LTC3441
1
3441fc
For more information www.linear.com/LTC3441
Typical applicaTion
FeaTures
applicaTions
DescripTion
High Current Micropower
Synchronous Buck-Boost
DC/DC Converter
The LT C
®
3441 is a high efficiency, fixed frequency, buck-
boost DC/DC converter that operates efficiently from input
voltages above, below or equal to the output voltage. The
topology incorporated in the IC provides a continuous
transfer function through all operating modes, making
the product ideal for single lithium ion or multicell ap-
plications where the output voltage is within the battery
voltage range.
The device includes two 0.10Ω N-channel MOSFET
switches and two 0.11Ω P-channel switches. External
Schottky diodes are optional, and can be used for a mod-
erate efficiency improvement. The operating frequency
is internally set to 1MHz and can be synchronized up to
1.7MHz. Quiescent current is only 25µA in Burst Mode
operation, maximizing battery life in portable applica-
tions. Burst Mode operation is user controlled and can
be enabled by driving the MODE/SYNC pin high. If the
MODE/SYNC pin is driven low or with a clock, then fixed
frequency switching is enabled.
Other features include a 1µA shutdown, soft-start control,
thermal shutdown and current limit. The LTC3441 is
available in a thermally enhanced 12-lead (4mm × 3mm)
DFN package.
Li-Ion to 3.3V at 1A Buck-Boost Converter
n Regulated Output with Input Above, Below or Equal
to the Output
n Single Inductor, No Schottky Diodes
n High Efficiency: Up to 95%
n 25µA Quiescent Current in Burst Mode
®
Operation
n Up to 1.2A Continuous Output Current from a Single
Lithium-Ion
n True Output Disconnect in Shutdown
n 2.4V to 5.5V Input Range
n 2.4V to 5.25V Output Range
n 1MHz Fixed Frequency Operation
n Synchronizable Oscillator
n Selectable Burst Mode or Fixed Frequency Operation
n <1µA Quiescent Current in Shutdown
n Small, Thermally Enhanced 12-Lead (4mm × 3mm)
DFN package
n Handheld Computers
n Handheld Instruments
n MP3 Players
n Digital Cameras
Efficiency vs VIN
SW1
PVIN
VIN
SHDN/SS
MODE/SYNC
PGND
5
8
12
11
2
6
4
9
10
1
7
3
SW2
VOUT
FB
VC
GND
PGND
LTC3441
CIN
10µF
*1 = Burst Mode OPERATION
0 = FIXED FREQUENCY
CIN: TAIYO YUDEN JMK212BJ106MG
COUT: TAIYO YUDEN JMK325BJ226MM
L1: TOKO A916CY-4R7M
2.5V TO 4.2V
Li-Ion *
15k
340k
COUT
22µF
VOUT
3.3V
1A
200k
1.5nF
3441 TA01
L1
4.7µH
VIN (V)
2.5
50
EFFICIENCY (%)
60
70
80
33.5 4 4.5
3441 TA02
5
90
100
55
65
75
85
95
5.5
IOUT = 200mA
IOUT = 1A
VOUT = 3.3V
L, LT, LTC, LTM, Linear Technology, Burst Mode and the Linear logo are registered trademarks
and ThinSOT is a trademark of Linear Technology Corporation. All other trademarks are the
property of their respective owners.
LTC3441
2
3441fc
For more information www.linear.com/LTC3441
pin conFiguraTionabsoluTe MaxiMuM raTings
VIN, VOUT Voltage ....................................... –0.3V to 6V
SW1, SW2 Voltage
DC ............................................................ –0.3V to 6V
Pulsed < 100ns ....................................... –0.3V to 7V
SHDN/SS, MODE/SYNC Voltage ................ –0.3V to 6V
Operating Temperature Range (Note 2) .. –40°C to 85°C
Maximum Junction Temperature (Note 4)............. 125°C
Storage Temperature Range .................. –65°C to 125°C
(Note 1)
The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VIN = VOUT = 3.6V,unless otherwise noted.
elecTrical characTerisTics
PARAMETER CONDITIONS MIN TYP MAX UNITS
Input Start-Up Voltage ●2.3 2.4 V
Output Voltage Adjust Range ●2.4 5.25 V
Feedback Voltage ●1.19 1.22 1.25 V
Feedback Input Current VFB = 1.22V 1 50 nA
Quiescent Current—Burst Mode Operation VC = 0V, MODE/SYNC = 3V (Note 3) 25 40 µA
Quiescent Current—SHDN VOUT = SHDN = 0V, Not Including Switch Leakage 0.1 1 µA
Quiescent Current—Active MODE/SYNC = 0V (Note 3) 520 900 µA
NMOS Switch Leakage Switches B and C 0.1 7 µA
PMOS Switch Leakage Switches A and D 0.1 10 µA
NMOS Switch On Resistance Switches B and C 0.10 Ω
PMOS Switch On Resistance Switches A and D 0.11 Ω
Input Current Limit ●2 3.2 A
Max Duty Cycle Boost (% Switch C On)
Buck (% Switch A In)
●
●
70
100
88 %
%
Min Duty Cycle ●0 %
Frequency Accuracy ●0.85 1 1.15 MHz
MODE/SYNC Threshold ●0.4 1.4 V
12
11
10
9
8
7
1
2
3
4
5
6
FB
VC
VIN
PVIN
VOUT
MODE/SYNC
SHDN/SS
GND
PGND
SW1
SW2
PGND
TOP VIEW
13
DE12 PACKAGE
12-LEAD (4mm × 3mm) PLASTIC DFN
TJMAX = 125°C
θJA = 53°C/W 1-LAYER BOARD, θJA = 43°C/W 4-LAYER BOARD
θJC = 4.3°C/W, EXPOSED PAD IS PGND (PIN 13)
MUST BE SOLDERED TO PCB
orDer inForMaTion
LEAD FREE FINISH TAPE AND REEL PART MARKING PACKAGE DESCRIPTION TEMPERATURE RANGE
LTC3441EDE#PBF LTC3441EDE#TRPBF 3441 12-Lead (4mm × 3mm) Plastic DFN –40°C to 85°C
Consult LTC Marketing for parts specified with wider operating temperature ranges.
