LT3048 Series
1
3048fa
For more information www.linear.com/LT3048
TYPICAL APPLICATION
FEATURES DESCRIPTION
Low Noise Bias Generator
in 2mm × 2mm DFN
The LT
®
3048 series generate low noise, low ripple bias
supplies from input voltages of 2.7V to 4.8V.
The LT3048 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 generates a program-
mable output and the LT3048-XX generate fixed output
voltages. High power supply ripple rejection combined
with a low noise internal reference results in less than
500µVP-P output ripple and noise.
The LT3048 is available in a 8-lead 2mm × 2mm DFN
package.
APPLICATIONS
n Generates Low Noise Bias Voltage from Single
CellLi-Ion Battery
n Output Current: Up to 40mA
n Low Output Ripple and Noise: <500µVP-P
n Boost Regulator
n 1MHz Operation (LT3048)
n 2.2MHz Operation (LT3048-XX)
n Integrated Schottky Diode
n Low Dropout Linear Regulator
n 1.235V Feedback Voltage (LT3048)
n Low Noise: <120µVRMS (10Hz to 100kHz)
n 0.1% Load Regulation
n Fixed 3.3V, 5V, 12V, 15V and Adjustable Output Options
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 Series
2
3048fa
For more information www.linear.com/LT3048
PIN CONFIGURATION
ABSOLUTE MAXIMUM RATINGS
VIN ..............................................................................6V
SW ............................................................................25V
BSTOUT ....................................................................23V
LDOIN .......................................................................22V
LDOOUT .................................................................... 22V
FB ...............................................................................6V
BYP ........................................................................±0.3V
EN ...............................................................................6V
(Note 1)
ORDER INFORMATION
LEAD FREE FINISH TAPE AND REEL PART MARKING PACKAGE DESCRIPTION TEMPERATURE RANGE
LT3048EDC#PBF LT3048EDC#TRPBF LGRR 8-Lead (2mm × 2mm) Plastic DFN –40°C to 125°C
LT3048IDC#PBF LT3048IDC#TRPBF LGRR 8-Lead (2mm × 2mm) Plastic DFN –40°C to 125°C
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
LT3048EDC-12#PBF LT3048EDC-12#TRPBF LGQQ 8-Lead (2mm × 2mm) Plastic DFN –40°C to 125°C
LT3048IDC-12#PBF LT3048IDC-12#TRPBF LGQQ 8-Lead (2mm × 2mm) Plastic DFN –40°C to 125°C
LT3048EDC-5#PBF LT3048EDC-5#TRPBF LGQR 8-Lead (2mm × 2mm) Plastic DFN –40°C to 125°C
LT3048IDC-5#PBF LT3048IDC-5#TRPBF LGQR 8-Lead (2mm × 2mm) Plastic DFN –40°C to 125°C
LT3048EDC-3.3#PBF LT3048EDC-3.3#TRPBF LGQS 8-Lead (2mm × 2mm) Plastic DFN –40°C to 125°C
LT3048IDC-3.3t#PBF LT3048IDC-3.3#TRPBF LGQS 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/
Operating Junction Temperature Range (Note 2)
E-Grade .............................................. –40°C to 125°C
I-Grade............................................... –40°C to 125°C
Maximum Junction Temperature .......................... 125°C
Storage Temperature Range .................. –65°C to 150°C
LT3048-XX LT3048
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
TOP VIEW
SW
VIN
GND
BYP
BSTOUT
EN
LDOOUT
FB
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
LT3048 Series
3
3048fa
For more information www.linear.com/LT3048
ELECTRICAL CHARACTERISTICS
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 applies
to all options unless specified.
