datasheet for LT3494A by Linear Technology
LT3494/LT3494A
Micropower Low Noise
Boost Converters with
Output Disconnect
FEATURES
■
■
■
■
■
■
■
■
■
DESCRIPTION
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
APPLICATIONS
■
■
■
OLED Power
Low Noise Power
MP3 Players
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 technique resulting in low output voltage ripple as well as high
efficiency 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.
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
*Patent pending.
TYPICAL APPLICATION
Output Voltage Ripple
vs Load Current
OLED Power Supply from One Li-Ion Cell
0.22µF
SW
CAP
VCC
VOUT
2.21M
LT3494
SHDN
FB
CTRL
GND
2.2µF
3494 TA01a
70
10
VOUT
16V
16mA
VIN = 3.6V
80
EFFICIENCY (%)
4.7µF
VOUT PEAK-TO-PEAK RIPPLE (mV)
15µH
90
LT3494
FIGURE 5 CIRCUIT
100MHz MEASUREMENT BW
5
0
0.1
1
10
LOAD CURRENT (mA)
100
3494 TA01b
280
LOAD FROM
CAPACITOR
240
LOAD FROM
VOUT
200
60
160
50
120
40
80
30
40
20
0.1
1
10
LOAD CURRENT (mA)
POWER LOSS (mW)
VIN
3V
TO 4.2V
15
Efficiency and Power Loss
vs Load Current
0
100
3494 TA01c
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LT3494/LT3494A
ABSOLUTE MAXIMUM RATINGS
PACKAGE/ORDER INFORMATION
(Note 1)
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
TOP VIEW
SW 1
8
GND 2
7
VOUT
6
FB
5
SHDN
VCC 3
9
CTRL 4
CAP
DDB PACKAGE
8-LEAD (3mm × 2mm) PLASTIC DFN
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 specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VCC = 3V, VSHDN = VCC, unless otherwise noted. (Note 2)
PARAMETER
CONDITIONS
MIN
Minimum Operating Voltage
TYP
MAX
2.3
2.5
V
16
V
V
Maximum Operating Voltage
Feedback Voltage
VCTRL = 3V (Note 3)
FB Resistor
●
1.205
1.225
1.245
●
179
182
184
UNITS
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)
Maximum Switch Off Time
VFB = 1.5V
Switch Current Limit
LT3494A (Note 5)
LT3494 (Note 5)
Switch VCESAT
LT3494A, ISW = 200mA
LT3494, ISW = 100mA
180
110
Switch Leakage Current
VSW = 5V, V⎯S⎯H⎯D⎯N = 0
0.01
1
µA
Schottky Forward Voltage
IDIODE = 100mA
900
1100
mV
0.05
1
µA
100
450
●
15
20
30
µs
225
115
350
180
450
250
mA
mA
Schottky Reverse Leakage
PMOS Disconnect VCAP – VOUT
IOUT = 10mA, VCAP = 5V
SHDN Input Voltage High
mV
mV
250
mV
1.5
V
SHDN Input Voltage Low
SHDN Pin Bias Current
ns
ns
VSHDN = 3V
VSHDN = 0V
5
0
0.3
V
10
0.1
µA
µA
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LT3494/LT3494A
ELECTRICAL CHARACTERISTICS
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VCC = 3V, VSHDN = VCC, unless otherwise noted. (Note 2)
PARAMETER
CONDITIONS
CTRL Pin Bias Current
VCTRL = 0.5V, Current Flows Out of Pin
MIN
CTRL to FB Offset
VCTRL = 0.5V
Maximum Shunt Current
VFB = 1.3V, VCAP = 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 LT3494/LT3494A are guaranteed to meet performance
specifications from 0°C to 85°C. Specifications over the –40°C to 85°C
operating temperature range are assured by design, characterization and
correlation with statistical process controls.
600
400
200
0
0.1
nA
8
15
mV
µA
VOUT vs CTRL Voltage
20
LT3494
1.5 FIGURE 5 CIRCUIT
VCC = 3.6V
1.0 VOUT = 16V
VOUT VOLTAGE (V)
VOUT VOLTAGE CHANGE (%)
SWITCHING FREQUENCY (kHz)
800
UNITS
100
TA = 25°C unless otherwise noted.
2.0
LT3494
FIGURE 5 CIRCUIT
1200 VCC = 3.6V
VOUT = 16V
1000
MAX
20
Note 3: Internal reference voltage is determined by finding 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.