Consult LTC Marketing for information on nonstandard 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/. Some packages are available in 500 unit reels through
designated sales channels with #TRMPBF suffix.
http://www.linear.com/product/LTC3441#orderinfo
LTC3441
3
3441fc
For more information www.linear.com/LTC3441
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 LTC3441E is guaranteed to meet performance specifications
from 0°C to 70°C. Specifications over the –40°C to 85°C operating
temperature range are assured by design, characterization and correlation
with statistical process controls.
Note 3: Current measurements are preformed when the outputs are not
switching.
Note 4: 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.
Typical perForMance characTerisTics
Efficiency VOUT Ripple at 1A Load
Load Transient Response,
100mA to 1A
Switch Pins in Buck-Boost Mode
Switch Pins Entering
Buck-Boost Mode
IOUT (mA)
30
EFFICIENCY (%)
90
100
20
10
80
50
70
60
40
0.1 10 100 1000
3441 G17
0
1
Burst Mode
OPERATION
VIN = 2.7V
VIN = 4.2V
VIN = 3.6V
VOUT = 3.3V
L = 4.7µH
COUT = 47µF
IOUT = 1A
VOUT = 3.3V
VOUT
10mV/DIV
AC-COUPLED
BUCK
VIN = 4.2V
BUCK-BOOST
VIN = 3.3V
BOOST
VIN = 2.7V
3441 G02
1µs/DIV
1A
100mA
VOUT
100mV/DIV
3441 G01
100µs/DIV VIN = 3.3V
VOUT = 3.3V
IOUT = 500mA
SW1
2V/DIV
SW2
2V/DIV
3441 G03
50ns/DIV VIN = 4.2V
VOUT = 3.3V
IOUT = 500mA
SW1
2V/DIV
SW2
2V/DIV
3441 G04
50ns/DIV
PARAMETER CONDITIONS MIN TYP MAX UNITS
MODE/SYNC Input Current VMODE/SYNC = 5.5V 0.01 1 µA
Error Amp AVOL 90 dB
Error Amp Source Current 14 µA
Error Amp Sink Current 300 µA
SHDN/SS Threshold When IC is Enabled ●0.4 1 1.4 V
SHDN/SS Threshold When EA is at Max Boost Duty Cycle 2 2.4 V
SHDN/SS Input Current VSHDN = 5.5V 0.01 1 µA
The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VIN = VOUT = 3.6V,unless otherwise noted.
LTC3441
4
3441fc
For more information www.linear.com/LTC3441
Typical perForMance characTerisTics
Switch Pins Before Entering
Boost Mode
Active Quiescent Current
Feedback Voltage
Burst Mode Quiescent Current
Feedback Voltage Line Regulation
Error Amp Source Current
Error Amp Sink Current
Output Frequency
Current Limit
VIN = 3V
VOUT = 3.3V
IOUT = 500mA
SW1
2V/DIV
SW2
2V/DIV
3441 G05
50ns/DIV
TEMPERATURE (°C)
–55
520
VIN + VOUT CURRENT (µA)
540
560
580
600
–25 5 35 65
3441 G06
95 125
620
530
550
570
590
610
630 VIN = VOUT = 3.6V
TEMPERATURE (°C)
–55
FEEDBACK VOLTAGE (V)
65
1.241
3441 G07
5
–25 95
35 125
1.236
1.231
1.226
1.221
1.216
1.211
1.206
1.201
1.196
VIN = VOUT = 3.6V
TEMPERATURE (°C)
–55
10
VIN + VOUT CURRENT (µA)
20
30
40
50
–25 5 35 65
3441 G08
95 125
VIN = VOUT = 3.6V
TEMPERATURE (°C)
–55
60
LINE REGULATION (dB)
70
80
90
–25 5 35 65
3441 G09
95 125
VIN = VOUT = 2.4V TO 5.5V
TEMPERATURE (°C)
–55
5
EA SOURCE CURRENT (µA)
10
15
20
–25 5 35 65
3441 G10
95 125
VIN = VOUT = 3.6V
TEMPERATURE (°C)
–55
200
EA SINK CURRENT (µA)
250
300
350
400
–25 5 35 65
3441 G11
95 125
VIN = VOUT = 3.6V
TEMPERATURE (°C)
–55
0.8
FREQUENCY (MHz)
0.9
1.0
1.1
1.2
–25 5 35 65
3441 G12
95 125
VIN = VOUT = 3.6V
TEMPERATURE (°C)
–55
2.8
CURRENT LIMIT (A)
3.0
3.2
3.4
–25 5 35 65
3441 G13
95 125
VIN = VOUT = 3.6V
LTC3441
5
3441fc
For more information www.linear.com/LTC3441
Typical perForMance characTerisTics
NMOS RDS(ON)
PMOS RDS(ON)
Minimum Start Voltage
TEMPERATURE (°C)
–55
0.05
NMOS R
DS(ON)
(Ω)
0.07
0.09
0.11
0.13
0.15
–25 5 35 65
3441 G14
95 125
VIN = VOUT = 3.6V
SWITCHES B AND C
TEMPERATURE (°C)
–50
0.05
PMOS RDS(ON) (Ω)
0.07
0.09
0.11
–25 535 65
3441 G15
95
0.13
0.15
0.06
0.08
0.10
0.12
0.14
125
VIN = VOUT = 3.6V
SWITCHES A AND D
TEMPERATURE (°C)
–55
2.10
MINIMUM START VOLTAGE (V)
2.15
2.20
2.25
2.30
–25 5 35 65
3441 G16
95 125
pin FuncTions
SHDN/SS (Pin 1): Combined Soft-Start and Shutdown.
