FEATURES
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LTC3428
4A, 2MHz Dual Phase
Step-Up DC/DC Converter
in 3mm
×
3mm DFN
DESCRIPTION
The LTC
®
3428 is a 2-phase, current mode boost con-
verter, capable of supplying 2A at 5V from a 3.3V input.
Two 93mΩ, 2A N-channel MOSFET switches allow the
LTC3428 to deliver high efficiency from input voltages as
low as 1.6V.
External parts count and size are minimized by a 1MHz
switching frequency and a 2-phase design. Two phase
operation significantly reduces peak inductor currents and
capacitor ripple current, doubling the effective switching
frequency and minimizing inductor and capacitor size.
External compensation allows the feedback loop response
to be optimized for a particular application.
Other features include: an active low shutdown pin re-
duces supply current to below 1μA, internal soft-start,
antiringing control and thermal shutdown. The LTC3428
is available in a low profile (0.75mm) 10-lead (3mm
×
3mm) DFN package.
L,
LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All other
trademarks are the property of their respective owners.
High Efficiency: Up to 92%
2-Phase Control Reduces Output Voltage Ripple
5V at 2A from 3.3V Input
3.3V at 1.5A from 1.8V Input
1.6V to 5.25V Adjustable Output Voltage
1.6V to 4.5V Input Range
Internal Soft-Start Operation
Low Shutdown Current: <1μA
Uses Small Surface Mount Components
10-Pin 3mm
×
3mm DFN Package
APPLICATIONS
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Networking Equipment
Handheld Instruments
Digital Cameras
Distributed Power
Local 3.3V to 5V Conversion
TYPICAL APPLICATION
3.3V to 5V at 2A Converter
V
IN
3.3V
2.2μH*
V
IN
OFF ON
10k
1000pF
22pF
SHDN
V
C
AGND
PGNDA
LTC3428
V
OUT
SWA
SWB
FB
PGNDB
22μF****
3428 TA01
Efficiency vs Load Current
95
90
4.7μF***
2.2μH*
V
OUT
5V/2A
**
383k
EFFICIENCY (%)
85
80
75
70
65
60
121k
55
50
45
0.1
LOAD CURRENT (A)
3428 TA02
**
* TOKO FDV06302R2
** PHILIPS PMEG1020
*** TAIYO YUDEN X5R JMK212BJ475MD
**** TAIYO YUDEN X5R JMK316BJ226ML
V
IN
= 3.3V
V
OUT
= 5V
L = 2.2μH
1
2
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LTC3428
ABSOLUTE MAXIMUM RATINGS
(Note 1)
PIN CONFIGURATION
TOP VIEW
PGNDA
SWA
V
OUT
SHDN
V
C
1
2
3
4
5
11
V
IN
, V
OUT
, SWA, SWB Voltage........................ –0.3 to 6V
SWA, SWB Voltage, Pulsed, <100ns ...........................7V
SHDN,
V
C
, FB Voltage .................................... –0.3 to 6V
Operating Temperature Range (Note 2)....–40°C to 85°C
Storage Temperature Range...................–65°C to 125°C
10 PGNDB
9 SWB
8 V
IN
7 AGND
6 FB
DD PACKAGE
10-LEAD (3mm 3mm) PLASTIC DFN
EXPOSED PAD MUST BE SOLDERED
TO GROUND PLANE ON PCB
T
JMAX
= 125°C,
θ
JA
= 45°C/W
θ
JC
= 3°C/W
ORDER INFORMATION
LEAD FREE FINISH
LTC3428EDD#PBF
LEAD BASED FINISH
LTC3428EDD
TAPE AND REEL
LTC3428EDD#TRPBF
TAPE AND REEL
LTC3428EDD#TR
PART MARKING
LBBG
PART MARKING
LBBG
PACKAGE DESCRIPTION
10-Lead (3mm
×
3mm) Plastic DFN
PACKAGE DESCRIPTION
10-Lead (3mm
×
3mm) Plastic DFN
TEMPERATURE RANGE
–40°C to 85°C
TEMPERATURE RANGE
–40°C to 85°C
Consult LTC Marketing for parts specified with wider operating temperature ranges.
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/
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 3.3V, V
OUT
= 5V unless otherwise noted.
PARAMETER
Minimum Startup Voltage
Quiescent Current, V
OUT
Quiescent Current, V
IN
Shutdown Current
Switching Frequency
FB Regulated Voltage
FB Input Current
Error Amp Transconductance
Output Adjust Voltage
1.6
V
FB
= 1.24V
SHDN
= V
IN
SHDN
= V
IN
SHDN
= 0V
Per Phase
l
l
ELECTRICAL CHARACTERISTICS
CONDITIONS
MIN
TYP
1.5
100
1.3
MAX
1.6
200
2.0
1
1.2
1.268
50
5.25
UNITS
V
μA
mA
μA
MHz
V
nA
μS
V
0.8
1.219
1.0
1.243
1
170
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LTC3428
ELECTRICAL CHARACTERISTICS
PARAMETER
NMOS Switch Leakage
NMOS Switch On Resistance
NMOS Current Limit
SHDN
Input Threshold
SHDN
Input Current
Maximum Duty Cycle
Minimum Duty Cycle
Current Limit Delay to Output
(Note 3)
l
l
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 3.3V, V
OUT
= 5V unless otherwise noted.
