LTC3401
1A, 3MHz Micropower
Synchronous Boost Converter
DESCRIPTIO
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FEATURES
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The LTC®3401 is a high efficiency, fixed frequency, stepup DC/DC converter that operates from an input voltage
below 1V. The device includes a 0.16Ω N-channel MOSFET
switch and a 0.18Ω P-channel synchronous rectifier.
Switching frequencies up to 3MHz are programmed with
an external timing resistor and the oscillator can be
synchronized to an external clock. An external Schottky
diode is optional but will slightly improve efficiency.
Synchronous Rectification: Up to 97% Efficiency
1A Switch Current Rating
Fixed Frequency Operation Up to 3MHz
Wide Input Range: 0.5V to 5.5V (Operating)
Very Low Quiescent Current: 38μA (Burst Mode®
Operation)
2.6V to 5.5V Adjustable Output Voltage
0.85V (Typ) Start-Up Voltage
No External Schottky Diode Required (VOUT < 4.3V)
Synchronizable Switching Frequency
Burst Mode Enable Control
Antiringing Control Reduces Switching Noise
PGOOD Output
OPTI-LOOP® Compensation
Very Low Shutdown Current: < 1μA
Small 10-Pin MSOP Package
Quiescent current is only 38μA 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
has either a clock or is driven low, then fixed frequency
switching is enabled.
Other features include 1μA shutdown, antiringing control,
open-drain power good output, thermal shutdown and
current limit. The LTC3401 is available in the 10-lead
thermally enhanced MSOP package. Higher current applications should use the 2A rated LTC3402 synchronous
boost converter. Applications that require VOUT < 2.6V
should use the LTC3423.
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APPLICATIO S
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Pagers
Handheld Instruments
Cordless Phones
Wireless Handsets
GPS Receivers
Battery Backup
CCFL Backlights
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
Burst Mode and OPTI-LOOP are registered trademarks of Linear Technology Corporation.
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TYPICAL APPLICATION
All-Ceramic-Capacitor 2-Cell to 3.3V at 500mA Step-Up Converter
L1
4.7μH
3
10
+2
CELLS
2
6
C1
4.7μF
1
LTC3401
VIN
SHDN
SW
VOUT
MODE/SYNC FB
PGOOD
Rt
Rt
30.1k
Efficiency
VOUT
3.3V
500mA
VC
GND
4
100
Burst Mode
90 OPERATION
R2
909k
80
7
8
C2
22μF
9
5
C3
470pF
C4
4.7pF
R1
549k
EFFICIENCY (%)
VIN = 1.8V to 3V
60
50
40
30
20
R5
82k
10
0
0 = FIXED FREQUENCY
1 = Burst Mode OPERATION
C1: TAIYO YUDEN JMK212BJ475MG
C2: TAIYO YUDEN JMK325BJ226MM
L1: SUMIDA CD43-4R7M
1MHz
FIXED
FREQUENCY
70
3404 TA01
VIN = 2.4V WITH SCHOTTKY
0.1
1
10
IOUT (mA)
100
1000
3401 TA02
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LTC3401
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ABSOLUTE
RATI GS
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PACKAGE/ORDER I FOR ATIO
(Note 1)
VIN, VOUT Voltages ...................................... – 0.5V to 6V
SW Voltage ................................................. – 0.5V to 6V
VC, Rt Voltages ......................... – 0.5V to (VOUT + 0.3V)
PGOOD, SHDN, FB, MODE Voltages ........... – 0.5V to 6V
Operating Temperature Range (Note 2) .. – 40°C to 85°C
Storage Temperature Range ................. – 65°C to 125°C
Lead Temperature (Soldering, 10 sec).................. 300°C
Order Options Tape and Reel: Add #TR
Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF
Lead Free Part Marking: http://www.linear.com/leadfree/
ORDER PART
NUMBER
TOP VIEW
Rt
MODE
VIN
SW
GND
1
2
3
4
5
10
9
8
7
6
SHDN
VC
FB
VOUT
PGOOD
MS PACKAGE
10-LEAD PLASTIC MSOP
LTC3401EMS
MS PART MARKING
TJMAX = 125°C
θJA = 130°C/ W 1 LAYER BOARD
θJA = 100°C/ W 4 LAYER BOARD
LTPG
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
The ● denotes specifications that apply over the full operating temperature range, otherwise specifications are at TA = 25°C.
VIN = 1.2V, VOUT = 3.3V unless otherwise noted.
