LTC3539EDCB#TRMPBF [Linear]
LTC3539/LTC3539-2 - 2A, 1MHz/2MHz Synchronous Step-Up DC/DC Converters; Package: DFN; Pins: 8; Temperature Range: -40°C to 85°C;型号: | LTC3539EDCB#TRMPBF |
厂家: | Linear |
描述: | LTC3539/LTC3539-2 - 2A, 1MHz/2MHz Synchronous Step-Up DC/DC Converters; Package: DFN; Pins: 8; Temperature Range: -40°C to 85°C 开关 光电二极管 |
文件: | 总14页 (文件大小:224K) |
中文: | 中文翻译 | 下载: | 下载PDF数据表文档文件 |
LTC3539/LTC3539-2
2A, 1MHz/2MHz
Synchronous Step-Up
DC/DC Converters
FEATURES
DESCRIPTION
The LTC®3539/LTC3539-2 are synchronous, 2A step-up
DC/DC converters with output disconnect. Synchronous
rectification enables high efficiency in the low profile
2mm × 3mm DFN package. Battery life is extended with
a 700mV start-up voltage and operation down to 500mV
once started.
n
Delivers 3.3V at 900mA From 2 Alkaline/NiMH Cells
n
Delivers 5V at 900mA From a Lithium-Polymer
Battery
n
V Start-Up Voltage: 700mV
IN
n
1.5V to 5.25V V
Range
OUT
n
n
n
n
Up to 94% Efficiency
V > V Operation
IN
OUT
A switching frequency of 1MHz (LTC3539) or 2MHz
(LTC3539-2) minimizes solution footprint by allowing the
use of tiny, low profile inductors and ceramic capacitors.
The current mode PWM design is internally compensated,
reducing external parts count. The LTC3539/LTC3539-2
feature a pin-enabled automatic Burst Mode operation at
light load conditions. Anti-ring circuitry reduces EMI by
damping the inductor in discontinuous mode. Additional
features include a low shutdown current of under 1µA and
thermal overload protection.
1.5ꢀ Feedback Voltage Tolerance
1MHz (LTC3539) or 2MHz (LTC3539-2) Fixed
Frequency Operation
n
n
n
n
n
n
Output Disconnect
Selectable Burst Mode® or PWM Operation
10µA Quiescent Current
Logic Controlled Shutdown: <1µA
Requires Only 6 External Components
Low Profile (2mm × 3mm × 0.75mm) DFN Package
APPLICATIONS
The LTC3539/LTC3539-2 are offered in a 2mm × 3mm ×
0.75mm DFN package.
L, LT, LTC, LTM and Burst Mode are registered trademarks and ThinSOT is a trademark of
Linear Technology Corporation. All other trademarks are the property of their respective owners.
n
Medical Instruments
n
Portable Bar Code Scanners
n
Noise Canceling Headphones
Portable GPS Navigation
n
n
Handheld PCs
TYPICAL APPLICATION
Wide VIN, High Power 3.3V Regulator
Efficiency and Power Loss vs Load Current
100
90
80
70
60
50
40
30
20
10
0
1000
100
10
4.7µH
V
IN
1.8V TO 3.6V
EFFICIENCY
2.2µF
V
SW
IN
LTC3539
V
V
= 2.4V
V
IN
OUT
OUT
PWM BURST
OFF ON
MODE
V
OUT
= 3.3V
3.3V
600mA
1M
33pF
POWER LOSS
SHDN
FB
22µF
×2
1
GND PGND
562k
FREQUENCY = 1MHz
FREQUENCY = 2MHz
3539 TA01a
0.1
1000
0.1
1
10
100
I
AVERAGE (mA)
3539 TA01b
LOAD
35392fc
1
For more information www.linear.com/3539/3539-2
LTC3539/LTC3539-2
ABSOLUTE MAXIMUM RATINGS
PIN CONFIGURATION
(Note 1)
TOP VIEW
V Voltage................................................... –0.3V to 6V
IN
8
7
6
5
SW
PGND
GND
1
2
3
4
V
OUT
SW Voltage
MODE
FB
DC............................................................ –0.3V to 6V
Pulsed <100ns......................................... –0.3V to 7V
SHDN, FB, MODE Voltage ............................ –0.3V to 6V
9
V
IN
SHDN
DCB PACKAGE
8-LEAD (2mm × 3mm) PLASTIC DFN
V
OUT
............................................................. –0.3V to 6V
Operating Temperature (Notes 2, 5).........–40°C to 85°C
Storage Temperature Range .................. –65°C to 125°C
T
= 125°C, θ = 64°C/W (NOTE 6)
JMAX
JA
EXPOSED PAD (PIN 9) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
LTC3539EDCB#PBF
LTC3539EDCB-2#PBF
TAPE AND REEL
PART MARKING
PACKAGE DESCRIPTION
8-Lead (2mm × 3mm) Plastic DFN
8-Lead (2mm × 3mm) Plastic DFN
TEMPERATURE RANGE
–40°C to 85°C
–40°C to 85°C
LTC3539EDCB#TRPBF
LDCS
LTC3539EDCB-2#TRPBF LDPH
Consult LTC Marketing for parts specified with wider operating temperature ranges.
