LINER LTC3526B-2 500ma 2mhz synchronous step-up dc/dc converters in 2mm x 2mm dfn Datasheet

LTC3526-2/LTC3526B-2
500mA 2MHz Synchronous
Step-Up DC/DC Converters
in 2mm × 2mm DFN
FEATURES
DESCRIPTION
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The LTC®3526-2/LTC3526B-2 are synchronous, fixed
frequency step-up DC/DC converters with output disconnect. 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 an 850mV start-up voltage and operation down to
500mV once started.
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APPLICATIONS
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A switching frequency of 2MHz 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 LTC3526-2 features Burst Mode operation at light load
conditions, while the LTC3526B-2 features continuous
switching. Anti-ring circuitry eliminates EMI concerns by
damping the inductor in discontinuous mode. Additional
features include a low shutdown current of under 1μA and
thermal shutdown.
The LTC3526-2/LTC3526B-2 are housed in a 6-pin
2mm × 2mm × 0.75mm DFN package.
L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. Burst Mode
is a trademark of Linear Technology Corporation. All other trademarks are the property of their
respective owners. Patents pending.
Medical Instruments
Flash-Based MP3 Players
Noise Canceling Headphones
Wireless Mice
Bluetooth Headsets
TYPICAL APPLICATION
LTC3526-2 Efficiency and Power Loss vs Load Current
100
2.2μH
90
VIN
1μF
OFF ON
EFFICIENCY
VOUT
3.3V
200mA
VOUT
LTC3526-2
SHDN
GND
1.78M
4.7μF
FB
100
70
60
10
50
POWER LOSS
40
1
30
1M
35262b2fA01a
20
POWER LOSS (mW)
SW
VIN
1.6V TO 3.2V
1000
VIN = 2.4V
80
EFFICIENCY (%)
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Delivers 3.3V at 100mA from a Single Alkaline/
NiMH Cell or 3.3V at 200mA from Two Cells
VIN Start-Up Voltage: 850mV
VIN Operating Range: 0.5V to 5V
1.6V to 5.25V VOUT Range
Up to 94% Efficiency
Output Disconnect
2MHz Fixed Frequency Operation
VIN > VOUT Operation
Integrated Soft-Start
Current Mode Control with Internal Compensation
Burst Mode® Operation with 9μA Quiescent Current
(LTC3526-2)
Low Noise PWM Operation (LTC3526B-2)
Internal Synchronous Rectifier
Logic Controlled Shutdown (IQ < 1μA)
Anti-Ringing Control
Low Profile (2mm × 2mm × 0.75mm) DFN-6 Package
0.1
10
0
0.01
0.1
1
10
100
0.01
1000
LOAD CURRENT (mA)
35262b2f TA01b
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1
LTC3526-2/LTC3526B-2
ABSOLUTE MAXIMUM RATINGS
PIN CONFIGURATION
(Note 1)
VIN Voltage ................................................... –0.3V to 6V
SW Voltage
DC............................................................ –0.3V to 6V
Pulsed <100ns ......................................... –0.3V to 7V
SHDN, FB Voltage ........................................ –0.3V to 6V
VOUT ............................................................. –0.3V to 6V
