LTC3124
15V, 5A 2-Phase Synchronous
Step-Up DC/DC Converter with
Output Disconnect
FEATURES
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DESCRIPTION
The
LTC
®
3124
is a dual-phase, synchronous step-up DC/
DC converter with true output disconnect and inrush
current limiting capable of providing output voltages up
to 15V. Dual-phase operation significantly reduces peak
inductor and capacitor ripple currents, minimizing induc-
tor and capacitor size. The 2.5A per phase current limit,
along with the ability to program output voltages up to 15V
make the LTC3124 well suited for a variety of demanding
applications. Once started, operation will continue with
inputs down to 500mV.
The LTC3124 switching frequency can be programmed
from 100kHz to 3MHz to optimize applications for highest
efficiency or smallest solution footprint. The oscillator can
be synchronized to an external clock for noise sensitive
applications. Selectable Burst Mode operation reduces
quiescent current to 25µA, ensuring high efficiency across
the entire load range. An internal soft-start limits inrush
current during start-up.
Other features include a <1µA shutdown current and robust
protection under short-circuit, thermal overload, and output
overvoltage conditions. The LTC3124 is offered in both
16-lead DFN and thermally-enhanced TSSOP packages.
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V
IN
Range: 1.8V to 5.5V, 500mV After Start-Up
Adjustable Output Voltage: 2.5V to 15V
1.5A Output Current for V
IN
= 5V and V
OUT
= 12V
Dual-Phase Control Reduces Output Voltage Ripple
Output Disconnects from Input When Shut Down
Synchronous Rectification: Up to 95% Efficiency
Inrush Current Limit
Up to 3MHz Programmable Switching Frequency
Synchronizable to External Clock
Selectable Burst Mode
®
Operation: 25µA I
Q
Output Overvoltage Protection
Internal Soft-Start
<1µA I
Q
in Shutdown
16-Lead, Thermally- Enhanced 3mm
×
5mm
×
0.75mm DFN and TSSOP Packages
APPLICATIONS
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RF, Microwave Power Amplifiers
Piezo Actuators
Small DC Motors, Thermal Printers
12V Analog Rail from Battery, 5V, or Backup Capacitor
L,
LT, LTC, LTM, Burst Mode, Linear Technology and the Linear logo are registered trademarks
and ThinSOT is a trademark of Linear Technology Corporation. All other trademarks are the
property of their respective owners.
TYPICAL APPLICATION
5V to 12V Synchronous Boost Converter
V
IN
5V
4.7µH
SWB
4.7µH
PGNDB
CAP
V
OUTB
100nF
22µF
×2
V
OUT
12V
1.5A
EFFICIENCY (%)
100
90
80
70
60
50
40
30
20
113k
84.5k
28k
680pF
3124 TA01a
Efficiency Curve
10
Burst Mode
OPERATION
PWM
0.1
Burst Mode
OPERATION
PWM
1
POWER LOSS (W)
V
OUTA
SWA
LTC3124
PGNDA
V
IN
SGND
SD
FB
V
C
0.01
BURST PWM
10µF
4.7µF
PWM/SYNC
V
CC
RT
OFF ON
1.02M
10
0
0.01
56pF
0.001
f
SW
= 1MHz
EFFICIENCY
POWER LOSS
0.0001
0.1
1
10
100
1000
LOAD CURRENT (mA)
3124 TA01b
3124f
For more information
www.linear.com/LTC3124
1
LTC3124
ABSOLUTE MAXIMUM RATINGS
(Note 1)
V
IN
Voltage ................................................... –0.3V to 6V
V
OUTA
, V
OUTB
Voltages ............................... –0.3V to 18V
SWA, SWB Voltages (Note 2)..................... –0.3V to 18V