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/
ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the specified
temperature range of –40°C to 85°C, otherwise specifications are at TA = 25°C. VIN = 1.2V, VOUT = 3.3V, unless otherwise noted.
PARAMETER
CONDITIONS
MIN
TYP
MAX
5
UNITS
V
Input Voltage Range
After Start-Up
0.5
Minimum Start-Up Voltage
I
= 1mA, V
= 0V
0.7
0.88
5.25
1.218
50
V
LOAD
OUT
l
l
Output Voltage Adjust Range
Feedback Voltage
1.5
V
1.182
1.200
1
V
Feedback Input Current
V
V
= 1.2V
nA
µA
µA
µA
µA
µA
Ω
FB
Quiescent Current - Shutdown
Quiescent Current - Active
= 0V, Not Including Switch Leakage, V
= 0V
0.01
300
10
1
SHDN
OUT
Measured on V , Non-Switching
500
18
OUT
Quiescent Current - Burst
Measured on V , FB > 1.230V
OUT
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 Current Limit
V
V
V
V
= 5V
0.1
10
SW
= 5V, V
= 3.3V
= 3.3V
= 0V
0.1
20
SW
OUT
0.09
0.125
2.6
OUT
OUT
Ω
l
2
A
35392fc
2
For more information www.linear.com/3539/3539-2
LTC3539/LTC3539-2
ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the specified
temperature range of –40°C to 85°C, otherwise specifications are at TA = 25°C. VIN = 1.2V, VOUT = 3.3V, unless otherwise noted.
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
ꢀ
l
l
Maximum Duty Cycle
Minimum Duty Cycle
Switching Frequency
V
FB
V
FB
= 1.15V
= 1.3V
87
90
0
ꢀ
l
l
LTC3539
LTC3539-2
0.7
1.8
1
2
1.3
2.4
MHz
MHz
MODE Input High Voltage
MODE Input Low Voltage
MODE Input Current
0.88
V
V
0.3
1
V
= 1.2V
0.3
µA
V
MODE
SHDN Input High Voltage
SHDN Input Low Voltage
SHDN Input Current
0.88
0.3
V
V
SHDN
V
SHDN
= 1.2V
= 3.3V
0.3
1
1
2
µA
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: The LTC3539E/LTC3539E-2 is guaranteed to meet performance
specifications from 0°C to 85°C. Specifications over –40°C to 85°C
operating temperature range are assured by design, characterization and
correlation with statistical process controls.
Note 4: Current measurements are made when the output is not switching.
Note 5: 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 result in device degradation or failure.
Note 6: Failure to solder the exposed backside of the package to the PC
board ground plane will result in a thermal resistance much higher than
64°C/W.
Note 3: Specification is guaranteed by design and not 100ꢀ tested in
production.
(TA = 25°C unless otherwise noted)
TYPICAL PERFORMANCE CHARACTERISTICS
Efficiency vs Load Current and
Efficiency vs Load Current and
VIN, VOUT = 3.3V
VIN, VOUT = 1.8V
100
1000
100
10
100
90
80
70
60
50
40
30
20
10
0
1000
100
10
90
80
70
60
50
40
30
20
10
0
EFFICIENCY
EFFICIENCY
POWER LOSS
1
POWER LOSS
1
0.1
0.01
V
V
V
= 1.2V
= 1.8V
= 3V
V
= 1V
= 1.2V
= 1.5V
IN
IN
IN
IN
IN
IN
V
V
0.1
1000
0.1
1
10
100
0.1
1
10
100
1000
LOAD CURRENT (mA)
LOAD CURRENT (mA)
3539 G02
3539 G01
35392fc
3
For more information www.linear.com/3539/3539-2
LTC3539/LTC3539-2
(TA = 25°C unless otherwise noted)
TYPICAL PERFORMANCE CHARACTERISTICS
Efficiency vs Load Current and
VIN, VOUT = 5V
No Load Input Current vs VIN
Maximum Output Current vs VIN
100
90
80
70
60
50
40
30
20
10
0
200
180
160
140
120
100
80
2000
1800
1600
1400
1200
1000
800
1000
100
10
L = 2.2µH
V
V
V
V
= 1.8V
= 2.5V
= 3.3V
= 5V
OUT
OUT
OUT
OUT
EFFICIENCY
