LTC3429/LTC3429B
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■
MP3 Players
■
Digital Cameras
■
LCD Bias Supplies
■
Handheld Instruments
■
Wireless Handsets
■
GPS Receivers
600mA, 500kHz Micropower
Synchronous Boost Converter
with Output Disconnect
Figure 1. 2-Cell to 3.3V Synchronous Boost Converter
SW
4.7µH
V
OUT
LTC3429
FB
V
IN
SHDN
3429 F01a
1.02M
604k
10µF
4.7µF
2-CELL
AA
+
V
OUT
3.3V
250mA
GND
OFF ON
2-Cell to 3.3V Efficiency
OUTPUT CURRENT (mA)
60
EFFICIENCY (%)
80
100
50
70
90
0.1 10 100 1000
3429 F01b
40
1
V
IN
= 3V
V
IN
= 3V
V
IN
= 2.4V
V
IN
= 2.4V
0.01
POWER LOSS (W)
1
100
0.001
0.1
10
0.0001
EFFICIENCY
POWER LOSS
■
Up to 96% Efficiency
■
True Output Load Disconnect
■
Inrush Current Limiting and Internal Soft-Start
■
Low Voltage Start-Up: 0.85V
■
Automatic Burst Mode
®
Operation with I
Q
~ 20µA
■
Continuous Switching at Light Loads (LTC3429B)
■
Internal Synchronous Rectifier
■
Current Mode Control with Internal Compensation
■
Short-Circuit Protection
■
500kHz Fixed Frequency Switching
■
Input Range: 0.5V to 4.4V
■
Output Range: 2.5V to 4.3V (Up to 5V with Schottky)
■
Shutdown Current: <1µA
■
Antiringing Control Minimizes EMI
■
Tiny External Components
■
Low Profile (1mm) SOT-23 Package
FEATURES
DESCRIPTIO
U
APPLICATIO S
U
TYPICAL APPLICATIO
U
The LTC
®
3429/LTC3429B are high efficiency synchro-
nous, fixed frequency, step-up DC/DC converters with true
output load disconnect, inrush current limiting and soft-
start in a low profile 6-lead ThinSOT
TM
package. These
devices are capable of supplying 100mA from a single AA
cell input or 250mA from a 2-cell AA with a 3.3V output.
A switching frequency of 500kHz minimizes overall solu-
tion footprint by allowing the use of tiny, low profile
inductors and ceramic capacitors. Current mode PWM
control with internal compensation reduces external parts
count thereby saving critical board real estate. The LTC3429
shifts automatically to power saving Burst Mode operation
at light loads while the LTC3429B features continuous
switching at light loads. Antiringing control circuitry re-
duces EMI concerns by damping the inductor in discon-
tinuous mode.
The devices also feature low shutdown current of under
1µA. The true output disconnect feature allows the output
to be completely discharged in shutdown. It also limits the
inrush of current during start-up, minimizing surge cur-
rents seen by the input supply.
, LTC and LT are registered trademarks of Linear Technology Corporation. All other
trademarks are the property of their respective owners. Burst Mode is a registered
trademark of Linear Technology Corporation. ThinSOT is a trademark of Linear Technology
Corporation.
LTC3429/LTC3429B
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V
IN
Voltage .............................................. –0.3V to 4.4V
SW Voltage ................................................. – 0.3V to 6V
SHDN, FB Voltage ....................................... – 0.3V to 6V
V
OUT
........................................................... – 0.3V to 6V
Operating Temperature Range (Note 2) .. – 40°C to 85°C
Storage Temperature Range ................... –65°C to 150°
Lead Temperature (Soldering, 10 sec).................. 300°C
ORDER PART
NUMBER
S6 PART MARKING
T
JMAX
= 125°C, θ
JC
= 102°C/W LTH5
LTBMS
LTC3429ES6
LTC3429BES6
(Note 1)
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2: The LTC3429ES6/LTC3429BES6 are 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.
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VIN = 1.2V, VOUT = 3.3V, unless otherwise specified.
