LTC3526LBEDC-TRPBF [Linear]
550mA 1MHz Synchronous Step-Up DC/DC Converters in 2mm × 2mm DFN; 550毫安1MHz同步升压型DC / DC转换器，采用2mm × 2mm DFN封装
| 型号： | LTC3526LBEDC-TRPBF |
| 厂家： | 
Linear |
| 描述： | 550mA 1MHz Synchronous Step-Up DC/DC Converters in 2mm × 2mm DFN |
| 文件： | 总16页 (文件大小：266K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
LTC3526L/LTC3526LB
550mA 1MHz Synchronous
Step-Up DC/DC Converters
in 2mm × 2mm DFN
DESCRIPTION
FEATURES
The LTC®3526L/LTC3526LB are synchronous, fixed
frequency step-up DC/DC converters with output discon-
nect. Synchronous rectification enables high efficiency in
the low profile 2mm × 2mm DFN package. Battery life in
single AA/AAA powered products is extended further with
a 680mV start-up voltage and operation down to 500mV
once started.
■
Delivers 3.3V at 100mA from a Single Alkaline/
NiMH Cell or 3.3V at 200mA from Two Cells
IN
■
V Start-Up Voltage: 680mV
■
■
■
■
■
■
■
■
■
■
■
■
■
1.5V 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 internally compensated, reducing external parts count.
The LTC3526L features Burst Mode operation at light load
conditions allowing it to maintain high efficiency over a
widerangeofload.TheLTC3526LBfeaturesfixedfrequency
operation for low noise applications. Anti-ring circuitry
reduces EMI by damping the inductor in discontinuous
mode. Additional features include a low shutdown current
of under 1μA and thermal shutdown.
Integrated Soft-Start
Current Mode Control with Internal Compensation
Burst Mode® Operation with 9μA I (LTC3526L)
Q
Low Noise PWM Operation (LT3526LB)
Internal Synchronous Rectifier
Logic Controlled Shutdown (I < 1μA)
Anti-Ring Control
Low Profile (2mm × 2mm × 0.75mm)
DFN-6 Package
Q
APPLICATIONS
The LTC3526L/LTC3526LB are housed in a 2mm × 2mm
× 0.75mm DFN package.
■
Medical Instruments
■
Noise Canceling Headphones
■
Wireless Mice
Bluetooth Headsets
, LT, LTC, LTM and Burst Mode are registered trademarks of Linear Technology
Corporation. All other trademarks are the property of their respective owners.
■
TYPICAL APPLICATION
Efficiency and Power Loss vs Load Current
100
90
1000
100
10
V
= 2.4V
IN
4.7μH
EFFICIENCY
80
SW
70
V
OUT
V
IN
3.3V
V
IN
V
OUT
60
50
1.6V TO 3.2V
200mA
4.7μF
LTC3526L
SHDN FB
GND
1.78M
1M
POWER LOSS
4.7μF
OFF ON
40
30
20
10
0
1
3526 TA01a
0.1
0.01
0.01
0.1
1
10
100
1000
LOAD CURRENT (mA)
3526 TA01b
3526lfb
1
LTC3526L/LTC3526LB
ABSOLUTE MAXIMUM RATINGS
PIN CONFIGURATION
(Note 1)
V Voltage................................................... –0.3V to 6V
TOP VIEW
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
SHDN
IN
V
............................................................. –0.3V to 6V
OUT
DC PACKAGE
6-LEAD (2mm × 2mm) PLASTIC DFN
Operating Temperature Range
T
= 125°C, θ = 60°C/W (NOTE 6)
JA
EXPOSED PAD (PIN 7) IS GND, MUST BE SOLDERED TO PC BOARD
JMAX
(Notes 2, 5).............................................. –40°C to 85°C
Storage Temperature Range................... –65°C to 150°C
ORDER INFORMATION
LEAD FREE FINISH
TAPE AND REEL
PART MARKING
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LTC3526LEDC#PBF
LTC3526LBEDC#PBF
LTC3526LEDC#TRPBF
LTC3526LBEDC#TRPBF
LCSS
LCST
6-Lead (2mm × 2mm) Plastic DFN
6-Lead (2mm × 2mm) Plastic DFN
–40°C to 85°C
–40°C to 85°C
