LINER LTC3526L 550ma 1mhz synchronous step-up dc/dc converter Datasheet

LTC3526L/LTC3526LB
550mA 1MHz Synchronous
Step-Up DC/DC Converters
in 2mm × 2mm DFN
Description
Features
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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: 680mV
1.5V to 5.25V VOUT Range
Up to 94% Efficiency
Output Disconnect
1MHz Fixed Frequency Operation
VIN > VOUT Operation
Integrated Soft-Start
Current Mode Control with Internal Compensation
Burst Mode® Operation with 9µA IQ (LTC3526L)
Low Noise PWM Operation (LT3526LB)
Internal Synchronous Rectifier
Logic Controlled Shutdown (IQ < 1µA)
Anti-Ring Control
Low Profile (2mm × 2mm × 0.75mm)
DFN-6 Package
Applications
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The LTC®3526L/LTC3526LB 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
a 680mV start-up voltage and operation down to 500mV
once started.
A switching frequency of 1MHz 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 LTC3526L features Burst Mode operation at light load
conditions allowing it to maintain high efficiency over a
wide range of load. The LTC3526LB features fixed frequency
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.
The LTC3526L/LTC3526LB are housed in a 2mm × 2mm
× 0.75mm DFN package.
Medical Instruments
Noise Canceling Headphones
Wireless Mice
Bluetooth Headsets
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.
Typical Application
Efficiency and Power Loss vs Load Current
100
4.7µH
90
EFFICIENCY
VIN
4.7µF
OFF ON
VOUT
LTC3526L
SHDN
GND
1.78M
VOUT
3.3V
200mA
4.7µF
FB
1M
3526l TA01a
100
70
60
10
50
POWER LOSS
40
1
30
20
POWER LOSS (mW)
VIN
1.6V TO 3.2V
SW
1000
VIN = 2.4V
80
EFFICIENCY (%)
n
0.1
10
0
0.01
0.1
1
10
100
0.01
1000
LOAD CURRENT (mA)
3526l TA01b
3526lfc
LTC3526L/LTC3526LB
Absolute Maximum Ratings
(Note 1)
Pin Configuration
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
(Notes 2, 5)...............................................–40°C to 85°C
Storage Temperature Range................... –65°C to 150°C
TOP VIEW
SW 1
GND 2
6 VOUT
7
VIN 3
5 FB
4 SHDN
DC PACKAGE
6-LEAD (2mm s 2mm) PLASTIC DFN
TJMAX = 125°C, θJA = 102°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
LTC3526LEDC#PBF
LTC3526LEDC#TRPBF
LCSS
6-Lead (2mm × 2mm) Plastic DFN
–40°C to 85°C
LTC3526LBEDC#PBF
LTC3526LBEDC#TRPBF
LCST
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
Input Voltage Range
After Start-Up. (Minimum Voltage is Load Dependent)
MIN
TYP
MAX
0.68
0.8
UNITS
V
l
0.5
5
V
Output Voltage Adjust Range
l
1.5
5.25
V
Feedback Pin Voltage
l
1.165
Feedback Pin Input Current
VFB = 1.30V
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 (LTC3526L Only)
N-Channel MOSFET Switch Leakage Current
VSW = 5V
9
18
µA
0.1
5
µA
10
µA
P-Channel MOSFET Switch Leakage Current
VSW = 5V, VOUT = 0V
0.1
N-Channel MOSFET Switch On Resistance
VOUT = 3.3V
0.4
P-Channel MOSFET Switch On Resistance
VOUT = 3.3V
N-Channel MOSFET Current Limit
l
Current Limit Delay to Output
(Note 3)
Maximum Duty Cycle
VFB = 1.15V
l
Minimum Duty Cycle
VFB = 1.3V
l
Switching Frequency
SHDN Pin Input High Voltage
SHDN Pin Input Low Voltage
l
550
87
Ω
0.6
Ω
750
mA
60
ns
90
%
0
0.75
1
1.25
0.8
%
MHz
V
0.3
V
3526lfc
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
reliability and lifetime.