PARAMETER CONDITIONS MIN TYP MAX UNITS
Minimum Start-Up Voltage I
LOAD
= 1mA, V
OUT
= 0V 0.85 1 V
Minimum Operating Voltage SHDN = V
IN
(Note 3) 0.5 0.65 V
Output Voltage Adjust Range (Note 5) 2.5 5 V
Feedback Voltage ●1.192 1.230 1.268 V
Feedback Input Current V
FB
= 1.25V 1 50 nA
Quiescent Current (Burst Mode Operation) V
FB
= 1.4V (Note 4) 20 30 µA
Quiescent Current (Shutdown) V
SHDN
= 0V, Not Including Switch Leakage, V
OUT
= 0V 0.01 1 µA
Quiescent Current (Active) Measured on V
OUT
, Nonswitching 380 550 µA
NMOS Switch Leakage V
SW
= 5V 0.1 5 µA
PMOS Switch Leakage V
SW
= 5V, V
OUT
= 0V 0.1 5 µA
NMOS Switch On Resistance 0.35 Ω
PMOS Switch On Resistance 0.45 Ω
NMOS Current Limit 600 850 mA
Burst Mode Operation Current Threshold L = 4.7µH (LTC3429 Only) 1.25 mA
Current Limit Delay to Output 40 ns
Max Duty Cycle V
FB
= 1.15V ●80 90 %
Switching Frequency ●380 500 620 kHz
SHDN Input High 1V
SHDN Input Low 0.35 V
SHDN Input Current V
SHDN
= 5.5V 0.01 1 µA
Soft-Start Time SHDN to 90% of V
OUT
2.5 ms
ABSOLUTE AXI U RATI GS
WWWU
PACKAGE/ORDER I FOR ATIO
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W
ELECTRICAL CHARACTERISTICS
Note 3: Minimum V
IN
operation after start-up is only limited by the
battery’s ability to provide the necessary power as it enters a deeply
discharged state.
Note 4: Burst Mode operation I
Q
is measured at V
OUT
. Multiply this value
by V
OUT
/V
IN
to get the equivalent input (battery) current.
Note 5: For applications where V
OUT
> 4.3V, an external Schottky diode is
required. See the Applications Information.
SW 1
GND 2
FB 3
6 V
IN
5 V
OUT
4 SHDN
TOP VIEW
S6 PACKAGE
6-LEAD PLASTIC TSOT-23
Consult LTC Marketing for parts specified with wider operating temperature ranges.
LTC3429/LTC3429B
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TYPICAL PERFOR A CE CHARACTERISTICS
UW
Single-Cell to 3.3V Efficiency
(LTC3429 Only)
OUTPUT CURRENT (mA)
60
EFFICIENCY (%)
80
100
50
70
90
0.1 10 100 1000
3429 G01
40
0.01
POWER LOSS (W)
1
100
0.001
0.1
10
0.0001
1
V
IN
= 1.5V
EFFICIENCY
POWER LOSS
V
IN
= 1.5V
V
IN
= 1.2V
V
IN
= 1.2V
OUTPUT CURRENT (mA)
60
80
100
50
70
90
0.1 10 100 1000
3429 G02
40
1
V
IN
= 3V
V
IN
= 3V
V
IN
= 2.4V
V
IN
= 2.4V
EFFICIENCY (%)
0.01
POWER LOSS (W)
1
100
0.001
0.1
10
0.0001
EFFICIENCY
POWER LOSS
OUTPUT CURRENT (mA)
60
80
100
50
70
90
0.1 10 100 1000
3429 G03
40
1
V
IN
= 3V
V
IN
= 3V
V
IN
= 2.4V
V
IN
= 2.4V
0.01
POWER LOSS (W)
1
100
0.001
0.1
10
0.0001
EFFICIENCY
POWER LOSS
EFFICIENCY (%)
2-Cell to 3.3V Efficiency
(LTC3429 Only)
2-Cell to 5V Efficiency
(LTC3429 Only)
(TA = 25°C unless otherwise specified)
Li-Ion to 5V Efficiency
(LTC3429 Only)
Efficiency vs Input Voltage
Burst Mode Output Current
Threshold vs Input Voltage
(LTC3429 Only)
OUTPUT CURRENT (mA)
60
80
100
50
70
90
0.1 10 100 1000
3429 G04
40
1
V
IN
= 3.6V
V
IN
= 3.6V
V
IN
= 4.2V
V
IN
= 4.2V
EFFICIENCY
POWER LOSS
0.01
POWER LOSS (W)
1
100
0.001
0.1
10
0.0001
EFFICIENCY (%)
INPUT VOLTAGE (V)
0.5
40
EFFICIENCY (%)
50
60
70
80
90
100
1.5 2.5 3.5 4.5
3429 G05
V
IN
> V
OUT
PMOS LDO
MODE
V
OUT
= 3.3V
I
OUT
= 50mA
INPUT VOLTAGE (V)
0.9
20
25
35
2.4 3.4
3429 G06
15
10
1.4 1.9 2.9 3.9 4.4
5
0
30
OUTPUT CURRENT (mA)
V
OUT
= 3.3V
L = 4.7µH
V
OUT
= 5V
