LT3495/LT3495B/
LT3495-1/LT3495B-1
1
3495b1b1fa
TYPICAL APPLICATION
FEATURES
APPLICATIONS
DESCRIPTION
650mA/350mA Micropower
Low Noise Boost Converter
with Output Disconnect
The LT
®
3495/LT3495B/LT3495-1/LT3495B-1 are low noise
boost converters with integrated power switch, feedback
resistor and output disconnect circuitry. The parts control
power delivery by varying both the peak inductor current
and switch off-time. This novel* control scheme results
in low output voltage ripple as well as high efficiency
over a wide load range. For the LT3495/LT3495-1, the
off-time of the switch is not allowed to exceed a fixed
level, guaranteeing the switching frequency stays above
the audio band for the entire load range. The parts feature
a high performance NPN power switch with a 650mA
and 350mA current limit for the LT3495/LT3495B and
LT3495-1/LT3495B-1 respectively. The quiescent current
is a low 60µA, which is further reduced to less than 0.1µA
in shutdown. The internal disconnect circuitry allows the
output voltage to be isolated from the input during shut-
down. An auxiliary reference input (CTRL pin) overrides
the internal 1.235V feedback reference with any lower
value allowing full control of the output voltage during
operation. The LT3495 series are available in a tiny 10-lead
3mm × 2mm DFN package.
OLED Power Supply from One Li-Ion Cell
n Low Quiescent Current
60µA in Active Mode
0.1µA in Shutdown Mode
n Low Noise Control Scheme (Switching Frequency
Always Stays Above Audible Range for LT3495/-1)
n Integrated Power NPN:
650mA Current Limit (LT3495/B)
350mA Current Limit (LT3495-1/B-1)
n Integrated Output Disconnect
n Integrated Output Dimming
n Wide input range: 2.5V to 16V
n Wide output range: Up to 40V
n Integrated feedback resistor
n Tiny 10-Lead 3mm × 2mm DFN Package
n OLED Power
n Low Noise Power
n MP3 Player
Output Voltage Ripple
vs Load Current Efficiency vs Load Current
L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners. *Patent pending.
LOAD CURRENT (mA)
0.1
VOUT PEAK-TO-PEAK RIPPLE (mV)
50
40
20
30
10
01
3495 TA01b
10010
1.0µF 0603
CAPACITOR AT VOUT
2.2µF 1206
CAPACITOR AT VOUT
SW CAP
VCC
SHDN
CTRL
VOUT
FB
GND
909k
3495 TA01a
LT3495
4.7µF
1µF
10µH
2.2µF
ONE
Li-Ion
CELL
VOUT
16V
70mA
LOAD CURRENT (mA)
EFFICIENCY (%)
POWER LOSS (mW)
3495 TA01c
90
80
50
60
70
40
400
320
80
160
240
0
0.1 10 1001
VIN = 3.6V LOAD FROM CAP
LOAD FROM VOUT
LT3495/LT3495B/
LT3495-1/LT3495B-1
2
3495b1b1fa
PIN CONFIGURATIONABSOLUTE MAXIMUM RATINGS
VCC Voltage ...............................................................16V
SW Voltage ...............................................................40V
CAP Voltage ..............................................................40V
VOUT Voltage .............................................................40V
SHDN Voltage ...........................................................10V
CTRL Voltage ............................................................10V
FB Voltage ................................................................2.5V
Maximum Junction Temperature........................... 125°C
Operating Temperature Range (Note 2).. –40°C to 125°C
Storage Temperature Range ................... –65°C to 150°C
(Note 1)
TOP VIEW
11
DDB PACKAGE
10-LEAD (3mm × 2mm) PLASTIC DFN
GND
GND
VCC
CTRL
SHDN
SW
CAP
CAP
VOUT
FB
6
8
7
9
10
5
4
2
3
1
TJMAX = 125°C, θJA = 76°C/W
EXPOSED PAD (PIN 11) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH TAPE AND REEL PART MARKING PACKAGE DESCRIPTION TEMPERATURE RANGE
LT3495EDDB#PBF LT3495EDDB#TRPBF LDSS 10-Lead (3mm × 2mm) Plastic DFN –40°C to 125°C
LT3495EDDB-1#PBF LT3495EDDB-1#TRPBF LDSV 10-Lead (3mm × 2mm) Plastic DFN –40°C to 125°C
LT3495BEDDB#PBF LT3495BEDDB#TRPBF LDST 10-Lead (3mm × 2mm) Plastic DFN –40°C to 125°C
LT3495BEDDB-1#PBF LT3495BEDDB-1#TRPBF LDSW 10-Lead (3mm × 2mm) Plastic DFN –40°C to 125°C
Consult LTC Marketing for parts specified with wider operating temperature ranges.
Consult LTC Marketing for information on non-standard lead based finish parts.
