LT3494/LT3494A
1
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TYPICAL APPLICATION
FEATURES
APPLICATIONS
DESCRIPTION
Micropower Low Noise
Boost Converters with
Output Disconnect
The LT
®
3494/LT3494A are low noise boost converters
with integrated power switch, Schottky diode and output
disconnect circuitry. The parts use a novel* control tech-
nique resulting in low output voltage ripple as well as high
effi ciency over a wide load current range. This technique
guarantees that the switching frequency stays above the
audio band for the entire load range. The parts feature a high
performance NPN power switch with a 350mA and 180mA
current limit for the LT3494A and LT3494 respectively. The
quiescent current is a low 65μA, which is further reduced
to less than 1μA in shutdown. The internal disconnect
circuitry allows the output voltage to be isolated from the
input during shutdown. An auxiliary reference input (CTRL
pin) overrides the internal 1.225V feedback reference with
any lower value allowing full control of the output voltage
during operation. The LT3494/LT3494A are available in a
tiny 8-lead 3mm × 2mm DFN package.
OLED Power Supply from One Li-Ion Cell
■ Low Quiescent Current
65μA in Active Mode
1μA in Shutdown Mode
■ Switching Frequency is Non-Audible Over Entire
Load Range
■ Integrated Power NPN:
350mA Current Limit (LT3494A)
180mA Current Limit (LT3494)
■ Integrated Schottky Diode
■ Integrated Output Disconnect
■ Integrated Output Dimming
■ Wide Input Range: 2.3V to 16V
■ Wide Output Range: Up to 40V
■ Tiny 8-Lead 3mm × 2mm DFN Package
■ OLED Power
■ Low Noise Power
■ MP3 Players
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
*Patent pending.
SW CAP
VCC
SHDN
CTRL
VOUT
FB
GND
2.21M
3494 TA01a
LT3494
4.7μF
2.2μF
15μH
0.22μF
VIN
3V
TO 4.2V
VOUT
16V
16mA
LOAD CURRENT (mA)
0.1
0
VOUT PEAK-TO-PEAK RIPPLE (mV)
10
15
1 10 100
3494 TA01b
5
LT3494
FIGURE 5 CIRCUIT
100MHz MEASUREMENT BW
LOAD CURRENT (mA)
0.1
60
EFFICIENCY (%)
POWER LOSS (mW)
70
80
90
1 10 100
3494 TA01c
50
40
30
20
160
200
240
280
120
80
40
0
VIN = 3.6V LOAD FROM
CAPACITOR
LOAD FROM
VOUT
Output Voltage Ripple
vs Load Current
Effi ciency and Power Loss
vs Load Current
LT3494/LT3494A
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ELECTRICAL CHARACTERISTICS
PACKAGE/ORDER INFORMATIONABSOLUTE MAXIMUM RATINGS
VCC Voltage ...............................................................16V
SW Voltage ...............................................................40V
CAP Voltage ..............................................................40V
VOUT Voltage .............................................................40V
SHDN Voltage ...........................................................16V
CTRL Voltage ............................................................16V
FB Voltage ................................................................2.5V
Maximum Junction Temperature .......................... 125°C
Operating Temperature Range (Note 2) ... –40°C to 85°C
Storage Temperature Range ................... –65°C to 125°C
(Note 1)
PARAMETER CONDITIONS MIN TYP MAX UNITS
Minimum Operating Voltage 2.3 2.5 V
Maximum Operating Voltage 16 V
Feedback Voltage VCTRL = 3V (Note 3) ●1.205 1.225 1.245 V
FB Resistor ●179 182 184 kΩ