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 ● 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
0.8
5
UNITS
V
Minimum Start-Up Input Voltage
Input Voltage Range
I
0.68
LOAD
●
●
●
After Start-Up. (Minimum Voltage is Load Dependent)
0.5
1.5
V
Output Voltage Adjust Range
Feedback Pin Voltage
5.25
1.225
50
V
1.165
1.195
1
V
Feedback Pin Input Current
Quiescent Current—Shutdown
Quiescent Current—Active
Quiescent Current—Burst
V
V
= 1.30V
nA
μA
μA
μA
μA
μA
Ω
FB
= 0V, Not Including Switch Leakage, V
= 0V
0.01
250
9
1
SHDN
OUT
Measured on V , Nonswitching
500
18
OUT
Measured on V , FB > 1.230V (LTC3526L Only)
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
750
60
5
SW
= 5V, V
= 3.3V
= 3.3V
= 0V
10
SW
OUT
OUT
OUT
Ω
●
550
87
mA
ns
%
(Note 3)
●
●
●
V
FB
V
FB
= 1.15V
= 1.3V
90
Minimum Duty Cycle
0
%
Switching Frequency
0.75
0.8
1
1.25
MHz
V
SHDN Pin Input High Voltage
SHDN Pin Input Low Voltage
0.3
V
3526lfb
2
LTC3526L/LTC3526LB
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 reli-
ability 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 LTC3526LE/LTC3526LBE are 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
No-Load Input Current vs VIN
(LTC3526L)
Efficiency vs Load Current and VIN
for VOUT = 1.8V (LTC3526L)
Efficiency vs Load Current and VIN
for VOUT = 3.3V (LTC3526L)
100
90
1000
100
10
100
90
1000
100
10
100
90
80
70
60
50
40
30
20
10
V
= 5V
OUT
80
80
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 = 1.5V
IN
PLOSS AT V = 3.0V
IN
2.5 3.0
V (V)
IN
0.01
0.1
1
10
100
1000
0.01
0.1
1
10
100
1000
0.5 1.0 1.5 2.0
3.5 4.0 4.5
LOAD CURRENT (mA)
LOAD CURRENT (mA)
3526 G01
3526 G02
3526 G04
Minimum Load Resistance
During Start-Up vs VIN
Efficiency vs Load Current and VIN
for VOUT = 5V (LTC3526L)
Maximum Output Current vs VIN
100
90
1000
100
10
10000
1000
400
350
300
250
200
150
100
50
V
= 3.3V
OUT
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
= 5V
OUT
40
30
20
10
0
1
100
PLOSS AT V = 1.2V
IN
0.1
0.01
PLOSS AT V = 2.4V
IN
PLOSS AT V = 3.6V
IN
PLOSS AT V = 4.2V
IN
L = 4.7μH
10
0.65
0
2.5 3.0
0.75
0.85
0.95
(V)
1.05
1.15
0.5 1.0 1.5 2.0
3.5 4.0 4.5
0.01
0.1
1
10
100
1000
V
(V)
IN
LOAD CURRENT (mA)
V
IN
3526 G03
3526 G06
3526 G05
3526lfb
3
LTC3526L/LTC3526LB
TYPICAL PERFORMANCE CHARACTERISTICS
Burst Mode Threshold Current
Burst Mode Threshold Current
vs VIN (LTC3526L)
Start-Up Delay Time vs VIN
vs VIN (LTC3526L)
100
90
80
70
60
50
40
30
20
10
0
30
25
30
25
20
15
10
5
V
C
= 1.8V
= 10μF
V
C
= 2.5V
= 10μF
OUT
OUT
OUT
OUT
LEAVE BURST
LEAVE BURST
L = 4.7μH
L = 4.7μH
20
15
ENTER BURST
ENTER BURST
10
5
0
0
1.0
1.25
(V)
1.5
1.0
2.0 2.5 3.0
(V)
3.5 4.0 4.5
1.0
1.25
1.5
(V)
1.75
2.0
1.5
V
V
V
IN
IN
IN
3526 G08a
3526 G07
3526 G08b
Oscillator Frequency Change
vs VOUT
Burst Mode Threshold Current
vs VIN (LTC3526L)
Burst Mode Threshold Current
vs VIN (LTC3526L)
50
40
30
20
10
0
3
2
1
0
40
35
30
25
20
15
10
5
NORMALIZED TO V
= 3.3V
V
C
= 3.3V
= 10μF
V
C
= 5V
OUT
OUT
OUT
OUT
OUT
= 10μF
LEAVE BURST
L = 4.7μH
L = 4.7μH
LEAVE BURST
ENTER BURST
ENTER BURST
–1
–2
–3
0
3.5
(V)
4.5
5.0
1.5 2.0
2.5 3.0
V
4.0
1.0
1.5
2.0
(V)
2.5
3.0
1.0 1.5
2.0 2.5 3.0 3.5
(V)
4.0
4.5
V
V
IN
OUT
IN
3526 G09
3526 G08c
3526 G08d
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
1.3
1.2
1.1
1.0
0.9
0.8
0.7