For more information on lead free part marking, go to: http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/
PARAMETER CONDITIONS MIN TYP MAX UNITS
Minimum Operating Voltage 2.2 2.5 V
Maximum Operating Voltage 16 V
FB Voltage VCTRL = 3V, (Note 3) l1.220 1.235 1.255 V
FB Voltage Line Regulation 0.03 %/V
FB Resistor FB Voltage = 1.235V l74.7 76 77 kΩ
Quiescent Current Not Switching 60 70 µA
Quiescent Current in Shutdown VSHDN = 0V, VCC = 3V 0 1 µA
Minimum Switch-Off Time After Start-Up (Note 4)
During Start-Up (Note 4)
200
500
ns
ns
Maximum Switch-Off Time LT3495/LT3495-1, VFB = 1.5V l17 26 35 µs
Maximum Switch-On Time 10 µs
Switch Current Limit LT3495/LT3495B l550 650 780 mA
The l 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)
ELECTRICAL CHARACTERISTICS
LT3495/LT3495B/
LT3495-1/LT3495B-1
3
3495b1b1fa
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 LT3495/LT3495B/LT3495-1/LT3495B-1 are guaranteed to
meet performance specifications from 0°C to 125°C junction temperature.
Specifications over the –40°C to 125°C operating junction temperature
range are assured by design, characterization and correlation with
statistical process controls.
ELECTRICAL CHARACTERISTICS
The l 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 TYP MAX UNITS
Switch Current Limit LT3495-1/LT3495B-1 l275 350 450 mA
Switch VCESAT LT3495/LT3495B, ISW = 400mA
LT3495-1/LT3495B-1, ISW = 200mA
200
125
mV
mV
Switch Leakage Current VSW = 5V 0.01 1 µA
PMOS Disconnect Current Limit After Start-Up
During Start-Up
250
110
370
150
450
190
mA
mA
PMOS Disconnect VCAP – VOUT IOUT = 50mA, VCAP = 15V 150 mV
VCAP – VOUT Clamp Voltage 8.7 V
SHDN Input Voltage High 1.5 V
SHDN Input Voltage Low 0.3 V
SHDN Pin Bias Current VSHDN = 3V
VSHDN = 0V
5.3
0
8 µA
µA
CTRL Pin Bias Current VCTRL = 0.5V, Current Flows Out of Pin l20 100 nA
CTRL to FB Offset VCTRL = 0.5V 6 14 mV
Maximum Shunt Current LT3495/LT3495-1, VFB = 1.5V 230 µA
Note 3: Internal reference voltage is determined by finding VFB voltage
level which causes quiescent current to increase 150µA 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.
TYPICAL PERFORMANCE CHARACTERISTICS
TA = 25°C unless otherwise noted.
Switching Frequency
vs Load Current
Load Regulation
VOUT vs CTRL Voltage
LOAD CURRENT (mA)
0
SWITCHING FREQUENCY (kHz)
1000
800
400
200
600
08040
3495 G01
1206020 100
VCC = 3.6V
VOUT = 16V
FIGURE 7 CIRCUIT
LOAD CURRENT (mA)
0
V
OUT
VOLTAGE CHANGE (%)
1.5
1.0
0.0
–0.5
–1.0
0.5
–1.5 8040
3495 G02
1206020 100
VCC = 3.6V
VOUT = 16V
FIGURE 7 CIRCUIT
CTRL VOLTAGE (V)
0
VOUT VOLTAGE (V)
18
15
9
6
3
12
01.20.6
3495 G03
1.50.90.3
FIGURE 7 CIRCUIT
LT3495/LT3495B/
LT3495-1/LT3495B-1
4
3495b1b1fa
SHDN Current vs SHDN Voltage
Peak Inductor Current
vs Temperature (LT3495)
Peak Inductor Current
vs Temperature (LT3495-1)
TYPICAL PERFORMANCE CHARACTERISTICS
Output Voltage vs Temperature
Minimum Switching Frequency
Quiescent Current - Not Switching
Quiescent Current vs Temperature
SW Saturation Voltage
vs Switch Current (LT3495)
SW Saturation Voltage
vs Switch Current (LT3495-1)
TA = 25°C unless otherwise noted.
