LINER LTC3441 High current micropower synchronous buck-boost dc/dc converter Datasheet

LTC3441
High Current Micropower
Synchronous Buck-Boost
DC/DC Converter
Description
Features
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Regulated Output with Input Above, Below or Equal
to the Output
Single Inductor, No Schottky Diodes
High Efficiency: Up to 95%
25µA Quiescent Current in Burst Mode® Operation
Up to 1.2A Continuous Output Current from a Single
Lithium-Ion
True Output Disconnect in Shutdown
2.4V to 5.5V Input Range
2.4V to 5.25V Output Range
1MHz Fixed Frequency Operation
Synchronizable Oscillator
Selectable Burst Mode or Fixed Frequency Operation
<1µA Quiescent Current in Shutdown
Small, Thermally Enhanced 12-Lead (4mm × 3mm)
DFN package
Applications
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Handheld Computers
Handheld Instruments
MP3 Players
Digital Cameras
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.
The LTC®3441 is a high efficiency, fixed frequency, buckboost 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 applications 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 moderate 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 applications. 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.
Typical Application
Efficiency vs VIN
Li-Ion to 3.3V at 1A Buck-Boost Converter
L1
4.7µH
9
2.5V TO 4.2V
10
1
Li-Ion
*
CIN
10µF
7
3
SW1
SW2
PVIN
VOUT
VIN
LTC3441
SHDN/SS
FB
VC
MODE/SYNC GND
PGND
*1 = Burst Mode OPERATION
0 = FIXED FREQUENCY
PGND
5
340k
8
12
11
2
6
COUT
22µF
15k
1.5nF
200k
VOUT = 3.3V
95
VOUT
3.3V
1A
IOUT = 200mA
90
EFFICIENCY (%)
4
100
85
IOUT = 1A
80
75
70
65
60
55
CIN: TAIYO YUDEN JMK212BJ106MG
COUT: TAIYO YUDEN JMK325BJ226MM
L1: TOKO A916CY-4R7M
50
3441 TA01
2.5
3
3.5
4
VIN (V)
4.5
5
5.5
3441 TA02
3441fb
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1
LTC3441
Absolute Maximum Ratings
Pin Configuration
(Note 1)
TOP VIEW
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
SHDN/SS
1
12 FB
GND
2
11 VC
PGND
3
SW1
4
SW2
PGND
13
10 VIN
9
PVIN
5
8
VOUT
6
7
MODE/SYNC
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/
electrical characteristics
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.
PARAMETER
CONDITIONS
MIN
TYP
2.3
Input Start-Up Voltage
●
Output Voltage Adjust Range
●
2.4
Feedback Voltage
●
1.19
1.22
MAX
UNITS
2.4
V
5.25
V
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
10
µA
PMOS Switch Leakage
Switches A and D
0.1
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
Max Duty Cycle
Boost (% Switch C On)
Buck (% Switch A In)
●
2
3.2
A
●
●
70
100
88
%
%
0
Min Duty Cycle
●
Frequency Accuracy
●
0.85
MODE/SYNC Threshold
●
0.4
1
%
1.15
MHz
1.4
V
3441fb
2
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LTC3441
Electrical Characteristics
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.
PARAMETER
CONDITIONS
MIN
MODE/SYNC Input Current
VMODE/SYNC = 5.5V
TYP
MAX
0.01
1
UNITS
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
SHDN/SS Threshold
When EA is at Max Boost Duty Cycle
SHDN/SS Input Current
VSHDN = 5.5V
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.