Quiescent Current Not Switching 65 75 μA
Quiescent Current in Shutdown V
⎯
S
⎯
H
⎯
D
⎯
N = 0V, VCC = 3V 0 1 μA
Minimum Switch Off Time After Start-Up Mode, VFB = 1V, VCTRL = 3V (Note 4)
During Start-Up Mode, VFB = 0.2V, VCTRL = 3V (Note 4)
100
450
ns
ns
Maximum Switch Off Time VFB = 1.5V ●15 20 30 μs
Switch Current Limit LT3494A (Note 5)
LT3494 (Note 5)
225
115
350
180
450
250
mA
mA
Switch VCESAT LT3494A, ISW = 200mA
LT3494, ISW = 100mA
180
110
mV
mV
Switch Leakage Current VSW = 5V, V
⎯
S
⎯
H
⎯
D
⎯
N = 0 0.01 1 μA
Schottky Forward Voltage IDIODE = 100mA 900 1100 mV
Schottky Reverse Leakage 0.05 1 μA
PMOS Disconnect VCAP – VOUT IOUT = 10mA, VCAP = 5V 250 mV
SHDN Input Voltage High 1.5 V
SHDN Input Voltage Low 0.3 V
SHDN Pin Bias Current VSHDN = 3V
VSHDN = 0V
5
0
10
0.1
μA
μA
TOP VIEW
9
DDB PACKAGE
8-LEAD (3mm × 2mm) PLASTIC DFN
5
6
7
8
4
3
2
1SW
GND
VCC
CTRL
CAP
VOUT
FB
SHDN
TJMAX = 125°C, θJA = 76°C/W
EXPOSED PAD (PIN 9) IS GND, MUST BE SOLDERED TO PCB
ORDER PART NUMBER DDB PART MARKING
LT3494EDDB
LT3494AEDDB
LCCD
LCRW
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/
Consult LTC Marketing for parts specifi ed with wider operating temperature ranges.
The ● denotes the specifi cations which apply over the full operating
temperature range, otherwise specifi cations are at TA = 25°C. VCC = 3V, VSHDN = VCC, unless otherwise noted. (Note 2)
LT3494/LT3494A
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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 LT3494/LT3494A are guaranteed to meet performance
specifi cations from 0°C to 85°C. Specifi cations over the –40°C to 85°C
operating temperature range are assured by design, characterization and
correlation with statistical process controls.
PARAMETER CONDITIONS MIN TYP MAX UNITS
CTRL Pin Bias Current VCTRL = 0.5V, Current Flows Out of Pin ●20 100 nA
CTRL to FB Offset VCTRL = 0.5V 8 15 mV
Maximum Shunt Current VFB = 1.3V, VCAP = 5V 230 μA
Note 3: Internal reference voltage is determined by fi nding VFB voltage
level which causes quiescent current to increase 20μA above “Not
Switching” level.
Note 4: If CTRL is overriding the internal reference, Start-Up mode occurs
when VFB is less then half the voltage on CTRL. If CTRL is not overriding
the internal reference, Start-Up mode occurs when VFB is less then half the
voltage of the internal reference.
Note 5: Current limit guaranteed by design and/or correlation to static test.
ELECTRICAL CHARACTERISTICS
The ● denotes the specifi cations which apply over the full operating
temperature range, otherwise specifi cations are at TA = 25°C. VCC = 3V, VSHDN = VCC, unless otherwise noted. (Note 2)
TYPICAL PERFORMANCE CHARACTERISTICS
Switching Frequency
vs Load Currrent Load Regulation VOUT vs CTRL Voltage
LOAD CURRENT (mA)
0.1
800
SWITCHING FREQUENCY (kHz)
1000
1200
1400
1 10 100
3494 G01
600
400
200
0
LT3494
FIGURE 5 CIRCUIT
VCC = 3.6V
VOUT = 16V
LOAD CURRENT (mA)
0
VOUT VOLTAGE CHANGE (%)
0
1.0
40
3494 G02
–1.0
–2.0 10 20 30
515 25 35
2.0
–0.5
0.5
–1.5
1.5
LT3494
FIGURE 5 CIRCUIT
VCC = 3.6V
VOUT = 16V
CTRL VOLTAGE (V)
0.1
0
VOUT VOLTAGE (V)
5
10
15
20
0.3 0.5 0.7 0.9
3494 G03
1.1 1.3 1.5
LT3494
FIGURE 5 CIRCUIT
VCC = 3.6V
VOUT = 16V
LOAD CURRENT = 1mA
TA = 25°C unless otherwise noted.