TEMPERATURE (°C)
–40
OUTPUT VOLTAGE CHANGE (%)
1.00
0.75
0.25
0.00
–0.75
–0.50
–0.25
0.50
–1.00 800
3495 G04
12540
VCC = 3.6V
VOUT = 16V
LOAD = 5mA
FIGURE 7 CIRCUIT
TEMPERATURE (°C)
–40
MINIMUM SWITCHING FREQUENCY (kHz)
50
40
35
45
30 800
3495 G05
12540
FIGURE 7 CIRCUIT
VCC (V)
2
QUIESCENT CURRENT (µA)
100
70
80
60
90
50 14121084
3495 G06
166
TEMPERATURE (°C)
–40
QUIESCENT CURRENT (µA)
100
70
80
60
90
50 800
3495 G07
12540
SWITCH CURRENT (mA)
0
SWITCH VCESAT (mV)
300
100
150
50
200
250
0600200100 300
3495 G08
700400 500
SWITCH CURRENT (mA)
0
SWITCH VCESAT (mV)
200
80
120
40
160
0200100 300
3495 G09
400
SHDN PIN VOLTAGE (V)
0
SHDN PIN CURRENT (µA)
20
5
10
15
042 6 8
3495 G10
10
TEMPERATURE (°C)
–40
INDUCTOR PEAK CURRENT (mA)
1000
700
800
900
600 400 80
3495 G11
125
VCC = 3.6V
VOUT = 16V
FIGURE 7 CIRCUIT
TEMPERATURE (°C)
–40
INDUCTOR PEAK CURRENT (mA)
600
350
400
450
500
550
300 400 80
3495 G12
125
FIGURE 9 CIRCUIT
LT3495/LT3495B/
LT3495-1/LT3495B-1
5
3495b1b1fa
TYPICAL PERFORMANCE CHARACTERISTICS
LT3495 Switching Waveform
at No Load
LT3495 Switching Waveform
at 10mA
LT3495 Switching Waveform
at 80mA
LT3495B-1 Switching Waveform
at No Load
LT3495B-1 Switching Waveform
at 10mA
LT3495B-1 Switching Waveform
at 60mA
TA = 25°C unless otherwise noted.
10µs/DIV
3495 G13
VOUT VOLTAGE
10mV/DIV
AC COUPLED
INDUCTOR CURRENT
100mA/DIV
SW VOLTAGE
10V/DIV
VCC = 3.6V
VOUT = 16V
2µs/DIV
3495 G14
VOUT VOLTAGE
50mV/DIV
AC COUPLED
INDUCTOR CURRENT
500mA/DIV
SW VOLTAGE
10V/DIV
VCC = 3.6V
VOUT = 16V
500ns/DIV
3495 G15
VOUT VOLTAGE
50mV/DIV
AC COUPLED
INDUCTOR CURRENT
500mA/DIV
SW VOLTAGE
10V/DIV
VCC = 3.6V
VOUT = 16V
20µs/DIV
3495 G16
VOUT VOLTAGE
20mV/DIV
AC COUPLED
INDUCTOR CURRENT
100mA/DIV
SW VOLTAGE
10V/DIV
VCC = 5V
VOUT = 16V
2µs/DIV
3495 G17
VOUT VOLTAGE
50mV/DIV
AC COUPLED
INDUCTOR CURRENT
200mA/DIV
SW VOLTAGE
10V/DIV
VCC = 5V
VOUT = 16V
500ns/DIV
3495 G18
VOUT VOLTAGE
50mV/DIV
AC COUPLED
INDUCTOR CURRENT
200mA/DIV
SW VOLTAGE
10V/DIV
VCC = 5V
VOUT = 16V
LT3495/LT3495B/
LT3495-1/LT3495B-1
6
3495b1b1fa
TYPICAL PERFORMANCE CHARACTERISTICS
Line Regulation
Output Disconnect PMOS Current
vs CAP to VOUT Voltage Difference
LT3495 Start-Up Waveforms
LT3495 Transient Response
LT3495-1 Transient Response
VCC VOLTAGE (V)
0
OUTPUT VOLTAGE CHANGE (%)
0.30
0.05
0.10
0.15
0.20
0.25
084 12
3495 G19
16
CAP TO VOUT VOLTAGE DIFFERENCE (V)
0
100
0
200
300
400
500
–100 642 8 10
3495 G20
12
AFTER START-UP
IN START-UP
IN SHUTDOWN
20µs/DIV
3495 G23
VOUT VOLTAGE
200mV/DIV
AC COUPLED
LOAD CURRENT
20mA/DIV
INDUCTOR CURRENT
200mA/DIV
VCC = 3.6V
VOUT = 16V
FIGURE 9 CIRCUIT
10mA → 30mA → 10mA LOAD PULSE
50µs/DIV
3495 G21
SHDN VOLTAGE
5V/DIV
CAP VOLTAGE
5V/DIV
VOUT VOLTAGE
5V/DIV
INDUCTOR CURRENT
500mA/DIV
VCC = 3.6V
VOUT = 16V
FIGURE 7 CIRCUIT
TA = 25°C unless otherwise noted.
20µs/DIV
3495 G22
LOAD CURRENT
20mA/DIV
VOUT VOLTAGE
200mV/DIV
AC COUPLED
INDUCTOR CURRENT
500mA/DIV
VCC = 3.6V
VOUT = 16V
FIGURE 7 CIRCUIT
20mA
→
60mA
→
20mA LOAD PULSE
LT3495/LT3495B/
LT3495-1/LT3495B-1
7
3495b1b1fa
BLOCK DIAGRAM
PIN FUNCTIONS
GND (Pins 1, 2): Ground. Tie directly to local ground
plane.