PARAMETER
CONDITIONS
Minimum Start-Up Voltage
ILOAD < 1mA
Minimum Operating Voltage
(Note 4)
MIN
TYP
MAX
UNITS
0.85
1.0
V
0.5
V
5.5
V
1.25
1.28
V
●
Output Voltage Adjust Range
●
2.6
Feedback Voltage
●
1.22
Feedback Input Current
VFB = 1.25V
1
50
nA
Quiescent Current—Burst Mode Operation
VC = 0V, MODE/SYNC = 3.3V (Note 3)
38
65
μA
Quiescent Current—SHDN
SHDN = 0V, Not Including Switch Leakage
0.1
1
μA
Quiescent Current—Active
VC = 0V, MODE/SYNC = 0V, Rt = 300k (Note 3)
440
800
μA
NMOS Switch Leakage
0.1
5
μA
PMOS Switch Leakage
0.1
10
μA
NMOS Switch On Resistance
0.16
Ω
PMOS Switch On Resistance
0.18
Ω
1.6
A
NMOS Current Limit
●
1
●
80
NMOS Burst Current Limit
Maximum Duty Cycle
Rt = 15k
A
85
%
●
Minimum Duty Cycle
Frequency Accuracy
0.66
Rt = 15k
MODE/SYNC Input High
●
0
1.6
2
2.4
1.4
0.4
VMODE/SYNC = 5.5V
Error Amp Transconductance
ΔI = – 5μA to 5μA, VC = VFB
PGOOD Threshold
Referenced to Feedback Voltage
0.01
1
–9
V
μA
μmhos
85
–6
MHz
V
MODE/SYNC Input Low
MODE/SYNC Input Current
%
– 12
%
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LTC3401
ELECTRICAL CHARACTERISTICS
The ● denotes specifications that apply over the full operating temperature range, otherwise specifications are at TA = 25°C.
VIN = 1.2V, VOUT = 3.3V unless otherwise noted.
PARAMETER
CONDITIONS
PGOOD Low Voltage
IPGOOD = 1mA
VOUT = 1V, IPGOOD = 20μA
MIN
PGOOD Leakage
VPGOOD = 5.5V
SHDN Input High
VSHDN = VIN = VOUT
TYP
MAX
UNITS
0.1
0.1
0.2
0.4
V
V
0.01
1
μA
1
V
SHDN Input Low
SHDN Input Current
VSHDN = 5.5V
0.01
Thermal Shutdown
0.4
V
1
μA
°C
170
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 LTC3401 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 is measured into VOUT since the supply current is
bootstrapped to the VOUT pin and in the application will reflect to the input
supply by (VOUT/VIN) • I/ Efficiency. The outputs are not switching.
Note 4: Once the output is started, the IC is not dependant upon the VIN
supply.
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TYPICAL PERFOR A CE CHARACTERISTICS
SW Pin and Inductor Current (IC)
in Discontinuous Mode. Ringing
Control Circuitry Eliminates High
Frequency Ringing
Switching Waveform on SW Pin
IL
50mA/DIV
0A
SW
1V/DIV
Transient Response 5mA to 50mA
VOUT
100mV/DIV
SW
1V/DIV
50mA
IOUT
5mA
0V
50ns/DIV
3401 G01
200ns/DIV
3401 G02
COUT = 22μF
L = 3.3μH
fOSC = 1MHz
200μs/DIV
3401 G03
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LTC3401
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TYPICAL PERFOR A CE CHARACTERISTICS
Transient Response 50mA to 500mA
Burst Mode Operation
Burst Mode Operation
VOUT
200mV/DIV
VOUT
AC
100mV/DIV
550mA
SW
1V/DIV
VOUT
AC
100mV/DIV
SW
1V/DIV
IOUT
50mA
COUT = 22μF
L = 3.3μH
fOSC = 1MHz
200μs/DIV
VIN = 1.2V
5ms/DIV
VOUT = 3.3V
COUT = 100μF
IOUT = 250μA
MODE/SYNC PIN = HIGH
3401 G04
Converter Efficiency 1.2V to 3.3V
300kHz
90
Burst Mode
OPERATION
80
100
Burst Mode
OPERATION
80
3MHz
60
1MHz
50
40
80
3MHz
70
EFFICIENCY (%)
70
300kHz
60
1MHz
50
40
40
20
20
20
10
10
10
1
10
100
OUTPUT CURRENT (mA)
30
0
0.1
1000
1
10
100
OUTPUT CURRENT (mA)
0
1000
0.1
TA = 25°C
1.80
TA = 25°C
1.75
12
1.70
10
CURRENT (A)
EFFICIENCY LOSS (%)
400
100
8
6
4
0.8
0.9
1
1.1
VIN (V)
1.2
1.3
1.4
3401 G09
0
0.2
1.65
1.60
1.55
1.50
2
0
1000
Current Limit
