LTC3526/LTC3526B
500mA 1MHz Synchronous
Step-Up DC/DC Converters
in 2mm × 2mm DFN
NOT RECOMMENDED FOR NEW DESIGNS
Contact Linear Technology for Potential Replacement
Features
Description
Delivers 3.3V at 100mA from a Single Alkaline/
NiMH Cell or 3.3V at 200mA from Two Cells
n V Start-Up Voltage: 850mV
IN
n 1.6V to 5.25V V
OUT Range
n Up to 94% Efficiency
n Output Disconnect
n 1MHz Fixed Frequency Operation
n V > V
IN
OUT Operation
n Integrated Soft-Start
n Current Mode Control with Internal Compensation
n Automatic Burst Mode® Operation with 9µA
Quiescent Current (LTC3526)
n Low Noise PWM Operation (LTC3526B)
n Internal Synchronous Rectifier
n Logic Controlled Shutdown (I < 1µA)
Q
n Anti-Ringing Control
n Low Profile (2mm × 2mm × 0.75mm) DFN Package
The LTC®3526/LTC3526B 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.
Applications
The LTC3526/LTC3526B are housed in a 2mm × 2mm ×
0.75mm DFN package.
n
n
Medical Instruments
Flash-Based MP3 Players
Noise Canceling Headphones
Wireless Mice
Bluetooth Headsets
For new designs, we recommend the LTC3526L/LTC3526LB.
L, LT, LTC, LTM, Linear Technology, the Linear logo and Burst Mode are registered trademarks
and ThinSOT is a trademark of Linear Technology Corporation. All other trademarks are the
property of their respective owners.
Typical Application
LTC3526 Efficiency and Power Loss vs Load Current
100
90
4.7µH
VIN
1µF
OFF ON
EFFICIENCY
VOUT
LTC3526
SHDN
GND
1.78M
VOUT
3.3V
200mA
4.7µF
FB
1M
100
70
60
10
50
POWER LOSS
40
1
30
20
3526 TA01a
POWER LOSS (mW)
SW
VIN
1.6V TO 3.2V
1000
VIN = 2.4V
80
EFFICIENCY (%)
n
n
n
n
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
LTC3526 features automatic Burst Mode operation at light
load conditions, while the LTC3526B features continuous
switching at light loads. Anti-ringing control circuitry also
reduces EMI concerns by damping the inductor in discontinuous mode. Additional features include a low shutdown
current of under 1µA and thermal shutdown.
0.1
10
0
0.01
0.1
1
10
100
0.01
1000
LOAD CURRENT (mA)
3526 TA01b
3526bfd
LTC3526/LTC3526B
Absolute Maximum Ratings
(Note 1)
Pin Configuration
VIN Voltage.................................................... –0.3V to 6V
SW Voltage
DC............................................................. –0.3V to 6V
Pulsed 1.230V
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
Ω
P-Channel MOSFET Switch On Resistance
VOUT = 3.3V
0.6
Ω
700
mA
60
ns
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
l
SHDN Pin Input High Voltage
500
85
90
0.7
1
1.3
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
3526bfd
LTC3526/LTC3526B
Electrical Characteristics
Note 1: Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2: The LTC3526E is guaranteed to meet performance specifications
from 0°C to 85°C. Specifications over –40°C to 85°C operating
temperature range are assured by design, characterization and correlation
with statistical process controls.
Note 3: Specification is guaranteed by design and not 100% tested in
production.