VCC (Pin 3): Input Supply Pin. Must be locally by-
passed.
CTRL (Pin 4): Dimming Pin. If not used, tie CTRL to 1.5V
or higher. If in use, drive CTRL below 1.235V to override
the internal reference. See Applications section for more
information.
SHDN (Pin 5): Shutdown Pin. Tie to 1.5V or more to en-
able chip. Ground to shut down.
FB (Pin 6): Feedback Pin. Minimize the metal trace area
to this pin to minimize noise. Reference voltage is 1.235V.
There is an internal 76k resistor from the FB pin to GND. To
achieve the desired output voltage, choose R1 according
to the following formula:
R1=76•(VOUT/1.235 – 1)kΩ
VOUT (Pin 7): Drain of Output Disconnect PMOS. Place a
bypass capacitor from this pin to GND. See Applications
information.
CAP (Pins 8, 9): Source of Output Disconnect PMOS.
Place a bypass capacitor from this pin to GND.
SW (Pin 10): Switch Pin. This is the collector of the in-
ternal NPN power switch. Minimize the metal trace area
connected to this pin to minimize EMI.
Exposed Pad (Pin 11): Ground. This pin must be soldered
to PCB.
10
+
–
+
+
63
4
FB
CTRL
76k
5
SHDN
VREF
SWITCH CONTROL
SHUNT CONTROL
DISCONNECT
CONTROL
START-UP CONTROL
VCC
INPUT
SW
2
GND
1 11
GND
8
CAP
9
CAP
7
VOUT
R1
3495 BD
LT3495/LT3495B/
LT3495-1/LT3495B-1
8
3495b1b1fa
OPERATION
The LT3495 series utilizes a variable peak current, variable
off-time control scheme to provide high efficiency over a
wide range of output current.
The operation of the part can be better understood by
referring 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 76k bottom feedback resistor. Assuming that
output voltage adjustment is not used (CTRL pin is tied to
1.5V or greater), the internal reference (VREF = 1.235V) sets
the voltage at which FB will servo to during regulation.
The Switch Control block senses the output of the ampli-
fier 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 ensure that
the inductor current remains under control.
For the LT3495/LT3495-1, the switching frequency is never
allowed to fall below approximately 45kHz. Because of this,
a minimum load must be present to prevent the output
voltage from drifting too high. For most applications, 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. However when the input
Table 1. Difference Between LT3495 and LT3495B/LT3495-1/LT3495B-1
PART SWITCH CURRENT LIMIT (mA) MINIMUM SWITCHING FREQUENCY (kHz) MINIMUM OUTPUT LOAD REQUIREMENT
LT3495 650 45 Required under certain conditions
LT3495B 650 0 Not Required
LT3495-1 350 45 Required under certain conditions
LT3495B-1 350 0 Not Required
voltage and output voltage are close, the internal shunt
current may not be large enough. Under this condition,
a minimum output load is required to prevent the output
voltage from drifting too high.
For the LT3495B/B-1, the minimum switching frequency
feature is disabled and the switching frequency can be as
low as zero. As a result, the output voltage will never drift
high and no minimum output load is required.
The LT3495 series also has a 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 LT3495 series also sets a maximum switch on time of
10µs. This feature guarantees that the parts can continue
to deliver energy to the output even if the input supply
impedance becomes so large that the commanded peak
switch current is never reached.
The difference between the LT3495/LT3495B and LT3495-1/
LT3495B-1 is the level of the current limit. LT3495/LT3495B
have a typical peak current limit of 650mA while the
LT3495-1/LT3495B-1 have a typical peak current limit of
350mA. The differences between the LT3495 and LT3495B/
LT3495-1/LT3495B-1 are listed in Table 1.
LT3495/LT3495B/
LT3495-1/LT3495B-1
9
3495b1b1fa
APPLICATIONS INFORMATION
Inductor Selection
Several inductors that work well with the LT3495/LT3495B
are listed in Table 2 and those for the LT3495-1/LT3495B-1
are listed in Table 3. These tables are not complete, and
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,
as many different sizes and shapes are available.
Inductors with a value of 3.3µH or higher are recommended
for most LT3495 series designs. Inductors with low core
losses and small DCR (copper wire resistance) are good
choices for LT3495 series applications. For full output
power, the inductor should have a saturation current rating
higher than the peak inductor current. The peak inductor
current can be calculated as:
IPK =ILIMIT +VIN •200 •10–9
L
amps
where ILIMIT is 0.65A and 0.35A for LT3495/LT3495B and
LT3495-1/LT3495B-1 respectively. L is the inductance
value in Henrys and VIN is the input voltage to the boost
circuit.
