LTC3526LEDC#PBF [Linear]
LTC3526L/LTC3526LB - 550mA 1MHz Synchronous Step-Up DC/DC Converters in 2mm x 2mm DFN; Package: DFN; Pins: 6; Temperature Range: -40°C to 85°C;
| 型号： | LTC3526LEDC#PBF |
| 厂家： | 
Linear |
| 描述： | LTC3526L/LTC3526LB - 550mA 1MHz Synchronous Step-Up DC/DC Converters in 2mm x 2mm DFN; Package: DFN; Pins: 6; Temperature Range: -40°C to 85°C 开关 光电二极管 |
| 文件： | 总16页 (文件大小：317K) |
| 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
NOT RECOMMENDED FOR NEW DESIGNS
Contact Linear Technology for Potential Replacement
FeaTures
DescripTion
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.
n
Delivers 3.3V at 100mA from a Single Alkaline/
NiMH Cell or 3.3V at 200mA from Two Cells
IN
n
V Start-Up Voltage: 850mV
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
For new designs, we recommend the LTC3526L/LTC3526LB.
L, LT, LTC, LTM, Linear Technology, the Linear logo 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
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
IN
= 2.4V
90
EFFICIENCY
4.7µH
80
70
SW
V
OUT
60
50
V
IN
3.3V
V
IN
V
OUT
1.6V TO 3.2V
200mA
1µF
LTC3526
SHDN
GND
POWER LOSS
1.78M
1M
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
3526bfd
ꢀ
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
............................................................. –0.3V to 6V
DC PACKAGE
6-LEAD (2mm × 2mm) PLASTIC DFN
= 125°C, θ = 102°C/W (NOTE 6)
JA
EXPOSED PAD (PIN 7) IS GND, MUST BE SOLDERED TO PC BOARD
OUT
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
–40°C to 85°C
–40°C to 85°C
6-Lead (2mm × 2mm) Plastic DFN
6-Lead (2mm × 2mm) Plastic DFN
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
OUT
10
SW
= 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
3526bfd
ꢁ
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
102°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
OUT
= 5V
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
40
30
20
10
0
1
40
30
20
10
0
1
V
OUT
= 1.8V
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 = 1.5V
IN
PLOSS AT V = 3.0V
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
LOAD CURRENT (mA)
LOAD CURRENT (mA)
IN
3526 G01
3526 G02
3526 G04
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
100
90
1000
100
10
1000
100
10
V
= 3.3V
OUT
V
= 2.5V
OUT
80
V
= 1.8V
OUT
70
60
50
V
V
V
V
= 1.2V
= 2.4V
= 3.6V
= 4.2V
IN
IN
IN
IN
V
OUT
= 5V
40
30
20
10
0
1
PLOSS AT V = 1.2V
IN
IN
IN
IN
0.1
0.01
PLOSS AT V = 2.4V
PLOSS AT V = 3.6V
L = 4.7µH
PLOSS AT V = 4.2V
0
2.5 3.0
0.5 1.0 1.5 2.0
3.5 4.0 4.5
0.01
0.1
1
10
100
1000
0.85
0.95
1.05
(V)
1.25
1.15
V
IN
(V)
V
LOAD CURRENT (mA)
IN
3526 G03
3526 G05
3526 G06
3526bfd
ꢂ
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
= 10µF
OUT
OUT
OUT
OUT
= 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
IN
(V)
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
= 10µF
NORMALIZED TO 3.3V
OUT
OUT
OUT
OUT
= 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
IN
(V)
IN
OUT
3526 G08d
3526 G09
3526 G08c
Oscillator Frequency Change
vs Temperature
RDS(ON) vs VOUT
RDS(ON) Change vs Temperature
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
1.3
1.2
1.1
1.0
0.9
0.8
0.7
NORMALIZED TO 25°C
NORMALIZED TO 25°C
6
4
2
PMOS
NMOS
(V)
0
–2
–4
–6
–8
–10
–50 –30 –10 10
30
50
70
90
1.5
2.5 3.0 3.5
4.0 4.5 5.0
2.0
–50 –30 –10 10
30
50
70
90
V
OUT
TEMPERATURE (°C)
TEMPERATURE (°C)
3526 G11
3526 G10
3526 G12
3526bfd
ꢃ
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
4.0 4.5
40 60
TEMPERATURE (°C)
–60 –40 –20
0
20
80 100
–50 –30 –10 10
30 –50 70
90
V
OUT
TEMPERATURE (°C)
3526 G15
3526 G13
3526 G14
Fixed Frequency Switching
Waveform and VOUT Ripple
Burst Mode Waveforms
V
OUT and IIN During Soft-Start