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 < VIN 1.1 V
VIN Quiescent Current Not Switching
EN ≤ 0.4V
475
0.1
600
1
µA
µA
Switching Frequency LT3048
l
0.75
0.7
1.00
1.00
1.25
1.30
MHz
MHz
LT3048-XX
l
1.7
1.6
2.2
2.2
2.7
2.8
MHz
MHz
Maximum Duty Cycle LT3048
LT3048-XX
93
86
95
90
%
%
Switch Current Limit (Note 3) 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
LDO Quiescent Current LT3048: Supplied by LDOIN 14 20 µA
LT3048-XX: Supplied by BSTOUT 14 20 µA
FB Pin Current 60 nA
FB Regulation Voltage LT3048: ILOAD = 100µA, FB = LDOOUT
LT3048: 100µA ≤ ILOAD ≤ 40mA
l
1.216
1.210
1.235
1.235
1.254
1.260
V
V
FB Load Regulation LT3048: ∆ILOAD = 100µA to 40mA 2 6 mV
LDOOUT Regulation Voltage LT3048-15: ILOAD = 100µA
LT3048-15: 100µA ≤ ILOAD ≤ 40mA
l
14.775
14.625
15.00
15.00
15.225
15.375
V
V
LT3048-12: ILOAD = 100µA
LT3048-12: 100µA ≤ ILOAD ≤ 40mA
l
11.82
11.70
12.00
12.00
12.18
12.30
V
V
LT3048-5: ILOAD = 100µA
LT3048-5: 100µA ≤ ILOAD ≤ 40mA
l
4.925
4.875
5.00
5.00
5.075
5.125
V
V
LT3048-3.3: ILOAD = 100µA
LT3048-3.3: 100µA ≤ ILOAD ≤ 40mA
l
3.250
3.217
3.300
3.300
3.350
3.383
V
V
LDOOUT Load Regulation LT3048-15: ∆ILOAD = 100µA to 40mA 20 45 mV
LT3048-12: ∆ILOAD = 100µA to 40mA 20 45 mV
LT3048-5: ∆ILOAD = 100µA to 40mA 12 25 mV
LT3048-3.3: ∆ILOAD = 100µA to 40mA 9 18 mV
LT3048 Series
4
3048fa
For more information www.linear.com/LT3048
PARAMETER CONDITIONS MIN TYP MAX UNITS
LDOOUT Voltage Noise
BW = 10Hz to 100kHz
COUT = 1µF
LT3048: CBYP = 0nF, ILOAD = 40mA, LDOOUT = 1.235V
LT3048: CBYP = 1nF, ILOAD = 40mA, LDOOUT = 1.235V
38
25
µVRMS
µVRMS
LT3048-15: CBYP = 0nF, ILOAD = 24mA
LT3048-15: CBYP = 1nF, ILOAD = 24mA
250
60
µVRMS
µVRMS
LT3048-12: CBYP = 0nF, ILOAD = 31mA
LT3048-12: CBYP = 1nF, ILOAD = 31mA
225
60
µVRMS
µVRMS
LT3048-5: CBYP = 0nF, ILOAD = 40mA
LT3048:-5: CBYP = 1nF, ILOAD = 40mA
145
50
µVRMS
µVRMS
LT3048-3.3: CBYP = 0nF, ILOAD = 40mA
LT3048-3.3: CBYP = 1nF, ILOAD = 40mA
120
42
µVRMS
µVRMS
Ripple Rejection LT3048: fRIPPLE = 1.0MHz, ILOAD = 40mA
LT3048: fRIPPLE = 2.2MHz, ILOAD = 40mA
60
53
dB
dB
Current Limit l45 80 mA
ELECTRICAL CHARACTERISTICS
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 applies
to all options unless specified.
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 LT3048E 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 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.
Note 3: Current limit guaranteed by design and/or correlation to static test.
Slope compensation reduces current limit at higher duty cycle.
