FEATURES
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LTC3543
600mA Synchronous Step
Down Buck Regulator with PLL,
Soft-Start and Spread Spectrum
DESCRIPTIO
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
®
0peration, 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.
, 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.
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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
APPLICATIO S
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Portable Instruments
Cellular Phones
TYPICAL APPLICATIO
2.5V TO 5.5V
10µF
LTC3543
PWR_EN
MODE
RUN
V
FB
V
IN
SW
Efficiency and Power Loss vs Load Current
3.3µH
100
1.5V
300k
10pF
10µF
EFFICIENCY (%)
V
OUT
1.5V
90
80
70
60
50
40
30
EXPOSED
PAD
MODE = V
IN
→
PULSE SKIP
MODE = V
FB
→
PULSE SKIP WITH SPREAD SPECTRUM
MODE = GND
→
BURST MODE
MODE = EXTERNAL CLOCK
→
PLL
3543 TA01
V
IN
= 2.7V
V
IN
= 4.2V
100
POWER LOSS (mW)
MODE
CAP
GND
4nF
200k
20
10
0
0.1
Burst Mode ENABLED
1
10
100
LOAD CURRENT (mA)
U
U
U
1000
V
IN
= 3.6V
10
POWER LOSS
AT V
IN
= 3.6V
10
0.1
1000
3543 TA01b
3543f
1
LTC3543
ABSOLUTE
(Note 1)
AXI U RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW
RUN
VFB
V
IN
6
5
4
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
7
1
SW
2
CAP
3
MODE
DCB PACKAGE
6-LEAD (2mm
×
3mm) PLASTIC DFN
PIN 7 IS GND
T
JMAX
= 125°C,
θ
JA
= 64°C/W
ORDER PART NUMBER
LTC3543EDCB
DCB PART MARKING
LCCK
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
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
●
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)
●
●
MIN
0.3
0.588
0.7
TYP
1
0.6
1
0.5
MAX
1.5
0.612
1
1.3
0.5
UNITS
V
V
µA
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
●
f
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
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.
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.
3543f
2
U
µA
W
U
U
W W
W
LTC3543
TYPICAL PERFOR A CE CHARACTERISTICS
Efficiency vs Input Voltage (V
IN
)
100
I
OUT
= 200mA
90
EFFICIENCY (%)
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
EFFICIENCY (%)
EFFICIENCY (%)
I
OUT
= 600mA
Power Loss vs Load Current
500
V
OUT
= 1.2V
V
OUT
= 1.5V
V
OUT
= 1.8V
V
OUT
= 2.5V
EFFICIENCY (%)
100
90
80
70
300
60
50
40
30
100
20
10
0
0.1
1
10
100
LOAD CURRENT (mA)
1000
3543 G04
400
POWER LOSS (mW)
EFFICIENCY (%)
200
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
MAIN SWITCH
R
DS(ON)
(mΩ)
V
IN
= 3.6V
R
DS(ON)
(mΩ)
SYNCHRONOUS SWITCH
U W
T
A
= 25°C unless otherwise noted. (From Figure 1a)
Efficiency vs Load Current
100
90
80
70
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
90
80
Burst Mode
ENABLED
V
IN
= 4.2V
Burst Mode
ENABLED
V
IN
= 2.7V
V
IN
= 4.2V
70
60
50
40
30
20
10
0
0.1
V
IN
= 2.7V
V
IN
= 3.6V
V
IN
= 3.6V
V
OUT
= 1.5V
1
10
100
LOAD CURRENT (mA)
1000
3543 G03
Efficiency vs Load Current
Burst Mode
ENABLED
100
90
80
V
IN
= 4.2V
70
60
50
40
30
V
IN
= 2.7V
V
OUT
= 1.8V
1
10
100
LOAD CURRENT (mA)
1000
3543 G05
Efficiency vs Load Current
Burst Mode
ENABLED
V
IN
= 4.2V
V
IN
= 3.6V
V
IN
= 3.6V
20
10
0
0.1
1
V
IN
= 2.7V
V
OUT
= 2.5V
10
100
LOAD CURRENT (mA)
1000
3543 G06
0
0.1
Main Switch Resistance vs
Temperature
500
450
400
350
300
250
200
–40 –25 –10 5 20 35 50 65 80 95 110 125
TEMPERATURE (°C)
3543 G08
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
V
IN
= 2.7V
V
IN
= 2.7V
V
IN
= 4.2V
3543f
3
LTC3543
TYPICAL PERFOR A CE CHARACTERISTICS
T
A
= 25°C unless otherwise noted.