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
OUT
= 10μF
OUT
200μs/DIV
V
V
C
= 1.2V
10µs/DIV
IN
IN
= 3.3V AT 100mA
= 3.3V
= 10µF
OUT
OUT
OUT
OUT
= 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
OUT
100µs/DIV
V
V
= 3.6V
OUT
100µs/DIV
IN
IN
= 5V
= 5V
20mA TO 170mA STEP
50mA TO 150mA STEP
C
= 10µF
C
= 10µF
OUT
OUT
3526bfd
ꢄ
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
VOUT =1.195V • 1+
V
(Pin6):Outputvoltagesenseanddrainoftheinternal
OUT
V (Pin 3): Input Supply Pin. Connect a minimum of 1µF
IN
synchronous rectifier. PCB trace from V
to the output
OUT
ceramic decoupling capacitor from this pin to ground
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.
GND (Exposed Pad Pin 7): The Exposed Pad must be sol-
dered 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
3526bfd
ꢅ
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
FB
1.6V
6
5
TO 5.25V
ANTI-RING
GATE DRIVERS
AND
R2
R1
ANTI-CROSS
CONDUCTION
SHDN
C
OUT
SHUTDOWN
4
SHUTDOWN
+
–
4.7µF
I
ZERO
COMP
4M
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
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.
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.
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.
With its low R
and low gate charge internal N-chan-
DS(ON)
When either V or V
exceeds 1.4V typical, the IC
IN
OUT
nel MOSFET switch and P-channel MOSFET synchronous
rectifier, the LTC3526 achieves high efficiency over a wide
enters normal operating mode. When the output voltage
3526bfd
ꢆ
LTC3526/LTC3526B
operaTion
(Refer to Block Diagram)
exceeds the input by 0.24V, the IC powers itself from
LTC3526/LTC3526B
4M
LTC3526/LTC3526B
4M
V
IN
V
instead of V . At this point the internal circuitry has
OUT
IN
no dependency on the V input voltage, eliminating the
30ꢀ
30ꢀ
IN
SHDN
SHDN
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.
V
CNTRL
R
ZETEX ZC2811E
1M
V
CNTRL
1M
R > (V
/(V + 0.4) – 1)MΩ
CNTRL IN
3526 F01
Figure 1. Recommended Shutdown Circuits when Driving
SHDN above VIN
Error Amplifier
LOW NOISE FIXED FREꢀUENCY OPERATION
Soft-Start
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
TheLTC3526/LTC3526Bcontaininternalcircuitrytoprovide
soft-start operation. The soft-start circuitry slowly ramps
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.
resistive voltage divider from V
to ground programs
OUT
the output voltage via FB from 1.6V to 5.25V.
R2
R1
VOUT =1.195V • 1+
Oscillator
An internal oscillator sets the switching frequency to
1MHz.
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.
Shutdown
Shutdown is accomplished by pulling the SHDN pin
below 0.3V and enabled by pulling the SHDN pin above
0.8V typical. Although SHDN can be driven above V
IN
or V
(up to the absolute maximum rating) without
OUT
Current Limit
damage, the LTC3526/LTC3526B have a proprietary test
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,
independent of input or output voltage, unless V
below 0.7V, in which case the current limit is cut in half.
mode that may be engaged if SHDN is held in the range
of 0.5V to 1V higher than the greater of V or V . If
IN
OUT
the test mode is engaged, normal PWM switching action
is interrupted, which can cause undesirable operation
in some applications. Therefore, in applications where
falls
OUT
SHDN may be driven above V , a resistor divider or other
IN
meansmustbeemployedtokeeptheSHDNvoltagebelow
Zero Current Comparator
(V + 0.4V) to prevent the possibility of the test mode
IN
being engaged. Please refer to Figure 1 for two possible
The zero current comparator monitors the inductor cur-
rent to the output and shuts off the synchronous rectifier
implementations.
