LTC3541
High Efficiency
Buck + VLDO Regulator
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High Efficiency, 500mA Buck Plus 300mA VLDO
TM
Regulator
Auto Start-Up Powers Buck Output Prior to
VLDO/Linear Regulator Output
Independent High Efficiency, 500mA Buck
(V
IN
: 2.7V to 5.5V)
300mA VLDO Regulator with 30mA Standalone Mode
No External Schottky Diodes Required
Buck Output Voltage Range: 0.8V to 5V
VLDO Input Voltage Range (LV
IN
): 0.9V to 5.5V
VLDO Output Voltage Range VLDO: 0.4V to 4.1V
Selectable Fixed Frequency, Pulse-Skip Operation or
Burst Mode
®
Operation
Short-Circuit Protected
Current Mode Operation for Excellent Line and Load
Transient Response
Constant Frequency Operation: 2.25MHz
Low Dropout Buck Operation: 100% Duty Cycle
Small, Thermally Enhanced, 10-Lead (3mm × 3mm)
DFN Package
The LTC
®
3541 combines a synchronous buck DC/DC
converter with a very low dropout linear regulator
(VLDO) to provide up to two output voltages from a single
input voltage with minimal external components. When
configured for dual output operation, the LTC3541’s auto
start-up feature will bring the Buck output into regulation
in a controlled manner prior to enabling the VLDO regulator
output without the need for external pin control. VLDO/
linear regulator output prior to Buck output sequencing
may also be obtained via external pin control. The input
voltage range is ideally suited for Li-Ion battery-powered
applications, as well as powering sub-3.3V logic from 5V
or 3.3V rails.
The synchronous buck converter provides a high efficiency
output, typically 90%, capable of providing up to 500mA
of continuous output current while switching at 2.25MHz,
allowing the use of small surface mount inductors and ca-
pacitors. 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 continuous
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 or a separate supply.
, LT, LTc and LTM are registered trademarks of Linear Technology corporation.
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
APPLICATIO S
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PDAs/Palmtop PCs
Digital Cameras
Cellular Phones
PC Cards
Wireless and DSL Modems
Other Portable Power Systems
LTC3541 Typical Application
V
IN
2.9V TO 5.5V
EFFICIENCY (%)
SW
2.2µH
243k
V
OUT1
2.5V
200mA
22pF
V
IN
ENVLDO
150k
MODE
LTC3541
ENBUCK
GND
BUCKFB
LV
IN
LFB
LV
OUT
PGND
10µF
115k
U
TYPICAL APPLICATIO
Buck (Burst) Efficiency and Power Loss vs Load Current
100
90
80
70
60
50
40
30
20
V
OUT2
1.5V
300mA
412k
10
0
1
V
IN
= 3.3V
V
OUT
= 2.5V
10
100
LOAD CURRENT (mA)
2.2µF
3541 TA01a
U
1
EFFICIENCY
0.1
POWER LOSS (W)
POWER LOSS
0.01
0.001
0.0001
1000
3541 TA01b
FEATURES
DESCRIPTIO
U
3541fa
LTC3541
(Note 1)
Supply Voltages:
V
IN
, LV
IN
.................................................. –0.3V to 6V
LV
IN
– V
IN
..........................................................<0.3V
Pin Voltages:
ENVLDO, ENBUCK, MODE, SW,
LFB, BUCKFB .............................–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 (Note 5) ............................. 125°C
Storage Temperature Range .................. –65°C to 125°C
.