LT3048 Series
5
3048fa
For more information www.linear.com/LT3048
TYPICAL PERFORMANCE CHARACTERISTICS
LT3048 LDOOUT Noise LT3048-15 Efficiency
LT3048-15 LDOOUT Load
Regulation
LT3048-15 LDOOUT Voltage LT3048-15 Transient Response LT3048-15 LDOOUT Noise
LT3048 FB Voltage
LT3048 FB Load Regulation
LT3048 Switching Frequency
LOAD CURRENT (mA)
0
EFFICIENCY (%)
30
40
50
15 25
3048 G05
20
10
05 10 20
60
70
80
VIN = 2.7V
VIN = 3.3V
VIN = 3.6V
LDOOUT = 15V
L = 10µH
DCR = 650mΩ
–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 G08
–200
0
0
10
30
40
50
70
20
60
VOUT
ILOAD
TEMPERATURE (°C)
–50
FB VOLTAGE (V)
1.260
1.255
1.245
1.235
1.225
1.215
1.250
1.240
1.230
1.220
1.210 25–25 75 100
3048 G01
1250 50
LOAD CURRENT (mA)
0
FB VOLTAGE (V)
1.260
1.255
1.245
1.235
1.225
1.250
1.240
1.230
1.220
1.210
1.215
2010 30
3048 G02
4015 355 25
TEMPERATURE (°C)
–50
SWITCHING FREQUENCY (MHz)
1.3
1.2
1.0
0.8
1.1
0.9
0.7 500 100
3048 G03
12525–25 75
FREQUENCY (Hz)
NOISE SPECTRAL DENSITY (nV/√Hz)
3048 G04
1000
100
10
1
0.1
0.0110 100 100k 1M10k1k
VIN = 3.6V
VOUT = 1.235V
L = 5.6μH
CBSTOUT = 4.7μF
CLDOOUT = 1μF
CBYP = 1nF
ILOAD = 40mA
LOAD CURRENT (mA)
0
LDOOUT VOLTAGE (V)
15.3
15.2
15.0
14.8
15.1
14.9
14.7 2010 30
3048 G06
4015 355 25
TEMPERATURE (°C)
LDOOUT VOLTAGE (V)
15.3
15.2
15.0
14.8
15.1
14.9
14.7
3048 G07
–50 25–25 75 100 1250 50
FREQUENCY (Hz)
NOISE SPECTRAL DENSITY (nV/√Hz)
3048 G09
10000
1000
100
10
1
0.1
10 100 100k 1M10k1k
VIN = 3.6V
VOUT = 15V
L = 10μH
CBSTOUT = 4.7μF
CLDOOUT = 1μF
CBYP = 1nF
ILOAD = 24mA
LT3048 Series
6
3048fa
For more information www.linear.com/LT3048
TYPICAL PERFORMANCE CHARACTERISTICS
Operating Waveforms: DCM Operating Waveforms: CCM
3048 G10
500ns/DIVVIN = 3.6V
VOUT = 15V
L = 2.2µH
ILOAD = 15mA
VSW
5V/DIV
IL
100mA/DIV
3048 G11
500ns/DIVVIN = 3.6V
VOUT = 15V
L = 10µH
ILOAD = 20mA
VSW
5V/DIV
IL
100mA/DIV
LT3048-12 LDOOUT
Load Regulation LT3048-12 LDOOUT Voltage LT3048-12 LDOOUT Noise
LT3048-5 Efficiency
LT3048-5 LDOOUT
Load Regulation LT3048-5 LDOOUT Voltage
LT3048-12 Efficiency
LOAD CURRENT (mA)
0
EFFICIENCY (%)
30
40
50
15 3025
3048 G12
20
10
05 10 20
60
70
80
VIN = 2.7V
VIN = 3.3V
VIN = 3.6V
VOUT = 12V
L = 10µH
DCR = 650mΩ
LOAD CURRENT (mA)
0
LDOOUT VOLTAGE (V)
12.3
12.2
12.0
12.8
12.1
12.9
12.7 2010 30
3048 G13
4015 355 25
TEMPERATURE (°C)
–50
LDOOUT VOLTAGE (V)
12.3
12.2
12.1
12.0
11.9
11.0
11.7 25–25 75 100
3048 G14
1250 50
FREQUENCY (Hz)
