= 3.6V
V
IN
= 3.6V
100
20
10
V
IN
= 2.7V
V
OUT
= 1.8V
1
10
100
LOAD CURRENT (mA)
1000
3543 G05
10
0
0.1
1
V
IN
= 2.7V
V
OUT
= 2.5V
10
100
LOAD CURRENT (mA)
1000
3543 G06
0
0.1
1
10
100
LOAD CURRENT (mA)
1000
3543 G04
0
0.1
3543fa
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LTC3543
TYPICAL PERFORMANCE CHARACTERISTICS
R
DS(ON)
vs Input Voltage (V
IN
)
500
450
400
350
R
DS(ON)
(mΩ)
300
250
200
150
100
50
0
2.5
3.0
4.0
4.5
3.5
INPUT VOLTAGE (V)
5.0
5.5
3543 G07
T
A
= 25°C, unless otherwise noted.
Synchronous Switch Resistance
vs Temperature
500
450
400
V
IN
= 3.6V
350
300
V
IN
= 4.2V
250
200
–40 –25 –10 5 20 35 50 65 80 95 110 125
TEMPERATURE (°C)
3543 G09
Main Switch Resistance
vs Temperature
500
450
V
IN
= 2.7V
V
IN
= 3.6V
R
DS(ON)
(mΩ)
MAIN SWITCH
R
DS(ON)
(mΩ)
400
350
300
250
V
IN
= 2.7V
SYNCHRONOUS SWITCH
V
IN
= 4.2V
200
–40 –25 –10 5 20 35 50 65 80 95 110 125
TEMPERATURE (°C)
3543 G08
Switching Frequency
vs Input Voltage (V
IN
)
2.8
2.7
SWITCHING FREQUENCY (MHz)
SWITCHING FREQUENCY (MHz)
2.6
2.5
2.4
2.3
2.2
2.1
2.0
1.9
1.8
2.5
3.0
4.0
4.5
3.5
INPUT VOLTAGE (V)
5.0
5.5
3543 G10
Switching Frequency
vs Temperature
2.40
2.35
1.54
2.25
2.20
2.15
2.10
2.05
2.00
–40 –25 –10 5 20 35 50 65 80 95 110 125
TEMPERATURE (°C)
3543 G11
Output Voltage vs Load Current
1.56
V
IN
= 3.6V
LOAD CURRENT (mA)
2.30
1.52
1.50
V
IN
= 2.7V
1.48
V
IN
= 3.6V
V
IN
= 4.2V
0
200
600
800
400
OUTPUT VOLTAGE (V)
1000
3543 G12
1.46
612
610
608
FEEDBACK VOLTAGE (mV)
606
604
602
600
598
596
594
592
590
588
Feedback Voltage (V
FB
)
vs Input Voltage (V
IN
)
Feedback Voltage (V
FB
)
vs Temperature
612
610
608
FEEDBACK VOLTAGE (mV)
606
604
602
600
598
596
594
592
590
588
–40 –25 –10 5 20 35 50 65 80 95 110 125
TEMPERATURE (°C)
3543 G14
V
IN
= 3.6V
2.5
3.0
4.5
4.0
3.5
INPUT VOLTAGE (V)
5.0
5.5
3543 G13
3543fa
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LTC3543
TYPICAL PERFORMANCE CHARACTERISTICS
Switch Leakage (I
SW
)
vs Temperature
800
700
LEAKAGE CURRENT (pA)
600
500
SYNCHRONOUS SWITCH
400
300
200
MAIN SWITCH
100
0
–40 –25 –10 5 20 35 50 65 80 95 110 125
TEMPERATURE (°C)
3543 G15
T
A
= 25°C, unless otherwise noted.
Dynamic Supply Current
vs Temperature
400
350
SUPPLY CURRENT (μA)
Dynamic Supply Current
vs Input Voltage (V
IN
)
400
I
LOAD
= 0A
V
OUT
= 1.5V
PULSE SKIP MODE
V
IN
= 5.5V
RUN = 0V
SUPPLY CURRENT (μA)
300
300
250
200
150
100
50
0
–40 –25 –10 5 20 35 50 65 80 95 110 125
TEMPERATURE (°C)
3543 G17
200
100
Burst Mode OPERATION
0
2.5
3.0
3.5
4.0
4.5
INPUT VOLTAGE (V)
5.0
5.5
3543 G16
Switch Leakage (I
SW
)
vs Input Voltage (V
IN
)
1000
900
800
LEAKAGE CURRENT (pA)
700
600
500
400
300
200
100
0
2.5
3.0
4.0
4.5
3.5
INPUT VOLTAGE (V)
5.0
5.5
3543 G18
Start-Up from Shutdown
RUN
5V/DIV
V
OUT
1V/DIV
INDUCTOR
CURRENT
200mA/DIV
200μs/DIV
RUN = 0V
MAIN SWITCH
SYNCHRONOUS SWITCH
V
IN
= 3.6V
V
OUT
= 1.5V
I
LOAD
= 300mA
3543 G19
Pulse Skip Operation
V
OUT
AC COUPLED
50mV/DIV
SW
5V/DIV
I
L
100mA/DIV
V
IN
= 3.6V
V
OUT
= 1.5V
I
LOAD
= 3mA
V
MODE
= 3.6V
10μs/DIV
3543 G20
Burst Mode Operation
V
OUT
AC COUPLED
50mV/DIV
SW
5V/DIV
I
L
100mA/DIV
V
IN
= 3.6V
V
OUT
= 1.5V
I
LOAD
= 3mA
V
MODE
= 0V
10μs/DIV
3543 G21
3543fa
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