TOP VIEW
V
IN
ENBUcK
BUcKFB
LFB
LV
OUT
1
2
3
4
5
11
10 SW
9 ENVLDO
8 MODE
7 GND
6 LV
IN
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 PART NUMBER
LTC3541EDD
DD PART MARKING
LCBS
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
I
PK
I
BUCKFB
I
LFB
V
IN
V
IN(LINEREG)
PARAMETER
Peak Inductor Current
BUCKFB Pin Input Current
LFB Pin Input Current
Input Voltage Range
Buck V
IN
Line Regulation
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 specified (Note 2)
CONDITIONS
V
IN
= 4.2V (Note 8)
V
BUCKFB
= 0.9V
V
LFB
= 0.45V
(Note 4)
V
IN
= 2.7V to 5.5V, ENBUCK = V
IN
,
ENVLDO = 0V, MODE = V
IN
(Note 6)
V
IN
= 2.7V to 5.5V, LV
OUT
= 1.2V, ENBUCK = V
IN
,
ENVLDO = V
IN
, I
OUT(VLDO)
= 100mA, LV
IN
= 1.5V
V
IN
= 2.7V to 5.5V, LV
OUT
= 1.2V, ENBUCK = 0V,
ENVLDO = V
IN
, I
OUT(LREG)
= 10mA
LV
IN
= 0.9V to 5.5V, V
IN
= 5.5V, LV
OUT
= 0.4V,
ENBUCK = V
IN
, ENVLDO = V
IN
, MODE = V
IN
,
I
OUT(VLDO)
= 100mA
LV
IN
= 1.5V, ENBUCK = V
IN
, ENVLDO = V
IN
,
MODE = V
IN
, I
OUT(VLDO)
= 50mA, V
LFB
= 0.3V
ENBUCK = V
IN
, ENVLDO = 0V, MODE = V
IN
(Note 6)
●
●
●
●
MIN
0.8
–200
2.7
TYP
0.95
–40
MAX
1.25
±50
5.5
UNITS
A
nA
nA
V
%/V
mV/V
mV/V
mV/V
0.04
0.6
0.6
0.3
28
0.5
0.25
0.25
0.784
0.782
0.78
0.392
0.391
0.8
0.8
0.8
0.4
0.4
0.4
0.4
VLDO V
IN
Line Regulation
(Referred to LFB)
Linear Regulator V
IN
Line
Regulation (Referred to LFB)
LV
IN(LINEREG)
LV
IN
Line Regulation
(Referred to LFB)
VLDO
DO
V
LOADREG
LV
IN
– LV
OUT
Dropout Voltage
(Note 9)
Buck Output Load Regulation
VLDO Output Load Regulation
Linear Regulator Output Load
V
BUCKFB
Reference Regulation Voltage
(Note 6)
Reference Regulation Voltage
(Note 7)
60
I
OUT(VLDO)
= 1mA – 300mA, LV
IN
= 1.5V, LV
OUT
= 1.2V,
●
ENBUCK = V
IN
, ENVLDO = V
IN
, MODE = V
IN
●
I
OUT(LREG)
= 1mA – 30mA, LV
OUT
= 1.2V,
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
●
0.5
0.5
0.816
0.818
0.82
0.408
0.409
0.410
V
LFB
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
●
0.390
3541fa
U
mV
%
%
%
V
V
V
V
V
V
W
U
U
W W
W
ABSOLUTE
AXI U RATI GS
PACKAGE/ORDER I FOR ATIO
LTC3541
ELECTRICAL CHARACTERISTICS
SYMBOL
I
S
PARAMETER
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
Quiscent Current
Buck
Pulse-Skip Mode Active
V
IN
Quiescent Current
Linear Regulator V
IN
Quiescent
Current
V
IN
Shutdown Quiescent Current
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 specified (Note 2)
CONDITIONS
LV
IN
= 1.5V, LV
OUT
= 1.2V, ENBUCK = V
IN
,
ENVLDO = V
IN
, MODE = 0V, I
OUT(VLDO)