Applied voltage < 0.4V shuts down the IC. Tie to >1.4V to
enable the IC and >2.4V to ensure the error amp is not
clamped from soft-start. An RC from the shutdown com-
mand signal to this pin will provide a soft-start function
by limiting the rise time of the VC pin.
GND (Pin 2): Signal Ground for the IC.
PGND (Pins 3, 6, 13 Exposed Pad): Power Ground for
the Internal NMOS Power Switches
SW1 (Pin 4): Switch pin where the internal switches A
and B are connected. Connect inductor from SW1 to SW2.
An optional Schottky diode can be connected from this
SW1 to ground. Minimize trace length to keep EMI down.
SW2 (Pin 5): Switch pin where the internal switches C
and D are connected. An optional Schottky diode can
be connected from SW2 to VOUT (it is required where
VOUT > 4.3V). Minimize trace length to keep EMI down.
MODE/SYNC (Pin 7): Burst Mode Select and Oscillator
Synchronization.
MODE/SYNC = High: Enable Burst Mode Operation.
During the period where the IC is supplying energy to
the output, the inductor peak inductor current will reach
0.8A and return to zero current on each cycle. In Burst
Mode operation the operation is variable frequency,
which provides a significant efficiency improvement at
light loads. The Burst Mode operation will continue until
the pin is driven low.
MODE/SYNC = Low: Disable Burst Mode operation
and maintain low noise, constant frequency operation .
MODE/SYNC = External CLK : Synchronization of the
internal oscillator and Burst Mode operation disable. A
clock pulse width between 100ns and 2µs and a clock
frequency between 2.3MHz and 3.4MHz (twice the
desired frequency) is required to synchronize the IC.
fOSC = fSYNC/2
VOUT (Pin 8): Output of the Synchronous Rectifier. A filter
capacitor is placed from VOUT to GND. A ceramic bypass
capacitor is recommended as close to the VOUT and GND
pins as possible.
PVIN (Pin 9): Power VIN Supply Pin. A 10µF ceramic ca-
pacitor is recommended as close to the PVIN and PGND
pins as possible
LTC3441
6
3441fc
For more information www.linear.com/LTC3441
block DiagraM
–
+
–
+
–
+
–
+
–
+
–
+
9
10
PWM
LOGIC
AND
OUTPUT
PHASING
GATE
DRIVERS
AND
ANTICROSS
CONDUCTION
Burst Mode
OPERATION
CONTROL
5µs DELAY
GND
UVLO
4A
2.4V
SLEEP
MODE/SYNC
1 = Burst Mode
OPERATION
0 = FIXED FREQUENCY
1MHz
OSC
SYNC
SUPPLY
CURRENT
LIMIT
SW A
SW1
PVIN
VIN
VCC
INTERNAL
SW2
VIN
2.4V TO 5.5V SW D
ISENSE
AMP
ERROR
AMP 1.22V
CLAMP
REVERSE
CURRENT
LIMIT
SW B
3.2A
AVERAGE
CURRENT LIMIT
SW C
PGND
–0.8A
7
2
1
+
4 5
PGND
6
VOUT 8
FB 12
VC11
SHDN/SS
SHUTDOWN
RSS
VIN
R2
CSS
R1
3440 BD
VOUT
2.4V TO 5.25V
PWM
COMPARATORS
–
+
1
100
gm = k
THERMAL
SHUTDOWN
÷2
pin FuncTions
VIN (Pin 10): Input Supply Pin. Internal VCC for the IC.
VC (Pin 11): Error Amp Output. A frequency compensa-
tion network is connected from this pin to the FB pin to
compensate the loop. See the section “Compensating the
Feedback Loop” for guidelines.
FB (Pin 12): Feedback Pin. Connect resistor divider tap
here. The output voltage can be adjusted from 2.4V to
5.25V. The feedback reference voltage is typically 1.22V.
