LTC3526LEDC [Linear]
IC SWITCHING CONTROLLER, 1250 kHz SWITCHING FREQ-MAX, PDSO6, 2 X 2 MM, 0.75 MM HEIGHT, PLASTIC, MO-229WCCD-2, DFN-6, Switching Regulator or Controller;型号: | LTC3526LEDC |
厂家: | Linear |
描述: | IC SWITCHING CONTROLLER, 1250 kHz SWITCHING FREQ-MAX, PDSO6, 2 X 2 MM, 0.75 MM HEIGHT, PLASTIC, MO-229WCCD-2, DFN-6, Switching Regulator or Controller 转换器 |
文件: | 总16页 (文件大小:255K) |
中文: | 中文翻译 | 下载: | 下载PDF数据表文档文件 |
LTC3526/LTC3526B
500mA 1MHz Synchronous
Step-Up DC/DC Converters
in 2mm × 2mm DFN
DESCRIPTION
FEATURES
n
Delivers 3.3V at 100mA from a Single Alkaline/
TheLTC®3526/LTC3526Baresynchronous,fixedfrequency
step-up DC/DC converters with output disconnect. Syn-
chronous rectification enables high efficiency in the low
profile 2mm × 2mm DFN package. Battery life in single
AA/AAA powered products is extended further with an
850mV start-up voltage and operation down to 500mV
once started.
NiMH Cell or 3.3V at 200mA from Two Cells
n
V Start-Up Voltage: 850mV
IN
n
n
n
n
n
n
n
n
1.6V to 5.25V V
Range
OUT
Up to 94% Efficiency
Output Disconnect
1MHz Fixed Frequency Operation
V > V
Operation
IN
OUT
A switching frequency of 1MHz minimizes solution foot-
print by allowing the use of tiny, low profile inductors and
ceramic capacitors. The current mode PWM design is
internallycompensated,reducingexternalpartscount.The
LTC3526 features automatic Burst Mode operation at light
load conditions, while the LTC3526B features continuous
switching at light loads. Anti-ringing control circuitry also
reduces EMI concerns by damping the inductor in discon-
tinuousmode. Additionalfeaturesincludealowshutdown
current of under 1μA and thermal shutdown.
Integrated Soft-Start
Current Mode Control with Internal Compensation
Automatic Burst Mode® Operation with 9μA
Quiescent Current (LTC3526)
n
n
n
n
n
Low Noise PWM Operation (LTC3526B)
Internal Synchronous Rectifier
Logic Controlled Shutdown (I < 1μA)
Q
Anti-Ringing Control
Low Profile (2mm × 2mm × 0.75mm) DFN Package
The LTC3526/LTC3526B are housed in a 2mm × 2mm ×
APPLICATIONS
0.75mm DFN package.
n
Medical Instruments
, LT, LTC, LTM and Burst Mode are registered trademarks of Linear Technology
Corporation. All other trademarks are the property of their respective owners.
n
Flash-Based MP3 Players
n
Noise Canceling Headphones
Wireless Mice
n
n
Bluetooth Headsets
TYPICAL APPLICATION
LTC3526 Efficiency and Power Loss vs Load Current
100
1000
100
10
V
= 2.4V
IN
90
4.7μH
EFFICIENCY
80
70
SW
V
OUT
V
IN
60
50
3.3V
V
IN
V
OUT
1.6V TO 3.2V
200mA
1μF
LTC3526
SHDN
GND
1.78M
1M
POWER LOSS
40
30
20
10
0
1
OFF ON
FB
4.7μF
0.1
0.01
3526 TA01a
0.01
0.1
1
10
100
1000
LOAD CURRENT (mA)
3526 TA01b
3526bfb
1
LTC3526/LTC3526B
ABSOLUTE MAXIMUM RATINGS
PIN CONFIGURATION
(Note 1)
TOP VIEW
V Voltage................................................... –0.3V to 6V
IN
SW Voltage
SW
1
