LINER LT3495B 650ma/350ma micropower low noise boost converter with output disconnect Datasheet

LT3495/LT3495B/
LT3495-1/LT3495B-1
650mA/350mA Micropower
Low Noise Boost Converter
with Output Disconnect
FEATURES
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DESCRIPTION
Low Quiescent Current
60µA in Active Mode
0.1µA in Shutdown Mode
Low Noise Control Scheme (Switching Frequency
Always Stays Above Audible Range for LT3495/-1)
Integrated Power NPN:
650mA Current Limit (LT3495/B)
350mA Current Limit (LT3495-1/B-1)
Integrated Output Disconnect
Integrated Output Dimming
Wide input range: 2.5V to 16V
Wide output range: Up to 40V
Integrated feedback resistor
Tiny 10-Lead 3mm × 2mm DFN Package
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 shutdown. 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.
APPLICATIONS
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OLED Power
Low Noise Power
MP3 Player
L, 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
4.7µF
2.2µF
CAP
VCC
VOUT
909k
LT3495
SHDN
FB
CTRL
GND
VOUT
16V
70mA
1µF
3495 TA01a
40
1.0µF 0603
CAPACITOR AT VOUT
80
30
20
10
0
0.1
2.2µF 1206
CAPACITOR AT VOUT
10
1
LOAD CURRENT (mA)
VIN = 3.6V
100
3495 TA01b
400
LOAD FROM CAP
320
LOAD FROM VOUT
70
240
60
160
50
80
40
0.1
1
10
LOAD CURRENT (mA)
POWER LOSS (mW)
SW
EFFICIENCY (%)
10µH
VOUT PEAK-TO-PEAK RIPPLE (mV)
ONE
Li-Ion
CELL
Efficiency vs Load Current
90
50
0
100
3495 TA01c
3495b1b1fa
1
LT3495/LT3495B/
LT3495-1/LT3495B-1
ABSOLUTE MAXIMUM RATINGS
PIN CONFIGURATION
(Note 1)
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
TOP VIEW
GND 1
10 SW
GND 2
VCC 3
11
9
CAP
8
CAP
CTRL 4
7
VOUT
SHDN 5
6
FB
DDB PACKAGE
10-LEAD (3mm × 2mm) PLASTIC DFN
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/
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
Minimum Operating Voltage
TYP
MAX
2.2
2.5
V
16
V
1.255
V
Maximum Operating Voltage
VCTRL = 3V, (Note 3)
l
FB Resistor
FB Voltage = 1.235V
l
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)
Maximum Switch-Off Time
LT3495/LT3495-1, VFB = 1.5V
FB Voltage
1.220
FB Voltage Line Regulation
0.03
74.7
%/V
200
500
l
17
Maximum Switch-On Time
Switch Current Limit
1.235
UNITS
26
ns
ns
35
10
LT3495/LT3495B
l
550
650
µs
µs
780
mA
3495b1b1fa
2
LT3495/LT3495B/
LT3495-1/LT3495B-1
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
Switch Current Limit
LT3495-1/LT3495B-1
Switch VCESAT
LT3495/LT3495B, ISW = 400mA
LT3495-1/LT3495B-1, ISW = 200mA
Switch Leakage Current
VSW = 5V
PMOS Disconnect Current Limit
After Start-Up
During Start-Up
PMOS Disconnect VCAP – VOUT
IOUT = 50mA, VCAP = 15V
275
l
TYP
MAX
350
450
250
110
SHDN Input Voltage High
1
µA
370
150
450
190
mA
mA
150
mV
8.7
V
1.5
SHDN Pin Bias Current
VSHDN = 3V
VSHDN = 0V
CTRL Pin Bias Current
VCTRL = 0.5V, Current Flows Out of Pin
CTRL to FB Offset
VCTRL = 0.5V
Maximum Shunt Current
LT3495/LT3495-1, VFB = 1.5V
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 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.
