LTC3541-2
High Efficiency
Buck + VLDO Regulator
FEATURES
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DESCRIPTION
The
LTC
®
3541-2
combines a synchronous buck DC/
DC converter with a very low dropout linear regulator
(VLDO
TM
regulator) and internal feedback resistor networks
to provide two output voltages from a single input volt-
age with minimal external components. When configured
for dual output operation, the LTC3541-2’s auto start-up
feature will bring the 1.875V buck output into regulation
in a controlled manner, prior to enabling the 1.5V VLDO
output without the need for external pin control. The 1.5V
VLDO/linear regulator output prior to 1.875V buck output
sequencing may also be obtained via external pin control.
The input voltage range is ideally suited for Li-Ion battery
applications powering sub-3.3V logic from 5V or 3.3V rails.
The synchronous buck converter provides a high efficiency
output, typically 90%. It can provide up to 500mA of output
current while switching at 2.25MHz, allowing the use of
small surface mount inductors and capacitors. A mode-
select pin allows Burst Mode operation to be enabled for
higher efficiency at light load currents, or disabled for lower
noise, constant frequency operation.
The VLDO regulator provides a low noise, low voltage
output capable of providing up to 300mA of output current
using only a 2.2µF ceramic capacitor. The input supply
voltage of the VLDO regulator (LV
IN
) may come from the
buck regulator output or a separate supply.
L,
LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and VLDO is a
trademark of Linear Technology Corporation. All other trademarks are the property of their respective
owners. Protected by U.S. Patents, including 5481178, 6611131, 6304066, 6498466, 6580258.
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High Efficiency, 500mA Buck Plus 300mA VLDO
Regulator
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Auto Start-Up Powers Buck Output Prior to VLDO/
Linear Regulator Output
Independent 500mA High Efficiency Buck
(V
IN
: 2.7V to 5.5V)
300mA VLDO Regulator with 30mA Standalone Mode
No External Schottky Diodes Required
Fixed Buck Output Voltage: 1.875V
VLDO Input Voltage Range (LV
IN
: 1.6V to 5.5V)
Fixed VLDO Output Voltage: 1.5V
Selectable Fixed Frequency, Pulse-Skip Operation
or Burst Mode
®
Operation
Short-Circuit Protected
Current Mode Operation for Excellent Line and Load
Transient Response
Shutdown Current: <3µA
Constant Frequency Operation: 2.25MHz
Low Dropout Buck Operation: 100% Duty Cycle
Small, Thermally Enhanced, 10-Lead (3mm × 3mm)
DFN Package
APPLICATIONS
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Digital Cameras
Cellular Phones
PC Cards
Wireless and DSL Modems
Other Portable Power Systems
TYPICAL APPLICATION
V
IN
2.9V TO 5.5V
10µF
2.2µH
ENBUCK
SW
V
IN
V
OUT1
1.875V
200mA
ENVLDO
EFFICIENCY (%)
Buck (Burst) Efficiency vs Load Current
100
90
80
70
60
50
40
30
20
10
35412 TA01a
V
IN
= 3V
EFFICIENCY
1
0.1
POWER LOSS (W)
MODE
LTC3541-2
V
OUT2
1.5V
300mA
POWER LOSS
V
OUT
LV
IN
10µF
PGND
LV
OUT
GND
2.2µF
0.01
0.001
0
1
10
100
LOAD CURRENT (mA)
0.0001
1000
35412 TA01b
35412fc
For more information
www.linear.com/LTC3541-2
1
LTC3541-2
ABSOLUTE MAXIMUM RATINGS
(Note 1)
PIN CONFIGURATION
TOP VIEW
V
IN
ENBUCK
V
OUT
NC
LV
OUT
1
2
3
4
5
11
10 SW
9 ENVLDO
8 MODE
7 GND
6 LV
IN
Supply Voltages:
V
IN
, LV
IN
.................................................. –0.3V to 6V
LV
IN
– V
IN
..........................................................<0.3V
Pin Voltages:
ENVLDO, ENBUCK, MODE, SW ..... –0.3V to V
IN
+ 0.3V
Linear Regulator I
OUT(MAX)
(100ms) (Note 9) ......100mA
Operating Ambient Temperature Range
(Note 2) ....................................................–40°C to 85°C
Junction Temperature (Notes 5, 10) ...................... 125°C
Storage Temperature Range .................. –65°C to 125°C
DD PACKAGE
10-LEAD (3mm × 3mm) PLASTIC DFN
T
JMAX
= 125°C,
θ
JA
= 43°C/W
EXPOSED PAD (PIN 11) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
LTC3541EDD-2#PBF
TAPE AND REEL
LTC3541EDD-2#TRPBF
http://www.linear.com/product/LTC3541-2#orderinfo
PART MARKING
LCHQ
PACKAGE DESCRIPTION
10-Lead (3mm × 3mm) Plastic DFN
TEMPERATURE RANGE
–40°C to 85°C
Consult LTC Marketing for parts specified with wider operating temperature ranges.