Table 2. Recommended Inductors for LT3495/LT3495B
PART
L
(µH)
DCR
(mΩ)
SIZE (mm)
VENDOR
LPS4018-103ML
MSS5131-103MLC
LPS3015-472MLC
LPS3015-682MLC
10
10
4.7
6.8
200
83
200
300
4.4 × 4.4 × 1.7
5.1 × 5.1 × 3.1
3.0 × 3.0 × 1.5
3.0 × 3.0 × 1.5
Coilcraft
www.coilcraft.com
LQH43CN4R7M03 4.7 150 4.5 × 3.2 × 2.8 Murata
www.murata.com
CR32-6R8 6.8 202 4.1 × 3.7 × 3.0 Sumida
www.sumida.com
744031004 4.7 105 3.8 × 3.8 × 1.7 Wurth Elektronik
www.we-online.com
Capacitor Selection
The small size and low ESR of ceramic capacitors makes
them suitable for most LT3495 series 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 1µF to 10µF output capacitor are
sufficient for most applications. Always use a capacitor
with a sufficient voltage rating. Many capacitors rated at
1µF to 10µF, particularly 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 0805 or 1206 size capacitor will be
adequate. A 2.2µF capacitor placed on the CAP node is
recommended to filter the inductor current while a 1µF to
10µF capacitor placed on the VOUT node will give excellent
transient response and stability. Table 4 shows a list of
several capacitor manufacturers. Consult the manufac-
turers for more detailed information and for their entire
selection of related parts.
Table 3. Recommended Inductors for LT3495-1/LT3495B-1
PART
L
(µH)
DCR
(mΩ)
SIZE (mm)
VENDOR
LPO4815-472MLC
LPO4815-682MLC
LPO4815-103MLC
LPS3008-472MLC
LPS3008-682MLC
LPS3008-103MLC
4.7
6.8
10
4.7
6.8
10
150
180
230
350
500
650
4.8 × 4.8 × 1.5
4.8 × 4.8 × 1.5
4.8 × 4.8 × 1.5
3.0 × 3.0 × 0.8
3.0 × 3.0 × 0.8
3.0 × 3.0 × 0.8
Coilcraft
www.coilcraft.com
LQH32CN4R7M53
LQH32CN100K33
4.7
10
150
300
3.2 × 2.5 × 1.6
3.2 × 2.5 × 2.0
Murata
www.murata.com
CDH28D09/S-6R2 6.2 369 3.3 × 3.0 × 1.0 Sumida
www.sumida.com
744030004 4.7 290 3.5 × 3.3 × 1.0 Wurth Elektronik
www.we-online.com
Table 4. Recommended Ceramic Capacitor Manufacturers
MANUFACTURER PHONE WEBSITE
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
TDK (847) 803-6100 www.tdk.com
Diode Selection
Schottky diodes, with their low forward voltage drops and
fast switching speeds, are recommended for use with the
LT3495 series. The Diodes Inc. B0540WS-7 is a very good
choice. This diode is rated to handle an average forward
current of 0.5A with 40V reverse breakdown.
LT3495/LT3495B/
LT3495-1/LT3495B-1
10
3495b1b1fa
APPLICATIONS INFORMATION
Figure 2. Feedback Connection Using
the CAP Pin or the VOUT Pin
SW CAP
VCC
SHDN
CTRL
VOUT
FB
GND
R1
LT3495
C1
C3
VOUT
SW CAP
VCC
SHDN
CTRL
VOUT
FB
GND
R1
3495 F02
LT3495
C1
SW CAP
VCC
SHDN
CTRL
VOUT
FB
GND
3495 F03
LT3495
C1 ILOAD
Figure 1. CTRL to FB Transfer Curve Figure 3. Improved Efficiency Connection
Setting Output Voltage and the Auxiliary Reference
Input
The LT3495 series is equipped with both an internal
1.235V reference and an auxiliary reference input. This
allows the user to select between using the built-in refer-
ence 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 for purposes such
as display dimming or contrast adjustment. To use the
internal 1.235V reference, the CTRL pin must be held
higher than 1.5V. When the CTRL pin is held between 0V
and 1.235V, the parts will regulate the output such that
the FB pin voltage is nearly equal to the CTRL pin voltage.
At CTRL voltages close to 1.235V, 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:
R1=76 •VOUT
1.235 – 1
⎛
⎝
⎜⎞
⎠
⎟kΩ
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 volt-
age source driving the CTRL pin is located at a distance
to the LT3495, 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. Regu-
lating 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.
Connecting the Load to the CAP Node
The efficiency 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.