= 10µA,
V
BUCKFB
= 0.9V
LV
IN
= 1.5V, LV
OUT
= 1.2V, ENBUCK = V
IN
,
ENVLDO = V
IN
, MODE = 0V, I
OUT(VLDO)
= 10µA,
V
BUCKFB
= 0.7V
LV
IN
= 1.5V, LV
OUT
= 1.2V, ENBUCK = V
IN
,
ENVLDO = V
IN
, MODE = V
IN
, I
OUT(VLDO)
= 10µA,
V
BUCKFB
= 0.7V
V
BUCKFB
= 0.9V, I
OUT(BUCK)
= 0A, ENBUCK = V
IN
,
ENVLDO = 0V, MODE = 0V
V
BUCKFB
= 0.7V, I
OUT(BUCK)
= 0A, ENBUCK = V
IN
,
ENVLDO = 0V, MODE = 0V
V
BUCKFB
= 0.7V, I
OUT(BUCK)
= 0A, ENBUCK = V
IN
,
ENVLDO = 0V, MODE = V
IN
LV
OUT
= 1.2V, ENBUCK = 0V, ENVLDO = V
IN
,
I
OUT(LREG)
= 10µA
ENBUCK = 0V, ENVLDO = 0V
●
MIN
TYP
85
315
300
55
300
285
50
2.5
0.1
MAX
UNITS
µA
µA
µA
µA
µA
µA
µA
µA
µA
f
OSC
R
PFET
R
NFET
I
LSW
V
IH
V
IL
I
MODE
,
I
ENBUCK
,
I
ENVLDO
LV
IN
Shutdown Quiescent Current LV
IN
= 3.6V, ENBUCK = 0V, ENVLDO = 0V
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
I
SW
= 100mA
I
SW
= 100mA
Enable = 0V, V
SW
= 0V or 6V, V
IN
= 6V
MODE, ENBUCK, ENVLDO
MODE, ENBUCK, ENVLDO
1.8
2.25
0.25
0.35
±0.01
2.7
MHz
Ω
Ω
±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 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 regulator
regulation is:
LV
IN
≥ LV
OUT
+ V
DROPOUT
and LV
IN
≥ 0.9V
Note 4: Minimum operating V
IN
voltage required for VLDO regulator and
linear regulator regulation is:
V
IN
≥ LV
OUT
+ 1.4V and V
IN
≥ 2.7V
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 is tested in a proprietary test mode that connects
V
BUCKFB
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 minimum and maximum of the signal range.
Note 7: Measurement made in closed loop linear regulator configuration
with LV
OUT
= 1.2V, 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.
3541fa
LTC3541
TYPICAL PERFOR A CE CHARACTERISTICS
Efficiency vs Input Voltage for
Buck (Burst)
100
95
90
EFFICIENCY (%)
85
80
75
70
65
60
55
50
2
3
4
5
INPUT VOLTAGE (V)
6
3541 G01
V
OUT
= 1.8V
I
OUT
= 500mA
EFFICIENCY (%)
I
OUT
= 100mA
I
OUT
= 30mA
80
75
70
65
60
55
50
2
3
4
5
INPUT VOLTAGE (V)
6
3541 G02
EFFICIENCY (%)
Efficiency vs Load Current for
Buck (Pulse Skip)
100
90
80
EFFICIENCY (%)
70
60
50
40
30
20
10
0
0.1
1
10
100
LOAD CURRENT (mA)
1000
3541 G04
V
OUT
= 1.8V
V
IN
= 2.7V
V
IN
= 3.6V
V
IN
= 4.2V
EFFIcIENcY (%)
60
50
40
30
20
10
V
OUT
= 2.5V
1
10
100
LOAD cURRENT (mA)
1000
3541 G05
EFFICIENCY (%)
VLDO Dropout Voltage vs
Load Current
100
V
OUT
= 1.5V
V
IN
= 3V
BIAS CURRENT (µA)
V
IN
= 3.6V
V
IN
= 4.2V
250
200
DROPOUT VOLTAGE (mV)
80
60
40
20
0
0
50
100
150
200
LOAD CURRENT (mA)
U W
250
3541 G07