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
V
TEMPERATURE (°C)
TEMPERATURE (°C)
OUT
3526 G11
3526 G12
3526 G10
3526lfb
4
LTC3526L/LTC3526LB
TYPICAL PERFORMANCE CHARACTERISTICS
Burst Mode Quiesent Current
VFB vs Temperature
Start-Up Voltage vs Temperature
vs VOUT (LTC3526L)
0.80
0.75
0.70
0.65
0.60
0.55
0.50
10.0
0.50
0.25
NORMALIZED TO 25°C
9.5
9.0
8.5
8.0
7.5
7.0
1mA LOAD
0
–0.25
–0.50
–0.75
–1.00
NO LOAD
–50
0
25
50
75
100
40 60
TEMPERATURE (°C)
25
3.5
(V)
5.0
–60 –40 –20
0
20
80 100
1.5 2.0 2.5 3.0
4.0 4.5
TEMPERATURE (°C)
V
OUT
3526 G14
3526 G13
3526 G15
Fixed Frequency Switching
Waveform and VOUT Ripple
Burst Mode Waveforms
(LTC3526L)
VOUT and IIN During Soft-Start
V
SW PIN
2V/DIV
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 G18
3526 G16
3526 G17
V
OUT
C
OUT
= 3.3V
= 10μF
200μs/DIV
V
V
C
= 1.2V
500ns/DIV
V
V
C
= 1.2V
IN
OUT
OUT
10μs/DIV
IN
= 3.3V AT 100mA
= 3.3V
= 10μF
OUT
OUT
= 10μF
Load Step Response (from Burst
Mode Operation) (LTC3526L)
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
3526lfb
5
LTC3526L/LTC3526LB
TYPICAL PERFORMANCE CHARACTERISTICS
Load Step Response
(Fixed Frequency)
Load Step Response (from Burst
Mode Operation) (LTC3526L)
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
PIN FUNCTIONS
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 1.5V 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.
ꢀ
ꢃ
R2
R1
VOUT =1.195V • 1+
ꢂ
ꢅ
ꢁ
ꢄ
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
ceramicdecouplingcapacitorfromthispintogroundusing
OUT
filter capacitor (4.7μF minimum) should be as short and
wide as possible.
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
3526lfb
6
LTC3526L/LTC3526LB
BLOCK DIAGRAM
L1
4.7μH
V
IN
0.8V
TO 5V
C
IN
2.2μF
3
1
V
SW
IN
V
OUT
V
SEL
WELL
SWITCH
V
BEST
V
B
V
OUT
V
OUT
FB
1.5V
6
5
ANTI-RING
TO 5.25V
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
3526lfb
7
LTC3526L/LTC3526LB
OPERATION
(Refer to Block Diagram)
The LTC3526L/LTC3526LB are 1MHz synchronous boost
converters housed in a 6-lead 2mm × 2mm DFN package.
With a guaranteed ability to start up and operate from
inputs less than 0.8V, this device features fixed frequency,
current mode PWM control for exceptional line and load
regulation. 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.
rampsthepeakinductorcurrentfromzerotoitspeakvalue
of750mA(typical)inapproximately0.5ms,allowingstart-
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
Shutdown is accomplished by pulling the SHDN pin below
0.3VandenabledbypullingtheSHDNpinabove0.8V.Note
With its low R
and low gate charge internal N-chan-
DS(ON)
nel MOSFET switch and P-channel MOSFET synchronous
rectifier,theLTC3526Lachieveshighefficiencyoverawide
range of load currents. 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.
that SHDN can be driven above V or V , as long as it
IN
OUT
is limited to less than the absolute 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 LTC3526L/LTC3526LB include an independent start-
up oscillator designed to start up at an input voltage of
0.68V (typical). Soft-start and inrush current limiting are
provided during start-up, as well as normal mode.
resistive voltage divider from V
to ground programs
OUT
the output voltage via FB from 1.5V to 5.25V.