POWER LOSS
60
600
1
V
OUT
V
OUT
V
OUT
V
OUT
= 1.8V
= 2.5V
= 3.3V
= 5V
40
400
V
= 2.4V
= 3.6V
= 4.2V
IN
V
IN
20
200
V
IN
0.1
1000
0
0
0.1
1
10
100
0
1
2
3
4
5
0.7 1.1 1.5 1.9 2.3 2.7 3.1 3.5 3.9 4.3 4.7 5.1
(V)
LOAD CURRENT (mA)
V
IN
(V)
V
IN
3539 G03
3539 G04
3539 G05
Minimum Load Resistance During
Start-Up vs VIN
Burst Mode Threshold Current
vs VIN; VOUT = 1.8V
Burst Mode Threshold Current
vs VIN; VOUT = 2.5V
10000
1000
100
10
50
45
40
35
30
25
20
15
10
5
50
45
40
35
30
25
20
15
10
5
f
= 1MHz
V
OUT
= 3.3V
C
OUT
= 44µF
SW
C
OUT
= 44µF
f
= 1MHz
SW
LEAVE BURST
LEAVE BURST
f
= 2MHz
SW
f
= 2MHz
SW
ENTER BURST
ENTER BURST
0
0
0.1
0.65
0.75
0.85
0.95
(V)
1.05
1.15
0.7 0.8 0.9
1
1.1 1.2 1.3 1.4 1.5
(V)
0.7 0.9 1.1 1.3 1.5 1.7 1.9 2.1
(V)
V
IN
V
IN
V
IN
3539 G06
3539 G07a
3539 G07b
Burst Mode Threshold Current
vs VIN; VOUT = 3.3V
Burst Mode Threshold Current
vs VIN; VOUT = 5V
Normalized Current Limit vs VOUT
1.10
1.05
1.00
0.95
0.90
0.85
0.80
100
90
80
70
60
50
40
30
20
10
0
60
50
40
30
20
10
0
C
OUT
= 44µF
C
OUT
= 44µF
LEAVE BURST
= 1MHz
f
= 1MHz
SW
LEAVE BURST
f
= 2MHz
f
SW
SW
ENTER BURST
f
= 2MHz
SW
ENTER BURST
1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
0.7 0.9 1.1 1.3 1.5 1.7 1.9 2.1 2.3 2.5 2.7
(V)
0.7 1.1 1.5 1.9 2.3 2.7 3.1 3.5 3.9 4.3
(V)
V
OUT
(V)
V
IN
V
IN
3539 G08
3539 G07c
3539 G07d
35392fc
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For more information www.linear.com/3539/3539-2
LTC3539/LTC3539-2
TYPICAL PERFORMANCE CHARACTERISTICS
RDS(ON) vs VOUT
RDS(ON) Change vs Temperature
VFB vs Temperature
0.30
0.25
0.20
0.15
0.10
0.05
0
1.3
1.2
1.1
1.0
0.9
0.8
0.7
0.50
0.25
0
PMOS
–0.25
–0.50
–0.75
–1.00
NMOS
1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5
–50 –30 –10 10
30
50
70
90
–60 –40 –20
0
20 40 60 80 100
V
OUT
(V)
TEMPERATURE (°C)
TEMPERATURE (°C)
3539 G09
3539 G10
3539 G11
Start-Up Voltage vs Temperature
Fixed Frequency SW and IL(AC)
Burst Mode SW and IL(AC)
0.80
0.75
0.70
0.65
0.60
0.55
0.50
SW PIN
2V/DIV
SW PIN
5V/DIV
V
V
OUT
1mA LOAD
NO LOAD
OUT
20mV/DIV
20mV/DIV
AC-COUPLED
AC-COUPLED
INDUCTOR
CURRENT
500mA/DIV
INDUCTOR
CURRENT
200mA/DIV
3539 G13
3539 G14
500ns/DIV
= 3.3V AT 400mA
5µs/DIV
V
V
C
= 2.4V
V
V
C
= 3.3V
IN
IN
= 5V
OUT
OUT
OUT
OUT
= 22µF
= 22µF
–50
–25
0
25
50
75
100
TEMPERATURE (°C)
3539 G12
Load Step, Fixed Frequency
Load Step, Burst Mode Operation
V
V
OUT
OUT
50mV/DIV
50mV/DIV
AC-COUPLED
AC-COUPLED
LOAD
CURRENT
200mA/DIV
LOAD
CURRENT
200mA/DIV
3539 G15
3539 G16
500µs/DIV
500µs/DIV
V
V
C
= 2.4V
V
V
C
= 2.4V
IN
IN
= 3.3V
= 3.3V
OUT
OUT
OUT
OUT
= 22µF
= 100mA TO 250mA STEP
= 22µF
= 20mA TO 170mA
I
I
LOAD
LOAD
35392fc
5
For more information www.linear.com/3539/3539-2
LTC3539/LTC3539-2
PIN FUNCTIONS
SW (Pin 1): Switch Pin. Connect inductor between SW
Connect resistor divider tap to this pin. The output volt-
and V . Keep PCB trace lengths as short and wide as pos-
age can be adjusted from 1.5V to 5.25V by: V
= 1.20V
IN
OUT
sible to reduce EMI. If the inductor current falls to zero,
• [1 + (R2/R1)]
or SHDN is low, an internal anti-ring resistor is connected
MODE (Pin 7): Burst Mode Pin. A logic controlled input
to select either automatic Burst Mode operation or forced
fixed frequency operation.
from SW to V to minimize EMI.