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.
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.
Typical Performance Characteristics
1000
100
100
80
10
50
1
40
30
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)
EFFICIENCY (%)
60
VIN = 1.2V
VIN = 1.8V
VIN = 2.4V
VIN = 3.0V
70
60
50
1
40
30
10
0.01
1000
0
0.01
3526l G01
3526l G02
Efficiency vs Load Current and VIN
for VOUT = 5V (LTC3526L)
Maximum Output Current vs VIN
1000
400
90
80
100
50
40
30
20
10
0
0.01
10
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)
3526l G03
300
IOUT (mA)
60
POWER LOSS (mW)
70
VOUT = 3.3V
60
VOUT = 2.5V
50
VOUT = 1.8V
40
30
20
10
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
VIN (V)
3526l G04
Minimum Load Resistance
During Start-Up vs VIN
10000
VOUT = 3.3V
350
VOUT = 5V
70
PLOSS AT VIN = 1.2V
0.1
PLOSS AT VIN = 1.8V
PLOSS AT VIN = 2.4V
PLOSS AT VIN = 3.0V
0.01
0.1
1
10
100
1000
LOAD CURRENT (mA)
20
0.1
10
POWER LOSS (mW)
VIN = 1.0V
VIN = 1.2V
VIN = 1.5V
70
POWER LOSS (mW)
EFFICIENCY (%)
100
90
80
100
20
EFFICIENCY (%)
1000
90
80
100
No-Load Input Current vs VIN
(LTC3526L)
IIN (µA)
90
Efficiency vs Load Current and VIN
for VOUT = 3.3V (LTC3526L)
VOUT = 3.3V
VOUT = 2.5V
VOUT = 1.8V
1000
250
200
LOAD (Ω)
100
Efficiency vs Load Current and VIN
for VOUT = 1.8V (LTC3526L)
VOUT = 5V
150
100
100
50
0
0.5
L = 4.7µH
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
VIN (V)
3526l G05
10
0.65
0.75
0.85
0.95
VIN (V)
1.05
1.15
3526l G06
3526lfc
LTC3526L/LTC3526LB
TYPICAL PERFORMANCE CHARACTERISTICS
VOUT = 1.8V
COUT = 10µF
25 L = 4.7µH
80
LOAD CURRENT (mA)
70
DELAY (µs)
30
30
90
60
50
40
30
20
20
ENTER BURST
15
10
1.0
1.5
2.0
2.5 3.0
VIN (V)
3.5
4.0
0
4.5
1.0
1.25
VIN (V)
40
25
20
15
ENTER BURST
10
1.5
2.0
VIN (V)
3
VOUT = 5V
COUT = 10µF
L = 4.7µH
20
ENTER BURST
10
0.85
8
1.5
2.0
2.5 3.0
VIN (V)
3.5
4.0
RDS(ON) (Ω)
PMOS
0.55
0.50
0.45
NMOS
0.40
–1
2.0
2.5
3.0 3.5
VOUT (V)
4.0
4.5
5.0
3526l G09
RDS(ON) Change vs Temperature
1.3
NORMALIZED TO 25°C
NORMALIZED TO 25°C
1.2
6
4
2
0
–2
–4
–6
1.1
1.0
0.9
0.8
–8
0.35
0.30
0
–3
1.5
4.5
NORMALIZED RDS(ON)
FREQUECNY CHANGE (%)
0.80
0.60
NORMALIZED TO VOUT = 3.3V
1
Oscillator Frequency Change
vs Temperature
0.90
0.65
2.0
Oscillator Frequency Change
vs VOUT
3526l G08d
RDS(ON) vs VOUT
0.70
1.75
–2
3526l G08c
0.75
1.5
2
LEAVE BURST
30
0
1.0
3.0
2.5
1.25
3526l G08b