2
3
6
5
4
V
OUT
DC............................................................ –0.3V to 6V
Pulsed <100ns......................................... –0.3V to 7V
SHDN, FB Voltage ........................................ –0.3V to 6V
GND
7
FB
V
IN
SHDN
V
OUT
............................................................. –0.3V to 6V
DC PACKAGE
6-LEAD (2mm × 2mm) PLASTIC DFN
= 125°C, θ = 60°C/W (NOTE 6)
JA
EXPOSED PAD (PIN 7) IS GND, MUST BE SOLDERED TO PC BOARD
Operating Temperature Range (Note 2).... –40°C to 85°C
Storage Temperature Range................... –65°C to 150°C
T
JMAX
ORDER INFORMATION
LEAD FREE FINISH
LTC3526EDC#PBF
LTC3526BEDC#PBF
TAPE AND REEL
PART MARKING
LCHW
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LTC3526EDC#TRPBF
LTC3526BEDC#TRPBF
6-Lead (2mm × 2mm) Plastic DFN
6-Lead (2mm × 2mm) Plastic DFN
–40°C to 85°C
–40°C to 85°C
LCNN
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/
The l denotes the specifications which apply over the specified operating
ELECTRICAL CHARACTERISTICS
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
= 1mA
MIN
TYP
MAX
UNITS
Minimum Start-Up Input Voltage
Output Voltage Adjust Range
I
0.85
1
V
LOAD
l
l
1.7
1.6
5.25
5.25
V
V
0°C to 85°C
Feedback Pin Voltage
1.165
1.195
1
1.225
50
V
nA
μA
μA
μA
μA
μA
Ω
Feedback Pin Input Current
V
V
= 1.30V
FB
Quiescent Current—Shutdown
Quiescent Current—Active
= 0V, Not Including Switch Leakage, V
= 0V
0.01
250
9
1
SHDN
OUT
Measured on V , Nonswitching, LTC3526 Only
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
Current Limit Delay to Output
Maximum Duty Cycle
V
V
V
V
= 5V
0.1
0.1
0.4
0.6
700
60
5
SW
= 5V, V
= 0V
10
SW
OUT
= 3.3V
= 3.3V
OUT
OUT
Ω
l
500
85
mA
ns
%
(Note 3)
l
l
l
V
FB
V
FB
= 1.15V
= 1.3V
90
Minimum Duty Cycle
0
%
Switching Frequency
0.7
0.9
1
1.3
MHz
V
SHDN Pin Input High Voltage
SHDN Pin Input Low Voltage
SHDN Pin Input Current
0.3
V
V
SHDN
V
SHDN
= 1.2V
= 3.3V
0.3
1
1
2
μA
μA
3526bfb
2
LTC3526/LTC3526B
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 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
60°C/W.
Note 2: The LTC3526E 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 3: Specification is guaranteed by design and not 100% tested in
production.
TYPICAL PERFORMANCE CHARACTERISTICS
Efficiency vs Load Current and VIN
for VOUT = 1.8V (LTC3526)
Efficiency vs Load Current and VIN
for VOUT = 3.3V (LTC3526)
No-Load Input Current vs VIN
100
90
80
70
60
50
40
30
20
10
100
90
1000
100
10
100
90
1000
100
10
80
80
V
= 5V
OUT
V
V
V
V
= 1.2V
= 1.8V
= 2.4V
= 3.0V
IN
IN
IN
IN
V
V
V
= 1.0V
= 1.2V
= 1.5V
70
70
IN
IN
IN
V
= 3.3V
OUT
V
60
50
60
50
= 2.5V
OUT
V
= 1.8V
OUT
40
30
20
10
0
1
40
30
20
10
0
1
PLOSS AT V = 1.2V
IN
0.1
0.01
0.1
0.01
PLOSS AT V = 1.0V
PLOSS AT V = 1.8V
IN
IN
PLOSS AT V = 1.2V
IN
PLOSS AT V = 2.4V
IN
PLOSS AT V = 3.0V
IN
PLOSS AT V = 1.5V
IN
2.5 3.0
(V)