IN
PGND (Pin 2), GND (Pin 3): Signal and Power Ground.
Provide a short direct PCB path between PGND, GND and
the (–) side of the input and output capacitors.
MODE = High: Burst Mode operation at light loads
MODE = Low: Fixed frequency PWM Mode
V (Pin 4): Battery Input Voltage. Connect a minimum of
IN
V
(Pin 8): Output Voltage Sense and Drain of the
2.2µFceramicdecouplingcapacitorfromthispintoground.
OUT
Internal Synchronous Rectifier. PCB trace length from
SHDN (Pin 5): Logic Controlled Shutdown Input. There
is an internal 4MΩ pull-down on this pin.
V
OUT
to the output filter capacitor should be as short and
wide as possible.
SHDN = High: Normal operation.
Exposed Pad (Pin 9): The exposed pad must be soldered
to the PCB ground plane. It serves as another ground
connection, and as a means of conducting heat away
from the die.
SHDN = Low: Shutdown, quiescent current <1µA.
FB (Pin 6): Feedback Input to the g Error Amplifier.
m
BLOCK DIAGRAM
V
IN
1
4
SW
V
IN
V
OUT
V
SEL
WELL
SWITCH
V
BEST
V
B
V
8
6
OUT
V
OUT
R2
R1
GATE DRIVERS
AND
ANTI-CROSS
CONDUCTION
I
ZERO
COMPARATOR
FB
OFF ON
5
SHUTDOWN
SHUTDOWN
SHDN
I
PK
COMPARATOR
Σ
–
+
–
SLOPE
COMPARATOR
V
V
REF
REF
V
REF
I
I
UVLO
PK
UVLO
+
FB
START-UP
ZERO
ERROR
AMPLIFIER/SLEEP
COMPARATOR
LOGIC AND
BURST MODE
CONTROL
CLK
TSD
1MHz/2MHz
OSC
BURST
WAKE
PWM BURST
7
CLAMP
MODE
THERMAL
SHUTDOWN
SOFT-START
EXPOSED PAD
PGND
GND
9
2
3
3539 BD
35392fc
6
For more information www.linear.com/3539/3539-2
LTC3539/LTC3539-2
OPERATION
DETAILED DESCRIPTION
to series resistance become critical, and greatly limit the
power delivery capability of the converter.
TheLTC3539isahighpowersynchronousboostconverter
in an 8-lead 2mm × 3mm DFN package. With the ability
to start up and operate from inputs of 700mV, the device
features fixed frequency, current mode PWM control for
exceptional line and load regulation. The current mode
architecture with adaptive slope compensation provides
excellenttransientloadresponse,requiringminimaloutput
filtering.Internalsoft-startandinternalloopcompensation
simplifiesthedesignprocesswhileminimizingthenumber
of external components. The switching frequency of the
LTC3539isnominally1MHz,whiletheLTC3539-2switches
at 2MHz. Operation of the LTC3539 and LTC3539-2 is
identical in all other respects.
Low Noise Fixed Frequency Operation
Soft-Start: The LTC3539/LTC3539-2 contains internal
circuitry to provide soft-start operation. The internal
soft-start circuitry ramps the peak inductor current from
zero to its peak value of 2.6A (typical) in approximately
0.5ms, allowing start-up into heavy loads. The soft-start
circuitry is reset in the event of a thermal shutdown or
shutdown command.
Oscillator: An internal oscillator sets the switching fre-
quency to 1MHz for the LTC3539, and 2MHz for the
LTC3539-2.
WithitslowR
andlowgatechargeinternalN-channel
DS(ON)
Shutdown: The part is shutdown by pulling the SHDN
pin below 0.3V, and activated by pulling the SHDN pin
MOSFET switch and P-channel MOSFET synchronous
rectifier, the LTC3539 achieves high efficiency over a wide
range of load current. Burst Mode operation maintains
high efficiency at very light loads, reducing the quiescent
current to just 10µA.
above 0.88V. Note that SHDN can be driven above V
IN
or V , as long as it is limited to less than the absolute
OUT
maximum rating.
Error Amplifier: The error amplifier is a transconductance
type. The non-inverting input is internally connected to
the 1.2V reference and the inverting input is connected
to FB. Clamps limit the minimum and maximum error
amp output voltage for improved large signal transient
response. Power converter control loop compensation is
Converter operation can be best understood by referring
to the Block Diagram.
Low Voltage Start-Up
The LTC3539 includes an independent start-up oscillator
designed to start up at an input voltage of 0.7V (typical).
Soft-start and inrush current limiting are provided during
start-up, as well as normal mode.
provided internally. A voltage divider from V
to ground
OUT
programs the output voltage via FB from 1.5V to 5.25V.
= 1.2V • [1 + (R2/R1)].
V
OUT
When either V or V
exceeds 1.4V typical, the IC
OUT
Current Sensing: Lossless current sensing converts the
peak current signal of the N-channel MOSFET switch
into a voltage which is summed with the internal slope
compensation. The summed signal is compared to the
error amplifier output to provide a peak current control
command for the PWM.
