LT3663
1.2A Step-Down
Switching Regulator with
Output Current Limit
Features
Description
Wide Input Range:
Operation from 7.5V to 36V
Overvoltage Lockout Protects Circuit through 60V
Transients
n Programmable Output Current Limit (0.4A to 1.2A)
n 3.3V and 5V Fixed Output Voltage Options
n Integrated Boost Diode
n Fixed Frequency, Peak Current Mode Control
LT3663 fSW = 1.5MHz
LT3663-X fSW = 1MHZ
n Low Switch V
CESAT: 275mV at 1A
n Internally Compensated
n Thermal Protection
n Thermally Enhanced 8-Pin 2mm × 3mm DFN and
MSOP Packages
The LT®3663 is a current mode step-down switching regulator with programmable output current limit. The current
limit accurately controls the system power dissipation and
reduces the size of the power path components.
n
Applications
n
n
n
n
The wide operating input voltage range of 7.5V to 36V (60V
transient) suits the LT3663 to a variety of input sources,
including unregulated 12V wall adapters, 24V industrial
supplies, and automotive power.
The LT3663 includes a low current shutdown mode, input
overvoltage and undervoltage lockout, and thermal shutdown. Internal compensation and boost diode minimize the
number of external exponents. 3.3V and 5V fixed output
voltage versions are available.
The LT3663 is available in 8-lead DFN and MSOP packages
with exposed pads for low thermal resistance.
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear
Technology Corporation. All other trademarks are the property of their respective owners.
Distributed Supply Regulation
Automotive Battery Regulation
Industrial Supplies
Wall Transformer Regulation
Typical Application
5V Step-Down Converter
VIN
100
BOOST
VIN
2.2µF
Efficiency
90
0.1µF
LT3663
ON OFF
EFFICIENCY (%)
SW
6.8µH
RUN
ISENSE
ILIM
VOUT
28.7k
VOUT
59k
22µF
VIN = 8V
VIN = 15V
80
VIN = 30V
70
60
50
FB
GND
11k
3663 TA01
40
0.1
0.3
0.5
0.7
0.9
OUTPUT CURRENT (A)
1.1
1.3
3663 TA01b
3663fc
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1
LT3663
Absolute Maximum Ratings
(Note 1)
Input Voltage (VIN) (Note 2).......................................60V
BOOST Pin Voltage....................................................50V
BOOST Pin Above SW Pin..........................................25V
VOUTS, VOUT, ISENSE, FB Pins........................................6V
RUN Pin (Note 2).......................................................60V
Operating Junction Temperature Range (Note 3)
LT3663E.............................................. –40°C to 125°C
LT3663I............................................... –40°C to 125°C
LT3663H............................................. –40°C to 150°C
Storage Temperature............................... –65°C to 150°C
Pin Configuration
LT3663
LT3663-X
TOP VIEW
TOP VIEW
RUN 2
9
GND
FB 3
7 BOOST
RUN 2
6 ISENSE
VOUTS 3
θJA = 64°C/W
EXPOSED PAD (PIN 9) IS GND, MUST BE SOLDERED TO PCB
θJA = 64°C/W
EXPOSED PAD (PIN 9) IS GND, MUST BE SOLDERED TO PCB
LT3663-X
TOP VIEW
VIN
RUN
FB
ILIM
1
2
3
4
9
GND
8
7
6
5
6 ISENSE
5 VOUT
DCB PACKAGE
8-LEAD (2mm × 3mm) PLASTIC DFN
DCB PACKAGE
8-LEAD (2mm × 3mm) PLASTIC DFN
LT3663
7 BOOST
9
GND
ILIM 4
5 VOUT
ILIM 4
8 SW
VIN 1
