LT3048-15
1
304815f
For more information www.linear.com/LT3048-15
TYPICAL APPLICATION
FEATURES DESCRIPTION
Low Noise Bias Generator
in 2mm × 2mm DFN
The LT
®
3048-15 generates a low noise, low ripple bias
supply from an input voltage of 2.7V to 4.8V.
The LT3048-15 includes a boost regulator and a LDO
linear regulator. The boost regulator provides power to
the linear regulator.
The boost regulator output voltage is regulated to 1.1V
above the LDO output, optimizing LDO ripple rejection and
transient response. Fixed frequency operation and current
mode control allow the use of very small inductors and
results in low, predictable output ripple.
The linear regulator in the LT3048-15 generates a fixed
15V output. High power supply ripple rejection combined
with a low noise internal reference results in less than
500µVP-P output ripple and noise.
The LT3048-15 is available in a 8-lead 2mm × 2mm DFN
package.
APPLICATIONS
n Generates Low Noise Bias Voltage from Single Cell
Li-Ion Battery
n Output Current: Up to 40mA
n Low Output Ripple and Noise: <500µVP-P
n Boost Regulator
n 2.2MHz Operation
n 300mA Power Switch
n Integrated Schottky Diode
n Low Dropout Linear Regulator
n Low Noise: <120µVRMS (10Hz to 100kHz)
n 0.1% Load Regulation
n Short-Circuit and Thermal Protection
n Load Disconnect in Shutdown
n Available in 2mm × 2mm DFN Package
n Sensor Bias
n Op Amp Supply L, LT, LT C , LT M, Linear Technology and the Linear logo are registered trademarks of Linear
Technology Corporation. All other trademarks are the property of their respective owners.
BSTOUTSW
LDOIN
LT3048-15
10µH
LDOOUT
VIN
EN
1nF
1µF
1µF
3048 TA01a
4.7µF
IN
2.7V TO 4.8V
OUT
15V
BYPOFF ON
GND
VIN (V)
2.7
3.3
3.6
IOUT (mA)
19
22
24
LOAD CURRENT (mA)
0
EFFICIENCY (%)
30
40
50
15 25
3048 TA01b
20
10
05 10 20
60
70
80
VIN = 2.7V
VIN = 3.3V
VIN = 3.6V
LDOOUT = 15V
L = 10µH
DCR = 650mΩ
Efficiency
LT3048-15
2
304815f
For more information www.linear.com/LT3048-15
PIN CONFIGURATIONABSOLUTE MAXIMUM RATINGS
VIN ..............................................................................6V
SW ............................................................................25V
BSTOUT ....................................................................23V
LDOIN .......................................................................22V
LDOOUT .................................................................... 22V
BYP ........................................................................±0.3V
EN ...............................................................................6V
Operating Junction Temperature Range (Note 2)
LT3048E-15 ........................................ –40°C to 125°C
LT3048I-15......................................... –40°C to 125°C
Maximum Junction Temperature .......................... 125°C
Storage Temperature Range .................. –65°C to 150°C
(Note 1)
TOP VIEW
SW
VIN
GND
BYP
BSTOUT
EN
LDOIN
LDOOUT
DC PACKAGE
8-LEAD (2mm × 2mm) PLASTIC DFN
9
GND
4
1
2
36
5
7
8
θJA = 102°C/W
EXPOSED PAD (PIN 9) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH TAPE AND REEL PART MARKING PACKAGE DESCRIPTION TEMPERATURE RANGE
LT3048EDC-15#PBF LT3048EDC-15#TRPBF LGKK 8-Lead (2mm × 2mm) Plastic DFN –40°C to 125°C
LT3048IDC-15#PBF LT3048IDC-15#TRPBF LGKK 8-Lead (2mm × 2mm) Plastic DFN –40°C to 125°C
Consult LTC Marketing for parts specified with wider operating temperature ranges.
Consult LTC Marketing for information on nonstandard 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/
LT3048-15
3
304815f
For more information www.linear.com/LT3048-15
ELECTRICAL CHARACTERISTICS
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.
The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VIN = 3.6V, EN/UVLO = 3V, unless otherwise noted.