ꢀ
ꢃ
R2
R1
When either V or V
exceeds 1.3V typical, the IC
IN
OUT
VOUT =1.195V • 1+
ꢂ
ꢅ
enters normal operating mode. When the output voltage
ꢁ
ꢄ
exceeds the input by 0.24V, the IC powers itself from
V
instead of V . At this point the internal circuitry has
IN
Current Sensing
OUT
no dependency on the V input voltage, eliminating the
IN
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.
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 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 750mA,
LOW NOISE FIXED FREQUENCY OPERATION
Soft-Start
independent of input or output voltage, unless V
falls
OUT
below 0.7V, in which case the current limit is cut in half.
The LTC3526L/LTC3526LB contain internal circuitry to
providesoft-startoperation.Thesoft-startcircuitryslowly
3526lfb
8
LTC3526L/LTC3526LB
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.
TheLTC3526LwillenterBurstModeoperationatlightload
currentandreturntofixedfrequencyPWMmodewhenthe
loadincreases.RefertotheTypicalPerformanceCharacter-
istics to see the output load Burst Mode threshold current
vs V . The load current at which Burst Mode operation is
IN
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 LTC3526L 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 LTC3526L transitions
to sleep mode where the outputs are off and the LTC3526L
OUT
IN
P-channel MOSFET synchronous rectifier is only enabled
when V > (V + 0.24V).
OUT
IN
Anti-Ringing Control
The anti-ring circuit connects a resistor across the in-
ductor to prevent high frequency ringing on the SW pin
during discontinuous current mode operation. Although
consumesonly9μAofquiescentcurrentfromV . 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 LTC3526L/LTC3526LB are designed to allow true
output disconnect by eliminating body diode conduction
of the internal P-channel MOSFET rectifier. This allows for
V
OUT
and FB.
V
OUT
to go to zero volts during shutdown, drawing no cur-
As the load current increases, the LTC3526L will auto-
matically leave Burst Mode operation. Note that larger
output capacitor values may cause this transition to
occur at lighter loads. Once the LTC3526L has left Burst
Mode operation and returned to normal operation, it will
remain there until the output load is reduced below the
burst threshold current.
rentfromtheinputsource. Italsoallowsforinrushcurrent
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
connected between SW and V . The output disconnect
OUT
feature also allows V
to be pulled high, without any
reverse current into a battery connected to V .
OUT
IN
BurstModeoperationisinhibitedduringstart-upandsoft-
start and until V
is at least 0.24V greater than V .
OUT
IN
Thermal Shutdown
The LTC3526LB features continuous PWM operation at
1MHz. At very light loads, the LTC3526LB will exhibit
pulse-skip operation.
If the die temperature exceeds 160°C, the LTC3526L/
LTC3526LB 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.
3526lfb
9
LTC3526L/LTC3526LB
APPLICATIONS INFORMATION
V > V
OPERATION
COMPONENT SELECTION
Inductor Selection
IN
OUT
TheLTC3526L/LTC3526LBwillmaintainvoltageregulation
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.
TheLTC3526L/LTC3526LBcanutilizesmallsurfacemount
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
component size while providing little improvement in
output current capability.
SHORT-CIRCUIT PROTECTION
The LTC3526L/LTC3526LB output disconnect feature al-
lows 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 400mA (typical).
The minimum inductance value is given by:
V
• VOUT(MAX) – V
(
)
IN(MIN)
IN(MIN)
L >
SCHOTTKY DIODE
Ripple• VOUT(MAX)
Althoughnotrecommended,addingaSchottkydiodefrom
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 LTC3526L/LTC3526LB
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
ferritecoreinductormaterialsreducefrequencydependent
power losses compared to cheaper powdered iron types,
improving efficiency. The inductor should have low ESR
(seriesresistanceofthewindings)toreducetheI2Rpower
losses, and must be able to support the peak inductor
LTC3526L
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
3526lfb
10
LTC3526L/LTC3526LB
APPLICATIONS INFORMATION
current without saturating. Molded chokes and some
chip inductors usually do not have enough core area to
support the peak inductor current of 750mA seen on the
LTC3526L/LTC3526LB. 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 ap-
plications. Larger values 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
The internal loop compensation of the LTC3526L/
LTC3526LB are designed to be stable with output capaci-
tor values of 4.7μF or greater (without the need for any
external series resistor). Although ceramic capacitors
are recommended, low ESR tantalum capacitors may be
used as well.