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/.
Some packages are available in 500 unit reels through
designated sales channels with #TRMPBF suffix.
2
35412fc
For more information
www.linear.com/LTC3541-2
LTC3541-2
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 specified (Note 2)
SYMBOL
I
PK
V
IN
V
IN(LINEREG)
PARAMETER
Peak Inductor Current
Input Voltage Range
Buck V
IN
Line Regulation
CONDITIONS
V
IN
= 4.2V (Note 8)
(Note 4)
l
l
ELECTRICAL CHARACTERISTICS
MIN
0.8
2.7
TYP
0.95
0.04
2.2
2.2
0.8
20
0.5
MAX
1.25
5.5
0.4
UNITS
A
V
%/V
mV/V
mV/V
mV/V
LV
IN(LINEREG)
VLDO
DO
V
LOADREG
V
IN
= 2.7V to 5.5V, ENBUCK = V
IN
,
ENVLDO = 0V, MODE = V
IN
(Note 6)
VLDO V
IN
Line Regulation
V
IN
= 2.9V to 5.5V, LV
OUT
= 1.5V, ENBUCK = V
IN
,
(Referred to LV
OUT
)
ENVLDO = V
IN
, MODE = 0V, I
OUT(VLDO)
= 100mA
Linear Regulator V
IN
Line
V
IN
= 2.9V to 5.5V, LV
OUT
= 1.5V, ENBUCK = 0V,
Regulation (Referred to LV
OUT
) ENVLDO = V
IN
, I
OUT(LDO)
= 10mA
LV
IN
Line Regulation
LV
IN
= 1.6V to 5.5V, V
IN
= 5.5V, LV
OUT
= 1.5V,
(Referred to LV
OUT
)
ENBUCK = V
IN
, ENVLDO = V
IN
, MODE = V
IN
,
I
OUT(VLDO)
= 100mA
LV
IN
– LV
OUT
Dropout Voltage LV
OUT
= 1.5V, ENBUCK = V
IN
, ENVLDO = V
IN
,
MODE = V
IN
, I
OUT(VLDO)
= 50mA (Note 9)
Buck Output Load Regulation
ENBUCK = V
IN
, ENVLDO = 0V, MODE = V
IN
(Note 6)
VLDO Output Load Regulation
Linear Regulator Output Load
Regulation
Reference Regulation Voltage
(Note 6)
Reference Regulation Voltage
(Note 7)
Buck + VLDO
Burst Mode Sleep
V
IN
Quiescent Current
Buck + VLDO
Burst Mode Active
V
IN
Quiescent Current
Buck + VLDO
Pulse-Skip Mode Active
V
IN
Quiescent Current
Buck
Burst Mode Sleep
V
IN
Quiescent Current
Buck
Burst Mode Active
V
IN
Quiescent Current
Buck
Pulse-Skip Mode Active
V
IN
Quiescent Current
Linear Regulator V
IN
Quiescent
Current
V
IN
Shutdown Quiescent
Current
LV
IN
Shutdown Quiescent
Current
I
OUT(VLDO)
= 1mA – 300mA, LV
IN
= 1.875V, LV
OUT
=
1.5V, ENBUCK = V
IN
, ENVLDO = V
IN
, MODE = V
IN
I
OUT(LDO)
= 1mA – 30mA, LV
OUT
= 1.5V,
ENBUCK = 0V, ENVLDO = V
IN
ENBUCK = V
IN
, ENVLDO = 0V, T
A
= 25°C
ENBUCK = V
IN
, ENVLDO = 0V, 0°C ≤ T
A
≤ 85°C