SWA, SWB (Pulsed < 100ns) (Note 2) ....... –0.3V to 19V
VC Voltage ..................................................–0.3V to V
CC
RT Voltage ..................................................–0.3V to V
CC
CAP Voltage
V
OUT
< 5.7V ............................–0.3V to (V
OUT
+ 0.3V)
5.7V ≤ V
OUT
≤ 11.7V...... (V
OUT
– 6V) to (V
OUT
+ 0.3V)
V
OUT
> 11.7V .................................(V
OUT
– 6V) to 12V
All Other Pins ............................................... –0.3V to 6V
Operating Junction Temperature Range (Notes 3, 4)
LTC3124E/LTC3124I ........................... –40°C to 125°C
LTC3124H .......................................... –40°C to 150°C
Storage Temperature Range .................. –65°C to 150°C
Lead Temperature (Soldering, 10 sec)
FE Package Only ............................................... 300°C
PIN CONFIGURATION
TOP VIEW
SWB
PGNDB
SWA
PGNDA
V
IN
PWM/SYNC
V
CC
RT
1
2
3
4
5
6
7
8
17
PGND
16 CAP
15 V
OUTB
14 NC
13 V
OUTA
12 SGND
11
SD
10 FB
9
VC
SWB
PGNDB
SWA
PGNDA
V
IN
PWM/SYNC
V
CC
RT
1
2
3
4
5
6
7
8
17
PGND
TOP VIEW
16 CAP
15 V
OUTB
14 NC
13 V
OUTA
12 SGND
11
SD
10 FB
9
VC
DHC PACKAGE
16-LEAD (5mm
×
3mm) PLASTIC DFN
T
JMAX
= 125°C,
θ
JA
= 43°C/W (NOTE 5),
θ
JC
= 5°C/W
EXPOSED PAD (PIN 17) IS PGND AND MUST BE SOLDERED TO PCB
FOR RATED THERMAL PERFORMANCE
FE PACKAGE
16-LEAD PLASTIC TSSOP
T
JMAX
= 150°C,
θ
JA
= 40°C/W (NOTE 5),
θ
JC
= 10°C/W
EXPOSED PAD (PIN 17) IS PGND AND MUST BE SOLDERED TO PCB
FOR RATED THERMAL PERFORMANCE
ORDER INFORMATION
LEAD FREE FINISH
LTC3124EDHC#PBF
LTC3124IDHC#PBF
LTC3124EFE#PBF
LTC3124IFE#PBF
LTC3124HFE#PBF
TAPE AND REEL
LTC3124EDHC#TRPBF
LTC3124IDHC#TRPBF
LTC3124EFE#TRPBF
LTC3124IFE#TRPBF
LTC3124HFE#TRPBF
PART MARKING*
3124
3124
3124FE
3124FE
3124FE
PACKAGE DESCRIPTION
16-Lead (5mm
×
3mm) Plastic DFN
16-Lead (5mm
×
3mm) Plastic DFN
16-Lead Plastic TSSOP
16-Lead Plastic TSSOP
16-Lead Plastic TSSOP
TEMPERATURE RANGE
–40°C to 125°C
–40°C to 125°C
–40°C to 125°C
–40°C to 125°C
–40°C to 150°C
Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping
container.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/
3124f
2
For more information
www.linear.com/LTC3124
LTC3124
ELECTRICAL CHARACTERISTICS
PARAMETER
Minimum Start-Up Voltage
Input Voltage Range
Output Voltage Adjust Range
Feedback Voltage
Feedback Input Current
Quiescent Current, Shutdown
Quiescent Current, Active
Quiescent Current, Burst
N-Channel MOSFET Switch Leakage Current
P-Channel MOSFET Switch Leakage Current
N-Channel MOSFET Switch On-Resistance
P-Channel MOSFET Switch On-Resistance
N-Channel MOSFET Peak Current Limit
Maximum Duty Cycle
Minimum Duty Cycle
Switching Frequency
SYNC Frequency Range
PWM/SYNC Input High Voltage
PWM/SYNC Input Low Voltage
PWM/SYNC Input Current
CAP Clamp Voltage
V
CC
Regulation Voltage
Error Amplifier Transconductance
Error Amplifier Sink Current
Error Amplifier Source Current
Soft-Start Time
SD
Input High Voltage
SD
Input Low Voltage
SD
Input Current
CONDITIONS
V
OUT
= 0V
V
OUT
≥ 2.5V
The
l
denotes the specifications which apply over the specified operating
junction temperature range, otherwise specifications are at T
A
= 25°C (Note 3). V
IN
= 3.6V, V
OUTA
= V
OUTB
= 12V, R
T
= 28k unless
otherwise noted.