NOISE SPECTRAL DENSITY (nV/√Hz)
3048 G15
10000
1000
100
10
1
0.1
10 100 100k 1M10k1k
VIN = 3.6V
VOUT = 12V
L = 10μH
CBSTOUT = 4.7μF
CLDOOUT = 1μF
CBYP = 1nF
ILOAD = 31mA
LOAD CURRENT (mA)
0
EFFICIENCY (%)
30
40
50
15 40353025
3048 G16
20
10
05 10 20
60
70
VIN = 2.7V
VIN = 3.3V
VIN = 3.6V
VOUT = 5V
L = 4.7µH
DCR = 350mΩ
LOAD CURRENT (mA)
0
LDOOUT VOLTAGE (V)
5.125
5.100
5.050
5.000
4.950
5.075
5.025
4.975
4.925
4.875
4.900
2010 30
3048 G17
4015 355 25
TEMPERATURE (°C)
–50
LDOOUT VOLTAGE (V)
5.125
5.100
5.050
5.0
4.950
4.900
5.075
5.025
4.975
4.925
4.875 25–25 75 100
3048 G18
1250 50
LT3048 Series
7
3048fa
For more information www.linear.com/LT3048
LT3048-3.3 LDOOUT Voltage LT3048-3.3 LDOOUT Noise LDOOUT Current Limit
Boost Switch Current Limit Boost Switch Current Limit LT3048-XX Switching Frequency
LT3048-5 LDOOUT Noise LT3048-3.3 Efficiency
LT3048-3.3 LDOOUT
Load Regulation
TYPICAL PERFORMANCE CHARACTERISTICS
TEMPERATURE (°C)
–50
0
CURRENT LIMIT (mA)
10
30
40
50
50
90
3048 G24
20
0
–25 75 100
25 125
60
70
80
DUTY CYCLE (%)
0
SWITCH CURRENT LIMIT (mA)
300
400
500
80
3048 G25
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 G26
100
400
450
300
–25 25 100 125 150
TEMPERATURE (°C)
–50
FREQUENCY (MHz)
1.5
2.0
2.5
25 75 150
3048 G27
1.0
0.5
0–25 0 50 100 125
FREQUENCY (Hz)
NOISE SPECTRAL DENSITY (nV/√Hz)
3048 G19
10000
1000
100
10
1
0.110 100 100k 1M10k1k
VIN = 3.6V
VOUT = 5V
L = 4.7μH
CBSTOUT = 2.2μF
CLDOOUT = 1μF
CBYP = 1nF
ILOAD = 40mA
LOAD CURRENT (mA)
0
EFFICIENCY (%)
30
40
50
15 40353025
3048 G20
20
10
05 10 20
60
VIN = 2.7V
VIN = 3.3V
VIN = 3.6V
VOUT = 3.3V
L = 3.3µH
DCR = 285mΩ
LOAD CURRENT (mA)
0
LDOOUT VOLTAGE (V)
3.38
3.36
3.34
3.32
3.28
3.26
3.24
3.30
3.22 2010 30
3048 G21
4015 355 25
TEMPERATURE (°C)
–50
LDOOUT VOLTAGE (V)
3.38
3.36
3.32
3.28
3.24
3.34
3.30
3.26
3.22 25–25 75 100
3048 G22
1250 50
VIN = 3.6V
VOUT = 3.3V
L = 3.3μH
CBSTOUT = 2.2μF
CLDOOUT = 1μF
CBYP = 1nF
ILOAD = 40mA
FREQUENCY (Hz)
NOISE SPECTRAL DENSITY (nV/√Hz)
3048 G23
10000
1000
100
10
1
10 100 100k 1M10k1k
0.1
LT3048 Series
8
3048fa
For more information www.linear.com/LT3048
PIN FUNCTIONS
LT3048
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.
FB (Pin 5): The LT3048 regulates the FB pin to 1.25V.
Connect the feedback resistor divider tap to this pin.
LDOOUT (Pin 6): LDO Linear Regulator Output. This pin
is programmed by the feedback resistor divider. Bypass
to ground with a minimum of 1μF.