0.5 1.0 1.5 2.0
3.5 4.0 4.5
0.01
0.1
1
10
100
1000
0.01
0.1
1
10
100
1000
V
IN
LOAD CURRENT (mA)
LOAD CURRENT (mA)
3526 G04
3526 G01
3526 G02
Minimum Load Resistance
During Start-Up vs VIN
Efficiency vs Load Current and VIN
for VOUT = 5V (LTC3526)
Maximum Output Current vs VIN
400
350
300
250
200
150
100
50
1000
100
10
V
= 3.3V
100
90
1000
100
10
OUT
V
= 2.5V
OUT
V
= 1.8V
80
OUT
70
60
50
V
V
V
V
= 1.2V
= 2.4V
= 3.6V
= 4.2V
IN
IN
IN
IN
V
= 5V
OUT
40
30
20
10
0
1
PLOSS AT V = 1.2V
IN
0.1
0.01
PLOSS AT V = 2.4V
IN
PLOSS AT V = 3.6V
IN
L = 4.7μH
PLOSS AT V = 4.2V
IN
0
2.5 3.0
0.5 1.0 1.5 2.0
3.5 4.0 4.5
0.85
0.95
1.05
(V)
1.25
1.15
0.01
0.1
1
10
100
1000
V
(V)
IN
V
IN
LOAD CURRENT (mA)
3526 G05
3526 G06
3526 G03
3526bfb
3
LTC3526/LTC3526B
TYPICAL PERFORMANCE CHARACTERISTICS
Burst Mode Threshold Current
vs VIN
Burst Mode Threshold Current
vs VIN
Start-Up Delay Time vs VIN
30
25
100
90
80
70
60
50
40
30
20
10
0
40
35
30
25
V
C
= 1.8V
V
C
= 2.5V
OUT
OUT
OUT
OUT
= 10μF
= 10μF
L = 4.7μH
L = 4.7μH
20
15
LEAVE BURST
LEAVE BURST
ENTER BURST
20
15
10
5
ENTER BURST
10
5
0
0
1
1.25
(V)
1.5
1.25
1.5
1
1.75
1.0
2.0 2.5 3.0
(V)
3.5 4.0 4.5
1.5
V
V
V
(V)
IN
IN
IN
3526 G08a
3526 G08b
3526 G07
Oscillator Frequency Change
vs VOUT
Burst Mode Threshold Current
vs VIN
Burst Mode Threshold Current
vs VIN
50
45
40
35
30
25
20
15
10
5
60
2
V
C
= 5V
V
C
= 3.3V
NORMALIZED TO 3.3V
OUT
OUT
OUT
OUT
= 10μF
= 10μF
1
0
50 L = 4.7μH
L = 4.7μH
40
LEAVE BURST
–1
–2
–3
–4
–5
LEAVE BURST
30
20
10
0
ENTER BURST
ENTER BURST
2.0 2.5
–6
0
3.0
(V)
4.0
4.5
2.0
2.5
3.3 4.0 4.5 5.0
1.0 1.5
3.5
1.5
3.0
V
1.0
1.5
2.0
(V)
2.5
3.0
V
V
(V)
IN
IN
OUT
3526 G08d
3526 G09
3526 G08c
Oscillator Frequency Change
vs Temperature
RDS(ON) vs VOUT
RDS(ON) Change vs Temperature
1.3
1.2
1.1
1.0
0.9
0.8
0.7
0.90
0.85
0.80
0.75
0.70
0.65
0.60
0.55
0.50
0.45
0.40
0.35
0.30
10
8
NORMALIZED TO 25°C
NORMALIZED TO 25°C
6
4
2
PMOS
NMOS
0
–2
–4
–6
–8
–10
–50 –30 –10 10
30
50
70
90
–50 –30 –10 10
30
50
70
90
1.5
2.5 3.0 3.5
(V)
4.0 4.5 5.0
2.0
TEMPERATURE (°C)
V
TEMPERATURE (°C)
OUT
3526 G12
3526 G11
3526 G10
3526bfb
4
LTC3526/LTC3526B
TYPICAL PERFORMANCE CHARACTERISTICS
VFB vs Temperature
Start-Up Voltage vs Temperature
Burst Mode Current vs VOUT
10.0
1.00
0.95
0.90
0.85
0.80
0.75
0.70
0.50
0.25
LOAD = 1mA
NORMALIZED TO 25°C
9.5
9.0
8.5
8.0
7.5
7.0
0
–0.25
–0.50
–0.75
–1.00
3.5
(V)
5.0
1.5 2.0 2.5 3.0
V
4.0 4.5
–50 –30 –10 10
30 –50 70
90
40 60
TEMPERATURE (°C)
–60 –40 –20
0
20
80 100
TEMPERATURE (°C)
OUT
3526 G15
3526 G14
3526 G13
Fixed Frequency Switching
Waveform and VOUT Ripple
VOUT and IIN During Soft-Start
Burst Mode Waveforms
SW PIN
2V/DIV
V
OUT
SW PIN
2V/DIV
1V/DIV
V
OUT
INPUT
CURRENT
0.2A/DIV
SHDN PIN
1V/DIV
20mV/DIV
V
OUT
AC COUPLED
10mV/DIV
INDUCTOR
CURRENT
0.2A/DIV
AC COUPLED
3526 G16
3526 G18
3526 G17
V
V
C
= 1.2V
500ns/DIV
V
C
= 3.3V
= 10μF
200μs/DIV
V
V
C
= 1.2V