MIN
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TYP
1.6
0.5
2.5
1.176
FB = 1.4V
SD
= 0V, V
OUT
= 0V, Not Including Switch Leakage
FB = 1.4V, Measured on V
IN
, Non-Switching
Measured on V
IN
, FB = 1.4V
Measured on V
OUT
, FB = 1.4V
SW = 15V, V
OUT
= 15V, Per Phase
SW = 0V, V
OUT
= 15V,
SD
= 0V, Per Phase
Per Phase
Per Phase
Per Phase
FB = 1.0V
FB = 1.4V
Per Phase
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2.5
90
0.83
0.2
0.9 • V
CC
1.200
1
0.2
600
25
10
0.1
0.1
0.130
0.200
3.5
94
1
MAX
1.8
5.5
15
1.224
50
1
840
40
20
40
70
4.5
0
1.17
6.0
0.1 • V
CC
1
–5.8
4.6
130
V
PWM/SYNC
= 5.5V
V
OUT
> 6.2V, Referenced to V
OUT
V
IN
< 2.8V, V
OUT
> 5V
l
–5.0
3.9
60
FB = 1.6V, VC = 1.15V
FB = 800mV, VC = 1.15V
l
l
0.01
–5.4
4.25
100
25
–25
10
1.6
1
0.25
2
SD
= 5.5V
UNITS
V
V
V
V
nA
µA
µA
µA
µA
µA
µA
Ω
Ω
A
%
%
MHz
MHz
V
V
µA
V
V
µS
µA
µA
ms
V
V
µA
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:
Voltage transients on the SW pin beyond the DC limit specified in
the Absolute Maximum Ratings are non-disruptive to normal operations
when using good layout practices, as shown on the demo board or
described in the data sheet or application notes.
Note 3:
The LTC3124 is tested under pulsed load conditions such that
T
A
≈ T
J
. The LTC3124E is guaranteed to meet performance specifications
from 0°C to 85°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
LTC3124I is guaranteed to meet specifications over the –40°C to 125°C
operating junction temperature range. The LTC3124H is guaranteed to
meet specifications over the full –40°C to 150°C operating junction range.
High junction temperatures degrade operating lifetimes; operating lifetime
is derated for junction temperatures greater than 125°C.
Note that the maximum ambient temperature consistent with these
specifications is determined by specific operating conditions in
conjunction with board layout, the rated package thermal impedance
and other environmental factors. The junction temperature (T
J
in °C) is
calculated from the ambient temperature (T
A
in °C) and power dissipation
(P
D
in Watts) according to the formula:
T
J
= T
A
+ (P
D
•
θ
JA
)
where
θ
JA
is the thermal impedance of the package.
Note 4:
The LTC3124 includes overtemperature protection that is intended
to protect the device during momentary overload conditions. Junction
temperature will exceed 150°C when overtemperature shutdown is active.
Continuous operation above the specified maximum operating junction
temperature may result in device degradation or failure.
Note 5:
Failure to solder the exposed backside of the package to the PC
board ground plane will result in a thermal impedance much higher than
the rated package specifications.
3124f
For more information
www.linear.com/LTC3124
3
LTC3124
TYPICAL PERFORMANCE CHARACTERISTICS
Configured as front page application at T
A
= 25°C, unless otherwise specified.