CONDITIONS
V
SWA
, V
SWB
= 5.5V, Per Phase
V
OUT
= 5V, Per Phase
Per Phase
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MIN
TYP
0.1
0.093
MAX
2.5
UNITS
μA
Ω
A
2
0.4
80
2.5
0.8
0.01
87
0
400
1.5
1
V
μA
%
%
ns
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 LTC3428E is guaranteed to meet performance specifications
from 0°C to 70°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:
Specification is guaranteed by design and not 100% tested in
production.
Note 4:
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.
TYPICAL PERFORMANCE CHARACTERISTICS
All characteristic curves at T
A
= 25°C unless otherwise noted.
SW Pin and Inductor Current in
Discontinuous Mode, Demonstrating
Anti-Ring Circuit Operation
SWA, SWB Switching Waveforms
Transient Response, 0.5A to 1.5A
SWA
2V/DIV
100mV/DIV
5V/DIV
SWB
500mA/DIV
500mA/DIV
500ns/DIV
3428 G01
500ns/DIV
3428 G02
100μs/DIV
3428 G03
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LTC3428
TYPICAL PERFORMANCE CHARACTERISTICS
All characteristic curves at T
A
= 25°C unless otherwise noted.
Output Voltage Ripple with 22μF
Ceramic Capacitor
95
3.3V TO 5V
90
85
EFFICIENCY (%)
80
75
70
65
60
55
0.05
3428 G04
Converter Efficiency
108
106
104
2.5V TO 5V
R
DS(ON)
(mΩ)
2
3428 G05
Switch R
DS(ON)
vs V
OUT
2.5V TO 3.3V
102
100
98
96
94
92
90
50mV/DIV
500ns/DIV
0.1
LOAD CURRENT (A)
1
88
2.5
3.0
4.0
4.5
3.5
OUTPUT VOLTAGE (V)
5.0
3428 G06
SWA, SWB Rise Time, I = 2A
120
110
Switch R
DS(ON)
vs Temperature
1.27
Feedback Voltage vs Temperature
1.26
FB VOLTAGE (V)
R
DS(ON)
(mΩ)
100
90
80
70
60
–45 –25 –5
1.25
1V/DIV
1.24
1.23
10ns/DIV
3428 G07
15 35 55 75
TEMPERATURE (°C)
95 115
3428 G08
1.22
–45 –25
–5
15 35
55 75
TEMPERATURE (°C)
95 115
3428 G09
Peak Current Limit
vs Temperature
3.4
3.2
PEAK CURRENT LIMIT (A)
3.0
2.8
2.6
2.4
2.2
2.0
–45
–25
35
15
55
–5
TEMPERATURE (°C)
75
95
3428 G10
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LTC3428
PIN FUNCTIONS
PGNDA, PGNDB (Pins 1, 10, 11 (Exposed Pad)):
Power
Ground for the IC. Tie directly to local ground plane.
SWA (Pin 2), SWB (Pin 9):
Phase B and Phase A Switch
Pins. The inductor and Schottky diodes for each phase
are connected to these pins. Minimize trace length to
reduce EMI.
V
OUT
(Pin 3):
Power Supply Output and Bootstrapped
Power Source for the IC. Connect low ESR output filter
capacitors from this pin to the ground plane.
SHDN
(Pin 4):
Shutdown Pin. Grounding this pin shuts
down the IC. Connect to a voltage greater than 1.5V to
enable.
V
C
(Pin 5):
Error Amp Output. A frequency compensation
network is connected to this pin to compensate the boost
converter loop.
FB (Pin 6):
Feedback Pin. A resistor divider from V
OUT
is
connected here to set the output voltage according to
V
OUT
= 1.243 • (1 + R1 / R2)
AGND (Pin 7):
Signal Ground for the IC. Connect to ground
plane near feedback resistor divider.
V
IN
(Pin 8):
Input Supply Pin. Bypass V
IN
with a low ESR
ceramic capacitor of at least 4.7μF. X5R and X7R dielectrics
are preferred for their superior voltage and temperature
characteristics.
BLOCK DIAGRAM
FB
ERROR AMPLIFIER/SOFT-START
V
IN
V
C
FB
–
+
1.243V
V
OUT
CURRENT
LIMIT
I
SENB
SWB
I
SENB
RAMP/
SLOPE COMP
CLK B
–
–
+
PWM
COMP
PWM
LOGIC
DRIVER
PGNDB
CHANNEL B
OSCILLATOR
CHANNEL A
CLK A
TSD
SWA
RAMP/
SLOPE COMP
I
SENA
SHDN
V
C
AGND
5pF
SHUTDOWN
CURRENT
LIMIT
I
SENA
3428 BD
+
–
–
PWM
LOGIC
PWM
COMP
DRIVER
PGNDA
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