No Load Input Current
vs Input Voltage (LTC3429 Only)
Maximum Load Current
Capability at Output 4% Below
Regulation Point
Minimum Start-Up Input Voltage
vs Load Current
INPUT VOLTAGE (V)
1.4
10
100
1000
2.4
3429 G07
INPUT CURRENT (µA)
0.9 4.41.9 2.9 3.4 3.9
VOUT = 3.3V
L = 4.7µH
VOUT = 5V
INPUT VOLTAGE (V)
0.5
0
OUTPUT CURRENT (mA)
100
200
300
400
1.5 2.5 3.5 4.5
3429 G08
500
600
12 34
V
OUT
= 3.3V
L = 4.7µH
V
OUT
= 5V
OUTPUT CURRENT (mA)
0
0.7
INPUT VOLTAGE (V)
0.9
1.1
1.3
1.5
1.9
50 100
3429 G09
150
1.7 CURRENT
SINK LOAD
RESISTOR
LOAD
LTC3429/LTC3429B
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TYPICAL PERFOR A CE CHARACTERISTICS
UW
Output Voltage vs Temperature
Normalized Oscillator Frequency
vs Temperature
Burst Mode Quiescent Current
vs Temperature (LTC3429 Only)
(TA = 25°C unless otherwise specified)
TEMPERATURE (°C)
–60
V
OUT
(V)
3.32
3.36
3.40
60
3429 G10
3.28
3.24
–29 20
–40 80
0 40 100
3.20
3.16
3.44 V
IN
= 1.5V
I
OUT
= 30mA
TEMPERATURE (°C)
–60
0.92
NORMALIZED FREQUECY
0.94
0.98
1.00
1.02
–20 20 40
3429 G11
0.96
–40 0 60 80 100
TEMPERATURE (°C)
–60
QUIESCENT CURRENT (µA)
20
30
100
3429 G12
10
0–20 20 60
–40 040 80
40
15
25
5
35
V
OUT
= 5V
V
OUT
= 3.3V
SW Pin Fixed Frequency
Continuous Mode Operation
SW Pin Discontinuous Mode
Antiringing Operation
Fixed Frequency and Burst Mode
Operation (LTC3429 Only)
Output Voltage Transient
Response
Inrush Current Control
and Soft-Start
Inrush Current Control
and Soft-Start
V
SW
1V/DIV
V
IN
= 1.5V
V
OUT
= 3.3V
I
OUT
= 50mA
L = 10µH
C
OUT
= 10µF
C
PL
= 150pF
200ns/DIV
3429 G13
V
SW
1V/DIV
V
IN
= 1.5V
V
OUT
= 3.3V
I
OUT
= 20mA
L = 10µH
C
OUT
= 10µF
C
PL
= 150pF
200ns/DIV
3429 G14
V
OUT
100mV/DIV
AC-COUPLED
50mA
120µA
I
OUT
V
IN
= 1.5V
V
OUT
= 3.3V
I
OUT
= 120µA TO 50mA STEP
L = 10µH
C
OUT
= 10µF
C
PL
= 150pF
5ms/DIV 3429 G15
V
OUT
100mV/DIV
AC-COUPLED
90mA
40mA
I
OUT
V
IN
= 1.5V
V
OUT
= 3.3V
I
OUT
= 40mA TO 90mA STEP
L = 10µH
C
OUT
= 10µF
C
PL
= 150pF
100µs/DIV
3429 G16
V
OUT
1V/DIV
INDUCTOR
CURRENT
100mA/DIV
V
IN
= 1.5V
V
OUT
= 3.3V
I
OUT
= 10mA
L = 4.7µH
C
OUT
= 10µF
C
PL
= 100pF
500µs/DIV 3429 G17
VOUT
2V/DIV
INDUCTOR
CURRENT
200mA/DIV
VIN = 2.5V
VOUT = 5V
IOUT = 50mA
L = 4.7µH
COUT = 10µF
CPL = 100pF
2ms/DIV
3429 G18
LTC3429/LTC3429B
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PI FU CTIO S
SW (Pin 1): Switch Pin. Connect inductor between SW
and V
IN
. Keep these PCB trace lengths as short and wide
as possible to reduce EMI and voltage overshoot. If the
inductor current falls to zero, or SHDN is low, an internal
150Ω antiringing switch is connected from SW to V
IN
to
minimize EMI.
GND (Pin 2): Signal and Power Ground. Provide a short
direct PCB path between GND and the (–) side of the output
capacitor(s).
FB (Pin 3): Feedback Input to the g
m
Error Amplifier.
Connect resistor divider tap to this pin. The output voltage
can be adjusted from 2.5V to 5V by:
V
OUT
= 1.23V • [1 + (R1/R2)]
SHDN (Pin 4): Logic Controlled Shutdown Input.
SHDN = High: Normal free running operation, 500kHz
typical operating frequency.
SHDN = Low: Shutdown, quiescent current <1µA.
Output capacitor can be completely discharged through
the load or feedback resistors. A 150Ω resistor is
internally connected between SW and V
IN
.