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-XX
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 a fixed voltage. 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 Series
9
3048fa
For more information www.linear.com/LT3048
LT3048 BLOCK DIAGRAMS
Figure 1a. LT3048 Block Diagram
–++
8
6
1
+
+
A1
VC
GND
3, 9 3048 F01a
Q1
Q2
SW
2
VIN
IN
BSTOUT
C2
C4 C3
L1
LDOOUT
OUT
4
5
BYP
FB
1.1V
OSC
C1
7EN
ON OFF
R1
R2
1.235V
Figure 1b. LT3048-XX Block Diagram
–++
8 6
5
1
+
+
A1
VC
GND
3, 9 3048 F01b
Q1
Q2
SW
2
VIN
IN
BSTOUT LDOIN
C2
C4 C3
L1
LDOOUT
OUT
4
BYP
1.1V
OSC
C1
7EN
ON OFF
LT3048 Series
10
3048fa
For more information www.linear.com/LT3048
OPERATION
APPLICATIONS INFORMATION
The LT3048 combines a boost regulator with a low drop-
out linear regulator to produce a programmable output
from a lower input voltage. The LT3048-15, LT3048-12,
LT3048-5, LT3048-3.3 regulate to 15V, 12V, 5V and 3.3V,
respectively. 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
FB Resistor Network
The output voltage is programmed with a resistor divider
between the output and FB pin. Choose the 1% resistors
according to:
R1=R2
V
OUT
1.235V −1
R2 should be 200k or less to avoid bias current errors.
Inductor Selection
A 5.6μH inductor will suffice for most LT3048 applications.
See Table 2 for recommended inductor values. Smaller
value inductors can be used at the cost of reduced maximum
load current. Figure 2 shows the maximum load current as
a function of output voltage. 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 3 lists several vendors.
Table 2. Recommended Inductor Values
PART # INDUCTANCE
LT3048 5.6μH
LT3048-15 10μH
LT3048-12 10μH
LT3048-5 4.7μH
LT3048-3.3 3.3μH
Table 3. Inductor Manufacturers
VENDOR URL
Coilcraft www.coilcraft.com
Sumida www.sumida.com
Toko www.toko.com
Würth Elektronik www.we-online.com
LT3048 Series
11
3048fa
For more information www.linear.com/LT3048
APPLICATIONS INFORMATION
Figure 3. Recommended PCB Layout
Reducing Output Noise With A Bypass Capacitor
The LT3048 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 3 shows the recommended layout for LT3048 cir-
cuits. 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 linear regulator requires an output capacitor
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
C2
C4 C3
3048 F03
C1
L1
Figure 2. LT3048 Typical and Guaranteed Load
Current vs. Output Voltage
LDOOUT VOLTAGE (V)
0
LOAD CURRENT (mA)
45
35
25
15
40
30
20
10
0
5
8 164 12 20
3048 F02
226 142 10 18
VIN = 2.7V
VIN = 3.3V
VIN = 3.6V
GUARANTEED
L = 5.6µH
DCR = 120mΩ
deviations and provide improved transient response for
larger load current changes. Bypass capacitors, used to
decouple individual components powered by the LT3048,
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 Figures4
and 5. 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
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.
LT3048 Series
12
3048fa
For more information www.linear.com/LT3048
APPLICATIONS INFORMATION
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.
Figure 6. Connecting the Inductor to a Separate Voltage Supply
BSTOUTSW
LDOUT
LT3048
5.6µH
FB
VIN
EN
1nF
1µF
1µF
3048 F06
4.7µF
PVIN
1V TO 23V
IN
2.7V TO 4.8V
OUT
5V
BYPOFF ON GND
301k
100k
Figure 4. Ceramic Capacitor Temperature Characteristics
Figure 5. Ceramic Capacitor DC Bias Characteristics
TEMPERATURE (°C)
–50
40
20
0
–20
–40
–60
–80
–100 25 75
3048 F04
–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 F05
20
0
–20
–40
–60
–80
–100 04810
2 6 12 14
X5R
Y5V
16
BOTH CAPACITORS ARE 16V,
1210 CASE SIZE, 10µF
Wide Input Voltage Applications
The LT3048 can be used in wide input voltage applica-
tions. The input supply voltage to the LT3048 must be
between 2.7V and 4.8V and capable of at least 10mA.
The inductor can run off a separate voltage supply (PVIN).
This technique allows the output to be powered from 1V
to 23V (see Figure 6).