Operating Temperature Range (Note 2).... –40°C to 85°C
Storage Temperature Range................... –65°C to 150°C
TOP VIEW
SW 1
GND 2
6 VOUT
7
5 FB
4 SHDN
VIN 3
DC PACKAGE
6-LEAD (2mm × 2mm) PLASTIC DFN
TJMAX = 125°C, θJA = 60°C/W (NOTE 6)
EXPOSED PAD (PIN 7) IS GND, MUST BE SOLDERED TO PC BOARD
ORDER INFORMATION
LEAD FREE FINISH
TAPE AND REEL
PART MARKING
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LTC3526EDC-2#PBF
LTC3526EDC-2#TRPBF
LCNM
6-Lead (2mm × 2mm) Plastic DFN
–40°C to 85°C
LTC3526BEDC-2#PBF
LTC3526BEDC-2#TRPBF
LCNP
6-Lead (2mm × 2mm) Plastic DFN
–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/
ELECTRICAL CHARACTERISTICS
The l denotes the specifications which apply over the specified operating
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
Minimum Start-Up Input Voltage
ILOAD = 1mA
Output Voltage Adjust Range
MIN
l
1.7
1.6
l
1.165
0°C to 85°C
Feedback Pin Voltage
Feedback Pin Input Current
VFB = 1.30V
TYP
MAX
0.85
1
UNITS
V
5.25
5.25
V
V
1.195
1.225
V
1
50
nA
Quiescent Current—Shutdown
VSHDN = 0V, Not Including Switch Leakage, VOUT = 0V
0.01
1
μA
Quiescent Current—Active
Measured on VOUT, Nonswitching
250
500
μA
Quiescent Current—Burst
Measured on VOUT, FB > 1.230V (LTC3526-2 Only)
9
18
μA
N-Channel MOSFET Switch Leakage Current
VSW = 5V
0.1
5
μA
P-Channel MOSFET Switch Leakage Current
VSW = 5V, VOUT = 0V
0.1
10
μA
N-Channel MOSFET Switch On Resistance
VOUT = 3.3V
0.4
Ω
P-Channel MOSFET Switch On Resistance
VOUT = 3.3V
0.6
Ω
700
mA
60
ns
l
N-Channel MOSFET Current Limit
Current Limit Delay to Output
500
(Note 3)
Maximum Duty Cycle
VFB = 1.15V, VOUT = 5V
l
Minimum Duty Cycle
VFB = 1.3V
l
l
Switching Frequency
SHDN Pin Input High Voltage
85
90
1.8
2
2.4
0.9
VSHDN = 1.2V
VSHDN = 3.3V
%
MHz
V
SHDN Pin Input Low Voltage
SHDN Pin Input Current
%
0
0.3
1
0.3
V
1
2
μA
μA
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LTC3526-2/LTC3526B-2
ELECTRICAL CHARACTERISTICS
Note 1: Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2: The LTC3526E-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 3: Specification is guaranteed by design and not 100% tested in
production.
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.
TYPICAL PERFORMANCE CHARACTERISTICS
Efficiency vs Load Current and VIN
for VOUT = 1.8V (LTC3526-2)
100
Efficiency vs Load Current and VIN
for VOUT = 3.3V (LTC3526-2)
100
1000
80
50
1
40
30
20
PLOSS AT VIN = 1.0V
PLOSS AT VIN = 1.2V
PLOSS AT VIN = 1.5V
10
0
0.01
0.1
1
10
100
LOAD CURRENT (mA)
60
10
50
1
40
30
10
0
0.01
0.01
1000
0.1
Efficiency vs Load Current and VIN
for VOUT = 5V (LTC3526-2)
1000
400
30
20
10
0
0.01
VIN = 1.2V
VIN = 2.4V
VIN = 3.6V 1
VIN = 4.2V
PLOSS AT VIN = 1.2V
0.1
PLOSS AT VIN = 2.4V
PLOSS AT VIN = 3.6V
PLOSS AT VIN = 4.2V
0.01
0.1
1
10
100
1000
LOAD CURRENT (mA)
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300
