LTC3541-2
High Efficiency
Buck + VLDO Regulator
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High Efficiency, 500mA Buck Plus 300mA VLDO
Regulator
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
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.
, 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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Digital Cameras
Cellular Phones
PC Cards
Wireless and DSL Modems
Other Portable Power Systems
V
IN
2.9V TO 5.5V
EFFICIENCY (%)
SW
2.2µH
ENVLDO
V
IN
MODE
LTC3541-2
ENBUCK
GND
V
OUT
LV
IN
10µF
LV
OUT
PGND
V
OUT2
1.5V
300mA
V
OUT1
1.875V
200mA
U
TYPICAL APPLICATIO
Buck (Burst) Efficiency vs Load Current
100
90
80
70
60
50
40
30
20
10
0
1
10
100
LOAD CURRENT (mA)
0.0001
1000
35412 TA01b
V
IN
= 3V
EFFICIENCY
2.2µF
35412 TA01a
U
1
0.1
POWER LOSS (W)
POWER LOSS
0.01
0.001
FEATURES
DESCRIPTIO
U
35412fb
LTC3541-2
(Note 1)
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
.
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
T
JMAX
= 125°C, θ
JA
= 43°C/W
EXPOSED PAD (PIN 11) IS PGND, MUST BE SOLDERED TO PCB
DD PAcKAGE
10-LEAD (3mm
×
3mm) PLASTIc DFN
ORDER PART NUMBER
LTC3541EDD-2
DD PART MARKING
LCHQ
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
V
IN
V
IN(LINEREG)
PARAMETER
Peak Inductor Current
Input Voltage Range
Buck V
IN
Line Regulation
(Note 4)
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)
●
●
MIN
0.8
2.7
TYP
0.95
0.04
2.2
2.2
0.8
20
0.5
0.25
0.25
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)
50
V
VOUT
VLDO Output Load Regulation I
OUT(VLDO)
= 1mA – 300mA, LV
IN
= 1.875V, LV
OUT
= 1.5V,
●
ENBUCK = V
IN
, ENVLDO = V
IN
, MODE = V
IN
●
Linear Regulator Output Load I
OUT(LDO)
= 1mA – 30mA, LV
OUT
= 1.5V,
ENBUCK = 0V, ENVLDO = V
IN
Regulation
Reference Regulation Voltage ENBUCK = V
IN
, ENVLDO = 0V, T
A
= 25°C
(Note 6)
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
1.913
1.917
1.922
1.53
1.534
1.538
1.837
1.833
1.828
1.47
1.466
1.875
1.875
1.875
1.5
1.5
1.5
V
LVOUT
Reference Regulation Voltage
(Note 7)
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
●
1.462
35412fb
U
mV
%
%
%
V
V
V
V
V
V
W
U
U
W W
W
ABSOLUTE
AXI U RATI GS
PACKAGE/ORDER I FOR ATIO
LTC3541-2
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
LV
IN
Shutdown Quiescent
Current
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
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
= 1.875V, 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
●
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
1.8
2.25
0.25
0.35
±0.01
2.7
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
●
●
●
±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 V
IN
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
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 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.