14
200
100
10
LOAD CURRENT (mA)
3401 G10
Efficiency Loss Without Schottky
vs Frequency
300
1
3401 G08
Start-Up Voltage
vs IOUT
500
1MHz
FIXED
FREQUENCY
50
30
3401 G07
OUTPUT CURRENT (mA)
70
60
30
0
0.1
Burst Mode OPERATION
90
EFFICIENCY (%)
90
3401 G06
Converter Efficiency 3.6V to 5V
Converter Efficiency 2.4V to 3.3V
100
100
EFFICIENCY (%)
VIN = 1.2V
200μs/DIV
VOUT = 3.3V
COUT = 100μF
IOUT = 20mA
MODE/SYNC PIN = HIGH
3401 G05
1.45
0.6
1.0 1.4 1.8 2.2
FREQUENCY (MHz)
2.6
3.0
3401 G11
1.40
–55
–15
25
65
TEMPERATURE (°C)
105 125
3401 G12
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LTC3401
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TYPICAL PERFOR A CE CHARACTERISTICS
EA FB Voltage
Oscillator Frequency Accuracy
1.28
2.10
NMOS RDS(ON)
0.30
Rt = 15k
1.27
0.25
1.25
1.24
RESISTANCE (Ω)
FREQUENCY (MHz)
VOLTAGE (V)
2.05
1.26
VOUT = 3.3V
2.00
0.20
0.15
1.95
0.10
1.23
1.22
–55
–15
25
65
TEMPERATURE (°C)
1.90
–55
105 125
–15
25
65
TEMPERATURE (°C)
3401 G13
–15
25
65
TEMPERATURE (°C)
3401 G14
PMOS RDS(ON)
0.30
0.05
–55
105 125
3401 G22
Shutdown Threshold
Start-Up Voltage
1.1
VOUT = 3.3V
105 125
1.10
1.05
1.0
1.00
0.20
0.15
VOLTAGE (V)
0.95
VOLTAGE (V)
RESISTANCE (Ω)
0.25
0.9
0.8
0.90
0.85
0.80
0.75
0.10
0.7
0.70
0.05
–55
0.6
–55
0.60
–55
0.65
–15
25
65
TEMPERATURE (°C)
105 125
–15
25
65
TEMPERATURE (°C)
105 125
3401 G16
VOUT Turn-Off Voltage
2.50
44
–7.5
105 125
3401 G18
Burst Mode Operation Current
–7.0
2.45
42
–8.0
2.40
40
–9.0
–9.5
–10.0
–10.5
2.35
VOLTAGE (V)
–8.5
CURRENT (μA)
PERCENT FROM VFB (%)
25
65
TEMPERATURE (°C)
3401 G17
PGOOD Threshold
38
36
2.30
2.25
2.20
2.15
34
–11.0
2.10
32
–11.5
–12.0
–55
–15
–15
25
65
TEMPERATURE (°C)
105 125
3401 G19
30
–55
2.05
–15
25
65
TEMPERATURE (°C)
105 125
3401 G20
2.00
–55
–15
25
65
TEMPERATURE (°C)
105 125
3401 G21
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LTC3401
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PI FU CTIO S
Rt (Pin 1): Timing Resistor to Program the Oscillator
Frequency.
fOSC =
3 • 1010
Hz
Rt
MODE/SYNC (Pin 2): Burst Mode Select and Oscillator
Synchronization.
MODE/SYNC = High. Enable Burst Mode operation. The
inductor peak inductor current will be 1/3 the current
limit value and return to zero current on each cycle.
During Burst Mode operation the operation is variable
frequency, providing a significant efficiency improvement at light loads. It is recommended the Burst Mode
operation only be entered once the part has started up.
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 of 100ns to 2μs is required to
synchronize.
VIN (Pin 3): Input Supply Pin.
SW (Pin 4): Switch Pin. Connect inductor and Schottky
diode here. For applications with output voltages over
4.3V, a Schottky diode is required to ensure that the SW
pin voltage does not exceed its absolute maximum rating.
Minimize trace length to keep EMI down. For discontinuous inductor current, a controlled impedance is placed
from SW to VIN from the IC to eliminate high frequency
ringing due to the resonant tank of the inductor and SW
node capacitance, therefore reducing EMI radiation.
GND (Pin 5): Signal and Power Ground for the IC.
PGOOD (Pin 6): Power Good Comparator Output. This
open-drain output is low when VFB < – 9% from its
regulation voltage.