V
Switching Frequency
vs Load Current
200
20
60
40
80
LOAD CURRENT (mA)
100
120
3495 G01
VCC = 3.6V
VOUT = 16V
1.0 FIGURE 7 CIRCUIT
µA
µA
20
100
nA
6
14
mV
µA
FIGURE 7 CIRCUIT
15
0.5
0.0
–0.5
–1.0
–1.5
8
VOUT vs CTRL Voltage
18
VOUT VOLTAGE (V)
VOUT VOLTAGE CHANGE (%)
SWITCHING FREQUENCY (kHz)
400
5.3
0
TA = 25°C unless otherwise noted.
Load Regulation
600
V
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.
1.5
VCC = 3.6V
VOUT = 16V
FIGURE 7 CIRCUIT
0
l
0.3
230
TYPICAL PERFORMANCE CHARACTERISTICS
0
mV
mV
0.01
SHDN Input Voltage Low
800
mA
200
125
VCAP – VOUT Clamp Voltage
1000
UNITS
12
9
6
3
0
20
60
40
80
LOAD CURRENT (mA)
100
120
3495 G02
0
0
0.3
0.9
0.6
CTRL VOLTAGE (V)
1.2
1.5
3495 G03
3495b1b1fa
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LT3495/LT3495B/
LT3495-1/LT3495B-1
TYPICAL PERFORMANCE CHARACTERISTICS
Output Voltage vs Temperature
Minimum Switching Frequency
50
0.25
0.00
–0.25
–0.50
–0.75
0
40
80
TEMPERATURE (°C)
FIGURE 7 CIRCUIT
45
40
35
30
–40
125
0
3495 G04
200
150
100
0
125
0
100
200 300 400 500
SWITCH CURRENT (mA)
3495 G07
1000
INDUCTOR PEAK CURRENT (mA)
SHDN PIN CURRENT (µA)
10
5
0
2
4
6
8
SHDN PIN VOLTAGE (V)
10
3495 G10
14
16
3495 G06
120
80
600
0
700
100
200
300
SWITCH CURRENT (mA)
0
Peak Inductor Current
vs Temperature (LT3495-1)
600
VCC = 3.6V
VOUT = 16V
FIGURE 7 CIRCUIT
900
800
700
600
–40
0
40
80
TEMPERATURE (°C)
400
3495 G09
Peak Inductor Current
vs Temperature (LT3495)
15
12
3495 G08
SHDN Current vs SHDN Voltage
20
8
10
VCC (V)
40
INDUCTOR PEAK CURRENT (mA)
80
40
TEMPERATURE (°C)
6
160
50
0
4
2
200
SWITCH VCESAT (mV)
SWITCH VCESAT (mV)
60
50
–40
60
SW Saturation Voltage
vs Switch Current (LT3495-1)
250
90
70
70
50
125
300
80
80
SW Saturation Voltage
vs Switch Current (LT3495)
100
QUIESCENT CURRENT (µA)
40
80
TEMPERATURE (°C)
90
3495 G05
Quiescent Current vs Temperature
0
Quiescent Current - Not Switching
100
QUIESCENT CURRENT (µA)
VCC = 3.6V
0.75 VOUT = 16V
LOAD = 5mA
0.50 FIGURE 7 CIRCUIT
MINIMUM SWITCHING FREQUENCY (kHz)
OUTPUT VOLTAGE CHANGE (%)
1.00
–1.00
–40
TA = 25°C unless otherwise noted.