8 SW
VIN 1
TOP VIEW
SW
BOOST
ISENSE
VOUT
VIN 1
RUN 2
VOUTS 3
ILIM 4
MSE PACKAGE
8-LEAD PLASTIC MSOP
9
GND
8
7
6
5
SW
BOOST
ISENSE
VOUT
MSE PACKAGE
8-LEAD PLASTIC MSOP
θJA = 35°C/W
EXPOSED PAD (PIN 9) IS GND, MUST BE SOLDERED TO PCB
θJA = 35°C/W
EXPOSED PAD (PIN 9) IS GND, MUST BE SOLDERED TO PCB
order information
LEAD FREE FINISH
TAPE AND REEL
PART MARKING*
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LT3663EDCB#PBF
LT3663EDCB#TRPBF
LDVK
8-Lead (2mm × 3mm) Plastic DFN
–40°C to 125°C
LT3663IDCB#PBF
LT3663IDCB#TRPBF
LDVK
8-Lead (2mm × 3mm) Plastic DFN
–40°C to 125°C
LT3663EDCB-3.3#PBF
LT3663EDCB-3.3#TRPBF
LFMW
8-Lead (2mm × 3mm) Plastic DFN
–40°C to 125°C
LT3663IDCB-3.3#PBF
LT3663IDCB-3.3#TRPBF
LFMW
8-Lead (2mm × 3mm) Plastic DFN
–40°C to 125°C
LT3663EDCB-5#PBF
LT3663EDCB-5#TRPBF
LFMY
8-Lead (2mm × 3mm) Plastic DFN
–40°C to 125°C
LT3663IDCB-5#PBF
LT3663IDCB-5#TRPBF
LFMY
8-Lead (2mm × 3mm) Plastic DFN
–40°C to 125°C
LT3663EMS8E#PBF
LT3663EMS8E#TRPBF
LTDWT
8-Lead Plastic MSOP
–40°C to 125°C
LT3663IMS8E#PBF
LT3663IMS8E#TRPBF
LTDWT
8-Lead Plastic MSOP
–40°C to 125°C
LT3663HMS8E#PBF
LT3663HMS8E#TRPBF
LTDWT
8-Lead Plastic MSOP
–40°C to 150°C
LT3663EMS8E-3.3#PBF
LT3663EMS8E-3.3#TRPBF LTFMX
8-Lead Plastic MSOP
–40°C to 125°C
LT3663IMS8E-3.3#PBF
LT3663IMS8E-3.3#TRPBF LTFMX
8-Lead Plastic MSOP
–40°C to 125°C
LT3663HMS8E-3.3#PBF
LT3663HMS8E-3.3#TRPBF LTFMX
8-Lead Plastic MSOP
–40°C to 150°C
LT3663EMS8E-5#PBF
LT3663EMS8E-5#TRPBF
8-Lead Plastic MSOP
–40°C to 125°C
2
LTFMZ
3663fc
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LT3663
order information
LEAD FREE FINISH
TAPE AND REEL
PART MARKING*
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LT3663IMS8E-5#PBF
LT3663IMS8E-5#TRPBF
LTFMZ
8-Lead Plastic MSOP
–40°C to 125°C
LT3663HMS8E-5#PBF
LT3663HMS8E-5#TRPBF
LTFMZ
8-Lead Plastic MSOP
–40°C to 150°C
Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
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. VIN = 12V, RILIM = 36.5k unless otherwise noted.
PARAMETER
CONDITIONS
VIN Undervoltage Lockout
Rising
MIN
l
VIN Undervoltage Lockout Hysteresis
VIN Overvoltage Lockout
TYP
MAX
7
7.5
500
Rising
l
36
VIN Overvoltage Lockout Hysteresis
39
Not Switching
VIN Supply Current in Shutdown
VRUN = 0V
Run Input Voltage High
41
V
2.4
3.2
mA
0.01
2
µA
V
2.5
V
Run Input Voltage Low
Run Pin Bias Current
VRUN = 2.3V (Note4)
VRUN = 0V
V
mV
1
VIN Supply Current
UNITS
6
0.01
0.3
V
15
0.1
µA
µA
VOUT Current Limit Range
l
0.4
1.2
A
VOUT Current Limit
l
0.8
1
1.2
A
1350
900
1500
1000
1650
1100
l
80
92
l
784
800
816
mV
50
150
nA
3.3
5
3.366
5.100
V
V
90
120
µA
2
2.5
Operating Frequency
LT3663
LT3663-X
Maximum Duty Cycle
%
Feedback Voltage
LT3663
FB Bias Current
VFB = 0.8V, LT3663
Regulated Output Voltage
LT3663-3.3
LT3663-5
VOUTS Bias Current
LT3663-X
Switch Peak Current Limit
(Note 5)
Switch VCESAT
ISW = 1A
275
Minimum BOOST Voltage
ISW = 1A (Note 6)
1.85
2.2
Boost Diode Drop
IDIODE = 60mA
0.9
1.2
Boost Pin Current
ISW = 1A
28
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: Absolute Maximum Voltage at VIN and RUN pins is 60V for
nonrepetitive 1 second transients.