LT3494/LT3494A
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Output Voltage vs Temperature Minimum Switching Frequency Quiescent Current–Not Switching
SHDN Current vs SHDN Voltage Peak Inductor Current (LT3494)
TEMPERATURE (°C)
–40
OUTPUT VOLTAGE CHANGE (%)
0
1.0
120
3494 G04
–1.0
–2.0 040 80
–20 20 60 100
2.0
–0.5
0.5
–1.5
1.5
LT3494
FIGURE 5 CIRCUIT
TEMPERATURE (°C)
–40
SWITCHING FREQUENCY (kHz)
49.0
50.0
120
3494 G05
48.0
47.0 040 80
–20 20 60 100
51.0
48.5
49.5
47.5
50.5
VCC = 3.6V
NO LOAD
VCC (V)
3
50
IVCC (μA)
55
65
70
75
100
85
578
3494 G06
60
90
95
80
46910
SHDN PIN VOLTAGE (V)
0
0
SHDN PIN CURRENT (μA)
5
10
15
20
2468
3494 G07
10 12 14 16
Peak Inductor Current (LT3494A)
TEMPERATURE (°C)
–40
100
PEAK INDUCTOR CURRENT (mA)
150
200
250
300
04080 120
3494 G08
350
400
–20 20 60 100
FIGURE 5 CIRCUIT
VCC = 3.6V
VOUT = 16V
LT3494 Switching Waveforms at
No Load
VOUT
10mV/DIV
AC
COUPLED
SW
VOLTAGE
10V/DIV
VCC = 3.6V
VOUT = 16V
INDUCTOR
CURRENT
50mA/DIV
5μs/DIV 3494 G10
FIGURE 5 CIRCUIT
VOUT
10mV/DIV
AC
COUPLED
SW
VOLTAGE
10V/DIV
INDUCTOR
CURRENT
100mA/DIV
2μs/DIV 3494 G11
FIGURE 5 CIRCUIT
VCC = 3.6V
VOUT = 16V
VOUT
10mV/DIV
AC
COUPLED
SW
VOLTAGE
10V/DIV
INDUCTOR
CURRENT
100mA/DIV
500ns/DIV 3494 G12
FIGURE 5 CIRCUIT
VCC = 3.6V
VOUT = 16V
LT3494 Switching Waveforms at
1mA Load
LT3494 Switching Waveforms at
25mA Load
TEMPERATURE (°C)
–40
400
PEAK INDUCTOR CURRENT (mA)
450
500
550
600
04080 120
3494 G09
650
700
–20 20 60 100
FIGURE 6 CIRCUIT
VCC = 3.6V
VOUT = 16V
TYPICAL PERFORMANCE CHARACTERISTICS
TA = 25°C unless otherwise noted.
LT3494/LT3494A
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LT3494A Switching Waveforms at
No Load
LT3494A Switching Waveforms at
5mA Load
LT3494A Switching Waveforms at
30mA Load
LT3494 Start-Up Waveforms LT3494 Transient Response LT3494A Transient Response
CAP
VOLTAGE
5V/DIV
VOUT
VOLTAGE
5V/DIV
INDUCTOR
CURRENT
100mA/DIV
200μs/DIV 3494 G16
FIGURE 5 CIRCUIT
VCC = 3.6V
VOUT = 16V
VOUT
VOLTAGE
50mV/DIV
AC COUPLED
INDUCTOR
CURRENT
100mA/DIV
100μs/DIV 3494 G17
FIGURE 5 CIRCUIT
10mA→15mA→10mA LOAD PULSE
VCC = 3.6V
VOUT = 16V
VOUT
10mV/DIV
AC
COUPLED
SW
VOLTAGE
10V/DIV
INDUCTOR
CURRENT
50mA/DIV
5
m
s/DIV 3494 G13
FIGURE 6 CIRCUIT
VCC = 3.6V
VOUT = 16V
VOUT
10mV/DIV
AC
COUPLED
SW
VOLTAGE
10V/DIV
INDUCTOR
CURRENT
100mA/DIV
2
m
s/DIVVCC = 3.6V
VOUT = 16V
3494 G14
FIGURE 6 CIRCUIT VOUT
10mV/DIV
AC
COUPLED
SW
VOLTAGE
10V/DIV
INDUCTOR
CURRENT
200mA/DIV
500ns/DIVVCC = 3.6V
VOUT = 16V
3494 G15
FIGURE 6 CIRCUIT
VOUT
50mV/DIV
AC
COUPLED
INDUCTOR
CURRENT
200mA/DIV
100μs/DIVVCC = 3.6V
VOUT = 16V
3494 G18
FIGURE 6 CIRCUIT
15mA→30mA→15mA LOAD PULSE
TYPICAL PERFORMANCE CHARACTERISTICS
TA = 25°C unless otherwise noted.