V
OUT
(Pin 5): Output Voltage Sense Input and Drain of the
Internal Synchronous Rectifier MOSFET. Bias is derived
from V
OUT
. PCB trace length from V
OUT
to the output filter
capacitor(s) should be as short and wide as possible. V
OUT
is completely disconnected from V
IN
when SHDN is low
due to the output disconnect feature.
V
IN
(Pin 6): Battery Input Voltage. The device gets its
start-up bias from V
IN
. Once V
OUT
exceeds V
IN
, bias
comes from V
OUT
. Thus, once started, operation is com-
pletely independent from V
IN
. Operation is only limited by
the output power level and the battery’s internal series
resistance.
1.23V
REF
Burst Mode
OPERATION
CONTROL
SHUTDOWN
CONTROL
SLOPE
COMP
PWM
CONTROL
START-UP
OSC MUX
A
B
A/B
RAMP
GEN
500kHz
FB
3429 BD
3
V
OUT
V
IN
L1
5
SW
0.45Ω
WELL
SWITCH
1
V
IN
1V TO 4.4V 6
SHDN
4GND
2
–
+
g
m
ERROR
AMP
–
+
V
OUT
GOOD
–
–
+
PWM
COMPARATOR
R
C
80k
SHUTDOWN
C
C
150pF
C
P2
2.5pF
R2
R1
SLEEP
Σ
SYNC
DRIVE
CONTROL 0.35Ω
2.3V
C
OUT
C
PL
(OPTIONAL)
2.5V TO 5V
C
IN
+
CURRENT
SENSE
BLOCK DIAGRA
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LTC3429/LTC3429B
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OPERATIO
U
The LTC3429/LTC3429B are 500kHz, synchronous boost
converters housed in a 6-lead SOT-23 package. Able to
operate from an input voltage below 1V, the device fea-
tures fixed frequency, current mode PWM control for
exceptional line and load regulation. Low R
DS(ON)
internal
MOSFET switches enable the device to maintain high
efficiency over a wide range of load current. Detailed
descriptions of the different operating modes follow.
Operation can be best understood by referring to the Block
Diagram.
LOW VOLTAGE START-UP
The LTC3429/LTC3429B include an independent start-up
oscillator designed to start up at input voltages of 0.85V
typically. The frequency and duty cycle of the start-up
oscillator are internally set to 150kHz and 67% respec-
tively. In this mode, the IC operates completely open-loop
and the current limit is also set internally to 850mA. Once
the output voltage exceeds 2.3V, the start-up circuitry is
disabled and normal close-loop PWM operation is initi-
ated. In normal mode, the LTC3429/LTC3429B power
themselves from V
OUT
instead of V
IN
. This allows the
battery voltage to drop to as low as 0.5V without affecting
the circuit operation. The only limiting factor in the appli-
cation becomes the ability of the battery to supply suffi-
cient energy to the output. Soft-start and inrush current
limiting are provided during start-up as well as normal
mode operation.
Soft-Start
The LTC3429/LTC3429B provide soft-start by charging an
internal capacitor with a very weak current source. The
voltage on this capacitor, in turn, slowly ramps the peak
inductor current from zero to a maximum value of 850mA.
The soft-start time is typically 2.5ms, the time it takes to
charge the capacitor from zero to 1.35V. However, this
time varies greatly with load current, output voltage and
input voltage (see Typical Performance Characteristics,
Inrush Current Control and Soft-Start). The soft-start
capacitor is discharged completely in the event of a
commanded shutdown or a thermal shutdown. It is dis-
charged only partially in case of a short circuit at the
output.
LOW NOISE FIXED FREQUENCY OPERATION
Oscillator
The frequency of operation is internally set to 500kHz.
Error Amp
The error amplifier is an internally compensated transcon-
ductance type (current output) with a transconductance
(g
m
) = 33 microsiemens. The internal 1.23V reference
voltage is compared to the voltage at the FB pin to generate
an error signal at the output of the error amplifier. A volt-
age divider from V
OUT
to ground programs the output
voltage via FB from 2.5V to 5V using the equation:
V
OUT
= 1.23V • [1 + (R1/R2)]
Current Sensing
Lossless current sensing converts the NMOS switch
current signal to a voltage to be summed with the internal
slope compensation. The summed signal is compared to
the error amplifier output to provide a peak current
control command for the PWM. Peak switch current is
limited to approximately 850mA independent of input or
output voltage. The switch current signal is blanked for
60ns to enhance noise rejection.
Zero Current Comparator
The zero current comparator monitors the inductor cur-
rent to the output and shuts off the synchronous rectifier
once this current reduces to approximately 27mA. This
prevents the inductor current from reversing in polarity
thereby improving efficiency at light loads.
Antiringing Control
The antiringing control circuitry prevents high frequency
ringing of the SW pin as the inductor current goes to zero
in discontinuous mode. The damping of the resonant
circuit formed by L and C
SW
(capacitance on SW pin) is
achieved by placing a 150Ω resistor across the inductor.