VOUT (Pin 7): Output of the Synchronous Rectifier and
Bootstrapped Power Source for the IC. A ceramic capacitor of at least 1μF is required and should be located as
close to the VOUT and GND pins as possible (Pins 7 and 5).
FB (Pin 8): Feedback Pin. Connect resistor divider tap
here. The output voltage can be adjusted from 2.6V to
5.5V. The feedback reference voltage is typically 1.25V.
VC (Pin 9): Error Amp Output. A frequency compensation
network is connected to this pin to compensate the loop.
See the section “Compensating the Feedback Loop” for
guidelines.
SHDN (Pin 10): Shutdown. Grounding this pin shuts down
the IC. Tie to >1V to enable (VIN or digital gate output). To
operate with input voltages below 1V once the converter
has started, a 1M resistor from SHDN to VIN, and a 5M
resistor from SHDN to VOUT will provide sufficient hysteresis During shutdown the output voltage will hold up to VIN
minus a diode drop due to the body diode of the PMOS
synchronous switch. If the application requires a complete disconnect during shutdown then refer to section
“Output Disconnect Circuits”.
3401fb
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LTC3401
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BLOCK DIAGRA
+
3
1V TO
VOUT + 0.3
VIN
SW
4
ANTIRING
P
7
SHDN
10
+
10mV
ISENSE
AMP
+
–
–
CURRENT
LIMIT
+
IZERO
AMP
+
5
1.6A TYP
1.25V
–
+
ERROR
AMP
–
CURRENT
COMP
–
R1
8
FB
+
PWM
LOGIC
+
SLEEP
Σ
–
9
VC
Burst Mode
CONTROL
Rt
VOUT
2.6V TO 5V
ANTICROSS
COND
SHUTDOWN
N
GND
VOUT
1
OSC
SYNC
R2
2 MODE/SYNC
SLOPE COMP
0 = FIXED FREQ
1 = BURST MODE
–
PGOOD 6
N
1.25V – 9%
3401 BD
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LTC3401
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APPLICATIO S I FOR ATIO
DETAILED DESCRIPTION
The LTC3401 provides high efficiency, low noise power
for applications such as portable instrumentation. The
current mode architecture with adaptive slope compensation provides ease of loop compensation with excellent
transient load response. The low RDS(ON), low gate charge
synchronous switches provide the pulse width modulation control at high efficiency.
The Schottky diode across the synchronous PMOS switch
provides a lower drop during the break-before-make time
(typically 20ns) of the NMOS to PMOS transition. The
Schottky diode improves efficiency (see graph “Efficiency
loss without Schottky vs Frequency”). While the IC’s
quiescent current is a low 38μA, high efficiency is achieved
at light loads when Burst Mode operation is entered.
Low Voltage Start-Up
The LTC3401 is designed to start up at input voltages of
typically 0.85V. The device can start up under some load,
(see graph “Start-Up vs Input Voltage”). Once the output
voltage exceeds a threshold of 2.3V, 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 below 0.5V without affecting the operation, but the limiting factor for the application becomes the
availability of the power source to supply sufficient energy
to the output at the low voltages.
Low Noise Fixed Frequency Operation
Oscillator. The frequency of operation is set through a
resistor from the Rt pin to ground:
f = 3 • 1010/Rt
An internally trimmed timing capacitor resides inside the
IC. The oscillator can be synchronized with an external
clock inserted on the MODE/SYNC pin. When synchronizing the oscillator, the free running frequency must be set
to approximately 30% lower than the desired synchronized frequency. Keeping the sync pulse width below 2μs
will ensure that Burst Mode operation is disabled.
Current Sensing. Lossless current sensing converts the
peak current signal to a voltage to sum in with the internal
slope compensation. This summed signal is compared to
the error amplifier output to provide a peak current control
command for the PWM. The slope compensation in the IC
is adaptive to the input and output voltage. Therefore, the
converter provides the proper amount of slope compensation to ensure stability and not an excess causing a loss of
phase margin in the converter.
Error Amp. The error amplifier is a transconductance
amplifier with gm = 0.1ms. A simple compensation network is placed from the VC pin to ground.
Current Limit. The current limit amplifier will shut the
NMOS switch off once the current exceeds its threshold.
The current amplifier delay to output is typically 50ns.
Zero Current Amp. The zero current amplifier monitors the
inductor current to the output and shuts off the synchronous rectifier once the current is below 50mA, preventing
negative inductor current.
Antiringing Control. The anitringing control will place an
impedance across the inductor to damp the ringing on the
SW pin during discontinuous mode operation. The LCSW
ringing (L = inductor, CSW = capacitance on the switch pin)
is low energy, but can cause EMI radiation.