125
3495 G11
FIGURE 9 CIRCUIT
550
500
450
400
350
300
–40
0
40
80
TEMPERATURE (°C)
125
3495 G12
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LT3495/LT3495B/
LT3495-1/LT3495B-1
TYPICAL PERFORMANCE CHARACTERISTICS
LT3495 Switching Waveform
at 10mA
LT3495 Switching Waveform
at No Load
VOUT VOLTAGE
10mV/DIV
AC COUPLED
VOUT VOLTAGE
50mV/DIV
AC COUPLED
SW VOLTAGE
10V/DIV
SW VOLTAGE
10V/DIV
INDUCTOR CURRENT
100mA/DIV
INDUCTOR CURRENT
500mA/DIV
VCC = 3.6V
VOUT = 16V
10µs/DIV
VCC = 3.6V
VOUT = 16V
3495 G13
VOUT VOLTAGE
50mV/DIV
AC COUPLED
VOUT VOLTAGE
20mV/DIV
AC COUPLED
SW VOLTAGE
10V/DIV
SW VOLTAGE
10V/DIV
INDUCTOR CURRENT
500mA/DIV
INDUCTOR CURRENT
100mA/DIV
500ns/DIV
VCC = 5V
VOUT = 16V
3495 G15
LT3495B-1 Switching Waveform
at 10mA
3495 G14
VOUT VOLTAGE
50mV/DIV
AC COUPLED
SW VOLTAGE
10V/DIV
SW VOLTAGE
10V/DIV
INDUCTOR CURRENT
200mA/DIV
INDUCTOR CURRENT
200mA/DIV
2µs/DIV
3495 G17
20µs/DIV
3495 G16
LT3495B-1 Switching Waveform
at 60mA
VOUT VOLTAGE
50mV/DIV
AC COUPLED
VCC = 5V
VOUT = 16V
2µs/DIV
LT3495B-1 Switching Waveform
at No Load
LT3495 Switching Waveform
at 80mA
VCC = 3.6V
VOUT = 16V
TA = 25°C unless otherwise noted.
VCC = 5V
VOUT = 16V
500ns/DIV
3495 G18
3495b1b1fa
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LT3495/LT3495B/
LT3495-1/LT3495B-1
TYPICAL PERFORMANCE CHARACTERISTICS
0.30
600
0.25
500
PMOS CURRENT (mA)
OUTPUT VOLTAGE CHANGE (%)
Line Regulation
0.20
0.15
0.10
Output Disconnect PMOS Current
vs CAP to VOUT Voltage Difference
400
AFTER START-UP
300
200
IN START-UP
100
0.05
0
TA = 25°C unless otherwise noted.
IN SHUTDOWN
0
0
4
8
12
VCC VOLTAGE (V)
–100
16
3495 G19
0
12
2
4
6
8
10
CAP TO VOUT VOLTAGE DIFFERENCE (V)
3495 G20
LT3495 Start-Up Waveforms
SHDN VOLTAGE
5V/DIV
INDUCTOR CURRENT
500mA/DIV
CAP VOLTAGE
5V/DIV
VOUT VOLTAGE
5V/DIV
VCC = 3.6V
VOUT = 16V
FIGURE 7 CIRCUIT
50µs/DIV
3495 G21
LT3495 Transient Response
LT3495-1 Transient Response
20mA → 60mA → 20mA LOAD PULSE
10mA → 30mA → 10mA LOAD PULSE
VOUT VOLTAGE
200mV/DIV
AC COUPLED
VOUT VOLTAGE
200mV/DIV
AC COUPLED
INDUCTOR CURRENT
500mA/DIV
INDUCTOR CURRENT
200mA/DIV
LOAD CURRENT
20mA/DIV
LOAD CURRENT
20mA/DIV
VCC = 3.6V
VOUT = 16V
FIGURE 7 CIRCUIT
20µs/DIV
3495 G22
VCC = 3.6V
VOUT = 16V
FIGURE 9 CIRCUIT
20µs/DIV
3495 G23
3495b1b1fa
6
LT3495/LT3495B/
LT3495-1/LT3495B-1
PIN FUNCTIONS
GND (Pins 1, 2): Ground. Tie directly to local ground
plane.
achieve the desired output voltage, choose R1 according
to the following formula:
VCC (Pin 3): Input Supply Pin. Must be locally bypassed.
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.
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.
CAP (Pins 8, 9): Source of Output Disconnect PMOS.
Place a bypass capacitor from this pin to GND.
SHDN (Pin 5): Shutdown Pin. Tie to 1.5V or more to enable chip. Ground to shut down.
SW (Pin 10): Switch Pin. This is the collector of the internal NPN power switch. Minimize the metal trace area
connected to this pin to minimize EMI.
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
Exposed Pad (Pin 11): Ground. This pin must be soldered
to PCB.