Synchronous Rectifier
To prevent the inductor current from running away, the
PMOS synchronous rectifier is only enabled when V
OUT
>
(V
IN
+ 0.1V) and the FB pin is >0.8V.
LTC3429/LTC3429B
7
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Thermal Shutdown
An internal temperature monitor will start to reduce the
peak current limit if the die temperature exceeds 125°C. If
the die temperature continues to rise and reaches 160°C,
the part will go into thermal shutdown, all switches will be
turned off and the soft-start capacitor will be reset. The
part will be enabled again when the die temperature drops
by about 15°C.
Burst Mode OPERATION (LTC3429 Only)
Portable devices frequently spend extended time in low
power or standby mode, only switching to high power
consumption when specific functions are enabled. To
improve battery life in these types of products, it is
important to maintain a high power conversion efficiency
over a wide output power range. The LTC3429 provides
automatic Burst Mode operation to increase efficiency of
the power converter at light loads. Burst Mode operation
is initiated if the output load current falls below an inter-
nally programmed threshold. This threshold has an in-
verse dependence on the duty cycle of the converter and
also the value of the external inductor (See Typical Perfor-
mance Characteristics, Output Current Burst Mode Thresh-
old vs V
IN
). Once Burst Mode operation is initiated, only
the circuitry required to monitor the output is kept alive
and the rest of the device is turned off. This is referred to
as the sleep state in which the IC consumes only 20µA
from the output capacitor. When the output voltage droops
by about 1% from its nominal value, the part wakes up and
commences normal PWM operation. The output capacitor
recharges and causes the part to re-enter the sleep state
if the output load remains less than the Burst Mode
threshold. The frequency of this intermittent PWM or
burst operation depends on the load current; that is, as the
load current drops further below the burst threshold, the
LTC3429 turns on less frequently. When the load current
increases above the burst threshold, the LTC3429
seamlessly resumes continuous PWM operation. Thus,
Burst Mode operation maximizes the efficiency at very
light loads by minimizing switching and quiescent losses.
However, the output ripple typically increases to about 2%
peak-to-peak. Burst Mode ripple can be reduced, in some
circumstances, by placing a small phase-lead capacitor
(C
PL
) between V
OUT
and FB pins (refer to the Block
Diagram). However, this may adversely affect the effi-
ciency and the quiescent current requirement at light
loads. Typical values of C
PL
range from 15pF to 220pF.
OUTPUT DISCONNECT AND INRUSH LIMITING
The LTC3429/LTC3429B are designed to allow true output
disconnect by eliminating body diode conduction of the
internal PMOS rectifier. This allows V
OUT
to go to zero
volts during shutdown, drawing zero current from the
input source. It also allows for inrush current limiting at
start-up, minimizing surge currents seen by the input
supply. Note that to obtain the advantage of output discon-
nect, there must not be an external Schottky diode con-
nected between the SWITCH pin and V
OUT
.
Board layout is extremely critical to minimize voltage
overshoot on the SWITCH pin due to stray inductance.
Keep the output filter capacitor as close as possible to the
V
OUT
pin and use very low ESR/ESL ceramic capacitors
tied to a good ground plane. For applications with V
OUT
over 4.3V, a Schottky diode is required to limit the peak
SWITCH voltage to less than 6V unless some form of
external snubbing is employed. This diode must also be
placed very close to the pins to minimize stray inductance.
See the Applications Information.
SHORT CIRCUIT PROTECTION
Unlike most boost converters, the LTC3429/LTC3429B
allow their output to be short circuited due to the output dis-
connect feature. The devices incorporate internal features
such as current limit foldback, thermal regulation and ther-
mal shutdown for protection from an excessive overload
or short circuit. In the event of a short circuit, the internal
soft-start capacitor gets partially discharged. This, in turn,
causes the maximum current limit to foldback to a smaller
value. In addition to this, a thermal regulation circuit starts
to dial back the current limit farther if the die temperature
rises above 125°C. If the die temperature still reaches
160°C, the device shuts off entirely.
V
IN
> V
OUT
OPERATION
The LTC3429/LTC3429B will maintain voltage regulation
even if the input voltage is above the output voltage. This
OPERATIO
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LTC3429/LTC3429B
8
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APPLICATIO S I FOR ATIO
WUUU
is achieved by terminating the switching of the synchro-
nous PMOS and applying V
IN
statically on its gate. This
ensures that the slope of the inductor current will reverse
during the time current is flowing to the output. Since the
PMOS no longer acts as a low impedance switch in this
mode, there will be more power dissipation within the IC.
This will cause a sharp drop in the efficiency (see Typical
Performance Characteristics, Efficiency vs V
IN
). The maxi-
mum output current should be limited in order to maintain
an acceptable junction temperature.