PARAMETER CONDITIONS MIN TYP MAX UNITS
VIN Operating Range 2.7 4.8 V
Boost Regulator
BSTOUT-LDOOUT Regulation Voltage l1 1.1 1.2 V
BSTOUT-VIN Regulation Voltage LDOOUT = 0V 1 V
VIN Quiescent Current Not Switching
EN ≤ 0.4V
475
0.1
600
1
µA
µA
Switching Frequency
l
1.7
1.6
2.2
2.2
2.7
2.8
MHz
MHz
Maximum Duty Cycle 86 90 %
Switch Current Limit 300 400 500 mA
Switch VCESAT ISW = 200mA 220 mV
Diode Forward Drop IDIODE = 100mA 0.84 V
EN Voltage High 1.25 V
EN Voltage Low 0.4 V
LDO Linear Regulator
LDOIN Quiescent Current 14 20 µA
LDOOUT Regulation Voltage ILOAD = 100µA
ILOAD = 100µA to 40mA
l
14.775
14.625
15
15
15.225
15.375
V
V
LDOOUT Load Regulation ∆ILOAD = 1mA to 40mA 10 30 mV
LDOOUT Voltage Noise COUT = 1µF, CBYP = 0nF, BW = 10Hz to 100kHz
COUT = 1µF, CBYP = 1nF, BW = 10Hz to 100kHz
450
120
µVRMS
µVRMS
Ripple Rejection fRIPPLE = 2.2MHz 20 dB
Current Limit LDOOUT = 15V l45 80 mA
Note 2: The LT3048E-15 is guaranteed to meet performance specifications
from 0°C to 125°C junction temperature. Specifications over the –40°C
to 125°C operating junction temperature range are assured by design,
characterization and correlation with statistical process controls. The
LT3048I-15 is guaranteed over the full –40°C to 125°C operating junction
temperature range. High junction temperatures degrade operating
lifetimes. Operating lifetime is derated at junction temperatures greater
than 125°C.
LT3048-15
4
304815f
For more information www.linear.com/LT3048-15
TYPICAL PERFORMANCE CHARACTERISTICS
LDOOUT Voltage Operating Waveforms: DCM Operating Waveforms: CCM
Transient Response LDOOUT Noise
Efficiency (10µH) Efficiency (2.2µH) LDOOUT Load Regulation
LOAD (mA)
0
14.5
LDOOUT VOLTAGE (V)
14.6
14.8
14.9
15.0
15.5
15.2
10 20 25
3048 G03
14.7
15.3
15.4
15.1
5 15 30 35 40
TEMPERATURE (°C)
–50
LDOOUT VOLTAGE (V)
15.075
25
3048 G04
15.000
14.950
–25 0 50
14.925
14.000
15.100
15.050
15.025
14.975
75 100 125 3048 G05
500ns/DIVVIN = 3.6V
VOUT = 15V
L = 2.2µH
ILOAD = 15mA
VSW
5V/DIV
IL
100mA/DIV
3048 G06
500ns/DIVVIN = 3.6V
VOUT = 15V
L = 10µH
ILOAD = 20mA
VSW
5V/DIV
IL
100mA/DIV
10Hz 1kHz 100kHz
VIN = 3.6V
VOUT = 15V
ILOAD = 40mA
L = 10µH
CBYP = 1nF
COUT = 1µF
10MHz
1nV/√Hz
0.1µV/√Hz
10µV/√Hz
LOAD CURRENT (mA)
0
EFFICIENCY (%)
30
40
50
15 25
3048 G01
20
10
05 10 20
60
70
80
VIN = 3.6V
LDOOUT = 15V
L = 10µH
DCR = 650mΩ
LOAD CURRENT (mA)
0
40
50
70
3 5
3048 G02
30
20
1 2 4 6 7
10
0
60
EFFICIENCY (%)
VIN = 3.6V
LDOOUT = 15V
L = 2.2µH
DCR = 175mΩ
–300
OUTPUT VOLTAGE DEVIATION (mV)
LOAD CURRENT (mA)
–250
–150
–100
–50
50
10µs/DIVVIN = 3.6V
VOUT = 15V
L = 10µH
CLDOOUT = 1µF
CBYP = 1nF
ILOAD = 4mA TO 20mA
3048 G07
–200
0
0
10
30
40
50
70
20
60
VOUT
ILOAD
LT3048-15
5
304815f
For more information www.linear.com/LT3048-15
TYPICAL PERFORMANCE CHARACTERISTICS
LDOOUT Current Limit
Boost Switch Current Limit
Boost Switch Current Limit
Switching Frequency
TEMPERATURE (°C)
–50
0
CURRENT LIMIT (mA)
10
30
40
50
50
90
3048 G09
20
0
–25 75 100
25 125
60
70
80
DUTY CYCLE (%)
0
SWITCH CURRENT LIMIT (mA)
300
400
500
80
3048 G10
200
100
250
350
450
150
50
020 40 60 100
TEMPERATURE (°C)
–50
0
SWITCH CURRENT LIMIT (mA)
50
150
200
250
500
350
050 75
3048 G11
100
400
450
300
–25 25 100 125 150
TEMPERATURE (°C)
–50
FREQUENCY (MHz)
1.5
2.0
2.5
25 75 150
3048 G12
1.0
0.5
0–25 0 50 100 125
LT3048-15
6
304815f
For more information www.linear.com/LT3048-15
PIN FUNCTIONS
SW (Pin 1): Boost Regulator Switch Node. This is the
collector of the internal power transistor and the anode
of the internal Schottky diode.