3526bfd
ꢇ
LTC3526/LTC3526B
operaTion
when this current reduces to approximately 30mA. This
prevents the inductor current from reversing in polarity,
improving efficiency at light loads.
(Refer to Block Diagram)
Burst Mode OPERATION
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-
Synchronous Rectifier
To control inrush current and to prevent the inductor
old current vs V . The load current at which Burst Mode
IN
current from running away when V
is close to V , the
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.
OUT
IN
P-channel MOSFET synchronous rectifier is only enabled
when V > (V + 0.24V).
OUT
IN
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
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
the ringing of the resonant circuit formed by L and C
SW
(capacitance on SW pin) is low energy, it can cause EMI
radiation.
consumes only 9µA of quiescent current from V . When
OUT
Output Disconnect
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
The LTC3526/LTC3526B are designed to allow true output
disconnect by eliminating body diode conduction of the
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
V
OUT
and FB.
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
OUT
any reverse current into a battery connected to V .
IN
Thermal Shutdown
BurstModeoperationisinhibitedduringstart-upandsoft-
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.
start and until V
is at least 0.24V greater than V .
OUT
IN
The LTC3526B features continuous PWM operation at
1MHz. At very light loads, the LTC3526B will exhibit
pulse-skip operation.
3526bfd
ꢈ
LTC3526/LTC3526B
applicaTions inFormaTion
COMPONENT SELECTION
Inductor Selection
V > V
OPERATION
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)
where:
Although it is not required, adding a Schottky diode from
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)
= Maximum output voltage
PCB LAYOUT GUIDELINES
OUT(MAX)
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
The high speed operation of the LTC3526/LTC3526B
demands careful attention to board layout. A careless
layout will result in reduced performance. Figure 2 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.
LTC3526
SW
V
OUT
1
2
3
6
5
4
MINIMIZE
TRACE ON FB
AND SW
GND
FB
V
IN
SHDN
+
V
IN
MULTIPLE VIAS
TO GROUND PLANE
3526 F02
Figure 2. Recommended Component Placement for Single Layer Board
3526bfd
ꢀ0
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
Würth
(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
3526bfd
ꢀꢀ
LTC3526/LTC3526B
Typical applicaTions
1-Cell to 1.8V Converter with <1mm Maximum Height
100
90
V
OUT
= 1.8V
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
1-Cell to 3.3V
100
V
OUT
= 3.3V
90
80
70
4.7µH*
SW
V
OUT
V
IN
3.3V
60
50
V
IN
V
OUT
1V TO 1.6V
75mA
1µF
LTC3526
SHDN
GND
1.78M
22pF
40
30
20
10
0
OFF ON
FB
10µF
1M
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
3526bfd
ꢀꢁ
LTC3526/LTC3526B
Typical applicaTions
2-Cell to 3.3V
100
90
V
OUT
= 3.3V
4.7µH*
80
70
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
2-Cell to 5V
100
V
OUT