Note 3: The LT3663E is guaranteed to meet performance specifications
from 0°C to 125°C. Specifications over the –40°C to 125°C operating
temperature range are assured by design, characterization, and
correlation with statistical process controls. The LT3663I specifications
l
l
l
3.234
4.900
1.6
kHz
kHz
A
mV
V
V
mA
are guaranteed over the full –40°C to 125°C temperature range. The
LT3663H specifications are guaranteed over the –40°C to 150°C operating
temperature range. High junction temperatures degrade operating
lifetimes. Operating lifetime is derated at junction temperatures greater
than 125°C.
Note 4: Current flows into pin.
Note 5: Switch Peak Current Limit guaranteed by design and/or correlation
to static test.
Note 6: This is the minimum voltage across the boost capacitor needed to
guarantee full saturation of the switch.
3663fc
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3
LT3663
Typical Performance Characteristics
VIN Overvoltage Lockout
VIN Undervoltage Lockout
8.0
42
800
7.5
41
700
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
40
6.5
FALLING
6.0
5.5
5.0
RISING
38
FALLING
37
36
35
0
32
–50 –25
25 50 75 100 125 150
TEMPERATURE (°C)
0
Output Current Limit
1.20
40
1.15
30
25
20
15
10
50
RILIM = 36.5k
1.05
1.00
0.95
0.90
Switching Frequency
0
LT3663-X
0
25 50 75 100 125 150
TEMPERATURE (°C)
3663 G02
4
0
25 50 75 100 125 150
TEMPERATURE (°C)
0
0.2
0.4 0.6 0.8
1
OUTPUT CURRENT (A)
1.2
1.4
3663 G12
Feedback Voltage
0.84
120
FEEDBACK VOLTAGE (V)
MINIMUM SWITCH-ON TIME (ns)
1.1
0.9
–50 –25
2
Minimum Switch On-Time
1.2
1.0
3
1
140
1.3
60
3663 G08
4
3663 G04
1.6
1.4
50
RILIM = 28.7k
1.10
3663 G11
LT3663
20
30
40
VIN VOLTAGE (V)
5
0.80
–50 –25
60
1.5
10
Output Current Limit
0.85
5
20
30
40
RUN PIN VOLTAGE (V)
0
6
OUTPUT VOLTAGE (V)
35
OUTPUT CURRENT LIMIT (A)
RUN PIN CURRENT (µA)
RUN Pin Current
10
300
3663 G06
45
0
400
0
25 50 75 100 125 150
TEMPERATURE (°C)
3663 G03
0
500
100
33
4.0
–50 –25
VRUN = 0V
200
34
4.5
VIN Shutdown Current
600
39
VIN CURRENT (µA)
RISING
7.0
SWITCHING FREQUENCY (MHz)
TA = 25°C, unless otherwise noted.
100
80
60
40
0.82
0.80
0.78
20
0
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
3663 G10
0.76
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
3663 G05
3663fc
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LT3663
Typical Performance Characteristics
Switch Voltage Drop
400
1.4
125°C
BOOST Pin Current
35
1.2
30
250
–45°C
200
150
100
BOOST PIN CURRENT (mA)
300
1
0.8
0.6
0.4
0.2
50
0
Boost Diode Vf
25°C
BOOST DIODE VF (V)
SWITCH VOLTAGE DROP (mV)
350
TA = 25°C, unless otherwise noted.
0
0.2
0.4
0.6
0.8
SWITCH CURRENT (A)
1
1.2
0
25
20
15
10
5
0
50
100
150
200
250
DIODE CURRENT (mA)
3663 G01
300
3653 G09
0
0
0.2
0.4
0.5
0.8
SWITCH CURRENT (A)
1.0
1.2
3653 G07
Pin Functions
BOOST: The BOOST pin is used to provide a drive voltage,
higher than the input voltage, to the internal power switch.
