LTC3672B-1
Monolithic Fixed-Output
400mA Buck Regulator with Dual
150mA LDOs in 2mm
×
2mm DFN
FEATURES
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DESCRIPTION
The LTC
®
3672B-1 is a triple power supply composed of a
400mA synchronous buck regulator and two 150mA low-
dropout linear regulators (LDOs), where one of the LDOs
can be powered from the buck output to improve efficiency.
Constant-frequency 2.25MHz operation is maintained
down to very light loads. The input supply range of 2.9V
to 5.5V is especially well-suited for single-cell Lithium-Ion
and Lithium-Polymer applications, and for powering low
voltage ASICs from 3.3V or 5V rails.
The LTC3672B-1 regulates 1.8V at the buck output, 1.2V
at the LDO1 output, and 2.8V at the LDO2 output. Exter-
nal component count is minimal—all that is needed is a
single inductor, an input capacitor, and output capacitors
for each of the three outputs. Control loop compensation
is internal to the LTC3672B-1.
The LTC3672B-1 is available in a 2mm
×
2mm
×
0.75mm
8-Lead DFN package.
L,
LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All other
trademarks are the property of their respective owners.
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Triple Output Supply From a Single 2.9V to 5.5V Input
Buck DC/DC: Fixed 1.8V Output, Up to 400mA
LDO1: Fixed 1.2V Output, Up to 150mA
LDO2: Fixed 2.8V Output, Up to 150mA
±2.5% Reference Accuracy
Constant Frequency 2.25MHz Operation
Minimum External Component Count
Current Mode Operation for Excellent Line and Load
Transient Response
Internal Soft-Start for Each Output
Single Enable Pin Turns On/Shuts Down All Three
Outputs
Tiny 2mm
×
2mm
×
0.75mm DFN Package
APPLICATIONS
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DMB Cellphones
Handheld Products (PDA, PMP, GPS)
Multivoltage Power for Digital Logic, I/O, FPGAs,
CPLDs, ASICs, CPUs, and RF Chipsets
TYPICAL APPLICATION
Buck DC/DC Efficiency vs Load
V
IN
2.9V TO 5.5V
4.7 H
SW
BUCKOUT
V
IN1
ENABLE
INPUT
ENALL
LDO1
1 F
LDO2
3672b1 TA01
100
95
V
OUT1
1.8V
400mA
(250mA IF LDO1
FULLY-LOADED)
V
OUT2
1.2V
150mA
V
OUT3
2.8V
UP TO 150mA
(SUBJECT TO DROPOUT
LIMITATIONS)
90
EFFICIENCY (%)
85
80
75
70
65
60
0
50
100 150 200 250 300 350 400
I
LOAD
(mA)
3672b1 TA01b
V
IN
= 2.9V
V
IN
= 3.6V
V
IN
= 5.5V
2.2 F
V
IN
GND
10 F
LTC3672B-1
1 F
3672B1f
1
LTC3672B-1
ABSOLUTE MAXIMUM RATINGS
(Notes 1, 2, 3)
PIN CONFIGURATION
TOP VIEW
SW 1
GND 2
ENALL 3
BUCKOUT 4
9
8 V
IN
7 LDO2
6 LDO1
5 V
IN1
V
IN
............................................................... –0.3V to 6V
V
IN1
, BUCKOUT, ENALL, SW,
LDO2 ...........–0.3V to the lesser of (V
IN
+ 0.3V) or 6V
LDO1 ............. –0.3V to the lesser of (V
IN1
+ 0.3V) or 6V
Junction Temperature ........................................... 125°C
Operating Temperature Range...................... –40 to 85°C
Storage Temperature Range....................... –65 to 125°C
DC PACKAGE
8-LEAD (2mm 2mm) PLASTIC DFN
T
JMAX
= 125°C,
θ
JA
= 102°C/W,
θ
JC
= 20°C/W
EXPOSED PAD (PIN 9) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
LTC3672BEDC-1#PBF
TAPE AND REEL
LTC3672BEDC-1#TRPBF
PART MARKING*
LCWH
PACKAGE DESCRIPTION
8-Lead (2mm
×
2mm) 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
V
IN
V
UVLO
I
Q,VIN
PARAMETER
Input Voltage Range
V
IN
Undervoltage Lockout Threshold
Undervoltage Lockout Hysteresis
V
IN
Quiescent Current
All Outputs Enabled, No Load
Shutdown
V
IN1
Quiescent Current
All Outputs Enabled, No Load
Shutdown
ENALL Pin Logic Low Voltage
ENALL Pin Logic High Voltage
ENALL Pin Pulldown Resistance
Oscillator Frequency
Regulated Output Voltage
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 noted.