IN
enters normal operating mode. Once the output voltage
exceeds the input by 0.24V, the IC powers itself from
V
instead of V . At this point the internal circuitry has
IN
OUT
no dependency on the V input voltage, eliminating the
IN
requirement for a large input capacitor. The input voltage
can drop as low as 0.5V. The limiting factor for the appli-
cation becomes the ability of the power source to supply
sufficient energy to the output at the low voltages, and the
maximum duty cycle, which is clamped at 90ꢀ typical.
Note that at low input voltages, small voltage drops due
Current Limit: The current limit comparator shuts off the
N-channel MOSFET switch once its threshold is reached.
Peak switch current is limited to approximately 2.6A,
independent of input or output voltage, unless V
falls
OUT
below 0.7V, in which case the current limit is cut in half.
35392fc
7
For more information www.linear.com/3539/3539-2
LTC3539/LTC3539-2
OPERATION
Zero Current Comparator: The zero current comparator
monitors the inductor current to the output and shuts off
the synchronous rectifier once this current reduces to ap-
proximately40mA.Thispreventstheinductorcurrentfrom
reversing in polarity, improving efficiency at light loads.
be changed by adjusting the inductor value. Raising the
inductor value will lower the load current at which Burst
Mode operation is entered.
In Burst Mode operation, the LTC3539 still switches at a
fixed frequency, using the same error amplifier and loop
compensation for peak current mode control. This control
method eliminates any output transient when switching
between modes. In Burst Mode operation, energy is deliv-
ered to the output until it reaches the nominal regulation
value, then the LTC3539 transitions to Sleep mode where
the outputs are off and the LTC3539 consumes only 10µA
Synchronous Rectifier: The P-channel MOSFET synchro-
nousrectifierisdisabledwhen V
ismuch less than V .
OUT
IN
This is to control inrush current and to prevent inductor
current from running away
Anti-ringing Control: The anti-ringing control connects
a resistor across the inductor to prevent high frequency
ringing on the SW pin during discontinuous current mode
operation. The ringing of the resonant circuit formed by L
of quiescent current from V . When the output voltage
OUT
droops slightly, switching resumes. This maximizes ef-
ficiency at very light loads by minimizing switching and
quiescent current losses. Burst Mode output voltage
ripple, which is application sensitive and typically 1ꢀ to
2ꢀ peak-to-peak if data sheet recommendations are fol-
lowed, can be reduced by using more output capacitance
(47µF or greater).
and C (capacitance on SW pin) is low energy, but can
SW
cause EMI radiation.
OutputDisconnect:TheLTC3539isdesignedtoallowtrue
outputdisconnectbyeliminatingbodydiodeconductionof
the internal P-channel MOSFET rectifier. This allows V
OUT
to go to zero volts during shutdown, drawing no current
from the input source. It also provides inrush current
limiting at turn-on, minimizing surge currents seen by the
input supply. Note that to obtain the advantages of output
disconnect, there must not be an external Schottky diode
As the load increases, the LTC3539 will automatically
leave Burst Mode operation. Once the LTC3539 has left
Burst Mode operation and returned to normal operation,
it will remain there until the output load is reduced below
the burst threshold.
connected between the SW pin and V . The output
OUT
disconnect feature also allows V
to be pulled high,
without any reverse current into a battery on V .
Burst Mode operation is inhibited during start-up until
OUT
soft-start is complete and V
is at least 0.24V greater
IN
OUT
than V .
IN
ThermalShutdown:Ifthedietemperatureexceeds160°C,
the device will go into thermal shutdown. All switches will
be turned off and the internal soft-start capacitor will be
discharged. The device will be enabled again when the die
temperature drops by about 15°C.
When the MODE pin is below 0.3V, the LTC3539 features
continuous PWM operation. In this mode, at very light
loads, the LTC3539 will exhibit pulse-skip operation. If
the MODE pin voltage exceeds the greater of V or V
IN
OUT
by 0.5V, the MODE pin will sink additional current.
Burst Mode Operation
Due to the high inductor current slew rate in 5V output
applications, the LTC3539-2 may not enter Burst Mode
operationforinputvoltageslessthan1.8V.For5Vapplica-
tions requiring Burst Mode operation, the 1MHz LTC3539
is recommended. Refer to the Typical Performance
Characteristics curves for the Burst Mode thresholds for
different input and output voltages.
When Burst Mode operation is enabled by bringing the
MODE pin above 0.88V, the LTC3539 will automatically
enter Burst Mode operation at light load current, then
return to fixed frequency PWM mode when the load in-
creases. Refer to the typical performance characteristics
to see the output load Burst Mode threshold vs V . The
IN
load current at which Burst Mode operation is entered can
35392fc
8
For more information www.linear.com/3539/3539-2
LTC3539/LTC3539-2
APPLICATIONS INFORMATION
COMPONENT SELECTION
V > V
Operation
IN
OUT
The LTC3539 will maintain output voltage regulation even
whentheinputvoltageisabovethedesiredoutput.Notethat
the efficiency and the maximum output current capability
arereduced.RefertoTypicalPerformanceCharacteristics.