VIN (Pin 2): Input Supply. Provides operating current to
the boost regulator. Bypass to ground.
GND (Pin 3): Ground. This pin must be soldered to PCB
ground. The exposed pad must also be soldered to PCB
ground.
BYP (Pin 4): Bypass. Add an optional capacitor from
LDOOUT to BYP to reduce noise at LDOOUT; otherwise
leave BYP unconnected. A capacitor also soft-starts the
linear regulator.
LDOOUT (Pin 5): LDO Linear Regulator Output. This pin is
regulated to 15V. Bypass to ground with a minimum of 1µF.
LDOIN (Pin 6): LDO Linear Regulator Input. Normally
connected to BSTOUT. Bypass to ground.
EN (Pin 7): Enable. Logic input to enable the boost and
linear regulator.
BSTOUT (Pin 8): Boost Regulator Output. This pin is con-
nected to the internal Schottky diode and is regulated to
1.1V above LDOOUT. Bypass to ground.
GND (Exposed Pad Pin 9): The internal boost power switch
is connected to the exposed pad. Tie to ground.
LT3048-15
7
304815f
For more information www.linear.com/LT3048-15
BLOCK DIAGRAM
–++
8 6
5
1
+
+
A1
VC
GND
3, 9 3048 F01
Q1
Q2
SW
2
VIN
IN
BSTOUT LDOIN
C2
C4 C3
L1
LDOOUT
OUT
4
BYP
1.1V
OSC
C1
7EN
ON OFF
Figure 1. LT3048-15 Block Diagram
LT3048-15
8
304815f
For more information www.linear.com/LT3048-15
OPERATION
APPLICATIONS INFORMATION
The LT3048-15 combines a boost regulator with a low
dropout linear regulator to produce a 15V output from a
lower input voltage. With EN below 0.4V, all circuits are
turned off, Q2 disconnects the load from the input, and
current consumption is less than 1µA. Driving EN high
enables the oscillator and all bias circuits including voltage
reference and regulation amplifiers.
The boost regulator uses peak current mode operation,
providing cycle-by-cycle current regulation and limiting,
fast transient response, and good stability. The error am-
plifier, A1, regulates BSTOUT (and LDOIN) to 1.1V above
LDOOUT or VIN, whichever is higher.
Regulating 1.1V between LDOIN and LDOOUT allows the
linear regulator to provide good transient response and
ripple rejection, while maintaining good efficiency. This
regulation loop also minimizes total power dissipation
in fault conditions. If the output is overloaded, the linear
regulator will enter current limit, LDOOUT voltage will
decrease. By reducing the boost regulator output voltage,
the voltage across Q2 will be reduced, limiting dissipation
in Q2. Thermal shutdown provides additional protection.
Capacitor Selection
A 4.7μF ceramic capacitor should be sufficient for the
boost regulator output bypass. Low ESR (equivalent
series resistance) ceramic capacitors should be used
at the outputs of the regulator to minimize the output
ripple voltage. Use only X5R or X7R dielectrics, as these
materials retain their capacitance over wider voltage and
temperature ranges better than other dielectrics.
Table 1. Ceramic Capacitor Manufacturers
MANUFACTURER PHONE WEB
Taiyo Yuden (408) 573-4150 www.t-yuden.com
AVX (803) 448-9411 www.avxcorp.com
Murata (714) 852-2001 www.murata.com
Inductor Selection
A 10μH inductor will suffice for most LT3048-15 applica-
tions, a 2.2μH inductor can be used if the load current is
below 15mA. The inductor’s RMS current rating must be
greater than the maximum input current. To keep efficiency
high, the DCR (series resistance) should be minimized.