CONDITIONS
●
MIN
2.9
TYP
1.7
12
MAX
5.5
2
100
400
1
5
1
0.4
UNITS
V
V
mV
μA
μA
μA
μA
V
V
MΩ
V
IN
Rising
(Note 4)
V
BUCKOUT
= 1.9V
V
ENALL
= 0V
V
IN1
= 1.8V
260
I
Q,VIN1
2.3
V
ENALL
= 0V
●
●
V
IL
V
IH
R
ENALL
f
OSC
V
BUCKOUT
I
MAXP
I
OUT,BUCK
R
P,BUCK
R
N,BUCK
1.2
5.5
1.8
2.25
1.8
800
0.6
0.7
2.7
1.845
1100
Synchronous Buck Regulator
MHz
V
mA
mA
Ω
Ω
3672B1f
●
1.755
550
400
PMOS Switch Maximum Peak Current (Note 5)
Available Output Current
PMOS Switch On-Resistance
NMOS Switch On-Resistance
2
LTC3672B-1
ELECTRICAL CHARACTERISTICS
SYMBOL
R
PD,BUCKOUT
R
PD,SW
t
SS,BUCK
V
LDO1
PARAMETER
BUCKOUT Pulldown Resistance in Shutdown
SW Pulldown Resistance in Shutdown
Soft-Start Time
Regulated Output Voltage
Line Regulation
with Respect to V
IN
with Respect to V
IN1
Load Regulation
Available Output Current
Short-Circuit Output Current
V
DROP1
t
SS,LDO1
R
PD,LDO1
LDO Regulator 2
V
LDO2
Regulated Output Voltage
Line Regulation with Respect to V
IN
Load Regulation
Available Output Current
Short-Circuit Output Current
V
DROP2
t
SS,LDO2
R
PD,LDO2
Dropout Voltage (Note 6)
Soft-Start Time
Output Pulldown Resistance in Shutdown
I
LDO2
= 150mA
LDO2 Output, I
LDO2
= 1mA
I
LDO2
= 1mA, V
IN
= 3V to 5.5V
I
LDO2
= 1mA to 150mA
150
453
188
0.1
10
250
●
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 noted.
CONDITIONS
V
ENALL
= 0V
V
ENALL
= 0V
MIN
TYP
10
10
0.2
LDO1 Output, I
LDO1
= 1mA
I
LDO1
= 1mA
V
IN
= 3V to 5.5V, V
IN1
= 1.8V
V
IN
= 3.6V, V
IN1
= 1.7V to 1.9V
I
LDO1
= 1mA to 150mA
150
347
I
LDO1
= 150mA
484
0.3
10
2.73
2.8
1
0.1
2.87
570
●
MAX
UNITS
kΩ
kΩ
ms
LDO Regulator 1: V
IN1
= 1.8V Unless Otherwise Noted
1.17
1.2
0.05
1
–0.05
1.23
V
mV/V
mV/V
mV/mA
mA
mA
mV
ms
kΩ
V
mV/V
mV/mA
mA
mA
mV
ms
kΩ
Dropout Voltage (Note 6)
Soft-Start Time
Output Pulldown Resistance in Shutdown
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 LTC3672B-1 is guaranteed to meet performance specifications
from 0°C to 85°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:
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.
Note 4:
Dynamic supply current is higher due to the gate charge delivered
to the buck regulator’s internal MOSFET switches at the switching
frequency.
Note 5:
The current limit features of this part are intended to protect the
IC from short term or intermittent fault conditions. Continuous operation
above the specified maximum specified pin current rating may result in
device degradation or failure.
Note 6:
Dropout voltage is the minimum input to output voltage differential
needed to maintain regulation at a specified output current. When LDO1 is
in dropout, its output voltage will be equal to: V
IN1
– V
DROP1
. When LDO2
is in dropout, its output voltage will be equal to: V
IN
– V
DROP2
.
3672B1f
3
LTC3672B-1
TYPICAL PERFORMANCE CHARACTERISTICS
V
IN
Quiescent Current vs
V
IN
Voltage
500
400
300
200
100
0
2.5
SW PIN NOT SWITCHING
130°C
90°C
I
VIN1
(μA)
25°C
–45°C
5
4
90°C
I
VIN1
(μA)
25°C
0.5
0
–50 –25
3
2
1
0
2.5
130°C
T
A
= 25°C unless otherwise specified.