ENBUCK = V
IN
, ENVLDO = 0V, –40°C ≤ T
A
≤ 85°C
50
mV
%
l
l
0.25
0.25
1.837
1.833
1.875
1.875
1.875
1.5
1.5
1.5
85
315
300
55
300
285
50
2.5
0.1
0.5
0.5
1.913
1.917
1.922
1.53
1.534
1.538
%
%
V
V
V
V
V
V
μA
μA
μA
μA
μA
μA
μA
μA
μA
V
VOUT
l
1.828
1.47
1.466
V
LVOUT
ENBUCK = 0V, ENVLDO = V
IN
, T
A
= 25°C
ENBUCK = 0V, ENVLDO = V
IN
, 0°C ≤ T
A
≤ 85°C
ENBUCK = 0V, ENVLDO = V
IN
, –40°C ≤ T
A
≤ 85°C
l
1.462
I
S
LV
IN
= 1.875V, LV
OUT
= 1.5V, ENBUCK = V
IN
,
ENVLDO = V
IN
, MODE = 0V, I
OUT(VLDO)
= 10μA,
V
VOUT
= 2.11V
LV
IN
= 1.875V, LV
OUT
= 1.5V, ENBUCK = V
IN
,
ENVLDO = V
IN
, MODE = 0V, I
OUT(VLDO)
= 10μA,
V
VOUT
= 1.64V
LV
IN
= 1.875V, LV
OUT
= 1.5V, ENBUCK = V
IN
,
ENVLDO = V
IN
, MODE = V
IN
, I
OUT(VLDO)
= 10μA,
V
VOUT
= 1.64V
V
VOUT
= 2.11V, I
OUT(BUCK)
= 0A, ENBUCK = V
IN
,
ENVLDO = 0V, MODE = 0V
V
VOUT
= 1.64V, I
OUT(BUCK)
= 0A, ENBUCK = V
IN
,
ENVLDO = 0V, MODE = 0V
V
VOUT
= 1.64V, I
OUT(BUCK)
= 0A, ENBUCK = V
IN
,
ENVLDO = 0V, MODE = V
IN
LV
OUT
= 1.5V, ENBUCK = 0V, ENVLDO = V
IN
,
I
OUT(VLDO)
= 10μA
ENBUCK = 0V, ENVLDO = 0V
LV
IN
= 3.6V, ENBUCK = 0V, ENVLDO = 0V
35412fc
For more information
www.linear.com/LTC3541-2
3
LTC3541-2
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 specified (Note 2)
SYMBOL
f
OSC
R
PFET
R
NFET
I
LSW
V
IH
V
IL
I
MODE
,
I
ENBUCK
,
I
ENVLDO
PARAMETER
Oscillator Frequency
R
DS(ON)
of P-Channel MOSFET
R
DS(ON)
of N-Channel MOSFET
SW Leakage
Input Pin High Threshold
Input Pin Low Threshold
Input Pin Current
CONDITIONS
l
ELECTRICAL CHARACTERISTICS
MIN
1.8
TYP
2.25
0.25
0.35
±0.01
MAX
2.7
UNITS
MHz
Ω
Ω
I
SW
= 100mA
I
SW
= –100mA
Enable = 0V, V
SW
= 0V or 6V, V
IN
= 6V
MODE, ENBUCK, ENVLDO
MODE, ENBUCK, ENVLDO
l
l
l
±1
0.3
μA
V
V
μA
0.9
±0.01
±1
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 LTC3541-2 is guaranteed to meet performance specifications
from 0°C to 85°C. VLDO/linear regulator output is tested and specified
under pulse load conditions such that T
J
≈ T
A
, and are 100% production
tested at 25°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:
Minimum operating LV
IN
voltage required for VLDO regulation is:
LV
IN
≥ LV
OUT
+ V
DROPOUT
.