0.4
●
1
1.4
V
2
2.4
V
0.01
1
µA
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
100
90
Burst Mode
OPERATION
EFFICIENCY (%)
80
BUCK
VIN = 4.2V
70
60
VOUT
10mV/DIV
AC-COUPLED
VIN = 4.2V
50
VIN = 2.7V
40
BUCK-BOOST
VIN = 3.3V
VIN = 3.6V
BOOST
VIN = 2.7V
30
20
10
L = 4.7µH
COUT = 47µF
IOUT = 1A
VOUT = 3.3V
VOUT = 3.3V
0
0.1
1
10
IOUT (mA)
100
1000
1µs/DIV
3441 G02
3441 G17
Load Transient Response,
100mA to 1A
Switch Pins Entering
Buck-Boost Mode
Switch Pins in Buck-Boost Mode
VOUT
100mV/DIV
1A
SW1
2V/DIV
SW1
2V/DIV
SW2
2V/DIV
SW2
2V/DIV
100mA
100µs/DIV
3441 G01
VIN = 3.3V
VOUT = 3.3V
IOUT = 500mA
50ns/DIV
3441 G03
VIN = 4.2V
VOUT = 3.3V
IOUT = 500mA
50ns/DIV
3441 G04
3441fb
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3
LTC3441
Typical Performance Characteristics
Switch Pins Before Entering
Boost Mode
Active Quiescent Current
630
620
SW1
2V/DIV
Feedback Voltage
1.241
VIN = VOUT = 3.6V
1.236
SW2
2V/DIV
VIN = 3V
VOUT = 3.3V
IOUT = 500mA
50ns/DIV
1.231
600
FEEDBACK VOLTAGE (V)
VIN + VOUT CURRENT (µA)
610
1.226
590
1.221
580
570
1.216
560
1.211
550
1.206
540
3441 G05
VIN = VOUT = 3.6V
1.201
530
520
–55
–25
5
35
65
TEMPERATURE (°C)
95
125
1.196
–55
–25
5
35
65
TEMPERATURE (°C)
95
3441 G06
LINE REGULATION (dB)
VIN + VOUT CURRENT (µA)
40
30
20
–25
5
35
65
TEMPERATURE (°C)
95
VIN = VOUT = 2.4V TO 5.5V
80
70
60
–55
125
–25
5
35
65
TEMPERATURE (°C)
95
3441 G08
10
5
–55
125
–25
5
35
65
TEMPERATURE (°C)
95
125
3441 G10
Current Limit
3.4
VIN = VOUT = 3.6V
VIN = VOUT = 3.6V
1.1
300
250
CURRENT LIMIT (A)
350
FREQUENCY (MHz)
EA SINK CURRENT (µA)
15
Output Frequency
1.2
VIN = VOUT = 3.6V
200
–55
VIN = VOUT = 3.6V
3441 G09
Error Amp Sink Current
400
Error Amp Source Current
20
EA SOURCE CURRENT (µA)
90
VIN = VOUT = 3.6V
10
–55
3441 G07
Feedback Voltage Line Regulation
Burst Mode Quiescent Current
50
125
1.0
0.9
–25
5
35
65
TEMPERATURE (°C)
95
125
3441 G11
0.8
–55
–25
5
35
65
TEMPERATURE (°C)
95
125
3441 G12
3.2
3.0
2.8
–55
–25
5
35
65
TEMPERATURE (°C)
95
125
3441 G13
3441fb
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LTC3441
Typical Performance Characteristics
NMOS RDS(ON)
PMOS RDS(ON)
0.15
VIN = VOUT = 3.6V
SWITCHES B AND C
0.14
VIN = VOUT = 3.6V
SWITCHES A AND D
0.13
PMOS RDS(ON) (Ω)
0.13
NMOS RDS(ON) (Ω)
Minimum Start Voltage
2.30
MINIMUM START VOLTAGE (V)
0.15
0.11
0.09
0.12
0.11
0.10
0.09
0.08
0.07
0.07
0.05
–55
0.05
–50
2.25
2.20
2.15
0.06
–25
5
35
65
TEMPERATURE (°C)
95
125
–25
35
65
5
TEMPERATURE (°C)
3441 G14
95
125
3441 G15
2.10
–55
–25
5
35
65
TEMPERATURE (°C)
95
125
3441 G16
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 command 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 capacitor is recommended as close to the PVIN and PGND
pins as possible
VIN (Pin 10): Input Supply Pin. Internal VCC for the IC.
VC (Pin 11): Error Amp Output. A frequency compensation 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.