V
IN1
Quiescent Current vs
Temperature
3.0
2.5
2.0
1.5
1.0
V
IN
= 2.8V TO 5.5V
V
IN1
= 1.8V
V
IN1
Quiescent Current vs
V
IN1
Voltage
V
IN
= V
IN1
I
VIN
(μA)
–45°C
3.0
3.5
4.0
V
IN
(V)
4.5
5.0
5.5
3.0
3.5
3672b1 G01
4.0
4.5
V
IN1
(V)
5.0
5.5
0
3672b1 G02
25 50 75 100 125 150
TEMPERATURE (°C)
3672b1 G03
Buck Regulated Output vs
Temperature
1.845
BUCK REGULATED OUTPUT (V)
1.830
1.815
BUCK AT NO LOAD
1.800
1.785
1.770
1.755
–50 –25
BUCK AT 400mA LOAD
V
IN
= 3.6V
V
IN1
= 1.8V
LDO1 REGULATED OUTPUT (V)
1.23
1.22
1.21
1.20
1.19
1.18
LDO1 Regulated Output vs
Temperature
V
IN
= 3.6V
V
IN1
= 1.8V
LDO2 REGULATED OUTPUT (V)
2.87
2.85
2.83
2.81
2.79
2.77
2.75
LDO2 Regulated Output vs
Temperature
V
IN
= 3.6V
V
IN1
= 1.8V
LDO1 AT NO LOAD
LDO2 AT NO LOAD
LDO2 AT 150mA LOAD
LDO1 AT 150mA LOAD
0
25 50 75 100 125 150
TEMPERATURE (°C)
3672b1 G04
1.17
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
3672b1 G05
2.73
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
3672b1 G06
Buck Regulated Output vs V
IN
Input Voltage
1.85
1.84
BUCK REGULATED OUTPUT (V)
1.83
1.82
1.81
1.80
1.79
1.78
1.77
1.76
1.75
2.5
3.0
3.5
4.0
4.5
5.0
V
IN
INPUT VOLTAGE (V)
5.5
BUCK AT 400mA LOAD
BUCK AT NO LOAD
BOTH LDOs UNLOADED
LDO1 REGULATED OUTPUT (V)
1.23
1.22
1.21
LDO1 Regulated Output vs V
IN1
Input Voltage
BUCK AND LDO2 UNLOADED
V
IN
= 3.6V
LDO2 REGULATED OUTPUT (V)
2.86
2.84
2.82
2.80
2.78
2.76
LDO2 Regulated Output Voltage
vs V
IN
Input Voltage
BUCK AND LDO1 UNLOADED
I
LDO1
= 0mA
1.20
1.19
1.18
1.17
1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5
V
IN1
INPUT VOLTAGE (V)
3672b1 G08
I
LDO2
= 0mA
I
LDO2
= 150mA
I
LDO1
= 150mA
2.74
2.5
3.0
3672b1 G07
3.5
4.0
4.5
5.0
V
IN
INPUT VOLTAGE (V)
5.5
3672b1 G09
3672B1f
4
LTC3672B-1
TYPICAL PERFORMANCE CHARACTERISTICS
V
IN1
-LDO1 Dropout Voltage
vs Load
600
500
DROPOUT VOLTAGE (mV)
DROPOUT VOLTAGE (mV)
400
300
200
130°C
100
0
25°C
300
250
200
150
100
50
0
–45°C
LDO1 SHORT CIRCUIT CURRENT (mA)
T
A
= 25°C unless otherwise specified.
V
IN
-LDO2 Dropout Voltage
vs Load
500
450
400
350
300
250
200
150
100
50
0
LDO1 Short Circuit Current vs V
IN1
V
IN
= 5.5V
130°C
25°C
–45°C
–45°C
25°C
90°C
0
1
2
3
V
IN1
(V)
4
5
6
3672b1 G12
0
25
50
75
100
LDO1 LOAD (mA)
125
150
0
25
3672b1 G10
50
75
100
LDO2 LOAD (mA)
125
150
3672b1 G11
LDO1 Short Circuit Current vs V
IN
500
LDO1 SHORT CIRCUIT CURRENT (mA)
400
300
200
100
0
2.5
LDO2 SHORT CIRCUIT CURRENT (mA)
V
IN1
= 1.8V
600
500
400
300
200
100
LDO2 Short Circuit Current vs V
IN
2.6
2.5
FREQUENCY (MHz)
2.4
2.3
2.2
2.1
2.0
Buck Oscillator Frequency vs
Temperature
V
IN
= 5.5V
V
IN
= 4.2V
V
IN
= 3.6V
–45°C
25°C
90°C
3.0
3.5
4.0
V
IN
(V)
4.5
5.0
5.5
0
2.5
–45°C
25°C
90°C
3.0
3.5
4.0
V
IN
(V)
4.5
5.0
5.5
V
IN
= 2.9V
3672b1 G13
3672b1 G14
1.9
–50 –30 –10 10 30 50 70 90 110 130
TEMPERATURE (°C)
3672b1 G15
PMOS Switch Maximum Peak
Current
PMOS SWITCH MAX PEAK CURRENT (mA)
1000
PMOS ON-RESISTANCE (mΩ)
900
800
900
700
600
500
400
300
200
100
Buck PMOS Switch On-Resistance
130°C
90°C
25°C
–45°C
ENALL
OUTPUT
VOLTAGES
500mV/DIV
0V
1V
0V
Startup Transient
V
OUT3
V
OUT1
V
OUT1
V
OUT2
800
50μs/DIV
3672b1 G18
700
V
IN
= 2.9V
V
IN
= 3.6V
V
IN
= 5.5V
FRONT PAGE APPLICATION
V
IN
= 3.6V
10mA RESISTIVE LOAD ON EACH OUTPUT
3.0
3.5
4.0
V
IN
(V)
4.5
5.0
5.5
600
–50 –30 –10 10 30 50 70 90 110 130
TEMPERATURE (°C)
3672b1 G16
0
2.5
3672b1 G17
3672B1f
5
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