VOUT =1.22V •1+R1
R2
⎛
⎝
⎜⎞
⎠
⎟
LTC3441
7
3441fc
For more information www.linear.com/LTC3441
operaTion
The LTC3441 provides high efficiency, low noise power
for applications such as portable instrumentation. The
LTC proprietary topology allows input voltages above,
below or equal to the output voltage by properly phasing
the output switches. The error amp output voltage on the
VC pin determines the output duty cycle of the switches.
Since the VC pin is a filtered signal, it provides rejection
of frequencies from well below the switching frequency.
The low RDS(ON), low gate charge synchronous switches
provide high frequency pulse width modulation control at
high efficiency. Schottky diodes across the synchronous
switch D and synchronous switch B are not required,
but provide a lower drop during the break-before-make
time (typically 15ns). The addition of the Schottky diodes
will improve peak efficiency by typically 1% to 2%. High
efficiency is achieved at light loads when Burst Mode
operation is entered and when the IC’s quiescent current
is a low 25µA.
LOW NOISE FIXED FREQUENCY OPERATION
Oscillator
The frequency of operation is factory trimmed to 1MHz.
The oscillator can be synchronized with an external clock
applied to the MODE/SYNC pin. A clock frequency of twice
the desired switching frequency and with a pulse width
of at least 100ns is applied. The oscillator sync range is
1.15MHz to 1.7MHz (2.3MHz to 3.4MHz sync frequency).
Error Amp
The error amplifier is a voltage mode amplifier. The loop
compensation components are configured around the
amplifier to obtain stability of the converter. The SHDN/
SS pin will clamp the error amp output, VC, to provide a
soft-start function.
Supply Current Limit
The current limit amplifier will shut PMOS switch A off
once the current exceeds 4A typical. Before the switch
current limit, the average current limit amp (3.2A typical)
will source current into the FB pin to drop the output volt-
age. The current amplifier delay to output is typically 50ns.
Reverse Current Limit
The reverse current limit amplifier monitors the inductor
current from the output through switch D. Once a nega-
tive inductor current exceeds –800mA typical, the IC will
shut off switch D.
Output Switch Control
Figure 1 shows a simplified diagram of how the four in-
ternal switches are connected to the inductor
, VIN, VOUT
and GND. Figure 2 shows the regions of operation for the
LTC3441 as a function of the internal control voltage, VCI.
The VCIvoltage is a level shifted voltage from the output of
the error amp (VC pin) (see Figure 5). The output switches
are properly phased so the transfer between operation
modes is continuous, filtered and transparent to the
user. When VIN approaches VOUT the Buck/Boost region
is reached where the conduction time of the four switch
region is typically 150ns. Referring to Figures 1 and 2,
the various regions of operation will now be described.
Figure 1. Simplified Diagram of Output Switches
Figure 2. Switch Control vs Internal Control Voltage, VCI
4
SW1
5
SW2
PMOS A
NMOS B
9
PV
IN
PMOS D
NMOS C
3441 F01
8
V
OUT
VOUT
75%
DMAX
BOOST
DMIN
BOOST
DMAX
BUCK
DUTY
CYCLE
0%
V4 (≈2.05V)
V3 (≈1.65V)
BOOST REGION
BUCK REGION
BUCK/BOOST REGION
V2 (≈1.55V)
V1 (≈0.9V)
3441 F02
A ON, B OFF
PWM CD SWITCHES
D ON, C OFF
PWM AB SWITCHES
FOUR SWITCH PWM
INTERNAL
CONTROL
VOLTAGE, VCI
LTC3441
8
3441fc
For more information www.linear.com/LTC3441
operaTion
Buck Region (VIN > VOUT)
Switch D is always on and switch C is always off during
this mode. When the internal control voltage, VCI, is above
voltage V1, output A begins to switch. During the off time of
switch A, synchronous switch B turns on for the remainder
of the time. Switches A and B will alternate similar to a
typical synchronous buck regulator. As the control volt-
age increases, the duty cycle of switch A increases until
the maximum duty cycle of the converter in Buck mode
reaches DMAX_BUCK, given by:
DMAX_BUCK = 100 – D4SW %
where D4SW = duty cycle % of the four switch range.
D4SW = (150ns • f) • 100 %
where f = operating frequency, Hz.
Beyond this point the “four switch,” or Buck/Boost region
is reached.
Buck/Boost or Four Switch (VIN ~ VOUT)
When the internal control voltage, VCI, is above voltage V2,
switch pair AD remain on for duty cycle DMAX_BUCK, and
the switch pair AC begins to phase in. As switch pair AC
phases in, switch pair BD phases out accordingly. When
the VCI voltage reaches the edge of the Buck/Boost range,
at voltage V3, the AC switch pair completely phase out the
BD pair, and the boost phase begins at duty cycle D4SW.
The input voltage, VIN, where the four switch region begins
is given by:
V
IN =
V
OUT
1– (150ns •f) V
The point at which the four switch region ends is given by:
VIN = VOUT(1 – D) = VOUT(1 – 150ns • f) V
Boost Region (VIN < VOUT)
Switch A is always on and switch B is always off during
this mode. When the internal control voltage, VCI, is
above voltage V3, switch pair CD will alternately switch
to provide a boosted output voltage. This operation is
typical to a synchronous boost regulator. The maximum
duty cycle of the converter is limited to 88% typical and
is reached when VCI is above V4.