The BOOST pin is also internally connected to the cathode
of the BOOST diode.
RUN: The Run pin is used to put the LT3663 into shutdown
mode. Tie to ground to shut down the LT3663. Tie to 2.5V
or more for normal operation. If the shutdown feature is
not used, connect this pin to VIN.
GND (Exposed Pad Pin 9) : Ground. The exposed pad
must be soldered to the PCB and electrically connected
to ground. Use a large ground plane and thermal vias to
optimize thermal performance.
SW: The SW pin is the output of the internal power switch.
Connect this pin to the inductor, catch diode and boost
capacitor.
FB (LT3663): The LT3663 regulates the FB pin to 0.8V.
Connect the feedback resistor divider tap to this pin.
VIN: The VIN pin supplies current to the LT3663’s internal
regulator and internal power switch. Capacitively bypass
the pin to ground.
ILIM: Output Current Limit Program Pin. Connect a resistor
to ground to program the regulator output current limit.
VOUT: The VOUT pin is connected to the negative terminal
of the internal output current limit sense resistor.
ISENSE: The ISENSE pin is the positive input to the internal
output current limit sense resistor. The ISENSE pin is also
the anode to the internal BOOST diode.
VOUTS (LT3663-X): Output Voltage Sense Pin. Connect to
the positive terminal of the output capacitor.
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5
LT3663
Functional Block Diagram
VIN
VIN
RSENSE1
C1
Q1
–
+
RUN
BOOST
D1
C3
+
Σ
A1
–
SLOPE
COMPENSATION
2.5V INTERNAL
REGULATOR,
REFERENCE,
UVLO AND OVP
SW
R
Q
L
S
DRIVER
D2
ISENSE
OSCILLATOR
+
–
G2
–
+
RSENSE2
VOUT
VOUT
C2
ILIM
RILIM
–
VC
G1
INTERNAL
COMPENSATION
+
FB
R1
R2
0.8V
NOTE: RESISTOR DIVIDER
IS INTERNAL ON LT3663-X
VERSIONS.
EXPOSED PAD (GND)
3663 BD
6
3663fc
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LT3663
Operation
(Refer to Block Diagram)
The LT3663 is a constant frequency, current mode step
down regulator. A switch cycle is initiated when the oscillator enables the RS flip flop, turning on the internal
power switch, Q1. The sense amplifier (A1) monitors the
switch current via the voltage dropped across the current
sense resistor RSENSE1. The comparator compares the
amplified current signal with the output (VC) of the error
amplifier (G1). The switch is turned off when this current
exceeds a value determined by the VC voltage. The error
amplifier monitors the VOUT voltage through an internal
resistor divider and, when not driven externally, servos
the VC voltage to regulate VOUT. If the VOUT voltage drops,
the VC voltage will be driven higher increasing the output
current and VOUT voltage. An active clamp (not shown)
on the VC node provides current limit. The LT3663 is
internally compensated with a pole-zero combination on
the VC node.
An external capacitor and internal diode, D2, generate a
voltage at the BOOST pin that is higher than the input supply.
This allows the driver to fully saturate the internal bipolar
NPN power switch for efficient operation. The switch driver
operates from either VIN or BOOST to ensure startup.
An internal regulator provides power to the control circuitry.
This regulator includes input undervoltage and overvoltage
protection which disables switching action when VIN is
out of range. When switching is disabled, the LT3663
safely sustains input voltages up to 60V. Note that while
switching is disabled the output will discharge.
Output current limiting is provided via the servo action of
amplifier G2. The voltage across sense resistor, RSENSE2,
is compared to a voltage programmed by external resistor
RILIM on the ILIM pin. A capacitor averages the inductor
ripple current. If the average inductor current exceeds the
programmed value then the VC voltage is pulled low, reducing the current in the regulator. The output current limit
circuit allows for a lower current rated inductor and diode
and provides better control of system power dissipation.
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7
LT3663
Applications Information
FB Resistor Network
The output voltage of the LT3663 is programmed with a
resistor divider. Choose the 1% resistors according to:
Figure 2. illustrates switching waveforms in pulse skip
mode a 3.3V output application with VIN = 30V.
