LTC3541-1
High Efficiency
Buck + VLDO Regulator
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High Efficiency, 500mA Buck Plus 300mA VLDO
TM
Regulator
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
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.
, LT, LTc, LTM and Burst Mode 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
LTC3541-1 Typical Application
V
IN
2.9V TO 5.5V
EFFICIENCY (%)
V
IN
V
OUT1
2.5V
200mA
22pF
243k
2.2µH
ENBUCK MODE
LTC3541-1
SW
GND
LV
IN
LFB
BUCKFB LV
OUT
PGND
10µF
115k
U
TYPICAL APPLICATIO
Buck (Burst) Efficiency and Power Loss vs Load Current
100
90
80
EFFICIENCY
0.1
POWER LOSS (W)
1
ENVLDO
150k
70
60
50
40
30
20
10
0
1
V
IN
= 3.3V
V
OUT
= 2.5V
10
100
LOAD CURRENT (mA)
POWER LOSS
412k
V
OUT2
1.5V
300mA
2.2µF
35411 TA01a
U
0.01
0.001
0.0001
1000
35411 TA01b
FEATURES
DESCRIPTIO
U
35411fa
LTC3541-1
(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
.
ORdeR INFORmATION
LEAD FREE FINISH
LTC3541EDD-1#PBF
TAPE AND REEL
LTC3541EDD-1#TRPBF
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.
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/
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)
●
●
●
●
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
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
U
W W
W
ABSOLUTE
AXI U RATI GS
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
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
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
0.4
60
mV
%
0.5
0.5
%
%
35411fa
LTC3541-1
ELECTRICAL CHARACTERISTICS
SYMBOL
V
BUCKFB
PARAMETER
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
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
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
●
●
●
MIN
0.784
0.782
0.78
0.392
0.391
0.390
TYP
0.8
0.8
0.8
0.4
0.4
0.4
85
315
300
55
300
285
50
2.5
0.1
MAX
0.816
0.818
0.82
0.408
0.409
0.410
UNITS
V
V
V
V
V
V
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 LTC3541-1 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 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 LTC3541-1 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.
35411fa
LTC3541-1
ELECTRICAL CHARACTERISTICS
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.
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
35411 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
35411 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
35411 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
35411 G05
EFFICIENCY (%)
U W
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
35412 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
35411 G06
35411fa
LTC3541-1
TYPICAL PERFOR A CE CHARACTERISTICS
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)
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
V
IN
= 3.6V
2.5
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
U W
250
35411 G10
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
150
100
50
I
VOUT
= 400mA
I
LVOUT
= 30mA
1
10
100
LOAD CURRENT (mA)
1000
35411 G08
4ms/DIV
35411 G09
300
0
0.1
35411 G07
Oscillator Frequency
vs Supply Voltage
V
IN
= 3.6V
0.410
0.408
0.406
0.404
0.402
0.400
0.398
0.396
0.394
0.392
3
5
4
SUPPLY VOLTAGE (V)
6
35411 G11
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
53411 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
35411 G15
53411 G13
35411 G14
35411fa
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