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
38μA. In this mode, the output ripple has a variable
frequency component with load current and the steady
state ripple will be typically below 3%.
During the period where the device is delivering energy to
the output, the peak current will be equal to 1/3 the current
limit value and the inductor current will terminate at zero
current for each cycle. In this mode the maximum output
current is given by:
I OUT(MAXBURST) ≈
VIN
Amps
6 • VOUT
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LTC3401
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APPLICATIO S I FOR ATIO
Burst Mode operation is user controlled by driving the
MODE/SYNC pin high to enable and low to disable. It is
recommended that Burst Mode operation be entered after
the part has started up.
Rt
SHDN
MODE
VC
VIN
FB
VOUT
SW
GND PGOOD
COMPONENT SELECTION
VOUT
Inductor Selection
The high frequency operation of the LTC3401 allows the
use of small surface mount inductors. The minimum
inductance value is proportional to the operating frequency and is limited by the following constraints:
(
)
VIN(MIN) • VOUT(MAX) – VIN(MIN)
3
H
L > μH and L >
f • Ripple • VOUT(MAX)
f
where
f = Operating Frequency (Hz)
Ripple = Allowable Inductor Current Ripple (A)
VIN(MIN) = Minimum Input Voltage (V)
VOUT(MAX) = Maximum Output Voltage (V)
The inductor current ripple is typically set to 20% to 40%
of the maximum inductor current.
For high efficiency, choose an inductor with a high frequency core material, such as ferrite, to reduce core
losses. The inductor should have low ESR (equivalent
series resistance) to reduce the I2R losses and must be
able to handle the peak inductor current at full load 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 a list of component suppliers.
Table 1. Inductor Vendor Information
SUPPLIER
PHONE
FAX
WEBSITE
Coilcraft
(847) 639-6400
(847) 639-1469
www.coilcraft.com
Coiltronics
(516) 241-7876
(516) 241-9339
www.coiltronics.com
Murata
(814) 237-1431
(800) 831-9172
(814) 238-0490
www.murata.com
Sumida
USA: (847) 956-0666 (847) 956-0702
Japan: 81-3-3607-5111 81-3-3607-5144
www.japanlink.com
sumida
3401 F01
Figure 1. Recommended Component Placement. Traces
Carrying High Current Are Direct. Trace Area FB and VC Pins
Are Kept Low. Lead Length to Battery Should be Kept Short
Output Capacitor Selection
The output voltage ripple has several components. The
bulk value of the capacitor is set to reduce the ripple due
to charge into the capacitor each cycle. The max ripple due
to charge is given by:
VRBULK =
IP • VIN
V
COUT • VOUT • f
where
IP = Peak Inductor Current
The ESR can be a significant factor for ripple in most power
converters. The ripple due to capacitor ESR is simply given
by:
VRCESR = IP • RESR V
where
RESR = Capacitor Series Resistance
Low ESR capacitors should be used to minimize output
voltage ripple. For surface mount applications, AVX TPS
series tantalum capacitors, Sanyo POSCAP, or TaiyoYuden ceramic capacitors are recommended. For throughhole applications Sanyo OS-CON capacitors offer low ESR
in a small package size. See Table 2 for a list of component
suppliers.
Table 2. Capacitor Vendor Information
SUPPLIER
PHONE
FAX
WEBSITE
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
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LTC3401
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APPLICATIO S I FOR ATIO
In some layouts it may be required to place a 1μF low ESR
capacitor as close to the VOUT and GND pins as possible.
Input Capacitor Selection
The input filter capacitor reduces peak currents drawn from
the input source and reduces input switching noise. Since
the IC can operate at voltages below 0.5V once the output
is regulated, demand on the input capacitor is much less
and in most applications a 3.3μF is sufficient.
Output Diode
For applications with output voltages over 4.3V, a Schottky
diode is required to ensure that the SW pin voltage does
not exceed its absolute maximum rating. The Schottky
diode across the synchronous PMOS switch provides a
lower drop during the break-before-make time (typically
20ns) of the NMOS to PMOS transition. The Schottky
diode improves peak efficiency (see graph “Efficiency
Loss Without Schottky vs Frequency”). Use of a Schottky
diode such as a MBRM120T3, 1N5817 or equivalent.
Since slow recovery times will compromise efficiency, do
not use ordinary rectifier diodes.
Operating Frequency Selection
100
Burst Mode
OPERATION
80
3MHz
EFFICIENCY (%)
70
60
300kHz
1MHz
50
40
30
20
10
0
0.1
1
10
100
OUTPUT CURRENT (mA)
The second consideration is the physical size of the
converter. As the operating frequency goes up, the inductor and filter caps go down in value and size. The trade off
is in efficiency since the switching losses due to gate
charge are going up proportional with frequency. For
example in Figure 2, for a 2.4V to 3.3V converter, the
efficiency at 100mA is 5% less at 2MHz compared to
300kHz.