3441fb
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5
LTC3441
block diagram
10
SW A
4
VIN
SW B
5
GATE
DRIVERS
AND
ANTICROSS
CONDUCTION
SW2
ISENSE
AMP
AVERAGE
CURRENT LIMIT
UVLO
+
PWM
LOGIC
AND
OUTPUT
PHASING
–
+
1.22V
–
FB
R1
12
CLAMP
+
2.4V
ERROR
AMP
PWM
COMPARATORS
–
VCC
INTERNAL
THERMAL
SHUTDOWN
SUPPLY
CURRENT
LIMIT
–
4A
8
PGND
–
+
VOUT
2.4V TO 5.25V
REVERSE
CURRENT
LIMIT
+
–
3.2A
VOUT
–0.8A
SW C
+
gm = 1 k
100
SW D
–
+
9
PVIN
SW1
+
VIN
2.4V TO 5.5V
VC
1MHz
OSC
11
R2
SYNC
SLEEP
Burst Mode
OPERATION
CONTROL
÷2
SHUTDOWN
SHDN/SS
1
RSS
VIN
5µs DELAY
7
MODE/SYNC
1 = Burst Mode
OPERATION
0 = FIXED FREQUENCY
CSS
2
GND
6
PGND
3440 BD
3441fb
6
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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
Reverse Current Limit
The reverse current limit amplifier monitors the inductor
current from the output through switch D. Once a negative 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 internal 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.
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).
PVIN
VOUT
9
8
PMOS A
VOUT
PMOS D
SW1
SW2
4
5
NMOS B
NMOS C
3441 F01
Figure 1. Simplified Diagram of Output Switches
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.
75%
DMAX
BOOST
A ON, B OFF
BOOST REGION
PWM CD SWITCHES
DMIN
BOOST
DMAX
BUCK
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 voltage. The current amplifier delay to output is typically 50ns.
V4 (≈2.05V)
V3 (≈1.65V)
FOUR SWITCH PWM
BUCK/BOOST REGION
V2 (≈1.55V)
D ON, C OFF
PWM AB SWITCHES BUCK REGION
V1 (≈0.9V)
0%
DUTY
CYCLE
3441 F02
INTERNAL
CONTROL
VOLTAGE, VCI
Figure 2. Switch Control vs Internal Control Voltage, VCI
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7
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 voltage 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:
VOUT
VIN =
V
1– (150ns • f)
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:
0.2 • VIN
IOUT(MAX)BURST ≈
A
VOUT + VIN
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 illustrated 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 maintain 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 ≈
(ηbm)•ILOAD
25µA +ILOAD
where (ηbm) is typically 75% during Burst Mode
operation.
3441fb
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LTC3441
operation
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. Lowering 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.
PVIN
VOUT
PVIN
VOUT
9
8
9
8
4
SW1
+
dI ≈ VIN
dt
L
L
A
D
–
5
SW2
B
C
IINDUCTOR
A
800mA
4
–
dI ≈ – VOUT
L
dt
+
L
SW1
0mA
D
5
SW2
B
C
IINDUCTOR
Burst Mode Operation to Fixed Frequency Transient
Response
800mA
0mA
3441 F03
T1
6
6
GND
GND
Figure 3. Inductor Charge Cycle During Burst Mode Operation
T2
3441 F04
Figure 4. Inductor Discharge Cycle During Burst Mode Operation
ERROR AMP
VIN
14µA
+
VOUT
1.22V
R1
FB
–
12
VC
SOFT-START
CLAMP
TO PWM
COMPARATORS
CP1
R2
11
VCI
SHDN/SS
RSS
ENABLE SIGNAL
1
CSS
+
CHIP
ENABLE
–
3441 F05
1V
Figure 5. Soft-Start Circuitry
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9
LTC3441
applications Information
COMPONENT SELECTION
1 SHDN/SS
FB 12
2 GND
VC 11
3 PGND
VIN 10
4 SW1
PVIN 9
5 SW2
VOUT 8
6 PGND
MODE 7
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.