IOUT (mA)
40
10
POWER LOSS (mW)
70
50
20
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
VIN (V)
35262b2f G04
Minimum Load Resistance
During Start-Up vs VIN
1000
VOUT = 3.3V
350
100
60
VOUT = 1.8V
10
0.5
Maximum Output Current vs VIN
90
80
VOUT = 2.5V
50
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35262b2f G01
100
VOUT = 3.3V
60
30
0.01
1000
1
10
100
LOAD CURRENT (mA)
VOUT = 5V
40
PLOSS AT VIN = 1.2V
0.1
PLOSS AT VIN = 2.4V
PLOSS AT VIN = 3.0V
20
0.1
80
70
IIN (μA)
10
100
VIN = 1.2V
VIN = 2.4V
VIN = 3.0V
70
POWER LOSS (mW)
60
POWER LOSS (mW)
VIN = 1.0V
VIN = 1.2V
VIN = 1.5V
EFFICIENCY (%)
100
70
VOUT = 2.5V
VOUT = 1.8V
250
LOAD (Ω)
80
EFFICIENCY (%)
90
90
90
EFFICIENCY (%)
No-Load Input Current vs VIN
100
1000
200
VOUT = 5V
150
100
100
50
0
0.5
L = 2.2μH
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
VIN (V)
35262b2f G05
10
0.85
0.95
1.05
VIN (V)
1.15
1.25
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LTC3526-2/LTC3526B-2
TYPICAL PERFORMANCE CHARACTERISTICS
Burst Mode Threshold Current
vs VIN
Start-Up Delay Time vs VIN
40
30
100
VOUT = 2.5V
35 COUT = 10μF
L = 2.2μH
LOAD CURRENT (mA)
80
70
60
50
40
30
20
LOAD CURRENT (mA)
VOUT = 1.8V
COUT = 10μF
25 L = 2.2μH
90
DELAY (μs)
Burst Mode Threshold Current
vs VIN
20
LEAVE BURST
15
ENTER BURST
10
5
1.5
2.0
2.5 3.0
VIN (V)
3.5
4.0
1.25
VIN (V)
1.5
LOAD CURRENT (mA)
LOAD CURRENT (mA)
50
25
20
15
2
NORMALIZED TO 3.3V
1
40
LEAVE BURST
30
20
ENTER BURST
10
1.5
2.0
VIN (V)
0
1.0
3.0
2.5
1.5
2.0
2.5 3.0
VIN (V)
3.5
0.90
10
0.85
8
0.75
RDS(ON) (Ω)
0.70
PMOS
0.55
0.50
NMOS
0.40
4.0
–3
–4
–6
1.5
4.5
2.0
2.5
3.0 3.5
VOUT (V)
4.0
4.5
5.0
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RDS(ON) Change vs Temperature
1.3
NORMALIZED TO 25˚C
NORMALIZED TO 25˚C
1.2
6
NORMALIZED RDS(ON)
FREQUENCY CHANGE (%)
0.80
0.45
–2
Oscillator Frequency Change
vs Temperature
RDS(ON) vs VOUT
0.60
–1
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0.65
0
–5
5
1.0
1.75
Oscillator Frequency Change
vs VOUT
VOUT = 5V
COUT = 10μF
L = 2.2μH
ENTER BURST
0
1.5
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FREQUENCY CHANGE (%)
60
VOUT = 3.3V
45 COUT = 10μF
L = 2.2μH
40
LEAVE BURST
1.25
1
VIN (V)
Burst Mode Threshold Current
vs VIN
50
10
ENTER BURST
35262b2f G08a
Burst Mode Threshold Current
vs VIN
30
15
0
1
4.5
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35
LEAVE BURST
20
5
0
1.0
25
10
10
0
30
4
2
0
–2
–4
–6
1.1
1.0
0.9
0.8
–8
0.35
0.30
1.5
2.0
2.5
3.0 3.5
VOUT (V)
4.0
4.5
5.0
35262b2f
–10
–50
–30
–10 10
30
50
TEMPERATURE (˚C)
70
90
35262b2f G11
0.7
–50
–30
–10 10
30
50
TEMPERATURE (˚C)
70
90
35262b2f G12
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LTC3526-2/LTC3526B-2
TYPICAL PERFORMANCE CHARACTERISTICS
VFB vs Temperature
1.00
10.0
LOAD = 1mA
NORMALIZED TO 25˚C
0.95
9.5
0
0.90
9.0
–0.25
IQ (μA)
0.25
VIN (V)
CHANGE IN VFB (%)