LT3048 Series
13
3048fa
For more information www.linear.com/LT3048
LT3048 LT3048 Efficiency
LT3048-15 LT3048-15: Efficiency
BSTOUTSW
LDOIN
LT3048-15
10µH
LPS3008-103MLB
LDOOUT
VIN
EN
1nF
1µF
1µF
3048 TA03a
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
APPLICATIONS INFORMATION
BSTOUTSW
LDOUT
LT3048
5.6µH
WE-LHMI4020
FB
VIN
EN
1nF
1µF
1µF
3048 TA2a
4.7µF
IN
2.7V TO 4.8V
OUT
5V
30mA
BYPOFF ON
GND
301k
100k
LOAD CURRENT (mA)
0
EFFICIENCY (%)
30
40
50
15 3025
3048 TA02b
20
10
05 10 20
60
70
VIN = 2.7V
VIN = 3.3V
VIN = 3.6V
VOUT = 5V
L = 5.6µH
DCR = 120mΩ
LOAD CURRENT (mA)
0
EFFICIENCY (%)
30
40
50
15 25
3048 TA03b
20
10
05 10 20
60
70
80
VIN = 2.7V
VIN = 3.3V
VIN = 3.6V
LDOOUT = 15V
L = 10µH
DCR = 650mΩ
LT3048-12 LT3048-12: Efficiency
BSTOUTSW
LDOIN
LT3048-12
10µH
LPS3008-103MR
LDOOUT
VIN
EN
1nF
1µF
1µF
3048 TA04a
4.7µF
IN
2.7V TO 4.8V
OUT
12V
BYPOFF ON
GND
VIN (V)
2.7
3.3
3.6
IOUT (mA)
25
29
30
LOAD CURRENT (mA)
0
EFFICIENCY (%)
30
40
50
15 3025
3048 TA04b
20
10
05 10 20
60
70
80
VIN = 2.7V
VIN = 3.3V
VIN = 3.6V
VOUT = 12V
L = 10µH
DCR = 650mΩ
LT3048 Series
14
3048fa
For more information www.linear.com/LT3048
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 Series
15
3048fa
For more information www.linear.com/LT3048
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.
REVISION HISTORY
REV DATE DESCRIPTION PAGE NUMBER
A 2/15 Clarified to Include All Fixed and Adjustable Output Options 1 − 16
LT3048 Series
16
3048fa
For more information www.linear.com/LT3048
LINEAR TECHNOLOGY CORPORATION 2014
LT 0215 REV A • PRINTED IN USA
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com/LT3048
RELATED PARTS
TYPICAL APPLICATIONS
PART NUMBER DESCRIPTION COMMENTS
LT3460 300mA, 38V ISW, 1.3MHz, High Efficiency Step-Up
DC/DC Converter
VIN: 2.5V to 16V, VOUT(MAX) = 36V, IQ = 2mA, ISD < 1µA, SC70,
ThinSOT™ Package
LT3461/LT3461A 300mA, 38V ISW, 1.3MHz, High Efficiency Step-Up
DC/DC Converters
VIN: 2.5V to 16V, VOUT(MAX) = 38V, IQ = 2.8mA, 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 = 25µA, 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
LT3048-5 LT3048-5: Efficiency
LT3048-3.3 LT3048-3.3: Efficiency
BSTOUTSW
LDOIN
LT3048-5
4.7µH
LPS3008-472MR
LDOOUT
VIN
EN
1nF
1µF
1µF
3048 TA05a
4.7µF
IN
2.7V TO 4.8V
OUT
5V
40mA
BYPOFF ON
GND
BSTOUTSW
LDOIN
LT3048-3.3
3.3µH
LPS3008-332MR
LDOOUT
VIN
EN
1nF
1µF
1µF
3048 TA06a
4.7µF
IN
2.7V TO 4.8V
OUT
3.3V
40mA
BYPOFF ON
GND
LOAD CURRENT (mA)
0
EFFICIENCY (%)
30
40
50
15 40353025
3048 TA05b
20
10
05 10 20
60
70
VIN = 2.7V
VIN = 3.3V
VIN = 3.6V
VOUT = 5V
L = 4.7µH
DCR = 350mΩ
LOAD CURRENT (mA)
0
EFFICIENCY (%)
30
40
50
15 40353025
3048 TA06b
20
10
05 10 20
60
VIN = 2.7V
VIN = 3.3V
VIN = 3.6V
VOUT = 3.3V
L = 3.3µH
DCR = 285mΩ