Another operating frequency consideration is whether the
application can allow “pulse skipping.” In this mode, the
minimum on time of the converter cannot support the duty
cycle, so the converter ripple will go up and there will be
a low frequency component of the output ripple. In many
applications where physical size is the main criterion then
running the converter in this mode is acceptable. In
applications where it is preferred not to enter this mode,
then the maximum operating frequency is given by:
fMAX _ NOSKIP =
VOUT – VIN
Hz
VOUT • tON(MIN)
where tON(MIN) = minimum on time = 120ns
There are several considerations in selecting the operating frequency of the converter. The first is determining
the sensitive frequency bands that cannot tolerate any
spectral noise. For example, in products incorporating
RF communications, the 455kHz IF frequency is sensitive
to any noise, therefore switching above 600kHz is desired. Some communications have sensitivity to 1.1MHz.
90
In this case, converter frequencies up to 3MHz may be
employed.
1000
Reducing Output Capacitance with a Load Feed
Forward Signal
In many applications the output filter capacitance can be
reduced for the desired transient response by having the
device commanding the change in load current, (i.e.
system microcontroller), inform the power converter of
the changes as they occur. Specifically, a “load feed
forward” signal coupled into the VC pin gives the inner
current loop a head start in providing the change in output
current. The transconductance of the LTC3401 converter
at the VC pin with respect to the inductor current is typically
130mA/100mV, so the amount of signal injected is proportional to the anticipated change of inductor current
with load. The outer voltage loop performs the remainder
of the correction, but because of the load feed forward
signal, the range over which it must slew is greatly
reduced. This results in an improved transient response.
3401 G08
Figure 2. Converter Efficiency 2.4V to 3.3V
3401fb
10
LTC3401
U
W
U U
APPLICATIO S I FOR ATIO
A logic level feed forward signal, VFF, is coupled through
components C5 and R6. The amount of feed forward
signal is attenuated with resistor R6 and is given by the
following relationship:
⎛ V • R5 • VIN • 1.5⎞
R6 ≈ ⎜ FF
⎟ – R5
⎝ VOUT • ΔIOUT ⎠
where COUT is the output filter capacitor.
The output filter zero is given by:
fFILTERZERO =
VOUT
10
2
6
1
VIN
fRHPZ =
SHDN
SW
VOUT
MODE/SYNC FB
PGOOD
Rt
VC
GND
Hz
A troublesome feature of the boost regulator topology is
the right half plane zero (RHP) and is given by:
VIN
LTC3401
2 • π • RESR • COUT
where RESR is the capacitor equivalent series resistance.
where ΔIOUT = load current change.
3
1
4
7
VIN2 • RO
2 • π • L • VO2
Hz
At heavy loads this gain increase with phase lag can occur
at a relatively low frequency. The loop gain is typically
rolled off before the RHP zero frequency.
8
9
The typical error amp compensation is shown in Figure 4.
The equations for the loop dynamics are as follows:
C3
5
R5
LOAD FEED
FORWARD
SIGNAL
R6
C5
3.3nF
VFF
3404 F03
Figure 3
Closing the Feedback Loop
The LTC3401 uses current mode control with internal
adaptive slope compensation. Current mode control eliminates the 2nd order filter due to the inductor and output
capacitor exhibited in voltage mode controllers, and simplifies it to a single-pole filter response. The product of the
modulator control to output DC gain plus the error amp
open-loop gain equals the DC gain of the system.
GDC = GCONTROLOUTPUT • GEA
1
fPOLE1 ≈
Hz
2 • π • 20 • 106 • CC1
which is extremelyclose to DC
1
f ZERO1 =
Hz
2 • π • RZ • CC1
1
fPOLE2 ≈
Hz
2 • π • RZ • CC2
VOUT
+
ERROR
AMP
–
1.25V
R1
FB
8
R2
VC
9
CC1
2 • VIN
GCONTROL =
, GEA ≈ 2000
IOUT
The output filter pole is given by:
fFILTERPOLE =
IOUT
Hz
π • VOUT • COUT
CC2
RZ
3401 F04
Figure 4
Refer to Application Note AN-76 for more closed loop
examples.