OPERATIO
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PCB LAYOUT GUIDELINES
The high speed operation of the LTC3429/LTC3429B
demands careful attention to board layout. You will not get
advertised performance with careless layout. Figure 2
shows the recommended component placement. A large
ground pin copper area will help to lower the chip tempera-
ture. A multilayer board with a separate ground plane is
ideal, but not absolutely necessary.
inductor ripple current. Increasing the inductance above
10µH will increase size while providing little improvement
in output current capability.
The approximate output current capability of the LTC3429
versus inductance value is given in the equation below and
illustrated graphically in Figure 3.
II
VD
fL D
OUT MAX P IN
()
•– •
•• •–=⎛
⎝
⎜⎞
⎠
⎟
()
η21
where:
η = estimated efficiency
I
P
= peak current limit value (0.6A)
V
IN
= input (battery) voltage
D = steady-state duty ratio = (V
OUT
– V
IN
)/V
OUT
f = switching frequency (500kHz typical)
L = inductance value
INDUCTANCE (µH)
3
OUTPUT CURRENT (mA)
120
160
200
19
3429 F03
80
40
100
140
180
60
20
075 119 15 17 21
13 23
V
IN
= 1.2V
V
OUT
= 3.3V
V
OUT
= 5V
Figure 3. Maximum Output Current vs
Inductance Based on 90% Efficiency
SW
GND
FB
1
2
3
6
5
4
V
IN
V
OUT
SHDN SHDN
3429 F02
V
OUT
V
IN
RECOMMENDED COMPONENT PLACEMENT. TRACES
CARRYING HIGH CURRENT ARE DIRECT. TRACE AREA AT
FB PIN IS SMALL. LEAD LENGTH TO BATTERY IS SHORT
Figure 2. Recommended Component Placement
for Single Layer Board
COMPONENT SELECTION
Inductor Selection
The
LTC3429/LTC3429B
can utilize small surface mount
and chip inductors due to its fast 500kHz switching
frequency.
Typically, a 4.7µH inductor is recommended
for most applications. Larger values of inductance will
allow greater output current capability by reducing the
LTC3429/LTC3429B
9
3429fa
The inductor current ripple is typically set for 20% to 40%
of the maximum inductor current (IP). High frequency
ferrite core inductor materials reduce frequency
depen
dent power losses compared to cheaper powdered
iron types, improving efficiency. The inductor should have
low ESR (series resistance of the windings) to reduce the
I
2
R power losses, and must be able to handle the peak
inductor current without saturating. Molded chokes and
some chip inductors usually do not have enough core to
support the peak inductor currents of 850mA seen on the
LTC3429/LTC3429B. To minimize radiated noise, use a
toroid, pot core or shielded bobbin inductor. See Table 1
for some suggested components and suppliers.
Table 1. Recommended Inductors
MAX
L DCR HEIGHT
PART (µH) mΩ(mm) VENDOR
CDRH5D18-4R1 4.1 57 2.0 Sumida
CDRH5D18-100 10 124 2.0 www.sumida.com
CDRH3D16-4R7 4.7 105 1.8
CDRH3D16-6R8 170 1.8
CR43-4R7 4.7 109 3.5
CR43-100 10 182 3.5
CMD4D06-4R7MC 4.7 216 0.8
CMD4D06-3R3MC 3.3 174 0.8
DS1608-472 4.7 60 2.9 Coilcraft
DS1608-103 10 75 2.9 www.coilcraft.com
DO1608C-472 4.7 90 2.9
D52LC-4R7M 4.7 84 2.0 Toko
D52LC-100M 10 137 2.0 www.tokoam.com
LQH32CN4R7M24 4.7 195 2.2 Murata
www.murata.com
Output and Input Capacitor Selection
Low ESR (equivalent series resistance) capacitors should
be used to minimize the output voltage ripple. Multilayer
ceramic capacitors are an excellent choice as they have
extremely low ESR and are available in small footprints. A
4.7µF to 15µF output capacitor is sufficient for most
applications. Larger values up to 22µF may be used to
obtain extremely low output voltage ripple and improve
transient response. An additional phase lead capacitor
may be required with output capacitors larger than 10µF
to maintain acceptable phase margin. X5R and X7R
dielectric materials are preferred for their ability to main-
tain capacitance over wide voltage and temperature ranges.
Low ESR input capacitors reduce input switching noise
and reduce the peak current drawn from the battery. It
follows that ceramic capacitors are also a good choice for
input decoupling and should be located as close as pos-
sible to the device. A 10µF input capacitor is sufficient for
virtually any application. Larger values may be used with-
out limitations. Table 2 shows a list of several ceramic
capacitor manufacturers. Consult the manufacturers di-
rectly for detailed information on their entire selection of
ceramic capacitors.