R1 = R2 (VOUT/0.8 – 1)
Reference designators refer to the Block Diagram.
The resistor divider is internal on the fixed output voltage
versions, LT3663-X.
IL
1A/DIV
Minimum Duty Cycle
As the input voltage increases the duty cycle decreases. At
some point, the minimum duty cycle of the IC is reached
and pulse skipping begins. The output voltage continues to
regulate but the output voltage ripple increases. The input
voltage at which this occurs is calculated as follows:
VIN =
( VOUT + VF ) – V
DCMIN
VSW
20V/DIV
VOUT
200mV/DIV
AC-COUPLED
2.5µs/DIV
3663 F02
Figure 2. Pulse-Skip Mode
Inductor Selection
F + VSW
A good first choice for the inductor value is:
Where VF is the forward voltage drop of the catch diode,
D1, and VSW is the voltage drop on the internal switch,
Q1. LT3663 DCMIN is typically 0.12.
For VF = 0.4V, VSW = 0.3V, and VOUT = 3.3V pulse skipping
occurs at about 24.5V.
Figure 1 illustrates switching waveforms in normal mode
for a 3.3V output application with VIN = 20V.
VSW
20V/DIV
IL
1A/DIV
VOUT
200mV/DIV
AC-COUPLED
2.5µs/DIV
L = VOUT + VD (µH)
where VD is the voltage drop of the catch diode (~0.4V)
and L is in µH. With this value there is no sub-harmonic
oscillation for applications with 50% or greater duty
cycle. The inductor’s RMS current rating must be greater
than the maximum load current. Size the inductor so the
saturation current rating is about 30% higher than the
maximum load current. The output current limit circuit
tightly controls the maximum average inductor current,
therefore the inductor RMS current rating does not have
to be overrated to handle short circuit or overload conditions. For high efficiency, keep the series resistance (DCR)
less than 0.1Ω. A higher value inductor is larger in size
and slows transient response but reduces output voltage
ripple. A lower value inductor has higher ripple currents
but is physically smaller or, for the same size, it has lower
DCR typically resulting in higher efficiency.
3663 F01
Figure 1. Normal Operation
8
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LT3663
Applications Information
Catch Diode
The catch diode conducts current only during switch-off
time. Average forward current in normal operation is
calculated from:
ID( AVG) = IOUT
VIN – VOUT
VIN
where IOUT is the maximum output load current programmed by the ILIM resistor. Peak reverse voltage is equal
to the regulator input voltage. Use a Schottky diode with a
reverse voltage rating greater than the input voltage. The
overvoltage protection feature in the LT3663 keeps the
switch off when VIN > 39V (typical) allowing the use of a
45V rated Schottky even when VIN ranges up to 60V.
Input Capacitor
Bypass the input of the LT3663 circuit with a 1µF or higher
value ceramic capacitor of X7R or X5R type. Y5V types
have poor performance over temperature and applied voltage and are not recommended. If the input power source
has high impedance, or there is significant inductance
due to long wires or cables, additional bulk capacitance
may be necessary. This can be provided with a low performance electrolytic capacitor. Step-down regulators
draw current from the input supply in pulses with very
fast rise and fall times. The input capacitor is required
to reduce the resulting voltage ripple at the LT3663 and
to force this very high frequency switching current into
a tight local loop, minimizing EMI. Place the capacitor in
close proximity to the LT3663 and the catch diode; (see
the PCB Layout section).
Use X5R or X7R types and keep in mind that a ceramic
capacitor biased with VOUT has less than its specified
nominal capacitance.
High performance electrolytic capacitors can be used for
the output capacitor. Low ESR is important, so choose
one that is intended for use in switching regulators. Keep
the ESR less than 0.1Ω.
ILIM Resistor
The LT3663 output current limit controls the maximum
current delivered from the LT3663 regulator. This allows
tighter control of the system power dissipation and also
protects the inductor and diode from overheating during
an overload or short circuit condition. A resistor connected from ILIM pin to GND programs the output current.
Table 1 details the ILIM resistor values for specific output
current limits.