LT3494/LT3494A
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BLOCK DIAGRAM
PIN FUNCTIONS
SW (Pin 1): Switch Pin. This is the collector of the internal
NPN power switch. Minimize the metal trace area connected
to this pin to minimize EMI.
GND (Pin 2): Ground. Tie directly to local ground plane.
VCC (Pin 3): Input Supply Pin. Must be locally
bypassed.
CTRL (Pin 4): Dimming Pin. If not used, tie CTRL to 1.5V
or higher. If in use, drive CTRL below 1.225V to override
the internal reference. See Applications Information for
more information.
SHDN (Pin 5): Shutdown Pin. Tie to 1.5V or more to
enable device. Ground to shut down.
FB (Pin 6): Feedback Pin. Reference voltage is 1.225V.
There is an internal 182k resistor from the FB pin to GND.
To achieve the desired output voltage, choose R1 accord-
ing to the following formula:
RVk
OUT MAX
1 182 1 225 1=⎛
⎝
⎜⎞
⎠
⎟
•.–
() Ω
VOUT (Pin 7): Drain of Output Disconnect PMOS. Place a
bypass capacitor from this pin to GND. See Applications
Information.
CAP (Pin 8): This is the cathode of the internal Schottky
diode. Place a bypass capacitor from this pin to GND.
Exposed Pad (Pin 9): Ground. This pin must be soldered
to PCB.
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LT3494/LT3494A
7
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OPERATION
The LT3494/LT3494A use a novel control scheme to pro-
vide high effi ciency over a wide range of output current.
In addition, this technique keeps the switching frequency
above the audio band over all load conditions.
The operation of the part can be better understood by
refering to the Block Diagram. The part senses the output
voltage by monitoring the voltage on the FB pin. The user
sets the desired output voltage by choosing the value of
the external top feedback resistor. The parts incorporate
a precision 182k bottom feedback resistor. Assuming that
output voltage adjustment is not used (CTRL pin is tied to
1.5V or greater), the internal reference (VREF = 1.225V) sets
the voltage at which FB will servo to during regulation.
The Switch Control block senses the output of the ampli-
fi er and adjusts the switching frequency as well as other
parameters to achieve regulation. During the start-up of
the circuit, special precautions are taken to insure that the
inductor current remains under control.
Because the switching frequency is never allowed to fall
below approximately 50kHz, a minimum load must be
present to prevent the output voltage from drifting too high.
This minimum load is automatically generated within the
part via the Shunt Control block. The level of this current
is adaptable, removing itself when not needed to improve
effi ciency at higher load levels.
The LT3494/LT3494A also have an integrated Schottky
diode and PMOS output disconnect switch. The PMOS
switch is turned on when the part is enabled via the SHDN
pin. When the parts are in shutdown, the PMOS switch
turns off, allowing the VOUT node to go to ground. This
type of disconnect function is often required in power
supplies.
The only difference between the LT3494A and LT3494
is the level of the current limit. The LT3494A has a typi-
cal peak current limit of 350mA while the LT3494 has a
180mA limit.
APPLICATIONS INFORMATION
Choosing an Inductor
Several recommended inductors that work well with the
LT3494/LT3494A are listed in Table 1, although there are
many other manufacturers and devices that can be used.
Consult each manufacturer for more detailed information
and for their entire selection of related parts. Many dif-
ferent sizes and shapes are available. Use the equations
and recommendations in the next few sections to fi nd the
correct inductance value for your design.
Inductor Selection—Boost Regulator
The formula below calculates the appropriate inductor
value to be used for a boost regulator using the LT3494/
LT3494A (or at least provides a good starting point).