= 5V
90
80
70
6.8µH*
SW
V
OUT
V
60
50
IN
5V
V
IN
V
OUT
2V TO 3.2V
150mA
1µF
LTC3526
SHDN
GND
22pF
3.24M
1.02M
40
30
20
10
0
OFF ON
FB
10µF
V
= 3.0V
= 2.4V
= 1.8V
3526 TA06a
IN
V
IN
V
IN
*TAIYO-YUDEN NP03SB6R8M
0.01
0.1
1
10
100
1000
LOAD CURRENT (mA)
3526 TA06b
Li-Ion to 5V
100
90
V
OUT
= 5V
6.8µH*
SW
80
70
V
OUT
V
IN
5V
60
50
V
IN
V
OUT
2.7V TO 4.3V
200mA
1µF
LTC3526
SHDN
GND
3.24M
22pF
40
30
20
10
0
OFF ON
FB
10µF
1.02M
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
3526bfd
ꢀꢂ
LTC3526/LTC3526B
package DescripTion
DC Package
6-Lead Plastic DFN (2mm × 2mm)
(Reference LTC DWG # 05-08-1703 Rev B)
0.70 p0.05
2.55 p0.05
0.61 p0.05
1.15 p0.05
(2 SIDES)
PACKAGE
OUTLINE
0.25 p 0.05
0.50 BSC
1.42 p0.05
(2 SIDES)
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
R = 0.125
TYP
0.56 p 0.05
(2 SIDES)
0.40 p 0.10
4
6
2.00 p0.10
PIN 1 NOTCH
(4 SIDES)
R = 0.20 OR
0.25 s 45o
CHAMFER
PIN 1 BAR
TOP MARK
(SEE NOTE 6)
(DC6) DFN REV B 1309
R = 0.05
TYP
3
1
0.25 p 0.05
0.50 BSC
0.75 p0.05
0.200 REF
1.37 p0.05
(2 SIDES)
BOTTOM VIEW—EXPOSED PAD
0.00 – 0.05
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
3526bfd
ꢀꢃ
LTC3526/LTC3526B
revision hisTory (Revision history begins at Rev D)
REV
DATE
DESCRIPTION
PAGE NUMBER
D
9/10
2
3
Updated θ on Pin Configuration
Updated Note 6
JA
8
Updated Shutdown section
Updated Related Parts
16
3526bfd
Information furnished by Linear Technology ꢀorporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology ꢀorporation makes no represen-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
ꢀꢄ
LTC3526/LTC3526B
Typical applicaTion
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
relaTeD parTs
PART NUMBER
DESCRIPTION
COMMENTS
94% Efficiency VIN: 0.85V to 5V, VOUT(MAX) = 5.25V, IQ = 9µA,
SD < 1µA, 2mm × 2mm DFN-6 Package
LTC3526-2/LTC3526B-2
LTC3526L/LTC3526LB
LTC3526L-2/LTC3526LB-2
500mA, 1MHz/2.2MHz, Synchronous Step-Up DC/DC
Converters with Output Disconnect
I
LTC3525L-3
400mA Micropower Synchronous Step-Up DC/DC
Converter with Output Disconnect
93% Efficiency VIN: 0.88V to 4.5V, VOUT = 3V, IQ = 7µA,
SD < 1µA, SC-70 Package
I
LTC3525-3
LTC3525-3.3
LTC3525-5
400mA Micropower Synchronous Step-Up DC/DC
Converter with Output Disconnect
95% Efficiency VIN: 1V to 4.5V, VOUT(MAX) = 3.3V or 5V, IQ = 7µA,
SD < 1µA, SC-70 Package
I
LTC3427
500mA ISW, 1.2MHZ, Synchronous Step-Up Dꢀ/Dꢀ
ꢀonverter with Output Disconnect
93% Efficiency VIN: 1.8V to 4.5V, VOUT(MAX) = 5V,
2mm × 2mm DFN Package
LTC3400/LTC3400B
LTC3527/LTC3527-1
600mA ISW, 1.2MHz, Synchronous Step-Up
DC/DC Converters
92% Efficiency VIN: 1V to 5V, VOUT(MAX) = 5V, IQ = 19µA/300µA,
I
SD < 1µA, ThinSOT™ Package
Dual 600mA/400mA I , 1.2MHz/2.2MHz Synchronous 94% Efficiency VIN: 0.7V to 5V, VOUT(MAX) = 5.25V, IQ = 12µA,
SW
Step-Up DC/DC Converters
ISD < 1µA, 3mm × 3mm QFN-16 Package
3526bfd
LT 0910 • REV D • PRINTED IN USA
Linear Technology Corporation
1630 Mcꢀarthy Blvd., Milpitas, ꢀA 95035-7417
ꢀꢅ
l
l
LINEAR TECHNOLOGY CORPORATION 2006
(408)432-1900 FAX: (408) 434-0507 www.linear.com
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