10μs/DIV
IN
OUT
OUT
IN
= 3.3V AT 100mA
= 3.3V
OUT
OUT
OUT
OUT
= 10μF
= 10μF
Load Step Response (from Burst
Mode Operation)
Load Step Response
(Fixed Frequency)
V
V
OUT
OUT
100mV/DIV
100mV/DIV
AC COUPLED
AC COUPLED
LOAD
CURRENT
50mA/DIV
LOAD
CURRENT
50mA/DIV
3526 G19
3526 G20
V
V
= 3.6V
= 5V
100μs/DIV
V
V
= 3.6V
= 5V
100μs/DIV
IN
OUT
IN
OUT
20mA TO 170mA STEP
= 10μF
50mA TO 150mA STEP
= 10μF
C
C
OUT
OUT
3526bfb
5
LTC3526/LTC3526B
TYPICAL PERFORMANCE CHARACTERISTICS
Load Step Response
(Fixed Frequency)
Load Step Response (from Burst
Mode Operation)
V
OUT
V
OUT
100mV/DIV
100mV/DIV
AC COUPLED
AC COUPLED
LOAD
CURRENT
50mA/DIV
LOAD
CURRENT
50mA/DIV
3526 G21
3526 G22
V
V
= 1.2V
100μs/DIV
V
V
= 1.2V
50μs/DIV
IN
OUT
IN
OUT
= 3.3V
= 3.3V
50mA TO 100mA STEP
= 10μF
5mA TO 100mA STEP
= 10μF
C
C
OUT
OUT
ELECTRICAL CHARACTERISTICS
SW(Pin1):SwitchPin.ConnectinductorbetweenSWand
FB (Pin 5): Feedback Input to the g Error Amplifier. Con-
m
V . Keep PCB trace lengths as short and wide as possible
nect resistor divider tap to this pin. The top of the divider
connects to the output capacitor, the bottom of the divider
connectstoGND.ReferringtotheBlockDiagram,theoutput
voltage can be adjusted from 1.6V to 5.25V by:
IN
to reduce EMI. If the inductor current falls to zero or SHDN
is low, an internal anti-ringing switch is connected from
SW to V to minimize EMI.
IN
GND (Pin 2): Signal and Power Ground. Provide a short
direct PCB path between GND and the (–) side of the input
and output capacitors.
R2
R1
ꢀ
ꢁ
ꢃ
ꢄ
VOUT =1.195V • 1+
ꢂ
ꢅ
V
(Pin6):Outputvoltagesenseanddrainoftheinternal
V (Pin 3): Input Supply Pin. Connect a minimum of 1μF
OUT
IN
synchronous rectifier. PCB trace from V
to the output
ceramic decoupling capacitor from this pin to ground
OUT
filter capacitor (4.7μF minimum) should be as short and
wide as possible.
using short direct PCB traces.
SHDN (Pin 4): Logic Controlled Shutdown Input. There
is an internal 4MΩ pull-down on this pin.
Exposed Pad (Pin 7): The Exposed Pad must be soldered
to the PCB ground plane. It serves as an additional ground
connection and as a means of conducting heat away from
the package.
• SHDN = High: Normal operation
• SHDN = Low: Shutdown, quiescent current < 1μA
3526bfb
6
LTC3526/LTC3526B
BLOCK DIAGRAM
L1
4.7μH
V
IN
0.85V
TO 5V
C
IN
2.2μF
3
1
V
IN
SW
V
OUT
V
SEL
WELL
SWITCH
V
BEST
V
B
V
OUT
V
OUT
1.6V
6
5
ANTI-RING
TO 5.25V
GATE DRIVERS
AND
R2
R1
ANTI-CROSS
CONDUCTION
FB
SHDN
C
OUT
SHUTDOWN
4
SHUTDOWN
+
–
4.7μF
I
ZERO
COMP
4M
Σ
SLOPE
COMP
I
PK
COMP
V
V
REF
REF
–
+
I
PK
UVLO
ERROR AMP
SLEEP COMP
I
ZERO
START-UP
V
REF
+
–
LOGIC
MODE
CLK
TSD
CONTROL
1MHz
OSC
CLAMP
WAKE
THERMAL
SHUTDOWN
C
SS
EXPOSED
PAD
GND
2
7
3526 BD
3526bfb
7
LTC3526/LTC3526B
OPERATION
(Refer to Block Diagram)
The LTC3526/LTC3526B are 1MHz synchronous boost
converters housed in a 6-lead 2mm × 2mm DFN package.