ME3220
DS1605, DO1608
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
3526lfb
11
LTC3526L/LTC3526LB
TYPICAL APPLICATIONS
1-Cell to 1.8V Converter with <1mm Maximum Height
100
90
V
= 1.8V
OUT
4.7μH*
80
SW
70
V
OUT
V
IN
1.8V
V
IN
V
OUT
0.8V TO 1.6V
60
50
150mA
1μF
LTC3526L
SHDN FB
GND
511k
1M
10μF**
OFF ON
40
30
20
10
0
3526 TA02a
V
V
V
= 1.5V
= 1.2V
= 0.9V
IN
IN
IN
*FDK MIP3226D4R7M
**MURATA GRM219R60J106KE19D
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
60
50
V
IN
V
OUT
0.8V TO 1.6V
100mA
1μF
LTC3526L
SHDN FB
GND
1.4M
1M
40
30
20
10
0
10μF
OFF ON
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
3526lfb
12
LTC3526L/LTC3526LB
TYPICAL APPLICATIONS
1-Cell to 3.3V
100
90
V
= 3.3V
OUT
4.7μH*
SW
80
70
V
OUT
V
IN
3.3V
60
50
V
IN
V
OUT
0.8V TO 1.6V
75mA
1.78M
1M
22pF
1μF
LTC3526L
SHDN FB
GND
40
30
20
10
0
10μF
OFF ON
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
1.6V TO 3.2V
200mA
1μF
LTC3526L
1.78M
40
30
20
10
0
4.7μF
OFF ON
SHDN
GND
FB
1M
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
3526lfb
13
LTC3526L/LTC3526LB
TYPICAL APPLICATIONS
2-Cell to 5V
100
90
V
= 5V
OUT
6.8μH*
SW
80
70
V
OUT
60
50
V
IN
5V
150mA
V
IN
V
OUT
1.6V TO 3.2V
1μF
LTC3526L
SHDN FB
GND
3.24M
1.02M
22pF
40
30
20
10
0
10μF
OFF ON
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
LTC3526L
SHDN FB
GND
DC/DC
10μF
OFF ON
3526 TA07a
Li-Ion to 5V
100
V
= 5V
OUT
6.8μH*
90
80
70
SW
V
OUT
V
IN
5V
200mA
V
V
OUT
IN
60
50
2.7V TO 4.3V
1μF
LTC3526L
SHDN FB
GND
3.24M
1.02M
22pF
10μF
OFF ON
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
3526lfb
14
LTC3526L/LTC3526LB
PACKAGE DESCRIPTION
DC Package
6-Lead Plastic DFN (2mm × 2mm)
(Reference LTC DWG # 05-08-1703)
0.675 ±0.05
2.50 ±0.05
0.61 ±0.05
1.15 ±0.05
(2 SIDES)
PACKAGE
OUTLINE
0.25 ± 0.05
0.50 BSC
1.42 ±0.05
(2 SIDES)
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
R = 0.115
TYP
0.38 ± 0.05
4
6
0.56 ± 0.05
(2 SIDES)
2.00 ±0.10
(4 SIDES)
PIN 1 BAR
TOP MARK
(SEE NOTE 6)
PIN 1
CHAMFER OF
EXPOSED PAD
(DC6) DFN 1103
3
1
0.25 ± 0.05
0.50 BSC
0.75 ±0.05
0.200 REF
1.37 ±0.05
(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
3526lfb
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 represen-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
15
LTC3526L/LTC3526LB
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I
ThinSOT is a trademark of Linear Technology Corporation.
3526lfb
LT 1108 REV B • PRINTED IN USA
LinearTechnology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
16
●
●
© LINEAR TECHNOLOGY CORPORATION 2007
(408) 432-1900 FAX: (408) 434-0507 www.linear.com
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