Burst Mode Threshold Current
vs VIN (LTC3526L)
10
1.0
10
VIN (V)
5
0
ENTER BURST
15
0
1.0
1.5
FREQUENCY CHANGE (%)
LEAVE BURST
LOAD CURRENT (mA)
LOAD CURRENT (mA)
50
30
20
3526l G08a
Burst Mode Threshold Current
vs VIN (LTC3526L)
VOUT = 3.3V
35 COUT = 10µF
L = 4.7µH
LEAVE BURST
5
3526l G07
40
VOUT = 2.5V
COUT = 10µF
25 L = 4.7µH
LEAVE BURST
5
10
0
Burst Mode Threshold Current
vs VIN (LTC3526L)
LOAD CURRENT (mA)
100
Burst Mode Threshold Current
vs VIN (LTC3526L)
Start-Up Delay Time vs VIN
1.5
2.0
2.5
3.0 3.5
VOUT (V)
4.0
4.5
5.0
3526l G10
–10
–50
–30
–10 10
30
50
TEMPERATURE (°C)
70
90
3526l G11
0.7
–50
–30
–10 10
30
50
TEMPERATURE (°C)
70
90
3526l G12
3526lfc
LTC3526L/LTC3526LB
TYPICAL PERFORMANCE CHARACTERISTICS
VFB vs Temperature
0.80
10.0
0.25
0.75
9.5
0
0.70
1mA LOAD
–0.25
0.65
9.0
IQ (µA)
NORMALIZED TO 25°C
VIN (V)
0.50
CHANGE IN VFB (%)
Burst Mode Quiesent Current
vs VOUT (LTC3526L)
Start-Up Voltage vs Temperature
NO LOAD
8.5
–0.50
0.60
8.0
–0.75
0.55
7.5
–1.00
20 40 60
–60 –40 –20 0
TEMPERATURE (°C)
80
100
0.50
–50
25
0
25
50
TEMPERATURE (°C)
3526l G13
100
7.0
1.5
VOUT
10mV/DIV
AC-COUPLED
3526l G16
2.5
3.0 3.5
VOUT (V)
4.0
4.5
SW PIN
2V/DIV
VOUT
20mV/DIV
AC-COUPLED
INDUCTOR
CURRENT
0.2A/DIV
5.0
3526l G15
Burst Mode Waveforms
(LTC3526L)
SW PIN
2V/DIV
2.0
3526l G14
Fixed Frequency Switching
Waveform and VOUT Ripple
VIN = 1.2V
500ns/DIV
VOUT = 3.3V AT 100mA
COUT = 10µF
75
VOUT and IIN During Soft-Start
VOUT
1V/DIV
INPUT
CURRENT
0.2A/DIV
SHDN PIN
1V/DIV
VIN = 1.2V
VOUT = 3.3V
COUT = 10µF
10µs/DIV
3526l G17
Load Step Response (from Burst
Mode Operation) (LTC3526L)
VOUT
100mV/DIV
AC-COUPLED
VOUT = 3.3V
COUT = 10µF
200µs/DIV
3526l G18
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
3526l G19
VIN = 3.6V
100µs/DIV
VOUT = 5V
50mA TO 150mA STEP
COUT = 10µF
3526l G20
3526lfc
LTC3526L/LTC3526LB
TYPICAL PERFORMANCE CHARACTERISTICS
Load Step Response
(Fixed Frequency)
Load Step Response (from Burst
Mode Operation) (LTC3526L)
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
3526l G21
VIN = 1.2V
50µs/DIV
VOUT = 3.3V
5mA TO 100mA STEP
COUT = 10µF
3526l G22
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, Exposed Pad Pin 7): Signal and Power Ground.
Provide a short direct PCB path between GND and the
(–) side of the input and output capacitors. 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.