Note 4:
Minimum operating VIN voltage required for VLDO and linear
regulator regulation is:
V
IN
≥ LV
OUT
+ 1.4V.
Note 5:
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
• 43°C/W)
Note 6:
The LTC3541-2 is tested in a proprietary test mode that connects
VBUCKFB to the output of the error amplifier. For the reference regulation
and line regulation tests, the output of the error amplifier is set to the
midpoint. For the load regulation test, the output of the error amplifier is
driven to the minimum and maximum of the signal range.
Note 7:
Measurement made in closed loop linear regulator configuration
with LV
OUT
= 1.5V, I
LOAD
= 10µA.
Note 8:
Measurement made in a proprietary test mode with slope
compensation disabled.
Note 9:
Measurement is assured by design, characterization and statistical
process control.
Note 10:
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.
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35412fc
For more information
www.linear.com/LTC3541-2
LTC3541-2
TYPICAL PERFORMANCE CHARACTERISTICS
Efficiency vs Input Voltage for
Buck (Pulse Skip)
95
90
85
EFFICIENCY (%)
I
OUT
= 100mA
EFFICIENCY (%)
80
75
70
65
60
55
50
2
3
4
INPUT VOLTAGE (V)
35412 G01
Efficiency vs Input Voltage for
Buck (Burst)
100
100
90
I
OUT
= 500mA
EFFICIENCY (%)
80
70
60
50
40
30
20
10
2
3
4
5
INPUT VOLTAGE (V)
6
35412 G02
Efficiency vs Load Current for
Buck (Pulse Skip)
V
IN
= 2.7V
V
IN
= 3.6V
V
IN
= 4.2V
I
OUT
= 500mA
95
90
85
80
75
70
65
60
55
I
OUT
= 100mA
I
OUT
= 30mA
I
OUT
= 30mA
5
6
50
0
0.1
1
10
100
LOAD CURRENT (mA)
1000
35412 G03
100
90
80
EFFICIENCY (%)
70
60
50
40
Efficiency vs Load Current for
Buck (Burst)
V
IN
= 3.6V
V
IN
= 2.7V
V
IN
= 4.2V
100
VLDO Dropout Voltage
vs Load Current
250
V
IN
= 3V
BIAS CURRENT ( A)
V
IN
= 3.6V
200
Buck (Burst) Plus VLDO Bias
Current vs VLDO Load Current
V
IN
= 3.6V
I
LOAD_BUCK
= 0
I
BIAS
= I
VIN
+ I
LVIN
– I
LOAD
DROPOUT VOLTAGE (mV)
80
60
V
IN
= 4.2V
40
150
100
30
20
10
0
0.1
1
10
100
LOAD CURRENT (mA)
1000
35412 G04
20
0
50
0
50
100
150
200
LOAD CURRENT (mA)
250
300
0
0.1
1
100
LOAD CURRENT (mA)
10
1000
35412 G06
35412 G05
Output (Auto Start-Up Sequence,
Buck in Pulse Skip) vs Time
2.50
2.45
V
OUT
1V/DIV
LV
OUT
1V/DIV
V
IN
2V/DIV
2.40
FREQUENCY (MHz)
2.35
2.30
2.25
2.20
2.15
2.10
I
VOUT
= 200mA
I
LVOUT
= 300mA
2ms/DIV
35412 G07
Oscillator Frequency
vs Temperature
V
IN
= 3.6V
2.05
2.00
–50 –25
50
25
0
75
TEMPERATURE (°C)
100
125
35412 G08
35412fc
For more information
www.linear.com/LTC3541-2
5
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