Burst Mode OPERATION
Burst Mode operation is when the IC delivers energy to
the output until it is regulated and then goes into a sleep
mode where the outputs are off and the IC is consuming
only 25µA. In this mode the output ripple has a variable
frequency component that depends upon load current.
During the period where the device is delivering energy to
the output, the peak current will be equal to 800mA typical
and the inductor current will terminate at zero current for
each cycle. In this mode the typical maximum average
output current is given by:
IOUT(MAX)BURST ≈
0.2 •V
IN
V
OUT
+V
IN
A
Burst Mode operation is user controlled, by driving the
MODE/SYNC pin high to enable and low to disable.
The peak efficiency during Burst Mode operation is less
than the peak efficiency during fixed frequency because
the part enters full-time 4-switch mode (when servicing
the output) with discontinuous inductor current as illus-
trated in Figures 3 and 4. During Burst Mode operation,
the control loop is nonlinear and cannot utilize the control
voltage from the error amp to determine the control mode,
therefore full-time 4-switch mode is required to main-
tain the Buck/Boost function. The efficiency below 1mA
becomes dominated primarily by the quiescent current and
not the peak efficiency. The equation is given by:
Efficiency Burst ≈
(
η
bm) • I
LOA
D
25µA +I
LOAD
where (ηbm) is typically 75% during Burst Mode
operation
.
LTC3441
9
3441fc
For more information www.linear.com/LTC3441
operaTion
Burst Mode Operation to Fixed Frequency Transient
Response
When transitioning from Burst Mode operation to fixed
frequency, the system exhibits a transient since the modes
of operation have changed. For most systems this transient
is acceptable, but the application may have stringent input
current and/or output voltage requirements that dictate a
broad-band voltage loop to minimize the transient. Lower-
ing the DC gain of the loop will facilitate the task (5M from
FB to VC) at the expense of DC load regulation. Type 3
compensation is also recommended to broad band the
loop and roll off past the two pole response of the LC of
the converter (see Closing the Feedback Loop).
SOFT-START
The soft-start function is combined with shutdown.
When the SHDN/SS pin is brought above typically 1V,
the IC is enabled but the EA duty cycle is clamped from
the VC pin. A detailed diagram of this function is shown
in Figure 5. The components RSS and CSS provide a
slow ramping voltage on the SHDN/SS pin to provide a
soft-start function.
Figure 3. Inductor Charge Cycle During Burst Mode Operation Figure 4. Inductor Discharge Cycle During Burst Mode Operation
Figure 5. Soft-Start Circuitry
9
PVIN
A
4
SW1
6
GND
5
SW2
L
+ –
8
VOUT
D
C
800mA
IINDUCTOR
0mA 3441 F03
T1
B
dI
dt
VIN
L
≈
9
PVIN
A
4
SW1
6
GND
5
SW2
L
– +
8
VOUT
D
C
800mA
IINDUCTOR
0mA 3441 F04
T2
B
dI
dt
VOUT
L
≈ –
–
+
12
11
VIN ERROR AMP
1.22V
14µA
FB R1
R2
CP1
VC
VOUT
1
SHDN/SS
CSS
1V
ENABLE SIGNAL
RSS
SOFT-START
CLAMP
TO PWM
COMPARATORS
CHIP
ENABLE
3441 F05
–
+
VCI
LTC3441
10
3441fc
For more information www.linear.com/LTC3441
applicaTions inForMaTion
COMPONENT SELECTION
Inductor Selection
The high frequency operation of the LTC3441 allows the
use of small surface mount inductors. The inductor cur-
rent ripple is typically set to 20% to 40% of the maximum
inductor current. For a given ripple the inductance terms
are given as follows:
L>V
IN(MIN) •VOUT – V
IN(MIN)
( )
•100
f•IOUT(MAX) •%Ripple •VOUT
H
,
L>VOUT •V
IN(MAX) – VOUT
( )
•100
f•IOUT(MAX) •%Ripple •V
IN(MAX)
H
where f = operating frequency, Hz
%Ripple = allowable inductor current ripple, %
VIN(MIN) = minimum input voltage, V
VIN(MAX) = maximum input voltage, V
VOUT = output voltage, V
IOUT(MAX) = maximum output load current
For high efficiency, choose an inductor with a high fre-
quency core material, such as ferrite, to reduce core loses.
The inductor should have low ESR (equivalent series
resistance) to reduce the I2R losses, and must be able to
handle the peak inductor current without saturating. Molded
chokes or chip inductors usually do not have enough core
to support the peak inductor currents in the 1A to 2A
region. To minimize radiated noise, use a toroid, pot core
or shielded bobbin inductor. See Table 1 for suggested
components and Table 2 for a list of component suppliers.