CTRL VOLTAGE (V)
0
FB VOLTAGE (V)
1.5
1.2
0.6
0.9
0.3
00.9
3495 F01
1.50.60.3 1.2
LT3495/LT3495B/
LT3495-1/LT3495B-1
11
3495b1b1fa
APPLICATIONS INFORMATION
Maximum Output Load Current
The maximum output current of a particular LT3495 series
circuit is a function of several circuit variables. The fol-
lowing method can be helpful in predicting the maximum
load current for a given circuit:
Step 1: Calculate the peak inductor current:
IPK =ILIMIT +VIN •200 •10–9
L
amps
where ILIMIT is 0.65A and 0.35A for LT3495/LT3495B and
LT3495-1/LT3495B-1 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
( )
•200 •10–9
L
amps
where VOUT is the desired output voltage. 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 –
I
RIPPLE
2
amps
Step 4: Calculate the nominal output current:
IOUT(NOM) =
I
IN(AVG)
•V
IN
•0.8
V
OUT
amps
Step 5: Derate output current:
IOUT = IOUT(NOM)•0.8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 voltage
while the output capacitor is discharged, a higher level of
inrush current may flow through the inductor and 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 chip is
designed to handle such events, the inrush current should
not be allowed to exceed 1.5A. 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.
Soft-Start
By connecting the SHDN and CTRL pins as shown in
Figure 4, using an RC filter at the CTRL pin to limit the
start-up current, the LT3495 is able to achieve soft-start.
The small bias current of the CTRL pin allows using a
small capacitor for a large RC time constant. The soft-
start waveform is shown in Figure 5. The soft-start time
Figure 5. Soft-Start Waveform
Figure 4. Soft-Start Circuitry
SW CAP
VCC
SHDN
CTRL
VOUT
FB
GND
3495 F04
LT3495
CCTRL
RCTRL
CHIP ENABLE
500µs/DIV
3495 F05
SHDN VOLTAGE
5V/DIV
INDUCTOR CURRENT
500mA/DIV
VOUT VOLTAGE
5V/DIV
CTRL VOLTAGE
2V/DIV
VCC = 3.6V
V
OUT
= 16V
LT3495/LT3495B/
LT3495-1/LT3495B-1
12
3495b1b1fa
APPLICATIONS INFORMATION
Figure 6. Recommended Board Layout
can be set by the value of RCTRL and CCTRL. The following
expression can be used to design the soft-start time:
TSTART−UP =RCTRL •CCTRL •In VSHDN
VSHDN – 1.235
⎛
⎝
⎜⎞
⎠
⎟
where VSHDN is the voltage at SHDN pin when the part is
enabled. To ensure soft-start will work, the initial voltage
at CTRL pin when the part is enabled should be close to
0V. The soft-start may not work if this initial condition is
not satisfied.
Output Disconnect
The LT3495 series has an output disconnect PMOS that
blocks the load from the input during shutdown. During
normal operation, the maximum current through the PMOS
is limited by circuitry inside the chip. When the CAP and
VOUT voltage difference is more than 8.7V (typ), the cur-
rent through the PMOS is no longer limited, and can be
much higher. As a result, forcing 8.7V or higher voltage
from the CAP to the VOUT pins can damage the PMOS.
In cases when the CAP voltage is high and/or a large ca-
pacitor is used at the CAP pin, shorting VOUT to GND can
cause large PMOS currents to flow. Under this condition,
the PMOS peak current should be kept at less than 1A.
Also be aware of the thermal dissipation in the PMOS at
all times. In addition, if the input voltage is more than 8V,
the PMOS will turn on during shutdown, resulting in the
output voltage no longer being blocked from the input.
Under this condition, the output voltage will be about 8V
lower than the input voltage.
Board Layout Considerations
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 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 pin
feeds into the internal error amplifier and is sensitive to
noise. Minimizing the length and area of all traces to this
pin is recommended. Connect the feedback resistor R1
directly from the VOUT pin to the FB pin and keep the trace
as short as possible. Recommended component placement
is shown in Figure 6.