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
FB (Pin 5): Feedback Input to the gm Error Amplifier. Connect 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 1.5V 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
3526lfc
LTC3526L/LTC3526LB
Block Diagram
VIN
0.8V
TO 5V
L1
4.7µH
CIN
2.2µF
3
1
VIN
VOUT
SW
VSEL
VBEST
WELL
SWITCH
VB
VOUT
VOUT
1.5V
TO 5.25V
6
ANTI-RING
4
SHDN
SHUTDOWN
SHUTDOWN
GATE DRIVERS
AND
ANTI-CROSS
CONDUCTION
– +
4M
IPK
COMP
VREF
IPK
UVLO
IZERO
IZERO
COMP
1MHz
OSC
CLK
COUT
4.7µF
R1
ERROR AMP
SLEEP COMP
START-UP
LOGIC
R2
5
SLOPE
COMP
+
–
VREF
FB
+
–
MODE
CONTROL
VREF
CLAMP
THERMAL
SHUTDOWN
Operation
TSD
WAKE
CSS
EXPOSED
PAD
GND
7
2
3526l BD
(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.
With its low RDS(ON) and low gate charge internal N-channel MOSFET switch and P-channel MOSFET synchronous
rectifier, the LTC3526L achieves high efficiency over a wide
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.
Low Voltage Start-Up
The LTC3526L/LTC3526LB include an independent startup 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.
When either VIN or VOUT exceeds 1.3V typical, the IC
enters normal operating mode. When the output voltage
3526lfc
LTC3526L/LTC3526LB
OPERATION
(Refer to Block Diagram)
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 LTC3526L/LTC3526LB contain internal circuitry to
provide soft-start operation. The soft-start circuitry slowly
ramps the peak inductor current from zero to its peak value
of 750mA (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.
Oscillator
An internal oscillator sets the switching frequency to
1MHz.
Shutdown
Shutdown is accomplished by pulling the SHDN pin
below 0.3V and enabled by pulling the SHDN pin above
0.8V. Although SHDN can be driven above VIN or VOUT
(up to the absolute maximum rating) without damage,
the LTC3526L/LTC3526LB have a proprietary test mode
that may be engaged if SHDN is held in the range of 0.5V
to 1V higher than the greater of VIN or VOUT. If the test
mode is engaged, normal PWM switching action is interrupted, which can cause undesirable operation in some
applications. Therefore, in applications where SHDN may
be driven above VIN, a resistor divider or other means
must be employed to keep the SHDN voltage below (VIN
+ 0.4V) to prevent the possibility of the test mode being
engaged. Please refer to Figure 1 for two possible implementations.
LTC3526L/LTC3526LB
4M
±30%
VCNTRL
R
LTC3526L/LTC3526LB
VIN
4M
±30%
SHDN
1M
ZETEX ZC2811E
VCNTRL
R > (VCNTRL/(VIN + 0.4) – 1)MΩ
SHDN
1M
3526l F01
Figure 1. Recommended Shutdown Circuits when Driving
SHDN above VIN
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 1.5V 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 750mA,
independent of input or output voltage, unless VOUT falls
below 0.7V, in which case the current limit is cut in half.
Zero Current Comparator
The zero current comparator monitors the inductor current to the output and shuts off the synchronous rectifier
3526lfc
LTC3526L/LTC3526LB
OPERATION
(Refer to Block Diagram)
when this current reduces to approximately 30mA. This
prevents the inductor current from reversing in polarity,
improving efficiency at light loads.
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-ring circuit 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 LTC3526L/LTC3526LB 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 SW 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 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.
Burst Mode OPERATION
The LTC3526L will enter Burst Mode operation at light load
current 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.
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 operation, 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
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 LTC3526L will automatically 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.
Burst Mode operation is inhibited during start-up and softstart and until VOUT is at least 0.24V greater than VIN.
The LTC3526LB features continuous PWM operation at
1MHz. At very light loads, the LTC3526LB will exhibit
pulse-skip operation.
3526lfc
LTC3526L/LTC3526LB
Applications Information
VIN > VOUT Operation
COMPONENT SELECTION
The LTC3526L/LTC3526LB 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.
Inductor Selection
Short-Circuit Protection
The LTC3526L/LTC3526LB 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).
The LTC3526L/LTC3526LB can utilize small surface mount
chip inductors due to their fast 1MHz switching frequency.