VIN
VOUT
Table 1. Inductor Vendor Information
SUPPLIER
MULTIPLE VIAS
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
Inductor Selection
The high frequency operation of the LTC3441 allows the
use of small surface mount inductors. The inductor current 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>
L>
(
)
VIN(MIN) • VOUT – VIN(MIN) • 100
f •IOUT(MAX) • %Ripple • VOUT
(
)
VOUT • VIN(MAX) – VOUT • 100
f •IOUT(MAX) • %Ripple • VIN(MAX)
H,
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 frequency 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
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:
www.japanlink.com/
(847) 956-0666 (847) 956-0702 sumida
Japan:
81(3) 3607-5111 81(3) 3607-5144
3441 F06
GND
PHONE
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 =
%Ripple _Buck =
(
)
%
(
)
%
IOUT(MAX) • VOUT – VIN(MIN) • 100
COUT • VOUT 2 • f
IOUT(MAX) • VIN(MAX) – VOUT • 100
COUT • VIN(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 (equivalent 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.
3441fb
10
For more information www.linear.com/LTC3441
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
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
WEB SITE
(408) 573-4159 www.t-yuden.com
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: 800e–12 • VIN • f
Boost: 400e–12 • (VIN + VOUT) • f
Buck/Boost: f • (1200e–12 • VIN + 400e–12 • VOUT)
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 output 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
where f = switching frequency
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
Hz
2 • π • L •COUT
(in buck mode)
fFILTER_POLE =
VIN
Hz
2 • VOUT • π • L •COUT
(in boost mode)
Where L is in Henries and COUT is the output filter capacitor in Farads.
The output filter zero is given by:
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
fFILTER _ ZERO =
1
2 • π • RESR • COUT
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:
VIN 2
fRHPZ =
Hz
2 • π •IOUT • L • VOUT
The loop gain is typically rolled off before the RHP zero
frequency.
3441fb
For more information www.linear.com/LTC3441
11
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.
12
CP1
VC
R2
11
3441 F07
Figure 7. Error Amplifier with Type I Compensation
VOUT
+
ERROR
AMP
–
1
Hz
2 • π •32e3 •R1• CP1
Which is extremely close to DC
1
Hz
fZERO1=
2 • π •R Z • CP1
1
Hz
fZERO2 =
2 • π •R1 • CZ 1
1.22V
R1
CZ1
FB
12
VC
11
CP1
RZ
R2
CP2
3441 F08
Figure 8. Error Amplifier with Type III Compensation
1
Hz
2 • π •R Z • CP 2
L1
4.7µH
4
9
2.5V TO 4.2V
10
1
*
C1
10µF
Li-Ion
R1
FB
–
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.
fPOLE2 =
1.22V
ERROR
AMP
The unity-gain frequency of the error amplifier with the
Type I compensation is given by:
1
fUG =
Hz
2 • π • R1• CP1
fPOLE1 ≈
VOUT
+
7
3
SW2
SW1
PVIN
VIN
LTC3441
SHDN/SS
VOUT
FB
VC
MODE/SYNC GND
PGND
*1 = Burst Mode OPERATION
0 = FIXED FREQUENCY
PGND
220pF
5
8
R1
348k
12
11
2
6
VOUT
3.3V
1A
VOUT
100mV/DIV
2.2k
C2
47µF
R3 15k
C4 220pF
5M
C1: TAIYO YUDEN JMK212BJ106MG
C2: TAIYO YUDEN JMK325BJ476MM
L1: TOKO A916CY-4R7M
Load Transient Response,
100mA to 1A
1A
R2
200k
100mA
3441 F09