0.50
Burst Mode Quiescent Current
vs VOUT
Start-Up Voltage vs Temperature
0.85
8.5
–0.50
0.80
8.0
–0.75
0.75
7.5
–1.00
20 40 60
–60 –40 –20 0
TEMPERATURE (˚C)
80
0.70
–50
100
–30
–10 10
30 –50
TEMPERATURE (°C)
70
90
Fixed Frequency Switching
Waveform and VOUT Ripple
2.5
3.0 3.5
VOUT (V)
4.0
SW PIN
2V/DIV
5.0
VOUT and IIN During Soft-Start
VOUT
1V/DIV
SW PIN
2V/DIV
INPUT
CURRENT
0.2A/DIV
SHDN PIN
1V/DIV
VOUT
50mV/DIV
AC COUPLED
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4.5
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Burst Mode Waveforms
VOUT
10mV/DIV
AC COUPLED
2.0
35262b2f G14
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200ns/DIV
VIN = 1.2V
VOUT = 3.3V AT 50mA
COUT = 4.7μF
7.0
1.5
35262b2
20μs/DIV
VIN = 1.2V
VOUT = 3.3V AT 5mA
COUT = 10μF
Load Step Response (from Burst
Mode Operation)
VOUT
100mV/DIV
AC COUPLED
VOUT = 3.3V
COUT = 10μF
200μs/DIV
35262b2f
Load Step Response
(Fixed Frequency)
VOUT
100mV/DIV
AC COUPLED
LOAD
CURRENT
50mA/DIV
LOAD
CURRENT
50mA/DIV
VIN = 3.6V
100μs/DIV
VOUT = 5V
20mA TO 170mA STEP
COUT = 10μF
35262b2f
VIN = 3.6V
100μs/DIV
VOUT = 5V
50mA TO 150mA STEP
COUT = 10μF
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5
LTC3526-2/LTC3526B-2
TYPICAL PERFORMANCE CHARACTERISTICS
Load Step Response
(Fixed Frequency)
Load Step Response (from Burst
Mode Operation)
VOUT
100mV/DIV
AC COUPLED
VOUT
100mV/DIV
AC COUPLED
LOAD
CURRENT
50mA/DIV
LOAD
CURRENT
50mA/DIV
VIN = 1.2V
100μs/DIV
VOUT = 3.3V
50mA TO 100mA STEP
COUT = 10μF
35262b2f
VIN = 1.2V
50μs/DIV
VOUT = 3.3V
5mA TO 100mA STEP
COUT = 10μF
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PIN FUNCTIONS
SW (Pin 1): Switch Pin. Connect inductor between SW and
VIN. Keep PCB trace lengths as short and wide as possible
to reduce EMI. If the inductor current falls to zero or SHDN
is low, an internal anti-ringing switch is connected from
SW to VIN to minimize EMI.
GND (Pin 2): Signal and Power Ground. Provide a short
direct PCB path between GND and the (–) side of the input
and output capacitors.
VIN (Pin 3): Input Supply Pin. Connect a minimum of 1μF
ceramic decoupling capacitor from this pin to ground
using short direct PCB traces.
SHDN (Pin 4): Logic Controlled Shutdown Input. There
is an internal 4MΩ pull-down on this pin.
• SHDN = High: Normal operation
• SHDN = Low: Shutdown, quiescent current < 1μA
nect resistor divider tap to this pin. The top of the divider
connects to the output capacitor, the bottom of the divider
connects to GND. Referring to the Block Diagram, the output
voltage can be adjusted from 1.6V to 5.25V by:
R2 VOUT = 1.195V • 1+ R1
VOUT (Pin 6): Output voltage sense and drain of the internal
synchronous rectifier. PCB trace from VOUT to the output
filter capacitor (4.7μF minimum) should be as short and
wide as possible.
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.