3401fb
11
LTC3401
UU
OUTPUT DISCO
ECT CIRCUITS
Single Cell Output Disconnect
ZETEX
FMMT717
VIN = 0.9V TO 1.5V
3
10
2
6
1
LTC3401
SW
VIN
VOUT
SHDN
MODE/SYNC FB
PGOOD
VC
Rt
GND
4
VOUT
RB*
7
8
C5
1μF
9
5
3404 TA03
(VOUT – VINMIN – 0.7V) • 100
* SET RB TO FORCE BETA OF ≤100; RB =
IOUTMAX
0 = FIXED FREQUENCY
1 = Burst Mode OPERATION
Dual Cell Output Disconnect Alllowing Full Load Start-Up
IRLML6401
VIN = 1.8V TO 3V
R7
1M
VOUT
3
10
2
6
1
LTC3401
VIN
SHDN
SW
VOUT
MODE/SYNC FB
PGOOD
Rt
VC
GND
4
RG
1M
7
8
C5
1μF
9
5
2N2222
3404 TA04
0 = FIXED FREQUENCY
1 = Burst Mode OPERATION
3401fb
12
LTC3401
U
TYPICAL APPLICATIO S
Single Cell to 3V at 50mA, 1.2mm High, 3MHz Step-Up Converter
3
10
+1
2
CELL
6
C1
2.2μF
1
LTC3401
SW
VIN
SHDN
VOUT
MODE/SYNC FB
PGOOD
VC
Rt
GND
Efficiency
D1
VOUT
3V
100mA
4
90
R2
866k
70
7
8
C2
4.7μF
9
C3
470pF
5
C4
20pF
R1
619k
FIXED
FREQUENCY
60
50
40
30
20
R5
39k
Rt
10k
Burst Mode
OPERATION
80
EFFICIENCY (%)
R3
1M
R4
5.1M
L1
1μH
VIN = 0.9V TO 1.5V
10
0
0.1
0 = FIXED FREQUENCY
1 = Burst Mode OPERATION
C1: TAIYO YUDEN JMK212BJ225MG
C2: TAIYO YUDEN JMK212BJ475MG
D1: CENTRAL SEMICONDUCTOR CMDSH-3
L1: TAIYO YUDEN LB2016
VIN = 1.2V
1
10
100
OUTPUT CURRENT (mA)
1000
3401 TA05b
3404 TA05a
Single Cell to 3V at 200mA, 600kHz Step-Up Converter
3
10
+1
2
CELL
6
C1
3.3μF
1
LTC3401
VIN
SHDN
SW
VOUT
MODE/SYNC FB
PGOOD
Rt
Rt
50k
VC
GND
D1
4
100
90
R2
866k
8
C2
22μF
9
C3
470pF
R5
82k
C4
4.7pF
Burst Mode
OPERATION
80
7
5
Efficiency
VOUT
3V
200mA
EFFICIENCY (%)
R3
1M
R4
5.1M
L1
10μH
VIN = 0.9V TO 1.5V
70
FIXED
FREQUENCY
60
50
40
30
R1
619k
20
10
VIN = 1.2V
0
0.1
0 = FIXED FREQUENCY
1 = Burst Mode OPERATION
C1: TAIYO YUDEN JMK212BJ335MG
C2: TAIYO YUDEN JMK325BJ226MM
D1: ON SEMICONDUCTOR MBRM120T3
L1: SUMIDA CD54-100
1
100
10
LOAD CURRENT (mA)
1000
3401 TA06b
3404 TA06a
3401fb
13
LTC3401
U
TYPICAL APPLICATIO S
Li-Ion to 5V at 300mA, 1MHz Step-Up Converter
L1
10μH
R3
1M
3
10
Li-Ion
2
6
C1
4.7μF
1
LTC3401
VIN
SHDN
SW
VOUT
MODE/SYNC FB
PGOOD
Rt
Efficiency
D1*
VC
GND
VOUT
5V
300mA
4
100
80
R2
1.65M
7
8
C2*
22μF
9
5
C3
470pF
70
1MHz
FIXED
FREQUENCY
60
50
40
30
R1
549k
C4
4.7pF
R5
82k
Rt
30k
Burst Mode OPERATION
90
EFFICIENCY (%)
VIN = 2.5V TO 4.2V
20
10
VIN = 3.6V
0
0.1
0 = FIXED FREQUENCY
1 = Burst Mode OPERATION
*LOCATE COMPONENTS AS CLOSE TO
IC AS POSSIBLE
C1: TAIYO YUDEN JMK212BJ475MG
C2: TAIYO YUDEN JMK325BJ226MM
D1: ON SEMICONDUCTOR MBRM120T3
L1: SUMIDA CDC5023-100
1
3404 TA07a
100
10
LOAD CURRENT (mA)
1000
3401 TA07b
High Efficiency, Compact CCFL Supply with Remote Dimming
C3
27pF
1kV
10
1
2
C2
Q1 0.22μF Q2
L1
33μF
D1
R5
Li-Ion 1M
3
10
2
6
C1
10μF
1
LTC3401
VIN
SHDN
SW
VOUT
MODE/SYNC FB
PGOOD
Rt
4
3
CCFL
R1
300Ω
VIN = 2.5V TO 4.2V
5
6
T1
VC
GND
D4
R4
20k
DIMMING
INPUT
0V TO 2.5V
4
7
D2
D3
8
R2
10k
9
5
Rt
150k
C5
1μF
R3
1k
C4
0.1μF