Load Regulation
1400
TYP
230
TYPICAL PERFORMANCE CHARACTERISTICS
Switching Frequency
vs Load Currrent
●
0.5
0
–0.5
LT3494
FIGURE 5 CIRCUIT
VCC = 3.6V
15 VOUT = 16V
LOAD CURRENT = 1mA
10
5
–1.0
–1.5
1
10
LOAD CURRENT (mA)
100
3494 G01
–2.0
0
5
10 15 20 25 30
LOAD CURRENT (mA)
35
40
3494 G02
0
0.1
0.3
0.5 0.7 0.9 1.1
CTRL VOLTAGE (V)
1.3
1.5
3494 G03
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LT3494/LT3494A
TYPICAL PERFORMANCE CHARACTERISTICS
Output Voltage vs Temperature
0.5
0
–0.5
–1.0
–1.5
95
90
50.0
85
49.5
IVCC (µA)
1.0
100
VCC = 3.6V
NO LOAD
50.5
SWITCHING FREQUENCY (kHz)
OUTPUT VOLTAGE CHANGE (%)
51.0
LT3494
1.5 FIGURE 5 CIRCUIT
49.0
48.5
0
20 40 60 80
TEMPERATURE (°C)
50
0
20 40 60 80
TEMPERATURE (°C)
100 120
SHDN Current vs SHDN Voltage
Peak Inductor Current (LT3494)
5
10 12
4
6
8
SHDN PIN VOLTAGE (V)
14
16
300
250
200
150
100
–40 –20
0
20 40 60 80
TEMPERATURE (°C)
100 120
500
450
400
–40 –20
3494 G10
20 40 60 80
TEMPERATURE (°C)
100 120
3494 G09
LT3494 Switching Waveforms at
25mA Load
FIGURE 5 CIRCUIT
SW
VOLTAGE
10V/DIV
INDUCTOR
CURRENT
100mA/DIV
INDUCTOR
CURRENT
100mA/DIV
INDUCTOR
CURRENT
50mA/DIV
0
VOUT
10mV/DIV
AC
COUPLED
SW
VOLTAGE
10V/DIV
5µs/DIV
550
FIGURE 5 CIRCUIT
VOUT
10mV/DIV
AC
COUPLED
VCC = 3.6V
VOUT = 16V
600
LT3494 Switching Waveforms at
1mA Load
FIGURE 5 CIRCUIT
10
9
FIGURE 6 CIRCUIT
VCC = 3.6V
650 VOUT = 16V
3494 G08
LT3494 Switching Waveforms at
No Load
SW
VOLTAGE
10V/DIV
8
Peak Inductor Current (LT3494A)
FIGURE 5 CIRCUIT
VCC = 3.6V
350 VOUT = 16V
3494 G07
VOUT
10mV/DIV
AC
COUPLED
7
6
VCC (V)
700
PEAK INDUCTOR CURRENT (mA)
PEAK INDUCTOR CURRENT (mA)
10
5
4
3494 G06
400
15
3
3494 G05
20
2
70
55
3494 G04
0
75
60
47.0
–40 –20
100 120
80
65
48.0
47.5
–2.0
–40 –20
SHDN PIN CURRENT (µA)
Quiescent Current–Not Switching
Minimum Switching Frequency
2.0
0
TA = 25°C unless otherwise noted.
VCC = 3.6V
VOUT = 16V
2µs/DIV
3494 G11
VCC = 3.6V
VOUT = 16V
500ns/DIV
3494 G12
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LT3494/LT3494A
TYPICAL PERFORMANCE CHARACTERISTICS
LT3494A Switching Waveforms at
No Load
VOUT
10mV/DIV
AC
COUPLED
LT3494A Switching Waveforms at
5mA Load
FIGURE 6 CIRCUIT
VOUT
10mV/DIV
AC
COUPLED
SW
VOLTAGE
10V/DIV
SW
VOLTAGE
10V/DIV
INDUCTOR
CURRENT
50mA/DIV
INDUCTOR
CURRENT
100mA/DIV
VCC = 3.6V
VOUT = 16V
5ms/DIV
3494 G13
FIGURE 6 CIRCUIT
VOUT
10mV/DIV
AC
COUPLED
VOUT
VOLTAGE
50mV/DIV
AC COUPLED
2ms/DIV
3494 G14
200µs/DIV
3494 G16
VCC = 3.6V
VOUT = 16V
500ns/DIV
3494 G15
LT3494A Transient Response
FIGURE 5 CIRCUIT
10mA→15mA→10mA LOAD PULSE
VOUT
50mV/DIV
AC
COUPLED
INDUCTOR
CURRENT
100mA/DIV
VCC = 3.6V
VOUT = 16V
FIGURE 6 CIRCUIT
INDUCTOR
CURRENT
200mA/DIV
LT3494 Transient Response
FIGURE 5 CIRCUIT
INDUCTOR
CURRENT
100mA/DIV
LT3494A Switching Waveforms at
30mA Load
SW
VOLTAGE
10V/DIV
VCC = 3.6V
VOUT = 16V
LT3494 Start-Up Waveforms
CAP
VOLTAGE
5V/DIV
VOUT
VOLTAGE
5V/DIV
TA = 25°C unless otherwise noted.