With the ability to start up and operate from inputs less
than 1V, these devices feature fixed frequency, current
mode PWM control for exceptional line and load regula-
tion. The current mode architecture with adaptive slope
compensation provides excellent transient load response,
requiring minimal output filtering. Internal soft-start and
internal loop compensation simplifies the design process
while minimizing the number of external components.
the peak inductor current from zero to its peak value of
700mA (typical) in approximately 0.5ms, allowing start-
up into heavy loads. The soft-start circuitry is reset in the
event of a shutdown command or a thermal shutdown.
Oscillator
An internal oscillator sets the switching frequency to
1MHz.
Shutdown
With its low R
and low gate charge internal N-chan-
DS(ON)
Shutdown is accomplished by pulling the SHDN pin
below 0.3V and enabled by pulling the SHDN pin above
nel MOSFET switch and P-channel MOSFET synchronous
rectifier, the LTC3526 achieves high efficiency over a wide
range of load currents. Automatic Burst Mode operation
maintains high efficiency at very light loads, reducing
the quiescent current to just 9μA. Operation can be best
understood by referring to the Block Diagram.
0.8V typical. 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 positive input of the transconductance error amplifier
is internally connected to the 1.195V reference and the
negative input is connected to FB. Clamps limit the mini-
mumandmaximumerrorampoutputvoltageforimproved
large-signal transient response. Power converter control
loop compensation is provided internally. An external
LOW VOLTAGE START-UP
The LTC3526/LTC3526B include an independent start-up
oscillator designed to start up at an input voltage of 0.85V
(typical).Soft-startandinrushcurrentlimitingareprovided
during start-up, as well as normal mode.
resistive voltage divider from V
to ground programs
OUT
When either V or V
exceeds 1.4V typical, the IC
IN
OUT
the output voltage via FB from 1.6V to 5.25V.
enters normal operating mode. When the output voltage
exceeds the input by 0.24V, the IC powers itself from
R2
R1
ꢀ
ꢁ
ꢃ
ꢄ
VOUT =1.195V • 1+
ꢂ
ꢅ
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 ap-
plication becomes the availability of the power source to
supply sufficient energy to the output at low voltages, and
maximum duty cycle, which is clamped at 90% typical.
Note that at low input voltages, small voltage drops due
to series resistance become critical, and greatly limit the
power delivery capability of the converter.
Current Sensing
Losslesscurrentsensingconvertsthepeakcurrentsignalof
theN-channelMOSFETswitchintoavoltagethatissummed
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.
Current Limit
The current limit comparator shuts off the N-channel
MOSFET switch once its threshold is reached. The cur-
rent limit comparator delay to output is typically 60ns.
Peak switch current is limited to approximately 700mA,
LOW NOISE FIXED FREQUENCY OPERATION
Soft-Start
TheLTC3526/LTC3526Bcontaininternalcircuitrytoprovide
soft-start operation. The soft-start circuitry slowly ramps
independent of input or output voltage, unless V
falls
OUT
below 0.7V, in which case the current limit is cut in half.
3526bfb
8
LTC3526/LTC3526B
OPERATION
Zero Current Comparator
(Refer to Block Diagram)
Burst Mode OPERATION
The zero current comparator monitors the inductor cur-
rent to the output and shuts off the synchronous rectifier
when this current reduces to approximately 30mA. This
prevents the inductor current from reversing in polarity,
improving efficiency at light loads.
The LTC3526 will automatically enter Burst Mode opera-
tion at light load and return to fixed frequency PWM mode
when the load increases. Refer to the Typical Performance
Characteristics to see the output load Burst Mode thresh-
old current vs V . The load current at which Burst Mode
IN
operation is entered can be changed by adjusting the
inductor value. Raising the inductor value will lower the
load current at which Burst Mode operation is entered.
Synchronous Rectifier
To control inrush current and to prevent the inductor
current from running away when V
is close to V , the
In Burst Mode operation, the LTC3526 still switches at a
fixed frequency of 1MHz, 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 opera-
tion, energy is delivered to the output until it reaches the
nominal regulation value, then the LTC3526 transitions to
sleep mode where the outputs are off and the LTC3526
OUT
IN
P-channel MOSFET synchronous rectifier is only enabled
when V > (V + 0.24V).
OUT
IN
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. Although
consumes only 9μA of quiescent current from V . When
the ringing of the resonant circuit formed by L and C
OUT
SW
the output voltage droops slightly, switching resumes.
Thismaximizesefficiencyatverylightloadsbyminimizing
switchingandquiescentlosses.BurstModeoutputvoltage
ripple, which is typically 1% peak-to-peak, can be reduced
by using more output capacitance (10μF or greater), or
with a small capacitor (10pF to 50pF) connected between
(capacitance on SW pin) is low energy, it can cause EMI
radiation.