Inductor Selection
The LTC3539 can utilize small surface mount and chip
inductors due to the high switching frequency. Inductor
values between 3.3µH and 4.7µH for the LTC3539 and
between 1.5µH and 2.5µH for the LTC3539-2 are suitable
for most applications.* Larger values of inductance will
allow slightly greater output current capability (and lower
the Burst Mode threshold) by reducing the inductor ripple
current. However, increasing the inductance above 10µH
will increase size while providing little improvement in
output current capability.
Short-Circuit Protection
The LTC3539 output disconnect feature allows an output
short circuit while maintaining a maximum internally set
current limit. To reduce power dissipation under short-
circuit conditions, the peak switch current limit is reduced
to 1.4A (typical).
Schottky Diode
The minimum inductance value is given by:
Although it is not required, adding a Schottky diode from
V
IN(MIN) • (VOUT(MAX) − V
)
IN(MIN)
L >
SW to V
will improve efficiency by about 2ꢀ. Note that
OUT
Ripple • VOUT(MAX) • f
this defeats the output disconnect, V > V
operation
IN
OUT
and short circuit protection features.
Where:
f = 1 for the LTC3539 or 2 for the LTC3539-2
Ripple = allowable inductor current ripple (Amps
peak-to-peak)
PCB LAYOUT GUIDELINES
ThehighspeedoperationoftheLTC3539demandscareful
attention to board layout. A careless layout will result in
reduced performance. Figure 1 shows the recommended
componentplacement.Alargegroundpincopperareawill
help to lower the die temperature. A multilayer board with
a separate ground plane is ideal.
V
V
= minimum input voltage
IN(MIN)
OUT(MAX)
= maximum output voltage
The inductor current ripple is typically set for 20ꢀ to 40ꢀ
of the maximum inductor current. High frequency ferrite
core inductor materials improve efficiency by reducing
frequency dependent power losses compared to cheaper
powdered iron types. The inductor should have low ESR
2
(seriesresistanceofthewindings)toreducetheI Rpower
LTC3539
SW
PGND
GND
V
OUT
1
2
3
4
8
7
6
5
losses, and must accommodate the peak inductor current
without saturating. Molded chokes and some chip induc-
tors usually do not have enough core area to support the
peak inductor current of 2.6A seen on the LTC3539. To
minimizeradiatednoise,useashieldedinductor.SeeTable
1forsuggestedsuppliersandrepresentativecomponents.
MODE
FB
MINIMIZE
TRACE ON FB
AND SW
V
IN
SHDN
+
V
IN
*Single cell applications (V < 1.6V) should use a 2.2µH inductor for the LTC3539
IN
MULTIPLE VIAS
TO GROUND PLANE
3539 F01
Figure 1. Recommended Component Placement for
Single Layer Board
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9
For more information www.linear.com/3539/3539-2
LTC3539/LTC3539-2
APPLICATIONS INFORMATION
Table 1. Representative Inductors
An output capacitor of up to 100µF is required at lower
output voltages. Even with V
greater than 3V, larger
OUT
VENDOR
PART/STYLE
values up to 100µF may be used to obtain extremely low
outputvoltagerippleandimprovetransientresponse.X5R
and X7R dielectric materials are preferred for their ability
tomaintaincapacitanceoverwidevoltageandtemperature
ranges. Y5V types should not be used.
Coilcraft
MSS5131
(847) 639-6400
www.coilcraft.com
LPS4018-222
MSS6132
MOS6020
Murata
www.murata.com
LQH55D
LQH66S
Sumida
CDRH4D22
CDRH4D28C
CDRH5D28
CDR6D23
Asmallceramiccapacitorinparallelwithalargertantalum
capacitor may be used in demanding applications which
havelargeloadtransients. Afeedforwardcapacitoracross
(847) 956-0666
www.sumida.com
TDK
VLF5014ST
the top resistor of the feedback divider (from V
to FB)
OUT
(847) 803-6100
www.component.tdk.com
isusuallyrequiredtoimprovetransientresponse.Atypical
value of 33pF will generally suffice.
Toko
(408) 432-8282
www.tokoam.com
D53LC
D63LCB
Low ESR input capacitors reduce input switching noise
and reduce the peak current drawn from the battery. It
follows that ceramic capacitors are also a good choice
for input decoupling and should be located as close as
possible to the device. A 2.2µF input capacitor is sufficient
for most applications. Larger values may be used without
limitations. Table 2 shows a list of several ceramic capaci-
tor manufacturers. Consult the manufacturers directly for
detailed information on their selection of ceramic parts.
Würth
(201) 785-8800
www.we-online.com
WE-TPC Type LH, X
WE-PD Type XS
Output and Input Capacitor Selection
TheinternalloopcompensationoftheLTC3539isdesigned
tobestablewithoutputcapacitorvaluesof22µForgreater.
