LTC3541-1
High Efficiency
Buck + VLDO Regulator
FEATURES
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DESCRIPTION
The
LTC
®
3541-1
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 LTC3541-1’s auto
start-up feature will bring the VLDO/linear regulator output
into regulation in a controlled manner prior to enabling the
Buck regulator output without the need for external pin
control. Buck output prior to VLDO/linear regulator 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.
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 VLDO/Linear Regulator
Output Prior to Buck 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
PDAs/Palmtop PCs
Digital Cameras
Cellular Phones
PC Cards
Wireless and DSL Modems
Other Portable Power Systems
APPLICATIONS
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TYPICAL APPLICATION
LTC3541-1 Typical Application
V
IN
2.9V TO 5.5V
10µF
2.2µH
V
OUT1
2.5V
200mA
10µF
115k
ENBUCK
SW
LV
IN
22pF
243k
LTC3541-1
BUCKFB
PGND
LFB
GND
150k
35411 TA01a
Buck (Burst) Efficiency and Power Loss vs Load Current
100
90
80
EFFICIENCY
0.1
POWER LOSS (W)
1
ENVLDO
MODE
LV
OUT
412k
V
OUT2
1.5V
300mA
2.2µF
EFFICIENCY (%)
V
IN
70
60
50
40
30
20
10
0
1
V
IN
= 3.3V
V
OUT
= 2.5V
10
100
LOAD CURRENT (mA)
POWER LOSS
0.01
0.001
0.0001
1000
35411 TA01b
35411fb
For more information
www.linear.com/LTC3541-1
1
LTC3541-1
ABSOLUTE MAXIMUM RATINGS
(Note 1)
PIN CONFIGURATION
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
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
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-1#PBF
TAPE AND REEL
LTC3541EDD-1#TRPBF
http://www.linear.com/product/LTC3541-1#orderinfo
PART MARKING
LCWQ
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.
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35411fb
For more information
www.linear.com/LTC3541-1
LTC3541-1
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
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
VLDO V
IN
Line Regulation
(Referred to LFB)
Linear Regulator V
IN
Line
Regulation (Referred to LFB)
LV
IN
Line Regulation
(Referred to LFB)
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)
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
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)
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
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
I
S
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
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ELECTRICAL CHARACTERISTICS
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
0.4
LV
IN(LINEREG)
VLDO
DO
V
LOADREG
60
mV
%
l
l
0.25
0.25
0.784
0.782
0.78
0.392
0.391
0.390
0.8
0.8
0.8
0.4
0.4
0.4
85
315
300
55
300
285
50
2.5
0.1
0.5
0.5
0.816
0.818
0.82
0.408
0.409
0.410
%
%
V
V
V
V
V
V
μA
µA
µA
µA
µA
µA
µA
µA
µA
LV
IN
Shutdown Quiescent Current LV
IN
= 3.6V, ENBUCK = 0V, ENVLDO = 0V
35411fb
For more information
www.linear.com/LTC3541-1
3
LTC3541-1
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 LTC3541-1 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 VIN voltage required for VLDO regulator and
linear regulator regulation is:
V
IN
≥ LV
OUT
+ 1.4V and V
IN
≥ 2.7V
Note 5:
TJ 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 LTC3541-1 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 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.
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35411fb
For more information
www.linear.com/LTC3541-1
LTC3541-1
TYPICAL PERFORMANCE 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
35411 G01
Efficiency vs Input Voltage for
Buck (Pulse Skip)
100
95
V
OUT
= 1.8V
I
OUT
= 500mA
Efficiency vs Load Current for
Buck (Burst)
100
90
80
EFFICIENCY (%)
70
60
50
40
30
20
10
V
OUT
= 1.8V
0
1
0.1
10
100
LOAD CURRENT (mA)
V
IN
= 2.7V
V
IN
= 4.2V
V
IN
= 3.6V
V
OUT
= 1.8V
I
OUT
= 500mA
EFFICIENCY (%)
I
OUT
= 100mA
I
OUT
= 30mA
90
85
80
75
70
65
60
55
50
2
3
I
OUT
= 100mA
I
OUT
= 30mA
4
5
INPUT VOLTAGE (V)
6
35411 G02
1000
35411 G03
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
35411 G04
Efficiency vs Load Current for
Buck (Burst)
100
90
V
IN
= 2.7V
V
IN
= 3.6V
V
IN
= 4.2V
100
90
80
EFFICIENCY (%)
70
60
50
40
30
20
V
OUT
= 2.5V
1
10
100
LOAD CURRENT (mA)
1000
35411 G05
Efficiency vs Load Current for
Buck (Pulse Skip)
V
OUT
= 2.5V
V
IN
= 2.7V
V
IN
= 3.6V
V
IN
= 4.2V
V
OUT
= 1.8V
V
IN
= 2.7V
V
IN
= 3.6V
V
IN
= 4.2V
EFFICIENCY (%)
80
70
60
50
40
30
20
10
10
0
0.1
1
10
100
LOAD CURRENT (mA)
1000
35411 G06
0
0.1
VLDO Dropout Voltage vs
Load Current
100
V
OUT
= 1.5V
V
IN
= 3V
BIAS CURRENT (µA)
250
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
V
OUT
2V/DIV
LV
OUT
2V/DIV
V
IN
2V/DIV
Output (Auto Start-Up Sequence,
Buck in Pulse Skip) vs Time
DROPOUT VOLTAGE (mV)
80
V
IN
= 3.6V
V
IN
= 4.2V
60
150
100
40
20
0
50
I
VOUT
= 400mA
I
LVOUT
= 30mA
4ms/DIV
35411 G09
0
50
100
150
200
LOAD CURRENT (mA)
250
300
0
0.1
1
100
LOAD CURRENT (mA)
10
1000
35411 G08
35411 G07
35411fb
For more information
www.linear.com/LTC3541-1
5
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