Output Disconnect
The LTC3526/LTC3526B are designed to allow true output
disconnect by eliminating body diode conduction of the
V
and FB.
OUT
internal P-channel MOSFET rectifier. This allows for V
OUT
to go to zero volts during shutdown, drawing no current
from the input source. It also allows for 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 current increases, the LTC3526 will automati-
cally leave Burst Mode operation. Note that larger output
capacitorvaluesmaycausethistransitiontooccuratlighter
loads.OncetheLTC3526hasleftBurstModeoperationand
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 dis-
OUT
connectfeaturealsoallowsV
tobepulledhigh,without
any reverse current into a battery connected to V .
OUT
BurstModeoperationisinhibitedduringstart-upandsoft-
IN
start and until V
is at least 0.24V greater than V .
OUT
IN
Thermal Shutdown
The LTC3526B features continuous PWM operation at
1MHz. At very light loads, the LTC3526B will exhibit
pulse-skip operation.
If the die temperature exceeds 160°C, the LTC3526/
LTC3526B will go into thermal shutdown. All switches
will be off and the soft-start capacitor will be discharged.
The device will be enabled again when the die temperature
drops by about 15°C.
3526bfb
9
LTC3526/LTC3526B
APPLICATIONS INFORMATION
V > V
OPERATION
COMPONENT SELECTION
Inductor Selection
IN
OUT
The LTC3526/LTC3526B will maintain voltage regulation
even when the input voltage is above the desired output
voltage.Notethattheefficiencyismuchlowerinthismode,
and the maximum output current capability will be less.
Refer to the Typical Performance Characteristics.
The LTC3526/LTC3526B can utilize small surface mount
chipinductorsduetotheirfast1MHzswitchingfrequency.
Inductor values between 3.3μH and 6.8μH are suitable for
most applications. Larger values of inductance will allow
slightly greater output current capability (and lower the
BurstModethreshold)byreducingtheinductorripplecur-
rent. Increasing the inductance above 10μH will increase
size while providing little improvement in output current
capability.
SHORT-CIRCUIT PROTECTION
The LTC3526/LTC3526B output disconnect feature allows
output short circuit while maintaining a maximum inter-
nally set current limit. To reduce power dissipation under
short-circuit conditions, the peak switch current limit is
reduced to 400mA (typical).
The minimum inductance value is given by:
V
• VOUT(MAX) – V
(
)
IN(MIN)
IN(MIN)
L >
SCHOTTKY DIODE
Ripple • VOUT(MAX)
Although it is not required, adding a Schottky diode from
where:
SW to V
will improve efficiency by about 2%. Note
OUT
Ripple = Allowable inductor current ripple (amps peak-
peak)
that this defeats the output disconnect and short-circuit
protection features.
V
V
= Minimum input voltage
IN(MIN)
PCB LAYOUT GUIDELINES
= Maximum output voltage
OUT(MAX)
The high speed operation of the LTC3526/LTC3526B
demands careful attention to board layout. A careless
layout will result in reduced performance. Figure 1 shows
the recommended component placement. A large ground
pin copper area will help to lower the die temperature. A
multilayer board with a separate ground plane is ideal, but
not absolutely necessary.
The inductor current ripple is typically set for 20% to
40% of the maximum inductor current. High frequency
ferrite core inductor materials reduce frequency depen-
dent power losses compared to cheaper powdered iron
types, improving efficiency. The inductor should have
low ESR (series resistance of the windings) to reduce the
I2R power losses, and must be able to support the peak
LTC3526
SW
V
OUT
1
2
3
6
5
4
MINIMIZE
TRACE ON FB
AND SW
GND
FB
V
SHDN
IN
+
V
IN
MULTIPLE VIAS
TO GROUND PLANE
3526 F01
Figure 1. Recommended Component Placement for Single Layer Board
3526bfb
10
LTC3526/LTC3526B
APPLICATIONS INFORMATION
inductor current without saturating. Molded chokes and
some chip inductors usually do not have enough core
area to support the peak inductor currents of 700mA
seen on the LTC3526/LTC3526B. To minimize radiated
noise, use a shielded inductor. See Table 1 for suggested
components and suppliers.
Output and Input Capacitor Selection
Low ESR (equivalent series resistance) 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 4.7μF to 10μF output capacitor is sufficient for most
applications. Larger values up to 22μF may be used to
obtain extremely low output voltage ripple and improve
transient response. X5R and X7R dielectric materials are
preferred for their ability to maintain capacitance over
wide voltage and temperature ranges. Y5V types should
not be used.
