LT3663
1
3663fb
OUTPUT CURRENT (A)
0.1
EFFICIENCY (%)
100
90
80
70
60
50
40 0.5 0.90.3 0.7 1.1
3663 TA01b
1.3
VIN = 15V
VIN = 8V
VIN = 30V
TYPICAL APPLICATION
DESCRIPTION
1.2A Step-Down
Switching Regulator with
Output Current Limit
The LT
®
3663 is a current mode step-down switching regu-
lator with programmable output current limit. The current
limit accurately controls the system power dissipation and
reduces the size of the power path components.
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 shut-
down. Internal compensation and boost diode minimize the
number of external exponents. 3.3V and 5V fi xed 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.
5V Step-Down Converter
FEATURES
APPLICATIONS
n 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 VCESAT: 275mV at 1A
n Internally Compensated
n Thermal Protection
n Thermally Enhanced 8-Pin 2mm × 3mm DFN and
MSOP Packages
n Distributed Supply Regulation
n Automotive Battery Regulation
n Industrial Supplies
n Wall Transformer Regulation
Effi ciency
3663 TA01
LT3663
VIN
VIN
RUN
ILIM
BOOST
SW
GND
0.1μF
2.2μF
22μF59k28.7k
11k
6.8μH
ISENSE
VOUT VOUT
FB
ON OFF
LT3663
2
3663fb
ABSOLUTE MAXIMUM RATINGS
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
(Note 1)
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 LTFMZ 8-Lead Plastic MSOP –40°C to 125°C
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
TOP VIEW
SW
BOOST
ISENSE
VOUT
VIN
RUN
FB
ILIM
DCB PACKAGE
8-LEAD (2mm × 3mm) PLASTIC DFN
9
GND
3
4
2
1
6
5
7
8
LT3663-X
TOP VIEW
SW
BOOST
ISENSE
VOUT
VIN
RUN
VOUTS
ILIM
DCB PACKAGE
8-LEAD (2mm × 3mm) PLASTIC DFN
9
GND
3
4
2
1
6
5
7
8
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
1
2
3
4
VIN
RUN
FB
ILIM
8
7
6
5
SW
BOOST
ISENSE
VOUT
TOP VIEW
9
GND
MSE PACKAGE
8-LEAD PLASTIC MSOP
LT3663-X
1
2
3
4
VIN
RUN
VOUTS
ILIM
8
7
6
5
SW
BOOST
ISENSE
VOUT
TOP VIEW
9
GND
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
LT3663
3
3663fb
ELECTRICAL CHARACTERISTICS
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 specifi cations
from 0°C to 125°C. Specifi cations over the –40°C to 125°C operating
temperature range are assured by design, characterization, and
correlation with statistical process controls. The LT3663I specifi cations
The l denotes the specifi cations which apply over the full operating
temperature range, otherwise specifi cations are at TA = 25°C. VIN = 12V, RILIM = 36.5k unless otherwise noted.
PARAMETER CONDITIONS MIN TYP MAX UNITS
VIN Undervoltage Lockout Rising l7 7.5 V
VIN Undervoltage Lockout Hysteresis 500 mV
VIN Overvoltage Lockout Rising l36 39 41 V
VIN Overvoltage Lockout Hysteresis 1V
VIN Supply Current Not Switching 2.4 3.2 mA
VIN Supply Current in Shutdown VRUN = 0V 0.01 2 μA
Run Input Voltage High 2.5 V
Run Input Voltage Low 0.3 V
Run Pin Bias Current VRUN = 2.3V (Note4)
VRUN = 0V
6
0.01
15
0.1
μA
μA
VOUT Current Limit Range l0.4 1.2 A
VOUT Current Limit l0.8 1 1.2 A
Operating Frequency LT3663
LT3663-X
1350
900
1500
1000
1650
1100
kHz
kHz
Maximum Duty Cycle l80 92 %
Feedback Voltage LT3663 l784 800 816 mV
FB Bias Current VFB = 0.8V, LT3663 50 150 nA
Regulated Output Voltage LT3663-3.3
LT3663-5
l
l
3.234
4.900
3.3
5
3.366
5.100
V
V
VOUTS Bias Current LT3663-X 90 120 μA
Switch Peak Current Limit (Note 5) l1.6 2 2.5 A
Switch VCESAT ISW = 1A 275 mV
Minimum BOOST Voltage ISW = 1A (Note 6) 1.85 2.2 V
Boost Diode Drop IDIODE = 60mA 0.9 1.2 V
Boost Pin Current ISW = 1A 28 mA
are guaranteed over the full –40°C to 125°C temperature range. The
LT3663H specifi cations 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 fl ows 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.