3404 TA08
C1: TAIYO YUDEN JMK212BJ106MG
C2: PANASONIC ECH-U
D1: ZETEX ZHCS-1000
D2 TO D4: 1N4148
L1: SUMIDA CD-54-330MC
Q1, Q2: ZETEX FMMT-617
T1: SUMIDA C1Q122
CCFL BACKLIGHT APPLICATION CIRCUITS
CONTAINED IN THIS DATA SHEET ARE
COVERED BY U.S. PATENT NUMBER 5408162
AND OTHER PATENTS PENDING
3401fb
14
LTC3401
U
PACKAGE DESCRIPTION
MS Package
10-Lead Plastic MSOP
(Reference LTC DWG # 05-08-1661)
0.889 ± 0.127
(.035 ± .005)
5.23
(.206)
MIN
3.20 – 3.45
(.126 – .136)
3.00 ± 0.102
(.118 ± .004)
(NOTE 3)
0.50
0.305 ± 0.038
(.0197)
(.0120 ± .0015)
BSC
TYP
RECOMMENDED SOLDER PAD LAYOUT
0.254
(.010)
0.497 ± 0.076
(.0196 ± .003)
REF
10 9 8 7 6
3.00 ± 0.102
(.118 ± .004)
(NOTE 4)
4.90 ± 0.152
(.193 ± .006)
DETAIL “A”
0° – 6° TYP
GAUGE PLANE
1 2 3 4 5
0.53 ± 0.152
(.021 ± .006)
DETAIL “A”
0.86
(.034)
REF
1.10
(.043)
MAX
0.18
(.007)
SEATING
PLANE
0.17 – 0.27
(.007 – .011)
TYP
0.50
(.0197)
BSC
0.127 ± 0.076
(.005 ± .003)
MSOP (MS) 0603
NOTE:
1. DIMENSIONS IN MILLIMETER/(INCH)
2. DRAWING NOT TO SCALE
3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS.
MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.152mm (.006") PER SIDE
4. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS.
INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.152mm (.006") PER SIDE
5. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.102mm (.004") MAX
3401fb
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
LTC3401
U
TYPICAL APPLICATIO
Triple Output Converter
D2
D3
D4
D5
8V
2mA
0.1μF
R3
1M
3
10
+
2
2
CELLS
6
C1
4.7μF
1
LTC3401
VIN
SHDN
SW
VOUT
MODE/SYNC FB
PGOOD
Rt
0.1μF
4.7μF
D1
L1, 4.7μH
VIN =1.8V TO 3V
0.1μF
VC
GND
4
R2
909k
7
8
C2
22μF
9
5
C3
470pF
R5
82k
Rt
30k
0 = FIXED FREQ
1 = Burst Mode OPERATION
VOUT
3.3V
500mA
R1
549k
C4
4.7pF
0.1μF
D6
C1: TAIYO YUDEN JMK212BJ475MG
C2: TAIYO YUDEN JMK325BJ226MM
D1: ON SEMICONDUCTOR MBRM120T3
D2 TO D7: ZETEX FMND7000 DUAL DIODE
L1: SUMIDA CD43-4R7M
4.7μF
D7
–2.5V
1mA
3401 TA09
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
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1.2MHz Step-Up DC/DC Converter
VIN = 0.85V to 5.5V, Up to 92% Efficiency Synchronizable
Oscillator from 100kHz to 1.2MHz, ThinSOTTM Package
LTC3402
Single Cell, High Current (2A) Micropower, Synchronous
3MHz Step-Up DC/DC Converter
VIN = 0.5V to 5.5V, Up to 97% Efficiency Synchronizable
Oscillator from 100kHz to 3MHz, 10-Lead MSOP Package
LTC3423
Single Cell, High Current (2A) Micropower, Synchronous
3MHz Step-Up DC/DC Converter for VOUT < 2.6V
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ThinSOT is a trademark of Linear Technology Corporation.
3401fb
16
Linear Technology Corporation
LT 0607 REV B • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507
●
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