Although ceramic capacitors are recommended, low ESR
(equivalent series resistance) tantalum capacitors may be
used as well.
Table 2. Capacitor Vendor Information
SUPPLIER
AVX
PHONE
WEBSITE
(803) 448-9411
(714) 852-2001
(408) 573-4150
(847) 803-6100
www.avxcorp.com
www.murata.com
www.t-yuden.com
www.component.tdk.com
Low ESR capacitors should be used to minimize the
output voltage ripple. Multilayer ceramic capacitors are
an excellent choice as they have extremely low ESR and
are available in small footprints. A 22µF to 47µF output
capacitor is sufficient for output voltages of 3V or greater.
Murata
Taiyo-Yuden
TDK
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10
For more information www.linear.com/3539/3539-2
LTC3539/LTC3539-2
TYPICAL APPLICATIONS
1 Cell to 1.8V
2.2µH
V
IN
1V TO 1.6V
2.2µF
V
SW
IN
LTC3539
V
OUT
PWM BURST
OFF ON
MODE
V
OUT
1.8V
500mA
1M
33pF
SHDN
FB
22µF*
×2
GND PGND
1.91M
*AT HIGH LOAD CURRENTS, A
TANTALUM CAPACITOR WILL
IMPROVE PERFORMANCE.
3539 TA02
1 Cell to 3.3V
2.2µH
V
IN
0.9V TO 1.6V
2.2µF
V
SW
IN
LTC3539
V
OUT
PWM BURST
OFF ON
MODE
V
OUT
3.3V
350mA
1M
33pF
SHDN
FB
22µF
×2
GND PGND
562k
3539 TA03
Li-Ion Cell to 5V
2.2µH
V
IN
3V TO 4.5V
2.2µF
V
SW
LTC3539-2
IN
V
OUT
PWM BURST
OFF ON
MODE
V
OUT
5V
750mA
1M
33pF
SHDN
FB
22µF
×2
GND PGND
309k
3539 TA04
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11
For more information www.linear.com/3539/3539-2
LTC3539/LTC3539-2
PACKAGE DESCRIPTION
Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings.
DCB Package
8-Lead Plastic DFN (2mm × 3mm)
(Reference LTC DWG # 05-08-ꢀ7ꢀ8 Rev A)
0.70 0.05
ꢀ.35 0.05
3.50 0.05
ꢀ.65 0.05
2.ꢀ0 0.05
PACKAGE
OUTLINE
0.25 0.05
0.45 BSC
ꢀ.35 REF
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED
R = 0.ꢀꢀ5
2.00 0.ꢀ0
(2 SIDES)
0.40 0.ꢀ0
TYP
5
R = 0.05
TYP
8
ꢀ.35 0.ꢀ0
ꢀ.65 0.ꢀ0
3.00 0.ꢀ0
(2 SIDES)
PIN ꢀ NOTCH
PIN ꢀ BAR
TOP MARK
(SEE NOTE 6)
R = 0.20 OR 0.25
× 45° CHAMFER
(DCB8) DFN 0ꢀ06 REV A
4
ꢀ
0.23 0.05
0.45 BSC
0.75 0.05
0.200 REF
ꢀ.35 REF
BOTTOM VIEW—EXPOSED PAD
0.00 – 0.05
NOTE:
ꢀ. 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.ꢀ5mm ON ANY SIDE
5. EXPOSED PAD SHALL BE SOLDER PLATED
6. SHADED AREA IS ONLY A REFERENCE FOR PIN ꢀ LOCATION ON THE
TOP AND BOTTOM OF PACKAGE
35392fc
12
For more information www.linear.com/3539/3539-2
LTC3539/LTC3539-2
REVISION HISTORY (Revision history begins at Rev B)
REV
DATE
DESCRIPTION
PAGE NUMBER
B
02/13 Improved feedback voltage tolerance spec
Clarified Burst Mode operation
1, 2
8
C
09/14 Corrected Block Diagram schematic
6
35392fc
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.