This value provides a good trade off in inductor size and
system performance. Pick a standard inductor close to
this value. A larger value can be used to slightly increase
the available output current, but limit it to around twice
the value calculated below, as too large of an inductance
will decrease the output voltage ripple without providing
much additional output current. A smaller value can be
used (especially for systems with output voltages greater
than 12V) to give a smaller physical size. Inductance can
be calculated as:
L = (VOUT – VIN(MIN) + 0.5V) • 0.66 (μH)
where VOUT is the desired output voltage and VIN(MIN) is
the minimum input voltage. Generally, a 10μH or 15μH
inductor is a good choice.
Table 1. Recommended Inductors
PART FOR USE WITH
VALUE
(μH)
MAX DCR
(Ω)
MAX DC I
(mA)
SIZE
(mm × mm × mm) VENDOR
LQH32CN100K53
LQH32CN150K53
LT3494/LT3494A
LT3494
10
15
0.3
0.58
450
300
3.5 × 2.7 × 1.7
3.5 × 2.7 × 1.7
Murata
www.murata.com
CDRH3D11-100
CDHED13/S-150
LT3494
LT3494/LT3494A
10
15
0.24
0.55
280
550
4.0 × 4.0 × 1.2
4.0 × 4.2 × 1.4
Sumida
www.sumida.com
LT3494/LT3494A
8
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APPLICATIONS INFORMATION
Capacitor Selection
The small size and low ESR of ceramic capacitors makes
them suitable for most LT3494/LT3494A applications. X5R
and X7R types are recommended because they retain their
capacitance over wider voltage and temperature ranges
than other types such as Y5V or Z5U. A 4.7μF input capaci-
tor and a 2.2μF to 10μF output capacitor are suffi cient for
most LT3494/LT3494A applications. Always use a capacitor
with a suffi cient voltage rating. Many capacitors rated at
2.2μF to 10μF, particularly 0805 or 0603 case sizes, have
greatly reduced capacitance when bias voltages are ap-
plied. Be sure to check actual capacitance at the desired
output voltage. Generally a 1206 size capacitor will be
adequate. A 0.22μF or 0.47μF capacitor placed on the
CAP node is recommended to fi lter the inductor current
while the larger 2.2μF to 10μF placed on the VOUT node
will give excellent transient response and stability. Table 2
shows a list of several capacitor manufacturers. Consult
the manufacturers for more detailed information and for
their entire selection of related parts.
Table 2. Recommended Ceramic Capacitor Manufacturers
MANUFACTURER PHONE URL
Taiyo Yuden 408-573-4150 www.t-yuden.com
AVX 843-448-9411 www.avxcorp.com
Murata 814-237-1431 www.murata.com
Kemet 408-986-0424 www.kemet.com
Setting Output Voltage and
the Auxiliary Reference Input
The LT3494/LT3494A are equipped with both an internal
1.225V reference and an auxiliary reference input. This al-
lows the user to select between using the built-in reference
and supplying an external reference voltage. The voltage
at the CTRL pin can be adjusted while the chip is operat-
ing to alter the output voltage of the LT3494/LT3494A for
purposes such as display dimming or contrast adjustment.
To use the internal 1.225V reference, the CTRL pin must be
held higher than 1.5V. When the CTRL pin is held between
0V and 1.5V, the LT3494 will regulate the output such that
the FB pin voltage is nearly equal to the CTRL pin voltage.
At CTRL voltages close to 1.225V, a soft transition occurs
between the CTRL pin and the internal reference. Figure 1
shows this behavior.
To set the maximum output voltage, select the values of
R1 according to the following equation:
RVk
OUT MAX
1 182 1 225 1=⎛
⎝
⎜⎞
⎠
⎟
•.–
() Ω
When CTRL is used to override the internal reference,
the output voltage can be lowered from the maximum
value down to nearly the input voltage level. If the voltage
source driving the CTRL pin is located at a distance to the
LT3494/LT3494A, a small 0.1μF capacitor may be needed
to bypass the pin locally.
Choosing a Feedback Node
The single feedback resistor may be connected to the VOUT
pin or to the CAP pin (see Figure 2). Regulating the VOUT
pin eliminates the output offset resulting from the voltage
drop across the output disconnect PMOS. Regulating the
CAP pin does not compensate for the voltage drop across
the output disconnect, resulting in an output voltage VOUT
that is slightly lower than the voltage set by the resistor
divider. Under most conditions, it is advised that the
feedback resistor be tied to the VOUT pin.