Table 1. Recommended Inductors
VENDOR
PART/STYLE
Coilcraft
(847) 639-6400
www.coilcraft.com
LPO4815
LPS4012, LPS4018
MSS5131
MSS4020
MOS6020
ME3220
DS1605, DO1608
TheinternalloopcompensationoftheLTC3526isdesigned
tobestablewithoutputcapacitorvaluesof4.7μForgreater
(withouttheneedforanyexternalseriesresistor).Although
ceramic capacitors are recommended, low ESR tantalum
capacitors may be used as well.
Coiltronics
www.cooperet.com
SD10, SD12, SD14, SD18, SD20,
SD52, SD3114, SD3118
FDK
(408) 432-8331
www.fdk.com
MIP3226D4R7M, MIP3226D3R3M
MIPF2520D4R7
MIPWT3226D3R0
Murata
LQH43C
Asmallceramiccapacitorinparallelwithalargertantalum
capacitormaybeusedindemandingapplicationsthathave
large load transients. Another method of improving the
transientresponseistoaddasmallfeed-forwardcapacitor
(714) 852-2001
www.murata.com
LQH32C (-53 series)
301015
Sumida
(847) 956-0666
www.sumida.com
CDRH5D18
CDRH2D14
CDRH3D16
across the top resistor of the feedback divider (from V
to FB). A typical value of 22pF will generally suffice.
OUT
CDRH3D11
CR43
CMD4D06-4R7MC
CMD4D06-3R3MC
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, although larger values may be
used without limitations. Table 2 shows a list of several
ceramiccapacitormanufacturers.Consultthemanufactur-
ers directly for detailed information on their selection of
ceramic capacitors.
Taiyo-Yuden
www.t-yuden.com
NP03SB
NR3015T
NR3012T
TDK
VLP
VLF, VLCF
(847) 803-6100
www.component.tdk.com
Toko
(408) 432-8282
www.tokoam.com
D412C
D518LC
D52LC
D62LCB
Wurth
(201) 785-8800
www.we-online.com
WE-TPC type S, M
Table 2. Capacitor Vendor Information
SUPPLIER
AVX
PHONE
WEBSITE
(803) 448-9411
(714) 852-2001
(408) 573-4150
(847) 803-6100
(408) 544-5200
www.avxcorp.com
www.murata.com
www.t-yuden.com
www.component.tdk.com
www.sem.samsung.com
Murata
Taiyo-Yuden
TDK
Samsung
3526bfb
11
LTC3526/LTC3526B
TYPICAL APPLICATIONS
1-Cell to 1.8V Converter with <1mm Maximum Height
100
90
V
= 1.8V
OUT
4.7μH
80
SW
V
70
OUT
V
IN
3.3V
V
IN
V
OUT
1.6V TO 3.2V
60
50
200mA
1μF
LTC3526
SHDN
GND
1.78M
1M
OFF ON
FB
4.7μF
40
30
20
10
0
3526 TA01a
V
V
V
= 1.5V
= 1.2V
= 0.9V
IN
IN
IN
0.01
0.1
1
10
100
1000
LOAD CURRENT (mA)
3526 TA02b
1-Cell to 2.85V Converter
100
V
= 2.85V
OUT
90
80
70
4.7μH*
SW
V
OUT
V
IN
2.85V
V
IN
V
OUT
60
50
1V TO 1.6V
100mA
1μF
LTC3526
SHDN
GND
1.4M
40
30
20
10
0
OFF ON
FB
10μF
1M
3526 TA03a
V
V
V
= 1.5V
= 1.2V
= 0.9V
IN
IN
IN
*SUMIDA CDRH3D16-4R7
0.01
0.1
1
10
100
1000
LOAD CURRENT (mA)
3526 TA03b
3526bfb
12
LTC3526/LTC3526B
TYPICAL APPLICATIONS
1-Cell to 3.3V
100
90
V
= 3.3V
OUT
4.7μH*
80
70
SW
V
OUT
V
IN
3.3V
V
IN
V
OUT
60
50
1V TO 1.6V
75mA
1.78M
1M
22pF
1μF
LTC3526
SHDN
GND
40
30
20
10
0
OFF ON
FB
10μF
3526 TA04a
V
V
V
= 1.5V
= 1.2V
= 0.9V
IN
IN
IN
*TAIYO-YUDEN NP03SB4R7M
0.01
0.1
1
10
100
1000
LOAD CURRENT (mA)
3526 TA04b
2-Cell to 3.3V
100
V
= 3.3V
OUT
90
80
70
4.7μH*
SW
V
OUT
V
IN
3.3V
V
IN
V
OUT
60
50
2V TO 3.2V
200mA
1μF
LTC3526
SHDN
GND
1.78M
1M
40
30
20
10