Table 1. Output Current Limit vs RLIM Value
OUTPUT CURRENT LIMIT (A)
RILIM VALUE (kΩ)
0.4
140
0.6
75
0.8
48.7
1.0
36.5
1.2
28.7
There may be a reason in some applications to move the
output current limit. The following simple circuit demonstrates how the output current limit can be adjusted:
ILIM
Output Capacitor
A 10µF or greater ceramic capacitor is recommended to
provide low output ripple and good transient response.
Ceramic capacitors have very low equivalent series resistance (ESR) and provide the best ripple performance.
LT3663
RA
ON, RILIM = RA
OFF, RILIM = RA + RB
3663 F03
RB
Figure 3. Circuit for Multiple Values of Output Current Limit
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9
LT3663
Applications Information
BOOST and BIAS Pin Considerations
boost diode. For reliable BOOST pin operation with 2.5V
outputs use a good external Schottky diode (such as the
ON Semi, MBR0540) and a 1µF boost capacitor (see Figure
4b). For lower output voltages connect an external Schottky
diode to the input (Figure 4c), or to another supply greater
than 2.8V. Using VIN reduces the maximum input voltage
to 25V. The circuit in Figure 4a is more efficient because
the BOOST pin current comes from a lower voltage source.
Take care to ensure that the maximum voltage ratings of
the BOOST pin is not exceeded.
Capacitor C3 and the internal boost diode (see the Block
Diagram) are used to generate a boost voltage that is higher
than the input voltage. In most cases a 0.1µF capacitor
works well. Figure 4 shows three ways to arrange the boost
circuit. The BOOST pin must be more than 2.3V above the
SW pin for best efficiency. For outputs of 3V and above, the
standard circuit (Figure 4a) is best. For outputs between
2.8V and 3V, use a 1µF boost capacitor. A 2.5V output
presents a special case because it is marginally adequate
to support the boosted drive stage while using the internal
VIN
VIN
BOOST
VIN
VIN
BOOST
C3
LT3663
C3
SW
SW
LT3663
ISENSE
D3
ISENSE
VOUT
VOUT
VOUT
(4a) For VOUT > 2.8V
VOUT
(4b) For 2.5V < VOUT < 2.8V
D3
VIN
VIN
BOOST
C3
LT3663
SW
ISENSE
VOUT
VOUT
3663 F04
(4c) For VOUT < 2.5V; VIN(MAX) = 25V
Figure 4. Three Circuits to Generate BOOST Pin Voltage
10
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LT3663
Applications Information
PCB Layout
Proper operation and minimum EMI, requires careful
printed circuit board layout. Figure 5 shows the recommended component placement with trace, ground plane
and via locations. Note that large, switched currents flow
in the LT3663’s VIN and SW pins, the catch diode (D2)
and the input capacitor (C1). Keep the loop formed by
these components as small as possible and tied to system
ground in only one place. Locate these components, along
with the inductor and output capacitor, on the same side
of the circuit board, and keep their connections on that
layer. Place a local, unbroken ground plane below these
components, and tie this ground plane to system ground
at one location, ideally at the ground terminal of the output
capacitor C1. Make the SW and BOOST PCB trace as short
as possible. Include vias near the exposed GND pad of
the LT3663 to help remove heat from the LT3663 to the
ground plane.
High Temperature Considerations
The die temperature of the LT3663 must not exceed the
maximum rating. This is generally not a concern unless
VIN
the ambient temperature is above 85°C. For higher temperatures, take care in the layout of the circuit to ensure
good heat sinking of the LT3663. De-rate the maximum
load current as the ambient temperature approaches the
maximum temperature rating. Calculate the die temperature by multiplying the LT3663 power dissipation by the
thermal resistance from junction to ambient. Estimate
the power dissipation within the LT3663 by calculating
the total power loss from an efficiency measurement
and subtracting the catch diode loss. Thermal resistance
depends on the layout of the circuit board, but 64°C/W is
typical for the (2mm × 3mm) DFN (DCB) package.
Other Linear Technology Publications
Application Notes 19, 35 and 44 contain more detailed
descriptions and design information for Buck regulators
and other switching regulators. The LT1376 data sheet
has a more extensive discussion of output ripple, loop
compensation and stability testing. Design Note 100
shows how to generate a bipolar output supply using a
Buck regulator.