FIGURE 6 CIRCUIT
15mA→30mA→15mA LOAD PULSE
INDUCTOR
CURRENT
200mA/DIV
VCC = 3.6V
VOUT = 16V
100µs/DIV
3494 G17
VCC = 3.6V
VOUT = 16V
100µs/DIV
3494 G18
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LT3494/LT3494A
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.
V CC (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 according to the following formula:
⎛ VOUT(MAX ) ⎞
– 1⎟ kΩ
R1 = 182 • ⎜
⎠
⎝ 1.225
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.
BLOCK DIAGRAM
฀
฀
฀
฀
3494fb
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LT3494/LT3494A
OPERATION
The LT3494/LT3494A use a novel control scheme to provide high efficiency 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 amplifier 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
efficiency 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 typical 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 different sizes and shapes are available. Use the equations
and recommendations in the next few sections to find the
correct inductance value for your design.
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:
Inductor Selection—Boost Regulator
L = (VOUT – VIN(MIN) + 0.5V) • 0.66 (µH)
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).
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)
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
VENDOR
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LT3494/LT3494A
APPLICATIONS INFORMATION
1.500
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 capacitor and a 2.2µF to 10µF output capacitor are sufficient for
most LT3494/LT3494A applications. Always use a capacitor
with a sufficient voltage rating. Many capacitors rated at
2.2µF to 10µF, particularly 0805 or 0603 case sizes, have
greatly reduced capacitance when bias voltages are applied. 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 filter 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.
1.250
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 allows 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 operating 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.
FB VOLTAGE (V)
Capacitor Selection
1.000
0.750
0.500
0.250
0
0
.25
0.5
.75
1.0
CTRL VOLTAGE (V)
1.25
1.5
3494 F01
Figure 1. CTRL to FB Transfer Curve
To set the maximum output voltage, select the values of
R1 according to the following equation:
⎛ VOUT(MAX ) ⎞
– 1⎟ kΩ
R1 = 182 • ⎜
⎠
⎝ 1.225
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.
3
5
4
1
8
SW
CAP
VCC
VOUT
LT3494
SHDN
FB
CTRL
GND
C1
7
6
2
VOUT
R1
C3
3
5
4
1
8
SW
CAP
VCC
VOUT
LT3494
SHDN
FB
CTRL
GND
C1
7
6
R1
2
3494 F02
Figure 2. Feedback Connection Using the CAP Pin or the VOUT Pin
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LT3494/LT3494A
APPLICATIONS INFORMATION
Connecting the Load to the CAP Node
The efficiency of the converter can be improved by connecting 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.
3
5
4
1
8
SW
CAP
VCC
VOUT
LT3494
SHDN
FB
CTRL
GND
C1
ILOAD
7
If the inductor ripple current is greater than the peak current, 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:
IIN( AVG) = IPK –
IRIPPLE
amps
2
Step 4: Calculate the nominal output current:
IOUT(NOM) =
IIN( AVG) • VIN • 0.75
VOUT
amps
Step 5: Derate output current:
IOUT = IOUT(NOM) • 0.7 amps
For low output voltages the output current capability will
be increased. When using output disconnect (load current 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.
6
2
3494 F03
Figure 3. Improved Efficiency
Maximum Output Load Current
Inrush 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:
When VCC is stepped from ground to the operating voltage while the output capacitor is discharged, a higher
level of inrush current may flow 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
Step 1: Calculate the peak inductor current:
IPK
VIN • 400 • 10 –9
= ILIMIT +
amps
L
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:
IRIPPLE =
(VOUT + 1– VIN) • 150 • 10 –9
L
where VOUT is the desired output voltage.
amps
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9
LT3494/LT3494A
APPLICATIONS INFORMATION
the CAP pin will improve efficiency and lower the stress
placed on the internal Schottky diode.
GND
Board Layout Considerations
SW
CAP
As with all switching regulators, careful attention must be
paid to the PCB board layout and component placement.
To maximize efficiency, switch rise and fall times are made
as short as possible. To prevent electromagnetic interference (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.