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
Efficiency vs Load Current and VIN
for VOUT = 1.8V (LTC3526)
100
Efficiency vs Load Current and VIN
for VOUT = 3.3V (LTC3526)
1000
100
90
80
10
50
1
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
50
1
40
30
10
0
0.01
0.01
1000
3526 G01
400
1000
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)
3526 G03
300
IOUT (mA)
EFFICIENCY (%)
40
10
POWER LOSS (mW)
70
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)
3526 G04
Minimum Load Resistance
During Start-Up vs VIN
1000
VOUT = 3.3V
350
100
60
VOUT = 2.5V
50
Maximum Output Current vs VIN
90
80
VOUT = 3.3V
60
3526 G02
Efficiency vs Load Current and VIN
for VOUT = 5V (LTC3526)
100
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
80
VOUT = 2.5V
VOUT = 1.8V
250
200
LOAD (7)
40
100
VIN = 1.2V
VIN = 1.8V
VIN = 2.4V
VIN = 3.0V
70
POWER LOSS (mW)
60
EFFICIENCY (%)
100
VIN = 1.0V
VIN = 1.2V
VIN = 1.5V
70
POWER LOSS (mW)
EFFICIENCY (%)
80
90
IIN (µA)
90
No-Load Input Current vs VIN
100
1000
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)
3526 G05
10
0.85
0.95
1.05
VIN (V)
1.15
1.25
3526 G06
3526bfd
LTC3526/LTC3526B
Typical Performance Characteristics
Burst Mode Threshold Current
vs VIN
Start-Up Delay Time vs VIN
30
100
40
VOUT = 1.8V
COUT = 10µF
25 L = 4.7µH
LOAD CURRENT (mA)
80
70
60
50
40
30
20
VOUT = 2.5V
35 COUT = 10µF
L = 4.7µH
LOAD CURRENT (mA)
90
DELAY (µs)
Burst Mode Threshold Current
vs VIN
20
LEAVE BURST
15
ENTER BURST
10
5
1.0
1.5
2.0
2.5 3.0
VIN (V)
3.5
4.0
0
4.5
1
1.25
VIN (V)
LOAD CURRENT (mA)
LOAD CURRENT (mA)
50
20
15
ENTER BURST
10
1.5
2.0
VIN (V)
2
VOUT = 5V
COUT = 10µF
L = 4.7µH
40
30
20
ENTER BURST
10
0.85
8
1.5
2.0
2.5 3.0
VIN (V)
3.5
4.0
RDS(ON) (7)
0.70
PMOS
0.55
0.50
NMOS
0.40
2.0
2.5
3.0 3.5
VOUT (V)
4.0
4.5
5.0
3526 G10
2.0
2.5
3.0 3.3
VOUT (V)
4.0
1.3
5.0
NORMALIZED TO 25°C
1.2
6
4
2
0
–2
–4
–10
–50
4.5
3526 G09
NORMALIZED TO 25°C
1.1
1.0
0.9
0.8
–8
1.5
–4
RDS(ON) Change vs Temperature
–6
0.35
0.30
–3
–6
1.5
4.5
NORMALIZED RDS(ON)
FREQUENCY CHANGE (%)
0.80
0.45
–2
Oscillator Frequency Change
vs Temperature
0.90
0.60
–1
3526 G08d
RDS(ON) vs VOUT
0.65
0
–5
3526 G08c
0.75
NORMALIZED TO 3.3V
1
LEAVE BURST
0
1.0
3.0
2.5
1.75
Oscillator Frequency Change
vs VOUT
10
1.0
1.5
3526 G08b
5
0
1.25
1
VIN (V)
FREQUENCY CHANGE (%)
60
VOUT = 3.3V
45 COUT = 10µF
L = 4.7µH
40
25
ENTER BURST
10
Burst Mode Threshold Current
vs VIN
50
30
15
3526 G08a
Burst Mode Threshold Current
vs VIN
LEAVE BURST
LEAVE BURST
20
0
1.5
3526 G07
35
25
5
10
0
30
–30
–10 10
30
50
TEMPERATURE (°C)
70
90
3526 G11
0.7
–50
–30
–10 10
30
50
TEMPERATURE (°C)
70
90
3526 G12
3526bfd
LTC3526/LTC3526B
Typical Performance Characteristics
VFB vs Temperature
Burst Mode Current vs VOUT
Start-Up Voltage vs Temperature
1.00
NORMALIZED TO 25°C
10.0
LOAD = 1mA
0.95
9.5
0
0.90
9.0
–0.25
IQ (µA)
0.25
VIN (V)
CHANGE IN VFB (%)
0.50
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)
3526 G13
90
7.0
1.5
VOUT
10mV/DIV
AC-COUPLED
3526 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
3526 G15
Burst Mode Waveforms
SW PIN
2V/DIV
2.0
3526 G14
Fixed Frequency Switching
Waveform and VOUT Ripple
VIN = 1.2V
500ns/DIV
VOUT = 3.3V AT 100mA
COUT = 10µF
70
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
3526 G17
10µs/DIV
Load Step Response (from Burst
Mode Operation)
VOUT
100mV/DIV
AC-COUPLED
VOUT = 3.3V
COUT = 10μF
200μs/DIV
3526 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
3526 G19
VIN = 3.6V
100µs/DIV
VOUT = 5V
50mA TO 150mA STEP
COUT = 10µF
3526 G20
3526bfd
LTC3526/LTC3526B
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
3526 G21
VIN = 1.2V
50µs/DIV
VOUT = 3.3V
5mA TO 100mA STEP
COUT = 10µF
3526 G22
Electrical Characteristics
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.
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 1.6V to 5.25V by:
GND (Pin 2): Signal and Power Ground. Provide a short
direct PCB path between GND and the (–) side of the input
and output capacitors.
R2
VOUT = 1.195V • 1+
R1
VIN (Pin 3): Input Supply Pin. Connect a minimum of 1µF
ceramic decoupling capacitor from this pin to ground
using short direct PCB traces.
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.
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
GND (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.