GND
GND
VCC
CTRL
SHDN
SW
CAP
CAP
VOUT
FB
GND
CTRL
VIAS TO GROUND PLANE REQUIRED
TO IMPROVE THERMAL PERFORMANCE
VIAS FOR CAP GROUND RETURN THROUGH
SECOND METAL LAYER, CAPACITOR GROUNDS
MUST BE RETURNED DIRECTLY TO IC GROUND
SHDN
3495 F06
GND
LT3495/LT3495B/
LT3495-1/LT3495B-1
13
3495b1b1fa
TYPICAL APPLICATIONS
Figure 8. One Li-Ion Cell Input Boost Converter with the LT3495B
Efficiency vs Load Current
LT3495/LT3495B Maximum Output Current vs Output Voltage
VOUT
R1 VALUE REQUIRED
(MΩ)
MAXIMUM OUTPUT
CURRENT AT 3V INPUT (mA)
40 2.37 26
35 2.05 31
30 1.78 37
25 1.47 43
20 1.15 57
15 0.845 74
10 0.536 120
5 0.232 250
SW CAP
VCC
SHDN
CTRL
VOUT
FB
GND
R1
909k
3495 F07a
LT3495
C1
4.7µF
L1
10µH
C2
2.2µF
C3
1µF
ONE Li-Ion CELL
TURN ON/OFF
VOUT DIMMING
C1: 4.7µF, 6.3V, X5R, 0603
C2: 2.2µF, 25V, X5R, 0805
C3: 1µF, 25V, X5R, 0603
D1: DIODES INC. B0540WS-7
L1: COILCRAFT LPS4018-103MLB
OUTPUT 16V
70mA
D1
Figure 7. One Li-Ion Cell Input Boost Converter with the LT3495
SW CAP
VCC
SHDN
CTRL
VOUT
FB
GND
R1
909k
3495 F08a
LT3495B
C1
4.7µF
L1
6.8µH
C2
2.2µF
C3
1µF
ONE Li-Ion CELL
TURN ON/OFF
VOUT DIMMING
C1: 4.7µF, 6.3V, X5R, 0603
C2: 2.2µF, 25V, X5R, 0805
C3: 1µF, 25V, X5R, 0603
D1: DIODES INC. B0540WS-7
L1: SUMIDA CR32-6R8
OUTPUT 16V
70mA
D1
Efficiency vs Load Current
LOAD CURRENT (mA)
EFFICIENCY (%)
POWER LOSS (mW)
3495 F07b
90
80
50
60
70
40
400
320
80
160
240
0
0.1 10 1001
VIN = 3.6V LOAD FROM CAP
LOAD FROM VOUT
LOAD CURRENT (mA)
EFFICIENCY (%)
POWER LOSS (mW)
3495 F08b
90
80
50
60
70
40
400
320
80
160
240
0
0.1 10 1001
VIN = 3.6V
LOAD FROM CAP
LOAD FROM VOUT
LT3495/LT3495B/
LT3495-1/LT3495B-1
14
3495b1b1fa
One Li-Ion Cell Input Boost Converter with the LT3495-1/LT3495B-1 Efficiency vs Load Current
TYPICAL APPLICATIONS
LT3495-1/LT3495B-1 Maximum Output Current vs Output Voltage
VOUT
R1 VALUE REQUIRED
(MΩ)
MAXIMUM OUTPUT
CURRENT AT 3V INPUT (mA)
40 2.37 12
35 2.05 15
30 1.78 18
25 1.47 21
20 1.15 28
15 0.845 36
10 0.536 63
5 0.232 120
Efficiency vs Load Current
SW CAP
VCC
SHDN
CTRL
VOUT
FB
GND
665k
3495 TA02a
LT3495B
C1
4.7µF
L1
10µH
C2
2.2µF
C3
10µF
VIN = 5V
TURN ON/OFF
VOUT DIMMING
C1: 4.7µF, 6.3V, X5R, 0603
C2: 2.2µF, 25V, X5R, 0805
C3: 10µF, 25V, X5R, 1206
D1: DIODES INC. B0540WS-7
L1: COILCRAFT LPS4018-103MLB
VOUT = 12V
130mA
D1
5V to 12V, 130mA Boost Converter
LOAD CURRENT (mA)
EFFICIENCY (%)
POWER LOSS (mW)
3495 TA02b
100
90
80
50
60
70
40
900
750
600
150
300
450
0
0.1 10 100 10001
LOAD FROM CAP
LOAD FROM VOUT
LOAD CURRENT (mA)
EFFICIENCY (%)
POWER LOSS (mW)
3495 F09b
90
80
50
60
70
40
250
200
50
100
150
0
0.1 10 1001
VIN = 3.6V
LOAD FROM CAP
LOAD FROM VOUT
SW CAP
VCC
SHDN
CTRL
VOUT
FB
GND
909k
3495 F09a
LT3495B-1/
LT3495-1
C1
2.2µF
L1
10µH
C2
1µF
C3
1µF
ONE LI-ION CELL
TURN ON/OFF
VOUT DIMMING
C1: 2.2µF, 6.3V, X5R, 0603
C2: 1µF, 25V, X5R, 0603
C3: 1µF, 25V, X5R, 0603
D1: DIODES INC. B0540WS-7
L1: MURATA LQH32CN100K33
OUTPUT 16V
30mA
D1
LT3495/LT3495B/
LT3495-1/LT3495B-1
15
3495b1b1fa
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.