GND
C1
D1
RUN
1
8
2
7
3
6
4
5
R1
C3
L
LT3663
R2
RILIM
C2
VOUT
3663 F05
Figure 5. LT3663 PCB Layout
3663fc
For more information For more information www.linear.com/LT3663
11
LT3663
Typical Applications
5V Step-Down Converter
VIN
7.5V TO 36V
TRANSIENT
TO 60V
VIN
7.5V TO 36V
TRANSIENT
TO 60V
BOOST
VIN
C1
4.7µF
2.5V Step-Down Converter
C3
0.1µF
LT3663
BOOST
VIN
C1
4.7µF
C3
1µF
LT3663
SW
ON OFF
SW
D1
RUN
L
6.8µH
ISENSE
RILIM
28.7k
ILIM
VOUT
R1
59k
C2
22µF
D1
RUN
ON OFF
ISENSE
VOUT
5V
1.2A
ILIM
RILIM
28.7k
VOUT
FB
GND
3663 TA02
D1: DIODES INC, DFLS260
L: TDK, VLCF5020T-6R8N1R3-1
3663 TA04
LT3663-5 5V Step-Down Regulator
with Isolated 3.3V Output
C4
47pF
50V
0603
C3
0.22µF
LT3663
1
L
3.3µH
R1
49.9k
FB
GND
3663 TA05
R2
100k
C2
22µF
3
CMPSH-3E
SOT-23
C5
2.2µF
0603
10V
2
3
1761ES5-3.3
IN
OUT
5
GND
SHDN
BYP
4
C6
0.01µF
10V
0403
C7
10µF
6.3V
0603
3.3V
50mA
RTN
VOUT
1.2V
1.2A
10µH
3
VIN
7.5V TO 36V
NOTE: 60V MAX
TRANSIENT VOLTAGE
R1
10k
C1
2.2µF
50V
1206
1
•
VOUT
1
SW
VIN
LT3663-5
C2
0.1µF
16V
BOOST
RUN
R2
100k
•
ISENSE
ILIM
D2
2
D1
RUN
D1: DIODES INC, DFLS240
D3: ON SEMI, MBR0540
L: TDK, VLCF5020T-3R3N2R0-1
R3
100
0805
BOOST
SW
RILIM
28.7k
VOUT
2.5V
1.2A
D1: DIODES INC, DFLS260
D3: ON SEMI, MBR0560
L: TDK, VLCF5020T-3R3N2R0-1
VIN
ON OFF
C2
22µF
R2
100k
GND
D3
C1
4.7µF
R1
210k
FB
R2
11k
1.2V Step-Down Converter
VIN
7.5V TO 23V
D3
L
3.3µH
ISENSE
ILIM
VOUT
RILIM
75k
GND
C3
47µF
1206
10V
20%
10µH
4
L16-0017
T1
BH ELECTRONICS
2
D1
DFLS260
60V
2A
HVBUCK
5V
600mA
VOUTS
3663 TA07
12
3663fc
For more information www.linear.com/LT3663
LT3663
Package Description
DCB Package
8-Lead Plastic DFN (2mm × 3mm)
(Reference LTC DWG # 05-08-1718 Rev A)
0.70 ±0.05
1.35 ±0.05
3.50 ±0.05
1.65 ±0.05
2.10 ±0.05
PACKAGE
OUTLINE
0.25 ±0.05
0.45 BSC
1.35 REF
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED
2.00 ±0.10
(2 SIDES)
R = 0.05
TYP
R = 0.115
TYP
5
0.40 ±0.10
8
1.35 ±0.10
1.65 ±0.10
3.00 ±0.10
(2 SIDES)
PIN 1 NOTCH
R = 0.20 OR 0.25
× 45° CHAMFER
PIN 1 BAR
TOP MARK
(SEE NOTE 6)
(DCB8) DFN 0106 REV A
4
0.200 REF
1
0.23 ±0.05
0.45 BSC
0.75 ±0.05
1.35 REF
0.00 – 0.05
BOTTOM VIEW—EXPOSED PAD
NOTE:
1. DRAWING IS NOT A JEDEC PACKAGE OUTLINE
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
3663fc
For more information For more information www.linear.com/LT3663
13
LT3663
MS8E Package
8-Lead Plastic MSOP, Exposed Die Pad
(Reference LTC DWG # 05-08-1662 Rev J)
BOTTOM VIEW OF
EXPOSED PAD OPTION
1.88
(.074)
1
1.88 ±0.102
(.074 ±.004)
0.29
REF
1.68
(.066)
0.889 ±0.127
(.035 ±.005)
0.05 REF
5.23
(.206)
MIN
DETAIL “B”
CORNER TAIL IS PART OF
DETAIL “B” THE LEADFRAME FEATURE.