Table 2 lists several vendors.
Table2. Inductor Manufacturers
VENDOR URL
Coilcraft www.coilcraft.com
Sumida www.sumida.com
Toko www.toko.com
Würth Elektronik www.we-online.com
LT3048-15
9
304815f
For more information www.linear.com/LT3048-15
APPLICATIONS INFORMATION
Figure 2. Recommended PCB Layout
Figure 3. Ceramic Capacitor Temperature Characteristics
Figure 4. Ceramic Capacitor DC Bias Characteristics
Reducing Output Noise With A Bypass Capacitor
The LT3048-15 relies on the power supply rejection of
the linear regulator to reduce switching regulator noise
at LDOOUT. The linear regulator also contributes thermal
noise to the output. The thermal noise can be reduced,
and transient response improved, by adding a capacitor
between LDOOUT and BYP. A typical value is 1nF. This
capacitor increases start-up time of the regulator.
Recommended PCB Layout
Figure 2 shows the recommended layout for LT3048-15
circuits. Most important is careful placement of the BSTOUT
bypass capacitor C2. High frequency AC current flows in a
loop formed by C2, internal power transistor Q1 and boost
diode D2. Keep this loop small. Also be sure to place an
unbroken ground plane below this loop, on the highest
copper layer below the surface. This prevents the AC loop
from coupling to LDOOUT and other nearby circuitry. Keep
the SW node as small as possible.
LDO Stability and Output Capacitance
The LT3048-15 linear regulator requires an output capaci-
tor for stability. It is designed to be stable with most low
ESR capacitors (typically ceramic, tantalum or low ESR
electrolytic). A minimum output capacitor of 1μF with an
ESR of 1Ω or less is recommended to prevent oscilla-
tions. Larger values of output capacitance decrease peak
deviations and provide improved transient response for
larger load current changes. Bypass capacitors, used to de-
couple individual components powered by the LT3048-15,
increase the effective output capacitor value.
Give consideration to the use of ceramic capacitors as
they are manufactured with a variety of dielectrics, each
with different behavior across temperature and applied
voltage. The most common dielectrics used are specified
with EIA codes of Z5U, Y5V, X5R and X7R. Typical volt-
age and temperature coefficients are shown in Figures3
and 4. The X5R and X7R dielectrics have more stable
characteristics and are most suitable for use as the output
capacitor. The X7R type has better stability across tem-
perature, while the X5R is less expensive and is available
in higher values. Care still must be exercised when using
X5R and X7R capacitors; the codes only specify operating
C2
C4 C3
3048 F02
C1
L1
TEMPERATURE (°C)
–50
40
20
0
–20
–40
–60
–80
–100 25 75
3048 F03
–25 0 50 100 125
Y5V
CHANGE IN VALUE (%)
X5R
BOTH CAPACITORS ARE 16V,
1210 CASE SIZE, 10µF
DC BIAS VOLTAGE (V)
CHANGE IN VALUE (%)
3048 F04
20
0
–20
–40
–60
–80
–100 04810
2 6 12 14
X5R
Y5V
16
BOTH CAPACITORS ARE 16V,
1210 CASE SIZE, 10µF
LT3048-15
10
304815f
For more information www.linear.com/LT3048-15
APPLICATIONS INFORMATION
temperature range and maximum capacitance change
over temperature. Capacitance change due to DC bias
with X5R and X7R capacitors can be significant enough
to drop capacitor values below appropriate levels. Capaci-
tor DC bias characteristics tend to improve as case size
increases, but expected capacitance at operating voltage
should be verified.
Voltage and temperature coefficients are not the only
sources of problems. Some ceramic capacitors have a
piezoelectric response. A piezoelectric device generates
voltage across its terminals due to mechanical stress. In a
ceramic capacitor, the stress can be induced by vibrations
in the system or thermal transients.
LT3048-15
11
304815f
For more information www.linear.com/LT3048-15
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no representa-
tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.
PACKAGE DESCRIPTION
Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings.