DDB Package
10-Lead Plastic DFN (3mm × 2mm)
(Reference LTC DWG # 05-08-1722 Rev Ø)
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
0.64 ± 0.05
(2 SIDES)
0.75 ±0.05
R = 0.115
TYP
R = 0.05
TYP
2.39 ±0.05
(2 SIDES)
3.00 ±0.10
(2 SIDES)
15
106
PIN 1 BAR
TOP MARK
(SEE NOTE 6)
0.200 REF
0 – 0.05
(DDB10) DFN 0905 REV
Ø
0.25 ± 0.05
2.39 ±0.05
(2 SIDES)
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
0.64 ±0.05
(2 SIDES)
1.15 ±0.05
0.70 ±0.05
2.55
±0.05
PACKAGE
OUTLINE
0.25 ± 0.05
0.50 BSC
PIN 1
R = 0.20 OR
0.25 × 45°
CHAMFER
0.50 BSC
Efficiency vs Load Current
TYPICAL APPLICATIONS
Wide Input Range SEPIC Converter with 5V Output
SW CAP
VCC
SHDN
CTRL
VOUT
FB
GND
232k
3495 TA03a
LT3495B
C1
2.2µF
L1
10µH
L2
10µH
C3
10µF
C2
1µF
INPUT
2.6V TO 12V
TURN ON/OFF
VOUT DIMMING
C1: 2.2µF, 16V, X5R, 0805
C2: 1µF, 16V, X5R, 0805
C3: 10µF, 16V, X5R, 1206
D1: FAIRCHILD SEMI MBR0540
L1, L2: COILCRAFT LPS4018-103MLB
VOUT = 5V
200mA, VIN = 3.3V,
300mA, VIN = 5V,
500mA, VIN = 8V
D1
LOAD CURRENT (mA)
EFFICIENCY (%)
POWER LOSS (mW)
3495 TA03b
90
80
50
60
70
40
1200
1000
400
200
600
800
0
0.1 10 100 10001
VCC = 3.3V
PACKAGE DESCRIPTION
LT3495/LT3495B/
LT3495-1/LT3495B-1
16
3495b1b1fa
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com
LINEAR TECHNOLOGY CORPORATION 2008
LT 0209 REV A • PRINTED IN USA
RELATED PARTS
TYPICAL APPLICATION
PART NUMBER DESCRIPTION COMMENTS
LT1930/LT1930A 1A (ISW), 1.2MHz/2.2MHz, High Efficiency Step-Up
DC/DC Converters
VIN: 2.6V to 16V, VOUT(MAX) = 34V, IQ = 4.2mA/5.5mA, ISD < 1µA,
ThinSOT Package
LT1945 (Dual) Dual Output, Boost/Inverter, 350mA (ISW), Constant Off-
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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
LT3463/LT3463A Dual Output, Boost/Inverter, 250mA (ISW), Constant
Off-Time, High Efficiency Step-Up DC/DC Converters with
Integrated Schottkys
VIN: 2.3V to 15V, VOUT(MAX) = ±40V, IQ = 40µA, ISD < 1µA,
DFN 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
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
LT3473/LT3473A 1A (ISW), 1.2MHz, High Efficiency Step-Up DC/DC
Converters with Integrated Schottky Diode and Output
Disconnect
VIN: 2.2V to 16V, VOUT(MAX) = 36V, IQ = 100µA, ISD < 1µA,
DFN Package
LT3494/LT3494A 180mA/350mA (ISW), High Efficiency Step-Up DC/DC
Converters with Output Disconnect
VIN: 2.1V to 16V, VOUT(MAX) = 40V, IQ = 65µA, ISD < 1µA,
DFN Package
LT3580 2A, 40V, 2.5MHz Boost DC/DC Converter VIN: 2.5V to 32V, VOUT(MAX) = 40V, IQ = 1mA, ISD < 1µA,
MS8E 3mm × 3mm DFN-8 Package
Adjustable High Voltage Power Supply Doesn’t Need a Transformer Output vs CTRL
LOAD CURRENT (mA)
EFFICIENCY (%)
POWER LOSS (mW)
3495 TA04c
90
80
50
40
60
70
30
600
500
200
100
300
400
0
0.1 10 1001
VIN = 5V
VOUT = 120V
LOAD CURRENT (mA)
0
VOUT PEAK-TO-PEAK RIPPLE (mV)
700
600
400
500
300
200
100
0168
3495 TA04d
20124
VIN = 5V
VOUT = 120V
SW CAP
VCC
SHDN
CTRL
VOUT
FB
GND 10.7k
VOUT 15V TO 120V
10mA (VIN = 3.3V)
18mA (VIN = 5V)
35mA (VIN = 8V)
3495 TA04a
LT3495B
C1
4.7µF
L1
22µH
C2
1µF
D1 D2 D3 D4
C4
1µF
C6
1µF
909k
C5
1µF
C7
1µF
C3
1µF
3.3V TO 8V
INPUT
TURN ON/OFF
VOUT DIMMING
C1: 4.7µF, 16V, X5R, 0805
C2-C7: 1µF, 50V, X5R, 0805
D1-D5: DIODE INC. B0540WS-7
L1: COILCRAFT LPS4018-223MLB
D5
DANGER HIGH VOLTAGE! OPERATION BY HIGH VOLTAGE TRAINED PERSONNEL ONLY
CTRL VOLTAGE (V)
0
VOUT VOLTAGE (V)
150
120
60
90
30
01.20.6 1.8
3495 TA04b
2.10.90.3 1.5
Output Voltage Ripple vs Load CurrentEfficiency vs Load Current