Table 1. Inductor Vendor Information
SUPPLIER PHONE FAX WEB SITE
Coilcraft (847) 639-6400 (847) 639-1469 www.coilcraft.com
Coiltronics (561) 241-7876 (561) 241-9339 www.coiltronics.com
Murata USA:
(814) 237-1431
(800) 831-9172
USA:
(814) 238-0490
www.murata.com
Sumida USA:
(847) 956-0666
Japan:
81(3) 3607-5111
(847) 956-0702
81(3) 3607-5144
www.japanlink.com/
sumida
Output Capacitor Selection
The bulk value of the capacitor is set to reduce the ripple
due to charge into the capacitor each cycle. The steady
state ripple due to charge is given by:
%Ripple _Boost =IOUT(MAX) •VOUT – V
IN(MIN)
( )
•100
COUT •VOUT2•f
%
%Ripple _Buck =IOUT(MAX) •V
IN(MAX) – VOUT
( )
•100
COUT •V
IN(MAX) •VOUT •f
%
where COUT = output filter capacitor, F
The output capacitance is usually many times larger in
order to handle the transient response of the converter. For
a rule of thumb, the ratio of the operating frequency to the
unity-gain bandwidth of the converter is the amount the
output capacitance will have to increase from the above
calculations in order to maintain the desired transient
response.
The other component of ripple is due to the ESR (equiva-
lent series resistance) of the output capacitor. Low ESR
capacitors should be used to minimize output voltage
ripple. For surface mount applications, Taiyo Yuden ceramic
capacitors, AVX TPS series tantalum capacitors or Sanyo
POSCAP are recommended.
Figure 6. Recommended Component Placement. Traces Carrying
High Current are Direct. Trace Area at FB and VC Pins are Kept
Low. Lead Length to Battery Should be Kept Short. VOUT and VIN
Ceramic Capacitors Close to the IC Pins
12
11
10
9
8
7
1
2
3
4
5
6
FB
VC
VIN
PVIN
VOUT
MODE
SHDN/SS
GND
PGND
SW1
SW2
PGND
VIN
VOUT
GND MULTIPLE VIAS
3441 F06
LTC3441
11
3441fc
For more information www.linear.com/LTC3441
applicaTions inForMaTion
Input Capacitor Selection
Since the VIN pin is the supply voltage for the IC it is
recommended to place at least a 4.7µF, low ESR bypass
capacitor.
Table 2. Capacitor Vendor Information
SUPPLIER PHONE FAX WEB SITE
AVX (803) 448-9411 (803) 448-1943 www.avxcorp.com
Sanyo (619) 661-6322 (619) 661-1055 www.sanyovideo.com
Taiyo Yuden (408) 573-4150 (408) 573-4159 www.t-yuden.com
Optional Schottky Diodes
The Schottky diodes across the synchronous switches B
and D are not required (VOUT < 4.3V), but provide a lower
drop during the break-before-make time (typically 15ns) of
the NMOS to PMOS transition, improving efficiency. Use a
Schottky diode such as an MBRM120T3 or equivalent. Do
not use ordinary rectifier diodes, since the slow recovery
times will compromise efficiency. For applications with an
output voltage above 4.3V, a Schottky diode is required
from SW2 to VOUT.
Output Voltage < 2.4V
The LTC3441 can operate as a buck converter with out-
put voltages as low as 0.4V. The part is specified at 2.4V
minimum to allow operation without the requirement of a
Schottky diode. Synchronous switch D is powered from
VOUT and the RDS(ON) will increase at low output voltages,
therefore a Schottky diode is required from SW2 to VOUT
to provide the conduction path to the output.
Output Voltage > 4.3V
A Schottky diode from SW to VOUT is required for output
voltages over 4.3V. The diode must be located as close to
the pins as possible in order to reduce the peak voltage
on SW2 due to the parasitic lead and trace inductance.
Input Voltage > 4.5V
For applications with input voltages above 4.5V which
could exhibit an overload or short-circuit condition, a
2Ω/1nF series snubber is required between the SW1 pin
and GND. A Schottky diode from SW1 to VIN should also
be added as close to the pins as possible. For the higher
input voltages, VIN bypassing becomes more critical;
therefore, a ceramic bypass capacitor as close to the VIN
and GND pins as possible is also required.
Operating Frequency Selection
Additional quiescent current due to the output switches
GATE charge is given by:
Buck: (0.8 • VIN • f) mA
Boost: [0.4 • (VIN + VOUT) • f] mA
Buck/Boost: [f • (1.2 • VIN + 0.4 • VOUT)] mA
where f = switching frequency in MHz
Closing the Feedback Loop
The LTC3441 incorporates voltage mode PWM control. The
control to output gain varies with operation region (Buck,
Boost, Buck/Boost), but is usually no greater than 15. The
output filter exhibits a double pole response is given by:
fFILTER_POLE =
1
2•π•L•COUT
H
z
(in buck mode)
fFILTER_POLE =
V
IN
2•VOUT •π•L•COUT
H
z
(in boost mode)
Where L is in Henries and COUT is the output filter capaci-
tor in Farads.
The output filter zero is given by:
fFILTER_ ZERO =
1
2•π•R
ESR
•C
OUT
Hz
where RESR is the capacitor equivalent series resistance.
A troublesome feature in Boost mode is the right-half
plane zero (RHP), and is given by:
fRHPZ =V
IN2
2•π•I
OUT
•L•V
OUT
Hz
The loop gain is typically rolled off before the RHP zero
frequency.
LTC3441
12
3441fc
For more information www.linear.com/LTC3441
applicaTions inForMaTion
A simple Type I compensation network can be incorporated
to stabilize the loop but at a cost of reduced bandwidth
and slower transient response. To ensure proper phase
margin, the loop requires to be crossed over a decade
before the LC double pole.