13
LTC3539/LTC3539-2
RELATED PARTS
PART NUMBER DESCRIPTION
COMMENTS
LTC3400/
LTC3400B
600mA I , 1.2MHz, Synchronous Step-Up DC/DC
92ꢀ Efficiency V : 0.85V to 5V, V
= 5V, I = 19µA/300µA, I <1µA,
OUT(MAX) Q SD
SW
IN
Converters
ThinSOT™ Package
LTC3401
LTC3402
LTC3421
LTC3422
1A I , 3MHz, Synchronous Step-Up DC/DC Converter 97ꢀ Efficiency V : 0.5V to 5V, V
= 6V, I = 38µA, I <1µA, 10-Lead
Q SD
SW
IN
OUT(MAX)
MS Package
2A I , 3MHz, Synchronous Step-Up DC/DC Converter 97ꢀ Efficiency V : 0.5V to 5V, V
= 6V, I = 38µA, I <1µA, 10-Lead
SW
IN
OUT(MAX)
Q
SD
MS Package
3A I , 3MHz, Synchronous Step-Up DC/DC Converter 95ꢀ Efficiency V : 0.5V to 4.5V, V
= 5.25V, I = 12µA, I <1µA,
Q SD
SW
IN
OUT(MAX)
OUT(MAX)
OUT(MAX)
OUT(MAX)
with Output Disconnect
QFN24 Package
1.5A I , 3MHz Synchronous Step-Up DC/DC
95ꢀ Efficiency V : 0.5V to 4.5V, V
= 5.25V, I = 25µA, I <1µA,
Q SD
SW
IN
Converter with Output Disconnect
3mm × 3mm DFN Package
LTC3423/
LTC3424
1A/2A I , 3MHz, Synchronous Step-Up DC/DC
95ꢀ Efficiency V : 0.5V to 5.5V, V
= 5.5V, I = 38µA, I <1µA,
Q SD
SW
IN
Converter
10-Lead MS Package
LTC3426
LTC3428
2A I , 1.2MHz, Step-Up DC/DC Converter
92ꢀ Efficiency V : 1.6V to 4.3V, V
= 5V, I <1µA, SOT-23 Package
SD
SW
IN
500mA I , 1.25MHz/2.5MHz, Synchronous Step-Up
92ꢀ Efficiency V : 1.8V to 5V, V
= 5.25V, I <1µA, 3mm × 3mm
SW
IN
OUT(MAX) SD
DC/DC Converters with Output Disconnect
DFN Package
LTC3429
LTC3458
LTC3458L
600mA I , 500kHz, Synchronous Step-Up DC/DC
96ꢀ Efficiency V : 0.5V to 4.4V, V
= 5V, I = 20µA/300µA,
SW
IN
OUT(MAX) Q
Converter with Output Disconnect and Soft-Start
1.4A I , 1.5MHz, Synchronous Step-Up DC/DC
93ꢀ Efficiency V : 1.5V to 6V, V
= 7.5V, I = 15µA, I <1µA,
SW
IN
OUT(MAX) Q SD
Converter/Output Disconnect/Burst Mode Operation
DFN12 Package
1.7A I , 1.5MHz, Synchronous Step-Up DC/DC
94ꢀ Efficiency V = 6V, I = 12µA, DFN12 Package
OUT(MAX) Q
SW
Converter with Output Disconnect, Automatic Burst
Mode Operation
LTC3459
70mA I , 10V Micropower Synchronous Boost
V : 1.5V to 5.5V, V
= 10V, I = 10µA, I <1µA, ThinSOT Package
SW
IN
OUT(MAX)
Q
SD
Converter/Output Disconnect/Burst Mode Operation
LTC3525-3/
LTC3525-3.3/
LTC3525-5
400mA Micropower Synchronous Step-Up DC/DC
Converter with Output Disconnect
95ꢀ Efficiency V : 1V to 4.5V, V
= 3.3V or 5V, I = 7µA, I <1µA,
OUT(MAX) Q SD
IN
SC-70 Package
LTC3525L-3
400mA Micropower Synchronous Step-Up DC/DC
Converter with Output Disconnect
95ꢀ Efficiency V : 0.88V to 4.5V, V
= 3V, I = 7µA, I <1µA,
OUT(MAX) Q SD
IN
SC-70 Package
LTC3526/
LTC3526B
500mA, 1MHz Synchronous Step-Up DC/DC Converter 94ꢀ Efficiency V : 0.85V to 5V, V
= 5.25V, I = 9µA, I <1µA,
Q SD
IN
OUT(MAX)
OUT(MAX)
OUT(MAX)
OUT(MAX)
with Output Disconnect
2mm × 2mm DFN-6 Package
LTC3526L
550mA, 1MHz Synchronous Step-Up DC/DC Converter 94ꢀ Efficiency V : 0.68V to 5V, V
= 5.25V, I = 9µA, I <1µA,
Q SD
IN
with Output Disconnect
2mm × 2mm DFN-6 Package
LTC3527/
LTC3527-1
Dual 800mA/400mA, 1.2MHz/2.2MHz Synchronous
Step-Up DC/DC Converter with Output Disconnect
94ꢀ Efficiency V : 0.68V to 5V, V
= 5.25V, I = 12µA, I <1µA,
Q SD
IN
3mm × 3mm QFN-16 Package
LTC3528/
LTC3528B
1A, 1MHz Synchronous Step-Up DC/DC Converter with 94ꢀ Efficiency V : 0.68V to 5V, V
= 5.25V, I = 12µA, I <1µA,
Q SD
IN
Output Disconnect
2mm × 3mm DFN-8 Package
35392fc
LT 0914 REV C • PRINTED IN USA
LinearTechnology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
14
(408)432-1900 FAX: (408) 434-0507 www.linear.com/3539/3539-2
●
●
LINEAR TECHNOLOGY CORPORATION 2008
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