LTC3427
500mA, 1.25MHz
Synchronous Step-Up
DC/DC Converter in
2mm
×
2mm DFN Package
FEATURES
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DESCRIPTIO
High Efficiency: Up to 94%
3.3V at 200mA from Two Alkaline Cells
5V at 200mA from a Single Li-Ion Cell
Inrush Current Limiting and Soft-Start
Output Disconnect in Shutdown
1.8V to 5V V
IN
Range
1.8V to 5.25V V
OUT
Range
1.25MHz Fixed Frequency, Low Noise PWM
Internal Synchronous Rectifier
Logic Controlled Shutdown (<1µA)
Anti-Ringing Control Minimizes EMI
Tiny External Components
Short-Circuit Protection
Low Profile (0.75mm
×
2mm
×
2mm) DFN Package
The LTC
®
3427 is the industry’s first high efficiency, fixed
frequency, step-up DC/DC converter with true output
disconnect in a 6-lead 2mm
×
2mm DFN package. Requir-
ing minimal external components, the LTC3427 operates
from an input voltage as low as 1.8V. The LTC3427
contains an internal 0.525Ω N-channel MOSFET switch
and a 0.575Ω P-channel MOSFET synchronous rectifier,
which enables it to supply 200mA at 3.3V from a 2-cell
alkaline battery input.
The LTC3427 limits inrush current during start-up and
provides a soft-start of V
OUT
. A switching frequency of
1.25MHz minimizes solution footprint by allowing the use
of tiny, low profile inductors and ceramic capacitors and
produces very low V
OUT
ripple. The current mode PWM
design is internally compensated, reducing external parts
count. Anti-ringing control reduces EMI in discontinuous
mode operation. The LTC3427 also features low shut-
down current of under 1µA and thermal shutdown.
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
APPLICATIO S
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Handheld Instruments
Digital Cameras
Wireless Handsets
GPS Receivers
Portable Medical Devices
MP3 Players
TYPICAL APPLICATIO
V
IN
1.8V TO 3.2V
2-CELL
ALKALINE
2.4V to 3.3V Efficiency
100
95
EFFICIENCY
POWER LOSS (mW)
EFFICIENCY (%)
2-Cell Alkaline to 3.3V Synchronous Boost Converter
4.7µH
+
2.2µF
V
IN
LTC3427
OFF ON
SHDN
V
OUT
1000k
GND
FB
604k
SW
V
OUT
3.3V
200mA
4.7µF
90
85
80
POWER LOSS
75
70
10
1000
3427 TA01b
3427 TA01a
10
U
1000
100
100
LOAD CURRENT (mA)
3427fa
U
U
1
LTC3427
ABSOLUTE
(Note 1)
AXI U
RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW
SHDN
V
OUT
FB
V
IN
, V
OUT
Voltages ...................................... – 0.3V to 6V
SHDN, FB Voltages ..................................... – 0.3V to 6V
SW Voltage
DC .......................................................... – 0.3V to 6V
Pulsed < 100ns ...................................... – 0.3V to 7V
Operating Temperature Range
(Notes 2, 5) ............................................ – 40°C to 85°C
Storage Temperature Range ................ – 65°C to 125°C
6
5
4
7
1
SW
2
GND
3
V
IN
DC PACKAGE
6-LEAD (2mm
×
2mm) PLASTIC DFN
T
JMAX
= 125°C,
θ
JA
= 60°C/W TO 85°C/W
EXPOSED PAD (PIN 7) IS GND, MUST BE SOLDERED TO PCB
ORDER PART NUMBER
LTC3427EDC
DC PART MARKING
LBSY
Order Options
Tape and Reel: Add #TR
Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF
Lead Free Part Marking:
http://www.linear.com/leadfree/
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
The
●
denotes specifications which apply over the full operating temperature range, otherwise specifications are T
A
= 25°C.
V
IN
= 2.4V, V
OUT
= 3.3V unless otherwise specified.