Figure 1. CTRL to FB Transfer Curve
SW CAP
VCC
SHDN
CTRL
VOUT
FB
GND
3
5
4
7
6
2
R1
LT3494
C1
C3
18
VOUT
SW CAP
VCC
SHDN
CTRL
VOUT
FB
GND
3
5
4
7
6
2
R1
3494 F02
LT3494
C1
18
Figure 2. Feedback Connection Using the CAP Pin or the VOUT Pin
CTRL VOLTAGE (V)
0
0
FB VOLTAGE (V)
0.250
0.500
0.750
1.000
1.500
.25 0.5 .75 1.0
3494 F01
1.25 1.5
1.250
LT3494/LT3494A
9
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APPLICATIONS INFORMATION
Connecting the Load to the CAP Node
The effi ciency of the converter can be improved by con-
necting the load to the CAP pin instead of the VOUT pin.
The power loss in the PMOS disconnect circuit is then
made negligible. By connecting the feedback resistor to
the VOUT pin, no quiescent current will be consumed in the
feedback resistor string during shutdown since the PMOS
transistor will be open (see Figure 3). The disadvantage
of this method is that the CAP node cannot go to ground
during shutdown, but will be limited to around a diode
drop below VCC. Loads connected to the part should only
sink current. Never force external power supplies onto
the CAP or VOUT pins. The larger value output capacitor
(2.2μF to 10μF) should be placed on the node to which
the load is connected.
Figure 3. Improved Effi ciency
Maximum Output Load Current
The maximum output current of a particular LT3494/
LT3494A circuit is a function of several circuit variables.
The following method can be helpful in predicting the
maximum load current for a given circuit:
Step 1: Calculate the peak inductor current:
II V
Lamps
PK LIMIT IN
=+
••
–
400 10 9
where ILIMIT is 0.180A and 0.350A for the LT3494 and
LT3494A respectively. L is the inductance value in Henrys
and VIN is the input voltage to the boost circuit.
Step 2: Calculate the inductor ripple current:
IVV
Lamps
RIPPLE OUT IN
=+
()
1 150 10 9
–••
–
where VOUT is the desired output voltage.
If the inductor ripple current is greater than the peak cur-
rent, then the circuit will only operate in discontinuous
conduction mode. The inductor value should be increased
so that IRIPPLE < IPK. An application circuit can be designed
to operate only in discontinuous mode, but the output
current capability will be reduced.
Step 3: Calculate the average input current:
II
Iamps
IN AVG PK RIPPLE
() –=2
Step 4: Calculate the nominal output current:
IIV
Vamps
OUT NOM
IN AVG IN
OUT
()
()
••.
=075
Step 5: Derate output current:
I
OUT = IOUT(NOM) • 0.7 amps
For low output voltages the output current capability will
be increased. When using output disconnect (load cur-
rent taken from VOUT), these higher currents will cause
the drop in the PMOS switch to be higher resulting in
reduced output current capability than those predicted
by the preceding equations.
Inrush Current
When VCC is stepped from ground to the operating volt-
age while the output capacitor is discharged, a higher
level of inrush current may fl ow through the inductor
and integrated Schottky diode into the output capacitor.
Conditions that increase inrush current include a larger
more abrupt voltage step at VIN, a larger output capacitor
tied to the CAP pin and an inductor with a low saturation
current. While the internal diode is designed to handle
such events, the inrush current should not be allowed to
exceed 1A. For circuits that use output capacitor values
within the recommended range and have input voltages
of less than 5V, inrush current remains low, posing no
hazard to the device. In cases where there are large steps
at VCC (more than 5V) and/or a large capacitor is used
at the CAP pin, inrush current should be measured to
ensure safe operation. The LT3494A circuits experience
higher levels of current during start-up and steady-state
operation. An external diode placed from the SW pin to
SW CAP
VCC
SHDN
CTRL
VOUT
FB
GND
3
5
4
7
6
2
3494 F03
LT3494
C1 ILOAD
18
LT3494/LT3494A
10
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TYPICAL APPLICATIONS
Figure 5. One Li-Ion Cell Input Boost Converter with the LT3494
APPLICATIONS INFORMATION
the CAP pin will improve effi ciency and lower the stress
placed on the internal Schottky diode.