The unity-gain frequency of the error amplifier with the
Type I compensation is given by:
fUG =
1
2•π•R1•CP1
Hz
Most applications demand an improved transient response
to allow a smaller output filter capacitor. To achieve a higher
bandwidth, Type III compensation is required. Two zeros
are required to compensate for the double-pole response.
fPOLE1 ≈
1
2•π•32e3•R1•CP1
Hz
Which is extremely close to DC
fZERO1=1
2•π•RZ•CP1
Hz
fZERO2 =1
2•π•R1 •CZ1
Hz
fPOLE2 =1
2•π•RZ•CP2
Hz
Figure 7. Error Amplifier with Type I Compensation
Figure 8. Error Amplifier with Type III Compensation
1.22V
R1
R2
3441 F07
FB
12
VCCP1
VOUT
11
–
+
ERROR
AMP
1.22V R1
R2
3441 F08
FB
12
VCCP1
CZ1
RZ
VOUT
11
CP2
–
+
ERROR
AMP
Figure 9. Fast Transient Response Compensation for Step Load or Mode Change
Load Transient Response,
100mA to 1A
SW1
PVIN
VIN
SHDN/SS
MODE/SYNC
PGND
5
8
12
11
2
6
4
9
10
1
7
3
SW2
VOUT
FB
VC
GND
PGND
LTC3441
C1
10µF
*1 = Burst Mode OPERATION
0 = FIXED FREQUENCY
C1: TAIYO YUDEN JMK212BJ106MG
C2: TAIYO YUDEN JMK325BJ476MM
L1: TOKO A916CY-4R7M
2.5V TO 4.2V
Li-Ion *
R3 15k
5M
R1
348k 2.2k
C2
47µF
VOUT
3.3V
1A
R2
200k
C4 220pF
220pF
3441 F09
L1
4.7µH
1A
100mA
VOUT
100mV/DIV
3441 G01
100µs/DIV
LTC3441
13
3441fc
For more information www.linear.com/LTC3441
Typical applicaTions
Li-Ion to 3.3V at 1.2A Converter
Efficiency
SW1
PVIN
VIN
SHDN/SS
MODE/SYNC
PGND
5
8
12
11
2
6
4
9
10
1
7
3
SW2
VOUT
FB
VC
GND
PGND
LTC3441
C1
10µF
*1 = Burst Mode OPERATION
0 = FIXED FREQUENCY
C1: TAIYO YUDEN JMK212BJ106MG
C2: TAIYO YUDEN JMK325BJ226MM
D1, D2: ON SEMICONDUCTOR MBRM120LT3
L1: TOKO A916CY-3R3M
2.8V TO 4.2V
Li-Ion D2 *
R3 15k
R1
340k
C2
22µF
VOUT
3.3V
1.2A
R2
200k
C4 1.5nF
3441 TA03a
L1
4.7µH D1
IOUT (mA)
0.1
40
EFFICIENCY (%)
50
60
70
80
1 10 10000100 1000
3441 TA03b
30
20
10
0
90
100
4.2VIN PWM
4.2VIN BURST
3.6VIN PWM
2.8VIN PWM
Li-Ion to 5V at 600mA Boost Converter with Output Disconnect
SW1
PVIN
VIN
SHDN/SS
MODE/SYNC
PGND
5
8
12
11
2
6
4
9
10
1
7
3
SW2
VOUT
FB
VC
GND
PGND
LTC3441
C1
10µF
0.047µF
*1 = Burst Mode OPERATION
0 = FIXED FREQUENCY
C1: TAIYO YUDEN JMK212BJ106MG
C2: TAIYO YUDEN JMK325BJ226MM
D1: MBRM120LT3
L1: TOKO A916CY-4R7M
2.5V TO 4.2V
Li-Ion *
R3 15k
R1
619k
COUT
22µF
VOUT
5V
600mA
R2
200k
C4 1.5nF
3441 TA04a
L1
4.7µH D1
1M
Efficiency
OUTPUT CURRENT (mA)
30
EFFICIENCY (%)
90
100
20
10
80
50
70
60
40
0.1 10 100 1000
3441 TA04b
0
1
Burst Mode
OPERATION
VIN = 2.7V
VIN = 4.2V
VIN = 3.6 V
LTC3441
14
3441fc
For more information www.linear.com/LTC3441
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 representa-
tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.
package DescripTion
4.00 ±0.10
(2 SIDES)
3.00 ±0.10
(2 SIDES)
NOTE:
1. DRAWING PROPOSED TO BE A VARIATION OF VERSION
(WGED) IN JEDEC PACKAGE OUTLINE M0-229
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
0.40 ±0.10
BOTTOM VIEW—EXPOSED PAD
1.70 ±0.10
0.75 ±0.05
R = 0.115
TYP
R = 0.05
TYP
2.50 REF
16
127
PIN 1 NOTCH
R = 0.20 OR
0.35 × 45°
CHAMFER
PIN 1
TOP MARK
(NOTE 6)
0.200 REF
0.00 – 0.05
(UE12/DE12) DFN 0806 REV D
2.50 REF
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED
2.20 ±0.05
0.70 ±0.05
3.60 ±0.05
PACKAGE OUTLINE
3.30 ±0.10
0.25 ±0.05
0.50 BSC
1.70 ±0.05
3.30 ±0.05
0.50 BSC
0.25 ±0.05
DE/UE Package
12-Lead Plastic DFN (4mm × 3mm)
(Reference LTC DWG # 05-08-1695 Rev D)
Please refer to http://www.linear.com/product/LTC3441#packaging for the most recent package drawings.