FB (Pin 5): Feedback Input to the gm Error Amplifier. Con-
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6
LTC3526-2/LTC3526B-2
BLOCK DIAGRAM
L1
2.2μH
CIN
2.2μF
3
1
SW
VIN
VOUT
VSEL
VBEST
WELL
SWITCH
VB
VOUT
ANTI-RING
4
SHDN
SHUTDOWN
SHUTDOWN
GATE DRIVERS
AND
ANTI-CROSS
CONDUCTION
– +
4M
Σ
VREF
IPK
COMP
1.195V
IPK
UVLO
COUT
4.7μF
5
R1
+
–
MODE
CONTROL
CLK
IZERO
COMP
ERROR AMP
SLEEP COMP
START-UP
LOGIC
FB
SLOPE
COMP
IZERO
2MHz
OSC
VOUT
1.6V
TO 5.25V
6
R2
+
–
VIN
0.85V
TO 5V
VREF
CLAMP
THERMAL
SHUTDOWN
TSD
WAKE
CSS
EXPOSED
PAD
GND
7
2
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7
LTC3526-2/LTC3526B-2
OPERATION
(Refer to Block Diagram)
The LTC3526-2/LTC3526B-2 are 2MHz 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 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.
ramps the peak inductor current from zero to its peak value
of 700mA (typical) in approximately 0.5ms, allowing startup into heavy loads. The soft-start circuitry is reset in the
event of a shutdown command or a thermal shutdown.
With its low RDS(ON) and low gate charge internal N-channel MOSFET switch and P-channel MOSFET synchronous
rectifier, the LTC3526-2 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.
Shutdown is accomplished by pulling the SHDN pin
below 0.3V and enabled by pulling the SHDN pin above
0.8V typical. Note that SHDN can be driven above VIN
or VOUT, as long as it is limited to less than the absolute
maximum rating.
LOW VOLTAGE START-UP
The LTC3526-2/LTC3526B-2 include an independent startup oscillator designed to start up at an input voltage of
0.85V (typical). Soft-start and inrush current limiting are
provided during start-up, as well as normal mode.
When either VIN or VOUT exceeds 1.4V typical, the IC
enters normal operating mode. When the output voltage
exceeds the input by 0.24V, the IC powers itself from
VOUT instead of VIN. At this point the internal circuitry has
no dependency on the VIN input voltage, eliminating the
requirement for a large input capacitor. The input voltage
can drop as low as 0.5V. The limiting factor for the application 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.
LOW NOISE FIXED FREQUENCY OPERATION
Soft-Start
The LTC3526-2/LTC3526B-2 contain internal circuitry to
provide soft-start operation. The soft-start circuitry slowly
Oscillator
An internal oscillator sets the switching frequency to
2MHz.
Shutdown
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 minimum and maximum error amp output voltage for improved
large-signal transient response. Power converter control
loop compensation is provided internally. An external
resistive voltage divider from VOUT to ground programs
the output voltage via FB from 1.6V to 5.25V.
R2 VOUT = 1.195V • 1+ R1
Current Sensing
Lossless current sensing converts the peak current signal of
the N-channel MOSFET switch into a voltage that 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.
Current Limit
The current limit comparator shuts off the N-channel
MOSFET switch once its threshold is reached. The current limit comparator delay to output is typically 60ns.
Peak switch current is limited to approximately 700mA,
independent of input or output voltage, unless VOUT falls
below 0.7V, in which case the current limit is cut in half.
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8
LTC3526-2/LTC3526B-2
OPERATION
(Refer to Block Diagram)
Zero Current Comparator
Burst Mode OPERATION
The zero current comparator monitors the inductor current 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 LTC3526-2 will automatically enter Burst Mode operation 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 threshold current vs VIN. The load current at which Burst Mode
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 VOUT is close to VIN, the
P-channel MOSFET synchronous rectifier is only enabled
when VOUT > (VIN + 0.24V).
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 CSW
(capacitance on SW pin) is low energy, it can cause EMI
radiation.
Output Disconnect
The LTC3526-2/LTC3526B-2 are designed to allow true
output disconnect by eliminating body diode conduction
of the internal P-channel MOSFET rectifier. This allows for
VOUT 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
connected between the SW pin and VOUT. The output disconnect feature also allows VOUT to be pulled high, without
any reverse current into a battery connected to VIN.