2.00 ±0.05
(4 SIDES)
2.00 SQ ±0.05
NOTE:
1. DRAWING IS NOT A JEDEC PACKAGE OUTLINE
2. DRAWING NOT TO SCALE
3. ALL DIMENSIONS ARE IN MILLIMETERS
4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE
MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE
5. EXPOSED PAD SHALL BE SOLDER PLATED
6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE
TOP AND BOTTOM OF PACKAGE
0.55 ±0.05
BOTTOM VIEW—EXPOSED PAD
0.23
REF
0.335
REF
0.335 REF
0.75 ±0.05
1
4
85
PIN 1 BAR
TOP MARK
(SEE NOTE 6)
0.200 REF
0.00 – 0.05
(DC8MA) DFN 0113 REV Ø
0.23 ±0.05
0.45 BSC
0.25 ±0.05
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED
0.90
REF
0.23
REF
0.85 ±0.05
1.8 REF
1.8 REF
2.60 ±0.05
PACKAGE
OUTLINE
0.45 BSC
PIN 1 NOTCH
R = 0.15
DC8 Package
8-Lead Plastic DFN (2mm × 2mm)
(Reference LTC DWG # 05-08-1939 Rev Ø)
Exposed Pad Variation AA
LT3048-15
12
304815f
For more information www.linear.com/LT3048-15
LINEAR TECHNOLOGY CORPORATION 2014
LT 0214 • PRINTED IN USA
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com/LT3048-15
RELATED PARTS
TYPICAL APPLICATIONS
High IOUT with 10µH Inductor
Low IOUT with Small 2.2µH Inductor
Efficiency
Efficiency (2.2µH)
BSTOUTSW
LDOIN
LT3048-15
10µH
LPS3008-103MLB
LDOOUT
VIN
EN
1nF
1µF
1µF
3048 TA02a
4.7µF
IN
2.7V TO 4.8V
OUT
15V
BYPOFF ON
GND
VIN (V)
2.7
3.3
3.6
IOUT (mA)
19
22
24
LOAD CURRENT (mA)
0
EFFICIENCY (%)
30
40
50
15 25
3048 TA02b
20
10
05 10 20
60
70
80
VIN = 2.7V
VIN = 3.3V
VIN = 3.6V
LDOOUT = 15V
L = 10µH
DCR = 650mΩ
BSTOUTSW
LDOIN
LT3048-15
2.2µH
LPS3008-222MLB
LDOOUT
VIN
EN
1nF
1µF
1µF
3048 TA03a
4.7µF
IN
2.7V TO 4.8V
OUT
15V
7mA
BYPOFF ON
GND
LOAD CURRENT (mA)
0
EFFICIENCY (%)
30
40
50
4 5 7
3048 TA03b
20
10
01 2 3 6
60
70
80
VIN = 2.7V
VIN = 3.3V
VIN = 3.6V
LDOOUT = 15V
L = 2.2µH
DCR = 175mΩ
PART NUMBER DESCRIPTION COMMENTS
LT3460 300mA, 38V ISW, 1.3MHz, High Efficiency Step-Up
DC/DC Converter
VIN: 2.5V to 16V, VOUT(MAX) = 38V, IQ = 2.8mA, ISD < 1µA, ThinSOT™
Package
LT3461/LT3461A 300mA, 38V ISW, 1.3MHz, High Efficiency Step-Up
DC/DC Converters
VIN: 2.5V to 16V, VOUT(MAX) = 36V, IQ = 2mA, ISD < 1µA, SC70, ThinSOT
Packages
LT3464 120mA, 38V ISW, High Efficiency Step-Up DC/DC
Converter with Integrated Schottky, Output Disconnect
VIN: 2.3V to 10V, VOUT(MAX) = 34V, IQ = 25mA, ISD < 1µA, ThinSOT
Package
LT1613 550mA ISW, 1.4MHz, High Efficiency Step-Up
DC/DC Converter
VIN: 0.9V to 10V, VOUT(MAX) = 34V, IQ = 3mA, ISD < 1µA, ThinSOT
Package
LT1761 20V, 100mA (IOUT) Low Noise LDO VIN: 1.8V to 20V, VOUT(MIN) = 1.22V, IQ = 20µA, ISD < 1µA, ThinSOT
Package
LT3009 20V, 20mA (IOUT) Low Noise LDO VIN: 1.6V to 20V, VOUT(MIN) = 0.6V, IQ = 3µA, ISD < 1µA, SC70,
2mm × 2mm DFN-6 Packages