Table 2. Capacitor Vendor Information
SUPPLIER WEBSITE
AVX www.avxcorp.com
Murata www.murata.com
Taiyo Yuden www.t-yuden.com
APPLICATIO S I FOR ATIO
WUUU
LTC3429/LTC3429B
10
3429fa
TYPICAL APPLICATIO S
U
Applications Where V
OUT
> 4.3V
When the output voltage is programmed above 4.3V, it is
necessary to add a Schottky diode either from SW to V
OUT
,
or to add a snubber network in order to maintain an
acceptable peak voltage on the SW pin. The Schottky diode
between SW and V
OUT
will provide a peak efficiency
improvement but will negate the output disconnect fea-
ture. If output disconnect is required, an active snubber
network is suggested as shown below. Examples of Schot-
tky diodes are: MBR0520L, PMEG2010EA, 1N5817 or
equivalent.
Application Circuit for VOUT > 4.3V Where Inrush Current Limiting and Output Disconnect are Required
SW
L1
4.7µH
VOUT
LTC3429
FB
VIN
VIN
2.7V TO 4.2V
SHDN
2
1
3
3429 TA04
R1
1.82M
R2
604k
C2
10µF
C3*
0.22µF
*LOCATE COMPONENTS CLOSE TO THE PIN
C1: TAIYO YUDEN X5R JMK212BJ475MM
C2: TAIYO YUDEN X5R JMK212BJ106MM
D1: MOTOROLA MBR0520L
L1: COILCRAFT D0160C-472
MP1: ZETEX ZXM61P02F
C1
4.7µF
Li-Ion VOUT
5V
250mA
MP1
5
D1*
4
6
GND
OFF ON
+
Application Circuit for VOUT > 4.3V Where Inrush Current Limiting and Output Disconnect are Not Required
SW
L1
4.7µH
V
OUT
LTC3429
FB
V
IN
V
IN
SHDN
2
1
3
5
3429 TA05
R1
1.82M
R2
604k
C2
10µF
C1
4.7µF
2 AA
CELL V
OUT
5V
150mA
D1*
4
6
+
GND
OFF ON
*LOCATE COMPONENTS CLOSE TO THE PIN
C1: TAIYO YUDEN X5R JMK212BJ475MM
C2: TAIYO YUDEN X5R JMK212BJ106MM
D1: MOTOROLA MBR0520L
L1: COILCRAFT D0160C-472
Li-Ion to 5V Efficiency
OUTPUT CURRENT (mA)
60
EFFICIENCY (%)
80
100
50
70
90
0.1 10 100 1000
3429 TA04b
40
1
V
IN
= 3.6V
V
IN
= 4.2V
V
IN
= 3.6V
V
IN
= 4.2V
POWER LOSS
0.01
POWER LOSS (W)
1
100
0.001
0.1
10
0.0001
EFFICIENCY
OUTPUT CURRENT (mA)
60
EFFICIENCY (%)
80
100
50
70
90
0.1 10 100 1000
3429 TA05b
40
1
V
IN
= 3V
0.01
POWER LOSS (W)
1
100
0.001
0.1
10
0.0001
POWER LOSS
V
IN
= 3V
V
IN
= 2.4V
EFFICIENCY
V
IN
= 2.4V
2-Cell to 5V Efficiency
LTC3429/LTC3429B
11
3429fa
U
PACKAGE DESCRIPTIO
1.50 – 1.75
(NOTE 4)
2.80 BSC
0.30 – 0.45
6 PLCS (NOTE 3)
DATUM ‘A’
0.09 – 0.20
(NOTE 3)
S6 TSOT-23 0302
2.90 BSC
(NOTE 4)
0.95 BSC
1.90 BSC
0.80 – 0.90
1.00 MAX 0.01 – 0.10
0.20 BSC
0.30 – 0.50 REF
PIN ONE ID
NOTE:
1. DIMENSIONS ARE IN MILLIMETERS
2. DRAWING NOT TO SCALE
3. DIMENSIONS ARE INCLUSIVE OF PLATING
4. DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR
5. MOLD FLASH SHALL NOT EXCEED 0.254mm
6. JEDEC PACKAGE REFERENCE IS MO-193
3.85 MAX
0.62
MAX
0.95
REF
RECOMMENDED SOLDER PAD LAYOUT
PER IPC CALCULATOR
1.4 MIN
2.62 REF
1.22 REF
S6 Package
6-Lead Plastic TSOT-23
(Reference LTC DWG # 05-08-1636)
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 represen-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