35412fb
LTC3541-2
TYPICAL PERFOR A CE 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
I
OUT
= 500mA
EFFICIENCY (%)
I
OUT
= 30mA
5
Efficiency vs Load Current for
Buck (Burst)
100
90
80
EFFICIENCY (%)
70
60
50
40
30
20
10
0
0.1
1
10
100
LOAD CURRENT (mA)
1000
35412 G04
V
IN
= 3.6V
V
IN
= 2.7V
V
IN
= 4.2V
DROPOUT VOLTAGE (mV)
BIAS CURRENT (µA)
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
FREQUENCY (MHz)
2.40
2.35
2.30
2.25
2.20
2.15
2.10
2.05
I
VOUT
= 200mA
I
LVOUT
= 300mA
U W
6
Efficiency vs Input Voltage for
Buck (Burst)
100
95
90
85
80
75
70
65
60
55
50
2
3
4
5
INPUT VOLTAGE (V)
6
35412 G02
Efficiency vs Load Current for
Buck (Pulse Skip)
100
90
V
IN
= 2.7V
V
IN
= 3.6V
V
IN
= 4.2V
I
OUT
= 500mA
80
70
60
50
40
30
20
10
0
0.1
1
I
OUT
= 100mA
I
OUT
= 30mA
10
100
LOAD CURRENT (mA)
1000
35412 G03
VLDO Dropout Voltage
vs Load Current
100
250
V
IN
= 3V
V
IN
= 3.6V
60
V
IN
= 4.2V
40
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
80
150
100
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
Oscillator Frequency
vs Temperature
V
IN
= 3.6V
2ms/DIV
35412 G07
2.00
–50 –25
50
25
0
75
TEMPERATURE (°C)
100
125
35412 G08
35412fb
LTC3541-2
TYPICAL PERFOR A CE CHARACTERISTICS
Oscillator Frequency
vs Supply Voltage
2.5
V
IN
= 3.6V
0.410
0.408
0.406
REFERENCE (V)
0.404
0.402
0.400
0.398
0.396
0.394
0.392
2.0
3
5
4
SUPPLY VOLTAGE (V)
6
35412 G09
2.4
FREQUENCY (MHz)
REFERENCE (V)
2.3
2.2
2.1
R
DS(0N)
vs Temperature
0.700
0.600
0.500
R
DS(ON)
(Ω)
0.400
0.300
0.200
0.100
MAIN SWITCH
V
IN
= 2.5V
V
IN
= 3.6V
V
IN
= 5.5V
100
125
L
VOUT
10mV/DIV
AC COUPLED
V
OUT
10mV/DIV
AC COUPLED
SYNCH SWITCH
0
–50 –25
50
25
75
0
TEMPERATURE (°C)
Buck (Burst) Load Step from
1mA to 500mA
V
OUT
100mV/DIV
AC COUPLED
I
L
500mA/DIV
I
LOAD
500mA/DIV
V
IN
= 3.6V
40µs/DIV
V
OUT
= 1.875V
I
LOAD
= 1mA TO 500mA
35412 G12
U W
35412 G10
VLDO/Linear Regulator Reference
vs Temperature
V
IN
= 3.6V
0.820
0.816
0.812
0.808
0.804
0.800
0.796
0.792
0.788
0.784
50
25
0
75
TEMPERATURE (°C)
100
125
Buck Reference vs Temperature
V
IN
= 3.6V
0.390
–50 –25
0.780
–50
–25
50
25
0
75
TEMPERATURE (°C)
100
125
35412 G19
35412 G20
Buck (Burst) and VLDO Output
V
OUT
100mV/DIV
AC COUPLED
I
L
500mA/DIV
I
LOAD
500mA/DIV
V
IN
= 3.6V
2µs/DIV
LV
OUT
= 1.5V
V
OUT
= 1.875V
I
LOAD
= 50mA
Burst Mode OPERATION
35412 G21
Buck (Pulse Skip) Load Step from
1mA to 500mA
V
IN
= 3.6V
40µs/DIV
V
OUT
= 1.875V
I
LOAD
= 1mA TO 500mA
35412 G11
VLDO Load Step from 1mA to
300mA
VLDO Load Step from 100mA to
300mA
LV
OUT
20mV/DIV
AC COUPLED
LV
OUT
20mV/DIV
AC COUPLED
I
LOAD
250mA/DIV
V
IN
= 3.6V
200µs/DIV
V
OUT
= 1.5V
I
LOAD
= 1mA TO 300mA
35412 G13
I
LOAD
250mA/DIV
V
IN
= 3.6V
200µs/DIV
LV
OUT
= 1.5V
I
LOAD
= 100mA TO 300mA
35412 G14
35412fb
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