0
OFF ON
FB
4.7μF
3526 TA05a
V
V
V
= 3.0V
= 2.4V
= 1.8V
IN
IN
IN
*TAIYO-YUDEN NP03SB4R7M
0.01
0.1
1
10
100
1000
LOAD CURRENT (mA)
3526 TA05b
3526bfb
13
LTC3526/LTC3526B
TYPICAL APPLICATIONS
2-Cell to 5V
100
90
V
= 5V
OUT
6.8μH*
80
70
SW
V
OUT
V
60
50
IN
5V
V
IN
V
OUT
2V TO 3.2V
150mA
22pF
1μF
3.24M
1.02M
LTC3526
SHDN
GND
40
30
20
10
0
OFF ON
FB
10μF
V
V
V
= 3.0V
= 2.4V
= 1.8V
3526 TA06a
IN
IN
IN
*TAIYO-YUDEN NP03SB6R8M
0.01
0.1
1
10
100
1000
LOAD CURRENT (mA)
3526 TA06b
3.3V Converter with Output OR’d with 5V USB Input
MBR120ESFT
5V USB
4.7μH
V
OUT
LDO
3.3V/5V
USB
SW
V
BATT
V
IN
V
OUT
1.8V TO 3.2V
1.78M
1M
1μF
LTC3526
SHDN
GND
DC/DC
OFF ON
FB
10μF
3526 TA07a
Li-Ion to 5V
100
V
= 5V
OUT
6.8μH*
90
80
70
SW
V
OUT
V
IN
5V
V
IN
V
OUT
60
50
2.7V TO 4.3V
200mA
3.24M
1.02M
22pF
1μF
LTC3526
SHDN
GND
OFF ON
FB
10μF
40
30
20
10
0
3526 TA08a
V
V
V
= 4.2V
= 3.6V
= 3.0V
IN
IN
IN
*TAIYO-YUDEN NP03SB6R8M
0.01
0.1
1
10
100
1000
LOAD CURRENT (mA)
3526 TA08b
3526bfb
14
LTC3526/LTC3526B
PACKAGE DESCRIPTION
DC Package
6-Lead Plastic DFN (2mm × 2mm)
(Reference LTC DWG # 05-08-1703)
R = 0.115
0.38 0.05
TYP
4
6
0.56 0.05
(2 SIDES)
0.675 0.05
2.50 0.05
1.15 0.05
0.61 0.05
(2 SIDES)
2.00 0.10
(4 SIDES)
PIN 1 BAR
PIN 1
PACKAGE
OUTLINE
TOP MARK
CHAMFER OF
(SEE NOTE 6)
EXPOSED PAD
(DC6) DFN 1103
3
1
0.25 0.05
0.25 0.05
0.50 BSC
0.50 BSC
0.75 0.05
0.200 REF
1.37 0.05
(2 SIDES)
1.42 0.05
(2 SIDES)
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
0.00 – 0.05
BOTTOM VIEW—EXPOSED PAD
NOTE:
1. DRAWING TO BE MADE A JEDEC PACKAGE OUTLINE M0-229 VARIATION OF (WCCD-2)
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
3526bfb
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.
15
LTC3526/LTC3526B
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PART NUMBER
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LTC3402
2A ISW, 3MHz, Synchronous Step-Up DC/DC Converter
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3A ISW, 3MHz, Synchronous Step-Up DC/DC Converter
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I
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LTC3423/LTC3424
LTC3426
1A/2A ISW, 3MHz, Synchronous Step-Up DC/DC
Converter
I
2A ISW, 1.2MHz, Step-Up DC/DC Converter
92% Efficiency VIN: 1.6V to 4.3V, VOUT(MAX) = 5V, ISD < 1μA,
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500mA ISW, 1.25MHz/2.5MHz, Synchronous Step-Up
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600mA ISW, 500kHz, Synchronous Step-Up DC/DC
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LTC3525-5
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I
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ThinSOT is a trademark of Linear Technology Corporation.
3526bfb
LT 0807 REV B • PRINTED IN USA
LinearTechnology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
16
●
●
© LINEAR TECHNOLOGY CORPORATION 2006
(408) 432-1900 FAX: (408) 434-0507 www.linear.com
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