FOR REFERENCE ONLY
NO MEASUREMENT PURPOSE
1.68 ±0.102 3.20 – 3.45
(.066 ±.004) (.126 – .136)
8
3.00 ±0.102
(.118 ±.004)
(NOTE 3)
0.65
(.0256)
BSC
0.42 ±0.038
(.0165 ±.0015)
TYP
8
7 6 5
0.52
(.0205)
REF
RECOMMENDED SOLDER PAD LAYOUT
0.254
(.010)
3.00 ±0.102
(.118 ±.004)
(NOTE 4)
4.90 ±0.152
(.193 ±.006)
DETAIL “A”
0° – 6° TYP
GAUGE PLANE
0.53 ±0.152
(.021 ±.006)
DETAIL “A”
1
2 3
4
1.10
(.043)
MAX
0.86
(.034)
REF
0.18
(.007)
SEATING
PLANE
0.22 – 0.38
(.009 – .015)
TYP
0.65
(.0256)
BSC
0.1016 ±0.0508
(.004 ±.002)
MSOP (MS8E) 0911 REV J
NOTE:
1. DIMENSIONS IN MILLIMETER/(INCH)
2. DRAWING NOT TO SCALE
3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS.
MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.152mm (.006") PER SIDE
4. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS.
INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.152mm (.006") PER SIDE
5. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.102mm (.004") MAX
6. EXPOSED PAD DIMENSION DOES INCLUDE MOLD FLASH. MOLD FLASH ON E-PAD
SHALL NOT EXCEED 0.254mm (.010") PER SIDE.
14
3663fc
For more information www.linear.com/LT3663
LT3663
Revision History
(Revision history begins at Rev B)
REV
DATE
DESCRIPTION
PAGE NUMBER
B
11/09
Additions to Features
1
Text Changes to Description
1
Addition of MSE Package to Pin Configuration
Additions Made to Order Information
Changes to Electrical Characteristics
Expanded Temperature Range of Typical Performance Curves
Addition of Note to Functional Block Diagram
C
05/13
2
2, 3
3
4, 5
6
Text Changes to Applications Information
8, 11
Addition of Typical Applications Drawing
12
Addition of MS8E Package Drawing
14
Clarified PCB Layout
11
3663fc
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 representaFor
more information
For more
information
www.linear.com/LT3663
tion that the
interconnection
of its circuits
as described
herein will
not infringe on existing patent rights.
15
LT3663
Typical Application
3.3V Step-Down Converter
BOOST
VIN
C1
4.7µF
90
C3
0.1µF
LT3663
ON OFF
D1
RUN
ISENSE
RILIM
28.7k
ILIM
VOUT
R1
316k
L
4.7µH
VOUT
3.3V
C2
1.2A
22µF
FB
R2
100k
GND
D1: DIODES INC, DFLS240
L: TDK, VLCF5020T-4R7N1R7-1
VIN = 8V
80
SW
3663 TA03
EFFICIENCY (%)
VIN
7.5V TO 36V
Efficiency
100
VIN = 15V
70
VIN = 30V
60
50
40
30
0.1
0.3
0.5
0.7
0.9
OUTPUT CURRENT (A)
1.1
1.3
3663 TA06
Related Parts
PART NUMBER DESCRIPTION
LT1766
COMMENTS
60V, 1.2A (IOUT), 200kHz, High Efficiency Step-Down DC/DC Converter
VIN: 5.5V to 60V, VOUTMAX = 1.20V, IQ = 2.5mA, ISD = 25µA,
TSSOP16/TSSOP16E Packages
VIN: 3.6V to 36V, VOUTMAX = 1.2V, IQ = 1.6mA, ISD
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