PARAMETER
Minimum Start-Up Voltage
Output Voltage Adjust Range
Feedback Voltage
Feedback Input Current
Quiescent Current—Shutdown
Quiescent Current—Active
NMOS Switch Leakage
PMOS Switch Leakage
NMOS Switch-On Resistance
PMOS Switch-On Resistance
NMOS Current Limit
Current Limit Delay to Output
Maximum Duty Cycle
Minimum Duty Cycle
Frequency
SHDN Input High
SHDN Input Low
SHDN Input Current
Soft-Start Time
V
SHDN
= 5.5V
0.01
2
(Note 4)
V
FB
= 1V
V
FB
= 1.5V
●
●
●
●
CONDITIONS
I
LOAD
< 1mA
●
●
●
MIN
1.8
1.215
TYP
1.6
1.24
1
0.01
350
0.1
0.1
0.525
0.575
MAX
1.8
5.25
1.265
50
1
550
5
5
UNITS
V
V
V
nA
µA
µA
µA
µA
Ω
Ω
mA
ns
%
V
FB
= 1.24V
V
SHDN
= 0V, V
OUT
= 0V
V
FB
= 1.5V (Note 3)
500
40
80
0.9
1
0.35
1
87
0
1.25
1.5
2
U
%
MHz
V
V
µA
ms
3427fa
W
U
U
W W
W
LTC3427
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.
Note 2:
The LTC3427E 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:
Current is measured into the V
OUT
pin since the supply current is
bootstrapped to the output. The current will reflect to the input supply by:
(V
OUT
/V
IN
) • Efficiency. The outputs are not switching.
Note 4:
Specification is guaranteed by design and not 100% tested in
production.
Note 5:
The LTC3427 includes an overtemperature shutdown that is
intended to protect the device during momentary overload conditions.
Junction temperature will exceed 125°C when the overtemperature
shutdown is active. Continuous operation above the specified maximum
operating junction temperature may impair device reliability.
TYPICAL PERFOR A CE CHARACTERISTICS
2-Cell Alkaline to 3.3V Efficiency
100
95
90
EFFICIENCY (%)
85
80
75
70
65
60
55
50
1
10
100
LOAD CURRENT (mA)
1000
3427 G01
V
IN
= 3.1V
V
IN
= 2.4V
EFFICIENCY (%)
V
IN
= 1.8V
80
75
70
65
60
55
50
1
EFFICIENCY (%)
Inrush Current Control
V
OUT
100mV/DIV
AC COUPLED
I
OUT
40mA
TO 100mA
10mV/DIV
V
OUT
1V/DIV
INDUCTOR
CURRENT
100mA/DIV
SHDN
5V/DIV
V
IN
= 2.4V
C
OUT
= 22µF
L = 4.7µH
500µs/DIV
3427 G04
U W
T
A
= 25°C unless otherwise specified.
2-Cell Alkaline to 5V Efficiency
100
95
90
85
80
75
70
65
60
55
50
V
IN
= 1.8V
V
IN
= 3.2V
V
IN
= 2.4V
Li-Ion to 5V Efficiency
100
95
90
85
V
IN
= 3.6V
V
IN
= 4.2V
V
IN
= 3.1V
10
100
LOAD CURRENT (mA)
1000
3427 G02
1
10
100
LOAD CURRENT (mA)
1000
3427 G03
Load Transient Response
I
LOAD
100mA
I
LOAD
50mA
I
LOAD
10mA
V
OUT
Ripple, AC Coupled
V
IN
= 1.8V
V
OUT
= 3.3V
C
OUT
= 4.7µF
L = 4.7µH
100µs/DIV
3427 G05
V
IN
= 2.4V
V
OUT
= 3.3V
L = 4.7µH
C
IN
= 2.2µF
C
OUT
= 4.7µF
500ns/DIV
3427 G13
3427fa
3
LTC3427
TYPICAL PERFOR A CE CHARACTERISTICS
Current Limit
0.90
V
IN
= 2.4V
V
OUT
= 3.3V
1.25
0.80
CURRENT LIMIT (A)
FB VOLTAGE (V)
0.70
1.24
EFFICIENCY (%)
0.60
50
0.50
–45
–30
–15
0
15 30
45 60
TEMPERATURE (°C)
Frequency Accuracy
vs Temperature
1.35
V
IN
= 2.4V
V
OUT
= 3.3V
1.30
FREQUENCY (MHz)
1.25
1.20
1.15
–45
–30
–15
R
DS(ON)
vs Temperature
0.70
0.65
0.60
R
DS(ON)
(Ω)
V
IN
= 2.4V
V
OUT
= 3.3V
PMOS
0.55
NMOS
0.50
0.45
0.40
0.35
–45 –30 –15
0 15 30 45 60
TEMPERATURE (°C)
75
90
V
IN
SUPPLY CURRENT (mA)
4
U W
75
T
A
= 25°C unless otherwise specified.