BLOCK DIAGRAM
INPUT
R1
6
3
10
VCC
FB
76k
9
8
CAP
SW
4
5
SHDN
+
VOUT
START-UP CONTROL
–
CTRL
7
CAP
+
+
DISCONNECT
CONTROL
SWITCH CONTROL
VREF
SHUNT CONTROL
GND
2
GND
1
11
3495 BD
3495b1b1fa
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LT3495/LT3495B/
LT3495-1/LT3495B-1
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 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 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
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.
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
3495b1b1fa
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LT3495/LT3495B/
LT3495-1/LT3495B-1
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
L
–9
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
DCR
(µH) (mΩ)
LPS4018-103ML
MSS5131-103MLC
LPS3015-472MLC
LPS3015-682MLC
10
10
4.7
6.8
200
83
200
300
4.4 × 4.4 × 1.7 Coilcraft
5.1 × 5.1 × 3.1 www.coilcraft.com
3.0 × 3.0 × 1.5
3.0 × 3.0 × 1.5
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
SIZE (mm)
VENDOR
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 manufacturers for more detailed information and for their entire
selection of related parts.
Table 3. Recommended Inductors for LT3495-1/LT3495B-1
PART
L
DCR
(µH) (mΩ)
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 Coilcraft
4.8 × 4.8 × 1.5 www.coilcraft.com
4.8 × 4.8 × 1.5
3.0 × 3.0 × 0.8
3.0 × 3.0 × 0.8
3.0 × 3.0 × 0.8
LQH32CN4R7M53
LQH32CN100K33
4.7
10
150
300
3.2 × 2.5 × 1.6 Murata
3.2 × 2.5 × 2.0 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
SIZE (mm)
VENDOR
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.
3495b1b1fa
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LT3495/LT3495B/
LT3495-1/LT3495B-1
APPLICATIONS INFORMATION
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 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 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:
⎛V
⎞
R1= 76 • ⎜ OUT – 1⎟ kΩ
⎝ 1.235 ⎠
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 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. 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.
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.
SW
CAP
VCC
VOUT
C1
SW
CAP
VCC
VOUT
R1
LT3495
SHDN
FB
SHDN
FB
CTRL
GND
CTRL
GND
3495 F02
1.2
FB VOLTAGE (V)
VOUT
C3
R1
LT3495
1.5
C1
Figure 2. Feedback Connection Using
the CAP Pin or the VOUT Pin
0.9
0.6
0.3
SW
CAP
VCC
VOUT
C1
ILOAD
LT3495
0
0
0.3
0.6
0.9
CTRL VOLTAGE (V)
1.2
1.5
3495 F01
Figure 1. CTRL to FB Transfer Curve
SHDN
FB
CTRL
GND
3495 F03
Figure 3. Improved Efficiency Connection
3495b1b1fa
10
LT3495/LT3495B/
LT3495-1/LT3495B-1
APPLICATIONS INFORMATION
Maximum Output Load Current
Inrush Current
The maximum output current of a particular LT3495 series
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 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.
Step 1: Calculate the peak inductor current:
IPK =ILIMIT +
VIN • 200 •10 –9
amps
L
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
(
=
amps
L
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.
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 softstart waveform is shown in Figure 5. The soft-start time
Step 3: Calculate the average input current:
IIN(AVG) =IPK –
IRIPPLE
amps
2
IIN(AVG) • VIN • 0.8
VOUT
CAP
VCC
VOUT
LT3495
CHIP ENABLE
RCTRL
IOUT = IOUT(NOM) • 0.8 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.
FB
CTRL
GND
CCTRL
amps
Step 5: Derate output current:
SHDN
3495 F04
Step 4: Calculate the nominal output current:
IOUT(NOM) =
SW
Figure 4. Soft-Start Circuitry
SHDN VOLTAGE
5V/DIV
INDUCTOR CURRENT
500mA/DIV
CTRL VOLTAGE
2V/DIV
VOUT VOLTAGE
5V/DIV
VCC = 3.6V
VOUT = 16V
500µs/DIV
3495 F05
Figure 5. Soft-Start Waveform
3495b1b1fa
11
LT3495/LT3495B/
LT3495-1/LT3495B-1
APPLICATIONS INFORMATION
can be set by the value of RCTRL and CCTRL. The following
expression can be used to design the soft-start time:
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.