LTC3441
15
3441fc
For more information www.linear.com/LTC3441
revision hisTory
REV DATE DESCRIPTION PAGE NUMBER
B 8/14 Modified filter pole equation in Closing the Feedback Loop section 11
C 10/16 Added equation to calculate VOUT
Modified Operating Frequency Selection section
6
11
(Revision history begins at Rev B)
LTC3441
16
3441fc
For more information www.linear.com/LTC3441
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
LINEAR TECHNOLOGY CORPORATION 2003
LT 1016 REV C • PRINTED IN USA
relaTeD parTs
Typical applicaTion
PART NUMBER DESCRIPTION COMMENTS
LT
®
1613 550mA (ISW) 1.4MHz High Efficiency Step-Up DC/DC Converter VIN: 0.9V to 10V, VOUT(MAX): 34V, IQ: 3mA,
ISD: ≤ 1µA, ThinSOT™
LT1615/LT1615-1 300mA/80mA (ISW) Constant Off-Time, High Efficiency Step-Up
DC/DC Converter
VIN: 1.2V to 15V, VOUT(MAX): 34V, IQ: 20µA,
ISD: ≤ 1µA, ThinSOT
LT1616 500mA (IOUT) 1.4MHz High Efficiency Step-Down DC/DC Converter High Efficiency, VIN: 3.6V to 25V, VOUT(MIN): 1.25V, IQ: 1.9mA,
ISD: ≤ 1µA, ThinSOT
LT1776 500mA (IOUT) 200kHz High Efficiency Step-Down DC/DC Converter High Efficiency, VIN: 7.4V to 40V, VOUT(MIN): 1.24V, IQ: 3.2mA,
ISD: 30µA, N8, S8
LTC1877 600mA (IOUT) 550kHz Synchronous Step-Down DC/DC Converter 95% Efficiency, VIN: 2.7V to 10V, VOUT(MIN): 0.8V, IQ: 10µA,
ISD: ≤ 1µA, MS8
LTC1878 600mA (IOUT) 550kHz Synchronous Step-Down DC/DC Converter 95% Efficiency, VIN: 2.7V to 6V, VOUT(MIN): 0.8V, IQ: 10µA,
ISD: ≤ 1µA, MS8
LTC1879 1.2A (IOUT) 550kHz Synchronous Step-Down DC/DC Converter 95% Efficiency, VIN: 2.7V to 10V, VOUT(MIN): 0.8V, IQ: 15µA,
ISD: ≤ 1µA, TSSOP16
LT1930/LT1930A 1A (ISW) 1.2MHz/2.2MHz High Efficiency Step-Up DC/DC Converter VIN: 2.6V to 16V, VOUT(MAX): 34V, IQ: 5.5mA,
ISD: ≤ 1µA, ThinSOT
LTC3405/
LTC3405A
300mA (IOUT) 1.5MHz Synchronous Step-Down DC/DC Converter 95% Efficiency, VIN: 2.7V to 6V, VOUT(MIN): 0.8V, IQ: 20µA,
ISD: ≤ 1µA, ThinSOT
LTC3406/
LTC3406B
600mA (IOUT) 1.5MHz Synchronous Step-Down DC/DC Converter 95% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN): 0.6V, IQ: 20µA,
ISD: ≤ 1µA, ThinSOT
LTC3407 600mA (IOUT) ×2 1.5MHz Dual Synchronous Step-Down
DC/DC Converter
96% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN): 0.6V, IQ: 40µA,
ISD: ≤ 1µA, 10-Lead MS
LTC3411 1.25A (IOUT) 4MHz Synchronous Step-Down DC/DC Converter 95% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN): 0.8V, IQ: 60µA,
ISD: ≤ 1µA, 10-Lead MS
LTC3412 2.5A (IOUT) 4MHz Synchronous Step-Down DC/DC Converter 95% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN): 0.8V, IQ: 60µA,
ISD: ≤ 1µA, TSSOP16E
LTC3440 600mA (IOUT) 2MHz Synchronous Buck-Boost DC/DC Converter 95% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN): 2.5V, IQ: 25µA,
ISD: ≤ 1µA, 10-Lead MS
PCMCIA Powered GSM Modem
SW1
PVIN
VIN
SHDN/SS
MODE/SYNC
PGND
5
8
12
11
2
6
4
9
10
1
7
3
SW2
VOUT
FB
VC
GND
PGND
LTC3441
C1
10µF
C1: TAIYO YUDEN JMK212BJ106MG
C2: SANYO MV-AX SERIES
L1: TOKO A916CY-4R7M
VIN
2.5V TO 5.5V
1A MAX
R6
24k
R4
1k
AVERAGE INPUT
CURRENT CONTROL
1N914
RS
0.05Ω
R1
392k
COUT
2200µF
VOUT
3.6V
2A (PULSED)
R2
200k
R5
24k
C4
10nF
3441 TA05
L1
10µH
–
+
1/2 LT1490A
1.22 • R4
R5 • RS
ICURRENTLIMIT =
2N3906
–
+
1/2 LT1490A
(408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com/LTC3441