Thermal Shutdown
If the die temperature exceeds 160°C, the LTC3526-2/
LTC3526B-2 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.
In Burst Mode operation, the LTC3526-2 still switches at
a fixed frequency of 2MHz, 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 delivered to the output until it reaches the nominal
regulation value, then the LTC3526-2 transitions to sleep
mode where the outputs are off and the LTC3526-2 consumes only 9μA of quiescent current from VOUT. When the
output voltage droops slightly, switching resumes. This
maximizes efficiency at very light loads by minimizing
switching and quiescent losses. Burst Mode output voltage
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
VOUT and FB.
As the load current increases, the LTC3526-2 will automatically leave Burst Mode operation. Note that larger output
capacitor values may cause this transition to occur at lighter
loads. Once the LTC3526-2 has left Burst Mode operation
and returned to normal operation, it will remain there until
the output load is reduced below the burst threshold.
Burst Mode operation is inhibited during start-up and softstart and until VOUT is at least 0.24V greater than VIN.
The LTC3526B-2 features continuous PWM operation at
2MHz. At very light loads, the LTC3526B-2 will exhibit
pulse-skip operation.
35262b2fa
9
LTC3526-2/LTC3526B-2
APPLICATIONS INFORMATION
VIN > VOUT OPERATION
COMPONENT SELECTION
The LTC3526-2/LTC3526B-2 will maintain voltage regulation even when the input voltage is above the desired output
voltage. Note that the efficiency is much lower in this mode,
and the maximum output current capability will be less.
Refer to the Typical Performance Characteristics.
SHORT-CIRCUIT PROTECTION
The LTC3526-2/LTC3526B-2 output disconnect feature
allows 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).
Inductor Selection
The LTC3526-2/LTC3526B-2 can utilize small surface
mount chip inductors due to their fast 2MHz switching
frequency. Inductor values between 1.5μH and 3.3μH 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. Increasing the inductance above 10μH will
increase size while providing little improvement in output
current capability.
The minimum inductance value is given by:
SCHOTTKY DIODE
L>
Although it is not required, adding a Schottky diode from
SW to VOUT will improve efficiency by about 2%. Note
that this defeats the output disconnect and short-circuit
protection features.
(
VIN(MIN) • VOUT(MAX) VIN(MIN)
where:
)
2 • RIPPLE • VOUT(MAX)
Ripple = Allowable inductor current ripple (amps peakpeak)
VIN(MIN) = Minimum input voltage
PCB LAYOUT GUIDELINES
VOUT(MAX) = Maximum output voltage
The high speed operation of the LTC3526-2/LTC3526B-2
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 dependent 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
LTC3526-2
SW 1
GND 2
+
VIN 3
6 VOUT
5 FB
MINIMIZE
TRACE ON FB
AND SW
4 SHDN
VIN
MULTIPLE VIAS
TO GROUND PLANE
35262b2f
Figure 1. Recommended Component Placement for Single Layer Board
35262b2fa
10
LTC3526-2/LTC3526B-2
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 LTC3526-2/LTC3526B-2. To minimize radiated
noise, use a shielded inductor. See Table 1 for suggested
components and suppliers.
Table 1. Recommended Inductors
VENDOR
PART/STYLE
Coilcraft
(847) 639-6400
www.coilcraft.com
LPO4815
LPS4012, LPS4018
MSS5131
MSS4020
MOS6020
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
(714) 852-2001
www.murata.com
LQH43C
LQH32C (-53 series)
301015
Sumida
(847) 956-0666
www.sumida.com
CDRH5D18
CDRH2D14
CDRH3D16
CDRH3D11
CR43
CMD4D06-4R7MC
CMD4D06-3R3MC
Taiyo-Yuden
www.t-yuden.com
NP03SB
NR3015T
NR3012T
TDK
(847) 803-6100
www.component.tdk.com
VLP
VLF, VLCF
Toko
(408) 432-8282
www.tokoam.com
D412C
D518LC
D52LC
D62LCB
Wurth
(201) 785-8800
www.we-online.com
WE-TPC type S, M
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.