GND
VOUT
GND
FB
VCC
CTRL
SHDN
3494 F04
CTRL
SHDN
VIAS TO GROUND PLANE REQUIRED
TO IMPROVE THERMAL PERFORMANCE
Figure 4. Recommended Layout
TYPICAL APPLICATIONS
3.6V to 16V Efficiency
90
C2
4.7µF
3
1
8
SW
CAP
VOUT
TURN ON/OFF
VOUT DIMMING
5
4
SHDN
R1
CTRL
FB
GND
80
7
LT3494
6
C3
2.2µF
VOUT
2
3494 F05
C1, C2: X5R OR X7R WITH SUFFICIENT VOLTAGE RATING
C3: MURATA GRM31MR71E225K
L1: MURATA LQH32CN150K53
Figure 5. One Li-Ion Cell Input Boost Converter with the LT3494
VOUT
25
24
23
22
21
20
19
18
17
16
15
R1 VALUE REQUIRED
(MΩ)
3.57
3.40
3.24
3.09
2.94
2.80
2.67
2.49
2.37
2.21
2.05
VIN = 3.6V
MAXIMUM OUTPUT CURRENT AT
3V INPUT (mA)
8.6
9.3
10.0
10.6
11.3
12.1
12.9
13.6
14.8
16.0
17.2
70
280
LOAD FROM
CAPACITOR
240
LOAD FROM
VOUT
200
60
160
50
120
40
80
30
40
20
0.1
1
10
LOAD CURRENT (mA)
POWER LOSS (mW)
VCC
C1
0.22µF
EFFICIENCY (%)
VIN
3V TO 4.2V
L1
15µH
0
100
3494 TA01c
3494fb
10
LT3494/LT3494A
PACKAGE DESCRIPTION
DDB Package
8-Lead Plastic DFN (3mm × 2mm)
(Reference LTC DWG # 05-08-1702 Rev B)
0.61 ±0.05
(2 SIDES)
0.70 ±0.05
2.55 ±0.05
1.15 ±0.05
PACKAGE
OUTLINE
0.25 ± 0.05
0.50 BSC
2.20 ±0.05
(2 SIDES)
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
3.00 ±0.10
(2 SIDES)
R = 0.115
TYP
5
R = 0.05
TYP
0.40 ± 0.10
8
2.00 ±0.10
(2 SIDES)
PIN 1 BAR
TOP MARK
(SEE NOTE 6)
0.56 ± 0.05
(2 SIDES)
0.200 REF
0.75 ±0.05
0 – 0.05
4
0.25 ± 0.05
1
PIN 1
R = 0.20 OR
0.25 × 45°
CHAMFER
(DDB8) DFN 0905 REV B
0.50 BSC
2.15 ±0.05
(2 SIDES)
BOTTOM VIEW—EXPOSED PAD
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
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 representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
11
LT3494/LT3494A
TYPICAL APPLICATION
L1
10µH
VIN
3V TO 4.2V
Efficiency and Power Loss vs Load Current
D1
300
80
3
8
SW
CAP
VCC
VOUT
7
LT3494A
5
4
SHDN
FB
CTRL
GND
LOAD FROM CAPACITOR
C1
0.47µF
6
75
70
VOUT
R1
C3
10µF
2
3494 F06
C1, C2: X5R OR X7R WITH SUFFICIENT VOLTAGE RATING
C3: TAIYO YUDEN TMK316BJ106ML
D1: CENTRAL SEMICONDUCTOR CMDSH-3
L1: MURATA LQH32CN100K53
200
65
150
60
55
100
50
50
45
40
0.1
Figure 6. One Li-Ion Cell Input Boost Converter with the LT3494A
VIN = 3.6V
VOUT = 16V
1
10
LOAD CURRENT (mA)
Output Voltage Ripple vs Load Current
VOUT PEAK-TO-PEAK RIPPLE (mV)
15
5
0
0.1
1
10
LOAD CURRENT (mA)
100
0
100
3494 F06b
100MHz MEASUREMENT BW
10
250
LOAD FROM VOUT
POWER LOSS (mW)
1
EFFICIENCY (%)
C2
4.7µF
VOUT
25
24
23
22
21
20
19
18
17
16
15
R1 VALUE REQUIRED
(MΩ)
3.57
3.40
3.24
3.09
2.94
2.80
2.67
2.49
2.37
2.21
2.05
MAXIMUM OUTPUT CURRENT AT
3V INPUT (mA)
13.0
14.0
15.0
16.5
17.5
19.0
20.0
21.5
23.0
25.0
27.0
3494 F06c
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
LT1613
550mA (ISW), 1.4MHz, High Efficiency 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 Efficiency 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 Efficiency 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
Efficiency 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 Efficiency 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 Efficiency 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 VIN: 2.3V to 15V, VOUT(MAX) = ±40V, IQ = 40µA, ISD < 1µA,
Efficiency Step-Up DC/DC Converters with Integrated Schottkys
DFN Package
LT3471
Dual Output, Boost/Inverter, 1.3A (ISW), High Efficiency
Boost-Inverting DC/DC Converter
VIN: 2.4V to 16V, VOUT(MAX) = ±40V, IQ = 2.5mA, ISD < 1µA,
DFN Package
3494fb
12 Linear Technology Corporation
LT 0507 REV B • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507
●
www.linear.com
© LINEAR TECHNOLOGY CORPORATION 2006
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