LTC3429/LTC3429B
12
3429fa
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900
●
FAX: (408) 434-0507
●
www.linear.com
© LINEAR TECHNOLOGY CORPORATION 2004
LT/TP 1104 1K REV A • PRINTED IN USA
Single AA Cell to 2.5V Synchronous Boost Converter
U
TYPICAL APPLICATIO
SW
L1
4.7µH
VOUT
LTC3429
FB
VIN
SHDN
2
1
3
3429 TA03
R1
1.02M
R2
1.02M
C2
10µF
C1
4.7µF
SINGLE
AA CELL VOUT
2.5V
130mA
5
4
6
GND
+
OFF ON
C1: TAIYO YUDEN X5R JMK212BJ475MM
C2: TAIYO YUDEN X5R JMK212BJ106MM
L1: COILCRAFT D0160C-472
PART NUMBER DESCRIPTION COMMENTS
LT1613 550mA (I
SW
), 1.4MHz High Efficiency Step-Up DC/DC 90% Efficiency, V
IN
: 0.9V to 10V, V
OUT(MAX)
= 34V, I
Q
= 3mA, I
SD
< 1µA,
Converter ThinSOT
LT1615/LT1615-1 300mA/80mA (I
SW
), High Efficiency Step-Up V
IN
: 1V to 15V, V
OUT(MAX)
= 34V, I
Q
= 20µA, I
SD
< 1µA, ThinSOT
DC/DC Converters
LT1618 1.5A (I
SW
), 1.25MHz High Efficiency Step-Up DC/DC 90% Efficiency, V
IN
: 1.6V to 18V, V
OUT(MAX)
= 35V, I
Q
= 1.8mA,
Converter I
SD
< 1µA
LTC1700 No R
SENSE
TM, 530kHz, Synchronous Step-Up DC/DC 95% Efficiency, V
IN
: 0.9V to 5V, I
Q
= 200µA, I
SD
< 10µA, MS10
Controller
LT1930/LT1930A 1A (I
SW
), 1.2MHz/2.2MHz, High Efficiency Step-Up High Efficiency, V
IN
: 2.6V to 16V, V
OUT(MAX)
= 34V, I
Q
= 4.2mA/5.5mA,
DC/DC Converters I
SD
< 1µA, ThinSOT
LT1946/LT1946A 1.5A (I
SW
), 1.2MHz/2.7MHz, High Efficiency Step-Up High Efficiency, V
IN
: 2.45V to 16V, V
OUT(MAX)
= 34V, I
Q
= 32mA,
DC/DC Converters I
SD
< 1µA, MS8
LT1961 1.5A (I
SW
), 1.25MHz High Efficiency Step-Up DC/DC 90% Efficiency, V
IN
: 3V to 25V, V
OUT(MAX)
= 35V, I
Q
= 0.9mA, I
SD
< 6µA,
Converter MS8E
LTC3400/LTC3400B 600mA (I
SW
), 1.2MHz, Synchronous Step-Up 92% Efficiency, V
IN
: 0.85V to 5V, V
OUT(MAX)
= 5V, I
Q
= 19µA/300µA,
DC/DC Converters I
SD
< 1µA, ThinSOT
LTC3401/LTC3402 1A/2A (I
SW
), 3MHz, Synchronous Step-Up 97% Efficiency, V
IN
: 0.5V to 5V, V
OUT(MAX)
= 5.5V, I
Q
= 38µA, I
SD
< 1µA,
DC/DC Converters MS10
LTC3421 3A (I
SW
), 3MHz, Synchronous Step-Up DC/DC 95% Efficiency, V
IN
: 0.5V to 4.5V, V
OUT(MAX)
= 5.25V, I
Q
= 12µA,
Converter with Output Disconnect I
SD
< 1µA, QFN24
LTC3425 5A (I
SW
), 8MHz, 4-Phase Synchronous Step-Up DC/DC 95% Efficiency, V
IN
: 0.5V to 4.5V, V
OUT(MAX)
= 5.25V, I
Q
= 12µA,
Converter with Output Disconnect I
SD
< 1µA, QFN32
LT3464 85mA (I
SW
), High Efficiency Step-Up DC/DC Converter V
IN
: 2.3V to 10V, V
OUT(MAX)
= 34V, I
Q
= 25µA, I
SD
< 1µA, ThinSOT
with Integrated Schottky and PNP Disconnect
No R
SENSE
is a trademark of Linear Technology Corporation.
RELATED PARTS
Single AA Cell to 3.3V
SW
L1
4.7µH
V
OUT
LTC3429
FB
V
IN
SHDN
2
3429 TA06
1
3C2
10µF
V
OUT
3.3V
100mA
R1
1.02M
C1
4.7µF
SINGLE
AA CELL 5
4
6
GND
+
OFF ON
R2
604k
C1: TAIYO YUDEN X5R JMK212BJ475MM
C2: TAIYO YUDEN X5R JMK212BJ106MM
L1: COILCRAFT D0160C-472