100µs/DIV
3441 G01
Figure 9. Fast Transient Response Compensation for Step Load or Mode Change
3441fb
12
For more information www.linear.com/LTC3441
LTC3441
typical applications
Li-Ion to 3.3V at 1.2A Converter
L1
4.7µH
10
PVIN
VIN
1
Li-Ion
D2
*
*1 = Burst Mode OPERATION
0 = FIXED FREQUENCY
PGND
2
C4 1.5nF
6
VOUT
3.3V
1.2A
C2
22µF
R3 15k
11
VC
PGND
R1
340k
12
FB
MODE/SYNC GND
3
C1
10µF
LTC3441
8
VOUT
SHDN/SS
7
5
SW2
SW1
9
2.8V TO 4.2V
100
R2
200k
90
80
EFFICIENCY (%)
4
Efficiency
D1
4.2VIN BURST
70
60
50
2.8VIN PWM
4.2VIN PWM
3.6VIN PWM
40
30
20
C1: TAIYO YUDEN JMK212BJ106MG
C2: TAIYO YUDEN JMK325BJ226MM
D1, D2: ON SEMICONDUCTOR MBRM120LT3
L1: TOKO A916CY-3R3M
3441 TA03a
10
0
0.1
1
10
100
IOUT (mA)
1000
10000
3441 TA03b
Li-Ion to 5V at 600mA Boost Converter with Output Disconnect
4
9
2.5V TO 4.2V
10
1M
Li-Ion
0.047µF
C1
10µF
1
*
7
3
*1 = Burst Mode OPERATION
0 = FIXED FREQUENCY
SW1
SW2
PVIN
VOUT
VIN
LTC3441
SHDN/SS
FB
VC
MODE/SYNC GND
PGND
Efficiency
D1
PGND
VOUT
5V
600mA
5
12
2
6
90
R1
619k
8
11
100
80
COUT
22µF
R3 15k
C4 1.5nF
R2
200k
EFFICIENCY (%)
L1
4.7µH
70
VIN = 4.2V
Burst Mode
OPERATION
VIN = 3.6 V
VIN = 2.7V
60
50
40
30
20
C1: TAIYO YUDEN JMK212BJ106MG
C2: TAIYO YUDEN JMK325BJ226MM
D1: MBRM120LT3
L1: TOKO A916CY-4R7M
3441 TA04a
10
0
0.1
10
100
1
OUTPUT CURRENT (mA)
1000
3441 TA04b
3441fb
For more information www.linear.com/LTC3441
13
LTC3441
Package Description
Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings.
DE/UE Package
12-Lead Plastic DFN (4mm × 3mm)
(Reference LTC DWG # 05-08-1695 Rev D)
0.70 ±0.05
3.30 ±0.05
3.60 ±0.05
2.20 ±0.05
1.70 ±0.05
PACKAGE OUTLINE
0.25 ±0.05
0.50 BSC
2.50 REF
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED
4.00 ±0.10
(2 SIDES)
7
R = 0.115
TYP
0.40 ±0.10
12
R = 0.05
TYP
PIN 1
TOP MARK
(NOTE 6)
0.200 REF
3.30 ±0.10
3.00 ±0.10
(2 SIDES)
1.70 ±0.10
0.75 ±0.05
6
0.25 ±0.05
1
PIN 1 NOTCH
R = 0.20 OR
0.35 × 45°
CHAMFER
(UE12/DE12) DFN 0806 REV D
0.50 BSC
2.50 REF
0.00 – 0.05
BOTTOM VIEW—EXPOSED PAD
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
3441fb
14
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.
For more
information
www.linear.com/LTC3441
LTC3441
Revision History
(Revision history begins at Rev B)
REV
DATE
DESCRIPTION
B
8/14
Modified filter pole equation in Closing the Feedback Loop section
PAGE NUMBER
11
3441fb
For more information www.linear.com/LTC3441
15
LTC3441
Typical Application
PCMCIA Powered GSM Modem
L1
10µH
4
VIN
2.5V TO 5.5V
1A MAX
9
RS
0.05Ω
10
1
7
C1
10µF
3
SW2
SW1
PVIN
VIN
LTC3441
SHDN/SS
VOUT
FB
VC
MODE/SYNC GND
PGND
PGND
5
8
R6
24k
12
1/2 LT1490A
11
2
6
+
1N914
R1
392k
COUT
2200µF
–
C4
10nF
R5
24k
VOUT
3.6V
2A (PULSED)
R2
200k
3441 TA05
+
R4
1k
1/2 LT1490A
–
2N3906
C1: TAIYO YUDEN JMK212BJ106MG
C2: SANYO MV-AX SERIES
L1: TOKO A916CY-4R7M
ICURRENTLIMIT = 1.22 • R4
R5 • RS
AVERAGE INPUT
CURRENT CONTROL
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3441fb
16 Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
For more information www.linear.com/LTC3441
(408) 432-1900 ● FAX: (408) 434-0507
●
www.linear.com/LTC3441
LT 0814 REV B • PRINTED IN USA
 LINEAR TECHNOLOGY CORPORATION 2003