FB Voltage vs Temperature
V
IN
= 2.4V
V
OUT
= 3.3V
100
90
80
70
60
Efficiency vs V
IN
V
OUT
= 3.3V
I
OUT
= 100mA
V
IN
> V
OUT
PMOS LDO MODE
90
1.23
–45 –30 –15
0 15 30 45 60
TEMPERATURE (°C)
75
90
40
1.5
2.5
3.5
V
IN
(V)
4.5
3427 G08
3427 G06
3427 G07
SW Pin Anti-Ringing Operation
INDUCTOR
CURRENT
50mA/DIV
SW
2V/DIV
3427 G10
V
IN
= 1.8V
V
OUT
= 3.3V
C
OUT
= 4.7µF
L = 4.7µH
0
15 30
45 60
TEMPERATURE (°C)
75
200ns/DIV
90
3427 G09
V
IN
Supply Current (No Load)
0.45
T
A
= 25°C
V
IN
= V
OUT
= V
FB
0.40
0.35
0.30
1.5
2.5
3.5
V
IN
(V)
4.5
5.5
3427 G12
3427 G11
3427fa
LTC3427
PI FU CTIO S
SW (Pin 1):
Switch Pin for the Inductor Connection.
Minimize trace length between SW and the inductor. For
discontinuous inductor current, an internal 200Ω imped-
ance is connected from SW to V
IN
to eliminate high
frequency ringing, reducing EMI radiation.
GND (Pin 2):
Signal and Power Ground. Provide a short,
direct PCB path between GND and the (–) side of the input
and output capacitor(s).
V
IN
(Pin 3):
Input Supply Voltage. Connect V
IN
to the input
supply and decouple with a 2.2µF or larger ceramic
capacitor as close to V
IN
as possible.
SHDN (Pin 4):
Shutdown Input. Less than 350mV on
SHDN shuts down the LTC3427. Placing 1V or more on
SHDN enables the LTC3427.
FB (Pin 5):
Feedback Input to the Error Amplifier. Connect
resistor divider tap to this pin. Referring to the Block
Diagram, V
OUT
can be adjusted from 1.8V to 5.25V by:
BLOCK DIAGRA
V
IN
1.8V TO 5V
+
C
IN
2.2µF
SLOPE COMPENSATION
7
EXPOSED PAD
– + –
W
U
U
U
⎛
R1
⎞
V
OUT
=
1.24V •
⎜
1
+
⎟
⎝
R2
⎠
V
OUT
(Pin 6):
Output Voltage Sense Input and Drain of the
Internal Synchronous Rectifier MOSFET. Driver bias is
derived from V
OUT
. PCB trace length from V
OUT
to the
output filter capacitor(s) should be as short and wide as
possible.
Exposed Pad (Pin 7):
Ground for the LTC3427. This pin
must be soldered to the PCB ground plane for electrical
connection and rated thermal performance.
L1
4.7µH
OPTIONAL
4
SHDN
3
V
IN
V
IN
1
SW
BULK CONTROL
SIGNALS
ANTIRING
V
OUT
6
V
OUT
1.8V TO 5.25V
SHUTDOWN
AND
V
BIAS
SHDN
PWM
LOGIC
AND
DRIVERS
CURRENT
SENSE
+
IZERO
COMP
–
1.24V
PWM
COMP
REFERENCE
1V
GAIN ERROR
AMPLIFIER
R1
THERMAL
SHUTDOWN
+
–
START-UP
SOFT-START
FB
5
R2
C
OUT
4.7µF
I
LIM
REF
Σ
+
+
1.24V
OSCILLATOR
GND
2
3427 BD
3427fa
5
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