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
Burst Mode threshold) by reducing the inductor ripple current. Increasing the inductance above 10µH will increase
component size while providing little improvement in
output current capability.
The minimum inductance value is given by:
L>
Schottky Diode
Although not recommended, 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)
Ripple • VOUT(MAX)
)
where:
Ripple = Allowable inductor current ripple (amps peakpeak)
VIN(MIN) = Minimum input voltage
PCB layout guidelines
The high speed operation of the LTC3526L/LTC3526LB
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.
VOUT(MAX) = Maximum output voltage
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
LTC3526L
SW 1
GND 2
VIN
+
VIN 3
6 VOUT
5 FB
MINIMIZE
TRACE ON FB
AND SW
4 SHDN
MULTIPLE VIAS
TO GROUND PLANE
3526l F02
Figure 2. Recommended Component Placement for Single Layer Board
3526lfc
10
LTC3526L/LTC3526LB
APPLICATIONS INFORMATION
losses, and must be able to support the peak inductor
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.
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 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 LTC3526L/LTC3526LB are 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
3526lfc
11
LTC3526L/LTC3526LB
Typical Applications
1-Cell to 1.8V Converter with <1mm Maximum Height
100
4.7µH*
90
VOUT = 1.8V
80
SW
1µF
LTC3526L
SHDN
OFF ON
VOUT
1.8V
150mA
VOUT
VIN
511k
EFFICIENCY (%)
VIN
0.8V TO 1.6V
10µF**
FB
GND
1M
70
60
50
40
30
20
3526l TA02a
VIN = 1.5V
VIN = 1.2V
VIN = 0.9V
10
*FDK MIP3226D4R7M
**MURATA GRM219R60J106KE19D
0
0.01
0.1
1
10
100
LOAD CURRENT (mA)
1000
3526l TA02b
1-Cell to 2.85V Converter
100
90
4.7µH*
VOUT = 2.85V
80
VIN
0.8V TO 1.6V
VOUT
VIN
1µF
LTC3526L
SHDN
OFF ON
1.4M
VOUT
2.85V
100mA
EFFICIENCY (%)
SW
10µF
FB
GND
1M
70
60
50
40
30
20
3526l TA03a
VIN = 1.5V
VIN = 1.2V
VIN = 0.9V
10
0
0.01
*SUMIDA CDRH3D16-4R7
0.1
1
10
100
LOAD CURRENT (mA)
1000
3526l TA03b
1-Cell to 3.3V
100
4.7µH*
90
VOUT = 3.3V
VIN
0.8V TO 1.6V
VOUT
VIN
1µF
OFF ON
LTC3526L
SHDN
1.78M
10µF
FB
GND
22pF
VOUT
3.3V
75mA
1M
3526l TA04a
EFFICIENCY (%)
80
SW
70
60
50
40
30
20
VIN = 1.5V
VIN = 1.2V
VIN = 0.9V
10
*TAIYO-YUDEN NP03SB4R7M
0
0.01
0.1
1
10
100
LOAD CURRENT (mA)
1000
3526l TA04b
3526lfc
12
LTC3526L/LTC3526LB
TYPICAL APPLICATIONS
2-Cell to 3.3V
100
90
4.7µH*
VOUT = 3.3V
80
SW
1µF
LTC3526L
SHDN
OFF ON
VOUT
3.3V
200mA
VOUT
VIN
1.78M
4.7µF
FB
GND
EFFICIENCY (%)
VIN
1.6V TO 3.2V
1M
70
60
50
40
30
20
3526l TA05a
VIN = 3.0V
VIN = 2.4V
VIN = 1.8V
10
0
0.01
*TAIYO-YUDEN NP03SB4R7M
0.1
1
10
100
LOAD CURRENT (mA)
1000
3526l TA05b
2-Cell to 5V
100
90
