LTC3542-1
500mA, 2.25MHz
2.8V Output Synchronous
Step-Down DC/DC Converter
FEATURES
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DESCRIPTION
The LTC
®
3542-1 is a high efficiency, fixed output voltage
of 2.8V, monolithic synchronous buck converter using a
constant frequency, current mode architecture. Supply
current during operation is only 26μA, dropping to <1μA in
shutdown. The 2.5V to 5.5V input voltage range makes the
LTC3542-1 ideally suited for single Li-Ion battery-powered
applications. 100% duty cycle provides low dropout opera-
tion, extending battery life in portable systems. Internal
power switches are optimized to provide high efficiency
and eliminate the need for an external Schottky diode.
Switching frequency is internally set at 2.25MHz, allowing
the use of small surface mount inductors and capacitors,
and it can synchronize to an external clock signal with a
frequency range of 1MHz to 3MHz through the MODE/SYNC
pin. The LTC3542-1 is specifically designed to work well
with ceramic output capacitors, achieving very low output
voltage ripple and a small PCB footprint.
The LTC3542-1 can be configured for the power saving
Burst Mode
®
Operation. For reduced noise and RF inter-
ference, the MODE/SYNC pin can be configured for pulse
skipping operation.
L,
LT, LTC, LTM and Burst Mode 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, 5994885.
High Efficiency: Up to 96%
Fixed Output Voltage: 2.8V
High Peak Switch Current: 1000mA
Low Output Ripple (<20mV
P-P
Typical)
Burst Mode Operation
Very Low Quiescent Current: Only 26μA
2.5V to 5.5V Input Voltage Range
2.25MHz Constant Frequency Operation
1MHz to 3MHz External Frequency Synchronization
Low Dropout Operation: 100% Duty Cycle
No Schottky Diode Required
Internal Soft-Start Limits Inrush Current
Shutdown Mode Draws <1μA Supply Current
±2% Output Voltage Accuracy
Current Mode Operation for Excellent Line and Load
Transient Response
Overtemperature Protected
Available in 6-Lead 2mm
×
2mm DFN
APPLICATIONS
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Cellular Telephones
Wireless and DSL Modems
Digital Cameras
MP3 Players
PDAs and Other Handheld Devices
TYPICAL APPLICATION
V
IN
3V TO 5.5V
10μF
2.2μH
V
IN
SW
LTC3542-1
RUN
V
OUT
V
OUT
2.8V
500mA
C
OUT
10μF
CER
35421 TA01a
Efficiency and Power Loss vs Output Current
100
90
80
70
EFFICIENCY (%)
60
50
40
30
20
10
0
0.1
1
V
IN
= 3.6V
V
OUT
= 2.8V
10
100
LOAD CURRENT (mA)
1
10
100
POWER LOSS (mW)
1000
MODE/SYNC
GND
0.1
1000
35421f
35421 TA01b
1
LTC3542-1
ABSOLUTE MAXIMUM RATINGS
(Note 1)
PIN CONFIGURATION
TOP VIEW
V
OUT
1
V
IN
2
GND 3
7
6 RUN
5 MODE/SYNC
4 SW
Input Supply Voltage (V
IN
) ........................... –0.3V to 6V
V
OUT
, RUN Voltages......................................–0.3V to V
IN
MODE Voltage ................................–0.3V to (V
IN
+ 0.3V)
SW Voltage ....................................–0.3V to (V
IN
+ 0.3V)
Operating Temperature Range (Note 2).... –40°C to 85°C
Junction Temperature (Note 7) ............................. 125°C
Storage Temperature Range................... –65°C to 150°C
Reflow Peak Body Temperature ............................ 260°C
DC PACKAGE
6-LEAD (2mm 2mm) PLASTIC DFN
T
JMAX
= 125°C,
θ
JA
= 89°C/W,
θ
JC
= 18°C/W
(SOLDERED TO A 4-LAYER BOARD, NOTE 3)
EXPOSED PAD (PIN 7) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
LTC3542EDC-1#PBF
TAPE AND REEL
LTC3542EDC-1#TRPBF
PART MARKING
LDWC
PACKAGE DESCRIPTION
6-Lead (2mm
×
2mm) 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/
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.
SYMBOL
V
IN
R
VOUT
V
OUT
ΔV
LINE_REG
ΔV
LOAD_REG
I
S
PARAMETER
Operating Voltage Range
Input Resistance of V
OUT
Pin
Output Feedback Voltage (Note 4)
Reference Voltage Line Regulation (Note 4) V
IN
= 2.5V to 5.5V
Output Voltage Load Regulation (Note 4)
Input DC Supply Current (Note 5)
Active Mode
Sleep Mode
Shutdown
Oscillator Frequency
Synchronous Frequency
Peak Switch Current
P-Channel On Resistance (Note 6)
N-Channel On Resistance (Note 6)
Switch Leakage Current
I
LOAD
= 100mA to 500mA
V
OUT
= 2.5V
V
OUT
= 2.9V, MODE = 0V
RUN = 0V
V
OUT
= 2.8V
V
OUT
= 2.8V
V
IN
= 3V, V
OUT
= 2.5V, Duty Cycle < 35%
I
SW
= 100mA
I
SW
= –100mA
V
IN
= 5V, V
RUN
= 0V, V
SW
= 0V or 5V
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ELECTRICAL CHARACTERISTICS
CONDITIONS
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MIN
2.5
504
2.744
TYP
840
2.8
0.04
0.02
300
26
0.1
MAX
5.5
1176
2.856
0.2
0.2
500
35
1
2.7
3
UNITS
V
kΩ
V
%/V
%
μA
μA
μA
MHz
MHz
mA
Ω
Ω
μA
f
OSC
f
SYNC
I
LIM
R
DS(ON)
I
SW(LKG)
1.8
1
650
2.25
1000
0.5
0.35
±0.01
0.65
0.55
±1
35421f
2
LTC3542-1
ELECTRICAL CHARACTERISTICS
SYMBOL
V
UVLO
V
RUN
I
RUN
V
MODE/SYNC
I
MODE/SYNC
PARAMETER
Undervoltage Lockout Threshold
RUN Threshold
RUN Leakage Current
MODE/SYNC Threshold
MODE/SYNC Leakage Current
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
V
IN
Rising
V
IN
Falling
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MIN
1.8
0.3
TYP
2.0
1.9
±0.01
MAX
2.3
1.5
±1
1.2
±1
UNITS
V
V
V
μA
V
μA
0.3
±0.01
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. No pin should exceed 6V.