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
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
LOAD CURRENT (mA)
Feedback Voltage (V
FB
)
vs Input Voltage (V
IN
)
612
610
608
FEEDBACK VOLTAGE (mV)
606
604
602
600
598
596
594
592
590
588
2.5
3.0
4.5
4.0
3.5
INPUT VOLTAGE (V)
5.0
5.5
3543 G13
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
LEAKAGE CURRENT (pA)
Dynamic Supply Current
vs Input Voltage (V
IN
)
400
I
LOAD
= 0A
V
OUT
= 1.5V
SUPPLY CURRENT (µA)
PULSE SKIP MODE
400
350
LEAKAGE CURRENT (pA)
SUPPLY CURRENT (µA)
300
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
4
U W
Switching Frequency
vs Temperature
2.40
2.35
1.54
2.30
V
IN
= 3.6V
1.56
Output Voltage vs Load Current
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
Feedback Voltage (V
FB
) vs
Temperature
612
610
608
V
IN
= 3.6V
800
700
600
500
Switch Leakage (I
SW
) vs
Temperature
V
IN
= 5.5V
RUN = 0V
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
Dynamic Supply Current
vs Temperature
1000
900
800
700
600
500
400
300
200
100
0
Switch Leakage (I
SW
) vs Input
Voltage (V
IN
)
RUN = 0V
300
250
200
150
100
50
0
–40 –25 –10 5 20 35 50 65 80 95 110 125
TEMPERATURE (°C)
3543 G17
MAIN SWITCH
SYNCHRONOUS SWITCH
2.5
3.0
4.0
4.5
3.5
INPUT VOLTAGE (V)
5.0
5.5
3543 G18
3543f
LTC3543
TYPICAL PERFOR A CE CHARACTERISTICS
T
A
= 25°C unless otherwise noted.
Startup from Shutdown
RUN
5V/DIV
V
OUT
1V/DIV
INDUCTOR
CURRENT
200mA/DIV
200µs/DIV
V
OUT
AC COUPLED
50mV/DIV
SW
5V/DIV
I
L
100mA/DIV
V
IN
= 3.6V
V
OUT
= 1.5V
I
LOAD
= 300mA
3543 G19
Load Step
V
OUT
AC COUPLED
100mV/DIV
I
L
200mA/DIV
I
LOAD
200mA/DIV
20µs/DIV
V
IN
= 3.6V
V
OUT
= 1.5V
I
LOAD
= 3mA TO 200mA
V
MODE
= 0V
3543 G22
Spread Spectrum Load Step
V
OUT
AC COUPLED
100mV/DIV
I
L
200mA/DIV
I
LOAD
200mA/DIV
V
IN
= 3.6V
V
OUT
= 1.5V
I
LOAD
= 100mA TO 200mA
V
MODE
= 0.6V
10µs/DIV
3543 G25
U W
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
IN
= 3.6V
V
OUT
= 1.5V
I
LOAD
= 3mA
V
MODE
= 0V
10µs/DIV
3543 G21
Load Step
V
OUT
AC COUPLED
200mV/DIV
I
L
200mA/DIV
I
LOAD
200mA/DIV
20µs/DIV
V
IN
= 3.6V
V
OUT
= 1.5V
I
LOAD
= 3mA TO 200mA
V
MODE
= 3.6V
3543 G24
Load Step
V
OUT
AC COUPLED
100mV/DIV
I
L
200mA/DIV
I
LOAD
200mA/DIV
10µs/DIV
V
IN
= 3.6V
V
OUT
= 1.5V
I
LOAD
= 100mA TO 600mA
V
MODE
= 3.6V
3543 G23
PLL Operation
V
C1
200mV/DIV
V
MODE
2V/DIV
PLL Operation at 3MHz
SW
2V/DIV
100µs/DIV
C1 = 4µF
3MHz TO 1MHz STEP
100ns/DIV
3543 G26
3543 G27
3543f
5
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