3526bfd
LTC3526/LTC3526B
Block Diagram
VIN
0.85V
TO 5V
L1
4.7µH
CIN
2.2µF
3
1
VIN
VOUT
SW
VSEL
VBEST
WELL
SWITCH
VB
VOUT
VOUT
1.6V
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
5
R1
ERROR AMP
SLEEP COMP
START-UP
LOGIC
R2
SLOPE
COMP
+
–
VREF
FB
+
–
MODE
CONTROL
VREF
CLAMP
THERMAL
SHUTDOWN
Operation
TSD
WAKE
CSS
EXPOSED
PAD
GND
7
2
3526 BD
(Refer to Block Diagram)
The LTC3526/LTC3526B are 1MHz synchronous boost
converters housed in a 6-lead 2mm × 2mm DFN package.
With the ability to start up and operate from inputs less
than 1V, these devices feature fixed frequency, current
mode PWM control for exceptional line and load 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 LTC3526 achieves high efficiency over a wide
range of load currents. Automatic Burst Mode operation
maintains high efficiency at very light loads, reducing
the quiescent current to just 9µA. Operation can be best
understood by referring to the Block Diagram.
Low Voltage Start-Up
The LTC3526/LTC3526B include an independent start-up
oscillator designed to start up at an input voltage of 0.85V
(typical). Soft-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
3526bfd
LTC3526/LTC3526B
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.
LTC3526/LTC3526B
4M
±30%
VCNTRL
R
LTC3526/LTC3526B
VIN
4M
±30%
SHDN
1M
ZETEX ZC2811E
VCNTRL
R > (VCNTRL/(VIN + 0.4) – 1)MΩ
SHDN
1M
3526 F01
Figure 1. Recommended Shutdown Circuits when Driving
SHDN above VIN
Error Amplifier
Low Noise Fixed Frequency Operation
Soft-Start
The LTC3526/LTC3526B 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
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.
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 typical. Although SHDN can be driven above VIN
or VOUT (up to the absolute maximum rating) without
damage, the LTC3526/LTC3526B 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.
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.
Zero Current Comparator
The zero current comparator monitors the inductor current to the output and shuts off the synchronous rectifier
3526bfd
LTC3526/LTC3526B
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-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/LTC3526B 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.
Burst Mode OPERATION
The LTC3526 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.
In Burst Mode operation, the LTC3526 still switches at a
fixed frequency of 1MHz, using the same error amplifier
and loop compensation for peak current mode control.
This control method eliminates any output transient
when switching between modes. In Burst Mode operation, energy is delivered to the output until it reaches the
nominal regulation value, then the LTC3526 transitions to
sleep mode where the outputs are off and the LTC3526
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.
Thermal Shutdown
As the load current increases, the LTC3526 will automatically leave Burst Mode operation. Note that larger output
capacitor values may cause this transition to occur at lighter
loads. Once the LTC3526 has left Burst Mode operation and
returned to normal operation, it will remain there until the
output load is reduced below the burst threshold.
If the die temperature exceeds 160°C, the LTC3526/
LTC3526B will go into thermal shutdown. All switches
will be off and the soft-start capacitor will be discharged.
The device will be enabled again when the die temperature
drops by about 15°C.
The LTC3526B features continuous PWM operation at
1MHz. At very light loads, the LTC3526B will exhibit
pulse-skip operation.
Burst Mode operation is inhibited during start-up and softstart and until VOUT is at least 0.24V greater than VIN.
3526bfd
LTC3526/LTC3526B
Applications Information
VIN > VOUT Operation
COMPONENT SELECTION
The LTC3526/LTC3526B 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 LTC3526/LTC3526B 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 LTC3526/LTC3526B 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
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.
where:
(
VIN(MIN) • VOUT(MAX ) – VIN(MIN)
Ripple • VOUT(MAX)
)
Ripple = Allowable inductor current ripple (amps peakpeak)
VIN(MIN) = Minimum input voltage
VOUT(MAX) = Maximum output voltage
PCB layout guidelines
The high speed operation of the LTC3526/LTC3526B
demands careful attention to board layout. A careless
layout will result in reduced performance. Figure 2 shows
the recommended component placement. A large ground
pin copper area will help to lower the die temperature. A
multilayer board with a separate ground plane is ideal, but
not absolutely necessary.
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
SW 1
GND 2
VIN
+
VIN 3
6 VOUT
5 FB
MINIMIZE
TRACE ON FB
AND SW
4 SHDN
MULTIPLE VIAS
TO GROUND PLANE
3526 F02
Figure 2. Recommended Component Placement for Single Layer Board
3526bfd
10
LTC3526/LTC3526B
Applications Information
inductor current without saturating. Molded chokes and
some chip inductors usually do not have enough core
area to support the peak inductor currents of 700mA
seen on the LTC3526/LTC3526B. To minimize radiated
noise, use a shielded inductor. See Table 1 for suggested
components and suppliers.
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
Würth
(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 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
3526bfd
11
LTC3526/LTC3526B
Typical Applications
1-Cell to 1.8V Converter with
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