Efficiency vs Input Voltage for
Buck (Pulse Skip)
100
95
90
85
V
OUT
= 1.8V
I
OUT
= 500mA
100
90
80
70
60
50
40
30
20
10
Efficiency vs Load Current for
Buck (Burst)
V
IN
= 2.7V
V
IN
= 4.2V
V
IN
= 3.6V
I
OUT
= 100mA
I
OUT
= 30mA
V
OUT
= 1.8V
0
0.1
1
10
100
LOAD CURRENT (mA)
1000
3541 G03
Efficiency vs Load Current for
Buck (Burst)
100
90
80
70
V
IN
= 2.7V
V
IN
= 3.6V
V
IN
= 4.2V
100
90
80
70
60
50
40
30
20
10
Efficiency vs Load Current for
Buck (Pulse Skip)
V
OUT
= 2.5V
V
IN
= 2.7V
V
IN
= 3.6V
V
IN
= 4.2V
0
0.1
0
0.1
1
10
100
LOAD CURRENT (mA)
1000
3541 G06
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
Output (Auto Start-Up Sequence,
Buck in Pulse Skip) vs Time
V
OUT
2V/DIV
LV
OUT
2V/DIV
V
IN
2V/DIV
150
100
50
I
VOUT
= 300mA
I
LVOUT
= 200mA
1
100
LOAD CURRENT (mA)
10
1000
3541 G08
2ms/DIV
3541 G09
300
0
0.1
3541fa
LTC3541
TYPICAL PERFOR A CE CHARACTERISTICS
Oscillator Frequency
vs Temperature
2.50
2.45
2.40
FREQUENCY (MHz)
FREQUENCY (MHz)
2.35
2.30
2.25
2.20
2.15
2.10
2.05
2.00
–50 –25
50
25
0
75
TEMPERATURE (°C)
100
125
2.0
3
5
4
SUPPLY VOLTAGE (V)
6
3541 G11
V
IN
= 3.6V
REFERENCE (V)
Buck Reference vs Temperature
0.820
0.816
0.812
REFERENCE (V)
0.808
0.804
0.800
0.796
0.792
0.788
0.784
0.780
–50 –25
50
25
0
75
TEMPERATURE (°C)
100
125
V
IN
= 3.6V
0.700
0.600
0.500
R
DS(ON)
(Ω)
0.400
0.300
0.200
0.100
Buck (Pulse Skip) Load Step from
1mA to 500mA
V
OUT
100mV/DIV
AC COUPLED
I
L
500mA/DIV
I
LOAD
500mA/DIV
40µs/DIV
V
IN
= 3.6V
V
OUT
= 1.8V
I
LOAD
= 1mA TO 500mA
3541 G16
U W
3541 G10
Oscillator Frequency
vs Supply Voltage
2.5
V
IN
= 3.6V
0.410
0.408
0.406
0.404
0.402
0.400
0.398
0.396
0.394
0.392
VLDO/Linear Regulator Reference
vs Temperature
V
IN
= 3.6V
2.4
2.3
2.2
2.1
0.390
–50 –25
50
25
0
75
TEMPERATURE (°C)
100
125
5341 G12
R
DS(ON)
vs Temperature
LV
OUT
10mV/DIV
AC COUPLED
V
OUT
10mV/DIV
AC COUPLED
Buck (Burst) and VLDO Output
SYNCH SWITCH
MAIN SWITCH
0
–50 –25
V
IN
= 2.5V
V
IN
= 3.6V
V
IN
= 5.5V
100
125
50
25
75
0
TEMPERATURE (°C)
2µs/DIV
V
IN
= 3.6V
LV
OUT
= 1.5V
V
OUT
= 1.8V
I
LOAD
= 50mA
Burst Mode OPERATION
3541 G15
5341 G13
3541 G14
Buck (Burst) Load Step from
1mA to 500mA
V
OUT
100mV/DIV
AC COUPLED
I
L
500mA/DIV
I
LOAD
500mA/DIV
40µs/DIV
V
IN
= 3.6V
V
OUT
= 1.8V
I
LOAD
= 1mA TO 500mA
3541 G17
VLDO Load Step from
1mA to 500mA
LV
OUT
20mV/DIV
AC COUPLED
I
LOAD
250mA/DIV
400µs/DIV
V
IN
= 3.6V
LV
OUT
= 1.5V
I
LOAD
= 1mA TO 300mA
3541 G18
3541fa
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