6.8µH*
VOUT = 5V
VIN
1.6V TO 3.2V
VOUT
VIN
1µF
OFF ON
LTC3526L
SHDN
3.24M
22pF
10µF
FB
GND
VOUT
5V
150mA
EFFICIENCY (%)
80
SW
1.02M
70
60
50
40
30
20
3526l TA06a
VIN = 3.0V
VIN = 2.4V
VIN = 1.8V
10
0
0.01
*TAIYO-YUDEN NP03SB6R8M
0.1
1
10
100
LOAD CURRENT (mA)
1000
3526l TA06b
Li-Ion to 5V
100
6.8µH*
90
VOUT = 5V
VIN
2.7V TO 4.3V
VOUT
VIN
1µF
OFF ON
LTC3526L
SHDN
3.24M
10µF
FB
GND
22pF
VOUT
5V
200mA
1.02M
3526l TA08a
EFFICIENCY (%)
80
SW
70
60
50
40
30
20
VIN = 4.2V
VIN = 3.6V
VIN = 3.0V
10
*TAIYO-YUDEN NP03SB6R8M
0
0.01
0.1
1
10
100
LOAD CURRENT (mA)
1000
3526l TA08b
3526lfc
13
LTC3526L/LTC3526LB
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
1.15 p0.05 0.61 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
(4 SIDES)
PIN 1 BAR
TOP MARK
(SEE NOTE 6)
PIN 1 NOTCH
R = 0.20 OR
0.25 s 45o
CHAMFER
R = 0.05
TYP
0.200 REF
0.75 p0.05
3
(DC6) DFN REV B 1309
1
0.25 p 0.05
0.50 BSC
1.37 p0.05
(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
3526lfc
14
LTC3526L/LTC3526LB
Revision History
(Revision history begins at Rev C)
REV
DATE
DESCRIPTION
PAGE NUMBER
C
9/10
Updated θJA on Pin Configuration
2
Updated Note 6
3
Updated Shutdown section
8
Updated Related Parts
16
3526lfc
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
LTC3526L/LTC3526LB
Typical Application
3.3V Converter with Output OR’d with 5V USB Input
MBR120ESFT
5V USB
4.7µH
VOUT
3.3V/5V
USB
SW
VBATT
1.8V TO 3.2V
VOUT
VIN
1µF
OFF ON
LTC3526L
SHDN
1.78M
10µF
FB
GND
LDO
DC/DC
1M
3526l TA07a
Related Parts
PART NUMBER
DESCRIPTION
COMMENTS
LTC3526/LTC3526B
500mA, 1MHz/2.2MHz, Synchronous Step-Up DC/DC
LTC3526-2/LTC3526B-2
Converters with Output Disconnect
LTC3526L-2/LTC3526LB-2
94% Efficiency VIN: 0.85V to 5V, VOUT(MAX) = 5.25V, IQ = 9µA,
ISD < 1µA, 2mm × 2mm DFN-6 Package
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,
ISD < 1µA, SC-70 Package
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,
ISD < 1µA, SC-70 Package
LTC3427
500mA ISW, 1.2MHZ, Synchronous Step-Up DC/DC
Converter with Output Disconnect
93% Efficiency VIN: 1.8V to 4.5V, VOUT(MAX) = 5V,
2mm × 2mm DFN Package
LTC3400/LTC3400B
600mA ISW, 1.2MHz, Synchronous Step-Up
DC/DC Converters
92% Efficiency VIN: 1V to 5V, VOUT(MAX) = 5V, IQ = 19µA/300µA,
ISD < 1µA, ThinSOT™ Package
LTC3527/LTC3527-1
Dual 600mA/400mA ISW, 1.2MHz/2.2MHz Synchronous 94% Efficiency VIN: 0.7V to 5V, VOUT(MAX) = 5.25V, IQ = 12µA,
Step-Up DC/DC Converters
ISD < 1µA, 3mm × 3mm QFN-16 Package
3526lfc
16
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507
●
www.linear.com
LT 0910 REV C • PRINTED IN USA
 LINEAR TECHNOLOGY CORPORATION 2007
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