Note 2:
The LTC3542-1 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:
Failure to solder the Exposed Pad of the package to the PC board
will result in a thermal resistance much higher than 89°C/W.
Note 4:
The converter is tested in a proprietary test mode that connects
the output of the error amplifier to the SW pin, which is connected to an
external servo loop.
Note 5:
Dynamic supply current is higher due to the internal gate charge
being delivered at the switching frequency.
Note 6:
The DFN switch on resistance is guaranteed by correlation to wafer
level measurements.
Note 7:
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
) • (θ
JA
).
35421f
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LTC3542-1
TYPICAL PERFORMANCE CHARACTERISTICS
Burst Mode Operation
T
A
= 25°C unless otherwise specified.
Start-Up from Shutdown
Pulse-Skip Mode Operation
SW
2V/DIV
V
OUT
50mV/DIV
AC COUPLED
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100mA/DIV
V
IN
= 3.6V
2μs/DIV
I
LOAD
= 25mA
FIGURE 3a CIRCUIT
35421 G01
SW
2V/DIV
V
OUT
50mV/DIV
AC COUPLED
I
L
100mA/DIV
RUN
2V/DIV
V
OUT
1V/DIV
I
L
200mA/DIV
V
IN
= 4.2V
I
LOAD
= 0A
400ns/DIV
35421 G02
400μs/DIV
V
IN
= 3.6V
I
LOAD
= 0A
FIGURE 3a CIRCUIT
35421 G03
Start-Up from Shutdown
V
OUT
100mV/DIV
AC COUPLED
I
L
500mA/DIV
Load Step
V
OUT
100mV/DIV
AC COUPLED
I
L
500mA/DIV
Load Step
RUN
2V/DIV
V
OUT
1V/DIV
I
L
200mA/DIV
I
LOAD
500mA/DIV
V
IN
= 3.6V
400μs/DIV
I
LOAD
= 500mA
FIGURE 3a CIRCUIT
35421 G04
I
LOAD
500mA/DIV
V
IN
= 3.6V
20μs/DIV
I
LOAD
= 30mA TO 500mA
FIGURE 3a CIRCUIT
35421 G05
V
IN
= 3.6V
20μs/DIV
I
LOAD
= 0mA TO 500mA
FIGURE 3a CIRCUIT
35421 G06
Reference Voltage
vs Temperature
2.85
V
IN
= 3.6V
PULSE-SKIP MODE
NO LOAD
FREQUENCY (MHz)
2.7
2.6
2.5
Oscillator Frequency
vs Temperature
2.7
2.6
2.5
FREQUENCY (MHz)
2.4
2.3
2.2
2.1
2.0
1.9
1.8
90 110
35421 G08
Oscillator Frequency
vs Supply Voltage
2.83
2.4
2.3
2.2
2.1
2.0
1.9
V
OUT
(V)
2.81
2.79
2.77
2.75
–50
–25
50
25
0
75
TEMPERATURE (°C)
100
125
1.8
–50 –30 –10 10 30 50 70
TEMPERATURE (°C)
2
3
5
4
SUPPLY VOLTAGE (V)
6
35421 G09
LTC1520 G01
35421f
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LTC3542-1
TYPICAL PERFORMANCE CHARACTERISTICS
Output Voltage vs Supply Voltage
1.0
0.8
0.6
V
OUT
ERROR (%)
0.4
0.2
0
V
T
A
= 25°C unless otherwise specified.
R
DS(ON)
vs Input Voltage
0.9
0.8
0.7
0.6
R
DS(ON)
(Ω)
MAIN SWITCH
0.5
0.4
0.3
0.2
0.1
0
SYNCHRONOUS
SWITCH
Output Voltage vs Load Current
–0.2
–0.4
–0.6
–0.8
–1.0
2
3
4
5
INPUT VOLTAGE (V)
6
35421 G10
1
2
3
4
V
IN
(V)
5
6
7
35421 G12
R
DS(ON)
vs Temperature
1000
900
LEAKAGE CURRENT (pA)
800
700
600
500
400
300
200
100
0
Switch Leakage vs Input Voltage
300
250
SWITCH LEAKAGE (nA)
200
150
100
50
Switch Leakage vs Temperature
MAIN SWITCH
SYNCHRONOUS
SWITCH
MAIN SWITCH
SYNCHRONOUS SWITCH
50
25
75
0
TEMPERATURE (°C)
100
125
0
1
2
3
V
IN
(V)
4
5
6
35421 G14
0
–50 –25
35421 G15
Efficiency vs Input Voltage
Efficiency vs Load Current
Efficiency vs Load Current
35421f
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