⎛
⎞
VSHDN
TSTART−UP = RCTRL • CCTRL •In ⎜
⎟
⎝ 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.
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 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 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.
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 current 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 capacitor 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.
GND
SW
GND
CAP
VCC
GND
CAP
CTRL
VOUT
SHDN
FB
GND
3495 F06
CTRL SHDN
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
Figure 6. Recommended Board Layout
3495b1b1fa
12
LT3495/LT3495B/
LT3495-1/LT3495B-1
TYPICAL APPLICATIONS
L1
10µH
C1
4.7µF
90
CAP
VOUT
OUTPUT 16V
70mA
R1
909k
LT3495
TURN ON/OFF
SHDN
FB
VOUT DIMMING
CTRL
GND
C3
1µF
400
VIN = 3.6V
LOAD FROM CAP
80
3495 F07a
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
320
LOAD FROM VOUT
70
240
60
160
50
80
40
0.1
POWER LOSS (mW)
SW
VCC
C2
2.2µF
EFFICIENCY (%)
ONE Li-Ion CELL
Efficiency vs Load Current
D1
0
100
1
10
LOAD CURRENT (mA)
3495 F07b
Figure 7. One Li-Ion Cell Input Boost Converter with the LT3495
L1
6.8µH
C1
4.7µF
90
CAP
VCC
VOUT
OUTPUT 16V
70mA
R1
909k
LT3495B
TURN ON/OFF
SHDN
FB
VOUT DIMMING
CTRL
GND
C3
1µF
3495 F08a
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
400
VIN = 3.6V
LOAD FROM CAP
80
320
LOAD FROM VOUT
70
240
60
160
50
80
40
0.1
1
10
LOAD CURRENT (mA)
POWER LOSS (mW)
SW
C2
2.2µF
EFFICIENCY (%)
ONE Li-Ion CELL
Efficiency vs Load Current
D1
0
100
3495 F08b
Figure 8. One Li-Ion Cell Input Boost Converter with the LT3495B
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
3495b1b1fa
13
LT3495/LT3495B/
LT3495-1/LT3495B-1
TYPICAL APPLICATIONS
One Li-Ion Cell Input Boost Converter with the LT3495-1/LT3495B-1
L1
10µH
SW
CAP
VCC
VOUT
OUTPUT 16V
30mA
TURN ON/OFF
SHDN
FB
VOUT DIMMING
CTRL
GND
909k
LOAD FROM CAP
80
C2
1µF
LT3495B-1/
LT3495-1
250
VIN = 3.6V
C3
1µF
200
70
150
LOAD FROM VOUT
60
100
50
50
POWER LOSS (mW)
C1
2.2µF
D1
EFFICIENCY (%)
ONE LI-ION CELL
Efficiency vs Load Current
90
3495 F09a
40
0.1
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
0
100
1
10
LOAD CURRENT (mA)
3495 F09b
LT3495-1/LT3495B-1 Maximum Output Current vs Output Voltage
R1 VALUE REQUIRED
(MΩ)
VOUT
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
5V to 12V, 130mA Boost Converter
100
L1
10µH
SW
VCC
LOAD FROM CAP
90
CAP
C2
2.2µF
VOUT = 12V
130mA
VOUT
LT3495B
665k
TURN ON/OFF
SHDN
FB
VOUT DIMMING
CTRL
GND
3495 TA02a
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
900
C3
10µF
750
LOAD FROM VOUT
80
600
70
450
60
300
50
150
40
0.1
1
10
100
LOAD CURRENT (mA)
POWER LOSS (mW)
C1
4.7µF
D1
EFFICIENCY (%)
VIN = 5V
Efficiency vs Load Current
0
1000
3495 TA02b
3495b1b1fa
14
LT3495/LT3495B/
LT3495-1/LT3495B-1
TYPICAL APPLICATIONS