The internal loop compensation of the LTC3526-2 is designed to be stable with output capacitor 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.
A small ceramic capacitor in parallel with a larger tantalum
capacitor may be used in demanding applications that have
large load transients. Another method of improving the
transient response is to add a small feed-forward capacitor
across the top resistor of the feedback divider (from VOUT
to FB). A typical value of 22pF will generally suffice.
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
ceramic capacitor manufacturers. Consult the manufacturers directly for detailed information on their selection of
ceramic capacitors.
Table 2. Capacitor Vendor Information
SUPPLIER
PHONE
WEBSITE
AVX
(803) 448-9411
www.avxcorp.com
Murata
(714) 852-2001
www.murata.com
Taiyo-Yuden
(408) 573-4150
www.t-yuden.com
TDK
(847) 803-6100
www.component.tdk.com
Samsung
(408) 544-5200
www.sem.samsung.com
35262b2fa
11
LTC3526-2/LTC3526B-2
TYPICAL APPLICATIONS
1-Cell to 1.8V Converter with <1mm Maximum Height
for Low-Noise Applications
100
90
2.2μH*
VOUT = 1.8V
80
SW
1μF
VOUT
1.8V
150mA
VOUT
VIN
LTC3526B-2
SHDN
OFF ON
EFFICIENCY (%)
VIN
1V TO 1.6V
511k
4.7μF**
FB
GND
70
60
50
40
30
1M
20
35262b2fA02a
VIN = 1.5V
VIN = 1.2V
VIN = 0.9V
10
*FDK MIPF2520D2R2
**MURATA GRM219R60J475KE19D
0
0.1
1
10
100
LOAD CURRENT (mA)
1000
35262b2f TA02b
1-Cell to 3.3V
100
90
2.7μH*
VOUT = 3.3V
SW
VIN
1V TO 1.6V
VOUT
VIN
1μF
OFF ON
LTC3526-2
SHDN
1.78M
10μF
FB
GND
22pF
VOUT
3.3V
75mA
EFFICIENCY (%)
80
70
60
50
40
30
1M
35262b2fA04a
20
VIN = 1.5V
VIN = 1.2V
VIN = 0.9V
10
*TAIYO-YUDEN NP03SB2R7M
0
0.01
0.1
1
10
100
LOAD CURRENT (mA)
1000
35262b2f TA04b
35262b2fa
12
LTC3526-2/LTC3526B-2
TYPICAL APPLICATIONS
2-Cell to 3.3V
100
90
2.7μH*
VOUT = 3.3V
80
SW
1μF
OFF ON
VOUT
3.3V
200mA
VOUT
VIN
LTC3526-2
SHDN
EFFICIENCY (%)
VIN
2V TO 3.2V
1.78M
4.7μF
FB
GND
70
60
50
40
30
1M
20
35262b2fA05a
VIN = 3.0V
VIN = 2.4V
VIN = 1.8V
10
*TAIYO-YUDEN NP03SB2R7M
0
0.01
0.1
1
10
100
LOAD CURRENT (mA)
1000
35262b2f TA05b
3.3V Converter with Output OR’d with 5V USB Input
MBR120ESFT
5V USB
2.2μH
VOUT
3.3V/5V
USB
SW
VBATT
1.8V TO 3.2V
VOUT
VIN
1μF
OFF ON
LTC3526-2
SHDN
GND
LDO
1.78M
DC/DC
4.7μF
FB
1M
35262b2fA07a
35262b2fa
13
LTC3526-2/LTC3526B-2
TYPICAL APPLICATIONS
2-Cell to 5V
100
VOUT = 5V
90
3.3μH*
SW
VIN
2V TO 3.2V
VOUT
VIN
1μF
LTC3526-2
SHDN
OFF ON
VOUT
5V
150mA
3.24M
22pF
10μF
FB
GND
EFFICIENCY (%)
80
70
60
50
40
30
1.02M
20
35262b2fA06a
VIN = 3.0V
VIN = 2.4V
VIN = 1.8V
10
*TAIYO-YUDEN NP03SB3R3M
0
0.01
0.1
1
10
100
LOAD CURRENT (mA)
1000
35262b2f TA06b
Li-Ion to 5V
100
3.3μH*
90
VOUT = 5V
VIN
2.7V TO 4.3V
VOUT
VIN
1μF
OFF ON
LTC3526-2
SHDN
3.24M
10μF
FB
GND
22pF
VOUT
5V
200mA
70
60
50
40
30
1.02M
35262b2fA08a
*TAIYO-YUDEN NP03SB3R3M
EFFICIENCY (%)
80
SW
20
VIN = 4.2V
VIN = 3.6V
VIN = 3.0V
10
0
0.01