Efficiency vs Load Current,
V
OUT
= 5V
100
Burst Mode
90 OPERATION
80
EFFICIENCY (%)
70
60
50
40
30
20
10
0
0.01
0.1
f
SW
= 1MHz
V
IN
= 4.2V
V
IN
= 3.3V
V
IN
= 0.6V
1
10
100
LOAD CURRENT (mA)
1000
3124 G01
Efficiency vs Load Current,
V
OUT
= 7.5V
100
Burst Mode
90 OPERATION
80
EFFICIENCY (%)
EFFICIENCY (%)
70
60
50
40
30
20
10
0
0.01
0.1
f
SW
= 1MHz
V
IN
= 5.4V
V
IN
= 3.8V
V
IN
= 2.3V
1
10
100
LOAD CURRENT (mA)
1000
3124 G02
Efficiency vs Load Current,
V
OUT
= 12V
100
90
80
Burst Mode
OPERATION
PWM
PWM
PWM
70
60
50
40
30
20
10
0
0.01
0.1
f
SW
= 1MHz
V
IN
= 5.4V
V
IN
= 4.2V
V
IN
= 2.6V
1
10
100
LOAD CURRENT (mA)
1000
3124 G03
PWM Mode Operation
V
OUT
20mV/DIV
AC-COUPLED
PHASE A
INDUCTOR
CURRENT
500mA/DIV
PHASE B
INDUCTOR
CURRENT
500mA/DIV
I
LOAD
= 500mA
2µs/DIV
3124 G04
Load Transient Response
SD
5V/DIV
Inrush Current Control
V
OUT
500mV/DIV
AC-COUPLED
1500mA
OUTPUT
CURRENT
500mA/DIV
V
OUT
5V/DIV
INDUCTOR A
CURRENT
1A/DIV
INDUCTOR B
CURRENT
1A/DIV
I
LOAD
= 100mA
2ms/DIV
3124 G06
150mA
150mA
R
C
= 169k
C
C
= 330pF
NO C
F
500µs/DIV
3124 G05
Feedback vs Temperature
0.05
CHANGE IN R
DS(ON)
FROM 25°C (%)
CHANGE IN V
FB
FROM 25°C (%)
0
80
60
40
20
0
–20
R
DS(ON)
vs Temperature,
Both NMOS and PMOS
0.5
CHANGE IN FREQUENCY FROM 25°C (%)
–10
70
110
30
TEMPERATURE (°C)
150
3124 G08
3124 G07
Switching Frequency
vs Temperature
–0.05
–0.10
0
–0.5
–0.15
–0.20
–1.0
–0.25
–0.30
–0.35
–40
0
120
80
TEMPERATURE (°C)
40
160
–1.5
–40
–50
–2.0
–50 –20
70
10
100
40
TEMPERATURE (°C)
130
160
3124 G09
3124f
4
For more information
www.linear.com/LTC3124
LTC3124
TYPICAL PERFORMANCE CHARACTERISTICS
Configured as front page application at T
A
= 25°C, unless otherwise specified.
PWM Mode Maximum Output
Current vs V
IN
3.6
3.2
OUTPUT CURRENT (A)
2.8
2.4
2.0
1.6
1.2
0.8
0.4
0
0.5
1
1.5
2
2.5 3 3.5
V
IN
(V)
4
4.5
5
5.5
V
OUT
= 5V
V
OUT
= 7.5V
V
OUT
= 12V
V
OUT
= 15V
PEAK CURRENT LIMIT CHANGE FROM 25°C (%)
4.0
2
1
INPUT CURRENT (mA)
0
–1
–2
–3
–4
–50
Peak Current Limit Change
vs Temperature
200
180
160
140
120
100
80
60
40
20
–10
70
110
30
TEMPERATURE (°C)
150
3124 G11
3124 G10
PWM Operation No-Load Input
Current vs V
IN
V
OUT
= 15V
V
OUT
= 12V
V
OUT
= 7.5V
V
OUT
= 5V
V
OUT
= 2.5V
0
0.5
1
1.5
2
2.5 3 3.5
V
IN
(V)
4
4.5
5
5.5
3124 G12
Burst Mode Output Current vs V
IN
400
350
OUTPUT CURRENT (mA)
INPUT CURRENT (µA)
300
250
200
150
100
50
0
0.5
1
1.5
2
2.5 3 3.5 4
V
IN
, FALLING (V)
4.5
5
5.5
10000
Burst Mode No-Load Input
Current vs V
IN
CHANGE IN CURRENT FROM 25°C (%)
V
OUT
= 15V
V
OUT
= 12V
V
OUT
= 7.5V
V
OUT
= 5V
V
OUT
= 2.5V
75
60
45
30
15
0
Burst Mode Quiescent Current
Change vs Temperature
1000
100
10
0.5
1
1.5
2
3124 G13
2.5 3 3.5 4
V
IN
, FALLING (V)
4.5
5
5.5
–15
–50
–10
70
110
30
TEMPERATURE (°C)
150
3124 G15
V
OUT
= 2.5V
V
OUT
= 5V
V
OUT
= 7.5V
V
OUT
= 12V
V
OUT
= 15V
3124 G14
SD
Pin Threshold
RT vs Frequency
900mV
V
SD
500mV/DIV
400mV
R
T
RESISTANCE (k )
3124 G16
V
OUT
5V/DIV
100
10
1s/DIV
10
100
1000
FREQUENCY (kHz)
3000
3124 G17
3124f
For more information
www.linear.com/LTC3124
5
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