Board Layout Considerations
As with all switching regulators, careful attention must be
paid to the PCB board layout and component placement.
To maximize effi ciency, switch rise and fall times are made
as short as possible. To prevent electromagnetic interfer-
ence (EMI) problems, proper layout of the high frequency
switching path is essential. The voltage signal of the SW pin
has sharp rising and falling edges. Minimize the length and
area of all traces connected to the SW pin and always use
a ground plane under the switching regulator to minimize
interplane coupling. In addition, the FB connection for
the feedback resistor R1 should be tied directly from the
Vout pin to the FB pin and be kept as short as possible,
ensuring a clean, noise-free connection. Recommended
component placement is shown in Figure 4.
SW
GND
VCC
CTRL
CAP
VOUT
FB
SHDN
GND
GND
CTRL
VIAS TO GROUND PLANE REQUIRED
TO IMPROVE THERMAL PERFORMANCE
SHDN
3494 F04
Figure 4. Recommended Layout
SW CAP
VCC
SHDN
CTRL
7
6
2
3
5
4
VOUT
FB
GND
TURN ON/OFF
VOUT DIMMING
R1
3494 F05
LT3494
C2
4.7μF
L1
15μH
C1
0.22μF
C3
2.2μF
C1, C2: X5R OR X7R WITH SUFFICIENT VOLTAGE RATING
C3: MURATA GRM31MR71E225K
L1: MURATA LQH32CN150K53
81
VIN
3V TO 4.2V
VOUT
LOAD CURRENT (mA)
0.1
60
EFFICIENCY (%)
POWER LOSS (mW)
70
80
90
1 10 100
3494 TA01c
50
40
30
20
160
200
240
280
120
80
40
0
VIN = 3.6V LOAD FROM
CAPACITOR
LOAD FROM
VOUT
3.6V to 16V Effi ciency
VOUT
R1 VALUE REQUIRED
(MΩ)
MAXIMUM OUTPUT CURRENT AT
3V INPUT (mA)
25 3.57 8.6
24 3.40 9.3
23 3.24 10.0
22 3.09 10.6
21 2.94 11.3
20 2.80 12.1
19 2.67 12.9
18 2.49 13.6
17 2.37 14.8
16 2.21 16.0
15 2.05 17.2
LT3494/LT3494A
11
3494fb
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no representa-
tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.
PACKAGE DESCRIPTION
DDB Package
8-Lead Plastic DFN (3mm × 2mm)
(Reference LTC DWG # 05-08-1702 Rev B)
2.00 ±0.10
(2 SIDES)
NOTE:
1. DRAWING CONFORMS TO VERSION (WECD-1) IN JEDEC PACKAGE OUTLINE M0-229
2. DRAWING NOT TO SCALE
3. ALL DIMENSIONS ARE IN MILLIMETERS
4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE
MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE
5. EXPOSED PAD SHALL BE SOLDER PLATED
6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE
0.40 ± 0.10
BOTTOM VIEW—EXPOSED PAD
0.56 ± 0.05
(2 SIDES)
0.75 ±0.05
R = 0.115
TYP
R = 0.05
TYP
2.15 ±0.05
(2 SIDES)
3.00 ±0.10
(2 SIDES)
14
85
PIN 1 BAR
TOP MARK
(SEE NOTE 6)
0.200 REF
0 – 0.05
(DDB8) DFN 0905 REV B
0.25 ± 0.05
0.50 BSC
PIN 1
R = 0.20 OR
0.25 × 45°
CHAMFER
0.25 ± 0.05
2.20 ±0.05
(2 SIDES)
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