0.1
1
10
100
LOAD CURRENT (mA)
1000
35262b2f TA08b
35262b2fa
14
LTC3526-2/LTC3526B-2
PACKAGE DESCRIPTION
DC Package
6-Lead Plastic DFN (2mm × 2mm)
(Reference LTC DWG # 05-08-1703)
R = 0.115
TYP
0.56 ± 0.05
(2 SIDES)
0.675 ±0.05
2.50 ±0.05
1.15 ±0.05 0.61 ±0.05
(2 SIDES)
PIN 1 BAR
PACKAGE
TOP MARK
OUTLINE
(SEE NOTE 6)
0.38 ± 0.05
4
2.00 ±0.10
(4 SIDES)
PIN 1
CHAMFER OF
EXPOSED PAD
3
0.25 ± 0.05
0.50 BSC
1.42 ±0.05
(2 SIDES)
0.200 REF
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
6
1
(DC6) DFN 1103
0.25 ± 0.05
0.50 BSC
0.75 ±0.05
1.37 ±0.05
(2 SIDES)
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
35262b2fa
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 representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
15
LTC3526-2/LTC3526B-2
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
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LTC3421
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LTC3422
1.5A ISW, 3MHz Synchronous Step-Up DC/DC Converter
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LTC3423/LTC3424
1A/2A ISW, 3MHz, Synchronous Step-Up DC/DC
Converter
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ISD < 1μA, 10-Lead MS Package
LTC3426
2A ISW, 1.2MHz, Step-Up DC/DC Converter
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500mA ISW, 1.25MHz, Synchronous Step-Up DC/DC
Converter with Output Disconnect
VIN: 1.8V to 5V, VOUT(MAX) = 5.25V, IQ = 350μA, ISD < 1μA,
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2mm × 2mm DFN Package
LTC3429
600mA ISW, 500kHz, Synchronous Step-Up DC/DC
Converter with Output Disconnect and Soft-Start
96% Efficiency VIN: 0.5V to 4.4V, VOUT(MAX) = 5V, IQ = 20μA/300μA,
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LTC3458
1.4A ISW, 1.5MHz, Synchronous Step-Up DC/DC
Converter/Output Disconnect/Burst Mode Operation
93% Efficiency VIN: 1.5V to 6V, VOUT(MAX) = 7.5V, IQ = 15μA,
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1.7A ISW, 1.5MHz, Synchronous Step-Up DC/DC
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94% Efficiency VOUT(MAX) = 6V, IQ = 12μA, DFN12 Package
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70mA ISW, 10V Micropower Synchronous Boost
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VIN: 1.5V to 5.5V, VOUT(MAX) = 10V, IQ = 10μA, ISD < 1μA,
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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,
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LTC3526/LTC3526B
500mA ISW, 1MHz, Synchronous Step-Up DC/DC
Converter in 2mm × 2mm DFN
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®
ThinSOT is a trademark of Linear Technology Corporation.
35262b2fa
16
Linear Technology Corporation
LT 0807 REV A • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507
●
www.linear.com
© LINEAR TECHNOLOGY CORPORATION 2006