Wide Input Range SEPIC Converter with 5V Output
C2
1µF
INPUT
2.6V TO 12V
SW
VCC
VOUT
LT3495B
TURN ON/OFF
SHDN
FB
VOUT DIMMING
CTRL
GND
232k
1000
80
C3
10µF
L2
10µH
CAP
1200
VCC = 3.3V
VOUT = 5V
200mA, VIN = 3.3V,
300mA, VIN = 5V,
500mA, VIN = 8V
800
70
600
60
400
50
3495 TA03a
200
40
0.1
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
POWER LOSS (mW)
C1
2.2µF
D1
EFFICIENCY (%)
L1
10µH
Efficiency vs Load Current
90
1
0
1000
10
100
LOAD CURRENT (mA)
3495 TA03b
PACKAGE DESCRIPTION
DDB Package
10-Lead Plastic DFN (3mm × 2mm)
(Reference LTC DWG # 05-08-1722 Rev Ø)
0.64 ±0.05
(2 SIDES)
3.00 ±0.10
(2 SIDES)
R = 0.05
TYP
0.70 ±0.05
2.55 ±0.05
1.15 ±0.05
PACKAGE
OUTLINE
0.25 ± 0.05
0.50 BSC
2.39 ±0.05
(2 SIDES)
PIN 1 BAR
TOP MARK
(SEE NOTE 6)
0.200 REF
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
R = 0.115
TYP
6
0.40 ± 0.10
10
2.00 ±0.10
(2 SIDES)
0.75 ±0.05
0.64 ± 0.05
(2 SIDES)
5
0.25 ± 0.05
0 – 0.05
PIN 1
R = 0.20 OR
0.25 × 45°
CHAMFER
1
(DDB10) DFN 0905 REV Ø
0.50 BSC
2.39 ±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
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 representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
15
LT3495/LT3495B/
LT3495-1/LT3495B-1
TYPICAL APPLICATION
Adjustable High Voltage Power Supply Doesn’t Need a Transformer
Output vs CTRL
150
DANGER HIGH VOLTAGE! OPERATION BY HIGH VOLTAGE TRAINED PERSONNEL ONLY
3.3V TO 8V
INPUT
L1
22µH
C6
1µF
D5
C1
4.7µF
D1
SW
CAP
VCC
VOUT
SHDN
VOUT DIMMING
CTRL
D2
C1: 4.7µF, 16V, X5R, 0805
C2-C7: 1µF, 50V, X5R, 0805
D1-D5: DIODE INC. B0540WS-7
L1: COILCRAFT LPS4018-223MLB
D4
C7
1µF
909k
FB
GND
D3
C5
1µF
C3
1µF
LT3495B
TURN ON/OFF
C2
1µF
120
VOUT VOLTAGE (V)
C4
1µF
10.7k
0
0.3
0.6 0.9 1.2 1.5
CTRL VOLTAGE (V)
1.8
2.1
3495 TA04b
Output Voltage Ripple vs Load Current
700
VOUT PEAK-TO-PEAK RIPPLE (mV)
600
VIN = 5V
VOUT = 120V
500
70
400
60
300
50
200
40
100
30
0.1
0
3495 TA04a
POWER LOSS (mW)
EFFICIENCY (%)
80
60
30
VOUT 15V TO 120V
10mA (VIN = 3.3V)
18mA (VIN = 5V)
35mA (VIN = 8V)
Efficiency vs Load Current
90
90
1
10
LOAD CURRENT (mA)
500
400
300
200
100
0
0
100
VIN = 5V
VOUT = 120V
600
0
4
12
8
16
LOAD CURRENT (mA)
20
3495 TA04d
3495 TA04c
RELATED PARTS
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 OffTime, 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
LT3463/LT3463A
VIN: 2.3V to 15V, VOUT(MAX) = ±40V, IQ = 40µA, ISD < 1µA,
Dual Output, Boost/Inverter, 250mA (ISW), Constant
Off-Time, High Efficiency Step-Up DC/DC Converters with DFN Package
Integrated Schottkys
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
3495b1b1fa
16 Linear Technology Corporation
LT 0209 REV A • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507
●
www.linear.com
 LINEAR TECHNOLOGY CORPORATION 2008
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