0.61 ±0.05
(2 SIDES)
1.15 ±0.05
0.70 ±0.05
2.55 ±0.05
PACKAGE
OUTLINE
0.50 BSC
LT3494/LT3494A
12
3494fb
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com
© LINEAR TECHNOLOGY CORPORATION 2006
LT 0507 REV B • PRINTED IN USA
RELATED PARTS
TYPICAL APPLICATION
PART NUMBER DESCRIPTION COMMENTS
LT1613 550mA (ISW), 1.4MHz, High Effi ciency Step-Up DC/DC Converter VIN: 0.9V to 10V, VOUT(MAX) = 34V, IQ = 3mA, ISD < 1μA,
ThinSOT Package
LT1615/LT1615-1 300mA/80mA (ISW), High Effi ciency Step-Up DC/DC Converters VIN: 1V to 15V, VOUT(MAX) = 34V, IQ = 20μA, ISD < 1μA,
ThinSOT Package
LT1930/LT1930A 1A (ISW), 1.2MHz/2.2MHz, High Effi ciency Step-Up DC/DC
Converters
VIN: 2.6V to 16V, VOUT(MAX) = 34V, IQ = 4.2A/5.5mA, ISD < 1μA,
ThinSOT Package
LT1945 (Dual) Dual Output, Boost/Inverter, 350mA (ISW), Constant Off-Time, High
Effi ciency Step-Up DC/DC Converter
VIN: 1.2V to 15V, VOUT(MAX) = ±34V, IQ = 40μA, ISD < 1μA,
10-Lead MS Package
LT1946/LT1946A 1.5A (ISW), 1.2MHz/2.7MHz, High Effi ciency Step-Up DC/DC
Converters
VIN: 2.45V to 16V, VOUT(MAX) = 34V, IQ = 3.2mA, ISD < 1μA,
8-Lead MS Package
LT3467/LT3467A 1.1A (ISW), 1.3MHz/2.1MHz, High Effi ciency Step-Up DC/DC
Converters with Soft-Start
VIN: 2.4V to 16V, VOUT(MAX) = 40V, IQ = 1.2mA, ISD < 1μA,
ThinSOT Package
LT3463/LT3463A Dual Output, Boost/Inverter, 250mA (ISW), Constant Off-Time, High
Effi ciency Step-Up DC/DC Converters with Integrated Schottkys
VIN: 2.3V to 15V, VOUT(MAX) = ±40V, IQ = 40μA, ISD < 1μA,
DFN Package
LT3471 Dual Output, Boost/Inverter, 1.3A (ISW), High Effi ciency
Boost-Inverting DC/DC Converter
VIN: 2.4V to 16V, VOUT(MAX) = ±40V, IQ = 2.5mA, ISD < 1μA,
DFN Package
Figure 6. One Li-Ion Cell Input Boost Converter with the LT3494A
SW CAP
D1
VCC
SHDN
CTRL
7
6
2
3
5
4
VOUT
FB
GND
R1
3494 F06
LT3494A
C2
4.7μF
C1, C2: X5R OR X7R WITH SUFFICIENT VOLTAGE RATING
C3: TAIYO YUDEN TMK316BJ106ML
D1: CENTRAL SEMICONDUCTOR CMDSH-3
L1: MURATA LQH32CN100K53
L1
10μH
C1
0.47μF
C3
10μF
81
VIN
3V TO 4.2V
VOUT
LOAD CURRENT (mA)
0.1
60
EFFICIENCY (%)
POWER LOSS (mW)
70
80
1 10 100
3494 F06b
50
55
65
75
45
40
100
200
300
50
150
250
0
VIN = 3.6V
VOUT = 16V
LOAD FROM CAPACITOR
LOAD FROM VOUT
LOAD CURRENT (mA)
0.1
0
VOUT PEAK-TO-PEAK RIPPLE (mV)
10
15
1 10 100
3494 F06c
5
100MHz MEASUREMENT BW
Effi ciency and Power Loss vs Load Current
Output Voltage Ripple vs Load Current
VOUT
R1 VALUE REQUIRED
(MΩ)
MAXIMUM OUTPUT CURRENT AT
3V INPUT (mA)
25 3.57 13.0
24 3.40 14.0
23 3.24 15.0
22 3.09 16.5
21 2.94 17.5
20 2.80 19.0
19 2.67 20.0
18 2.49 21.5
17 2.37 23.0
16 2.21 25.0
15 2.05 27.0