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 specifi ed with wider operating temperature ranges. *The temperature grade is identifi ed by a label on the shipping container.
Consult LTC Marketing for information on non-standard lead based fi nish parts.
For more information on lead free part marking, go to: http://www.linear.com/leadfree/
For more information on tape and reel specifi cations, go to: http://www.linear.com/tapeandreel/
ORDER INFORMATION
LT3663
4
3663fb
Minimum Switch On-Time
RUN Pin Current Output Current Limit
Feedback Voltage
TEMPERATURE (°C)
–50
OUTPUT CURRENT LIMIT (A)
500 100
3663 G04
15012525–25 75
1.20
1.15
1.05
1.10
1.00
0.90
0.95
0.85
0.80
RILIM = 36.5k
TEMPERATURE (°C)
–50
FEEDBACK VOLTAGE (V)
500 100
3663 G05
15012525–25 75
0.84
0.82
0.80
0.78
0.76
TEMPERATURE (°C)
–50
MINIMUM SWITCH-ON TIME (ns)
500 100
3663 G10
15012525–25 75
140
120
100
80
40
60
20
0
RUN PIN VOLTAGE (V)
0
RUN PIN CURRENT (μA)
3010 50
3663 G11
6020 40
45
40
30
35
25
15
5
20
10
0
TEMPERATURE (°C)
SWITCHING FREQUENCY (MHz)
1.6
3663 G02
0.9
1.0
1.1
1.2
1.3
1.4
1.5
–50 –25 0 25 50 75 100 150125
LT3663-X
LT3663
Switching Frequency
OUTPUT CURRENT (A)
OUTPUT VOLTAGE (V)
6
5
4
3663 G12
0
1
2
3
0 0.2 0.4 0.6 0.8 1 1.2 1.4
RILIM = 28.7k
Output Current Limit
TYPICAL PERFORMANCE CHARACTERISTICS
TA = 25°C, unless otherwise noted.
VIN Shutdown Current
VIN Overvoltage Lockout
TEMPERATURE (°C)
–50
INPUT VOLTAGE (V)
500 100
3663 G06
15012525–25 75
42
32
33
34
35
36
37
38
39
40
41
RISING
FALLING
VIN VOLTAGE (V)
0
VIN CURRENT (μA)
3010 50
3663 G08
6020 40
800
700
500
600
400
200
300
100
0
VRUN = 0V
TEMPERATURE (°C)
INPUT VOLTAGE (V)
8.0
7.5
7.0
3663 G03
4.0
4.5
5.0
5.5
6.0
6.5
–50 –25 0 25 50 75 100 150125
RISING
FALLING
VIN Undervoltage Lockout
LT3663
5
3663fb
TYPICAL PERFORMANCE CHARACTERISTICS
BOOST Pin CurrentBoost Diode Vf
TA = 25°C, unless otherwise noted.
SWITCH CURRENT (A)
BOOST PIN CURRENT (mA)
35
30
25
20
3653 G07
0
5
15
10
0 0.2 0.4 0.5 0.8 1.0 1.2
DIODE CURRENT (mA)
BOOST DIODE VF (V)
1.4
1.2
1
0.8
3653 G09
0
0.2
0.6
0.4
0 50 100 150 200 250 300
SWITCH CURRENT (A)
SWITCH VOLTAGE DROP (mV)
400
350
3663 G01
0
50
100
150
200
250
300
0 0.2 0.4 0.6 0.8 1 1.2
125°C
–45°C
25°C
Switch Voltage Drop
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.
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.
FB (LT3663): The LT3663 regulates the FB pin to 0.8V.
Connect the feedback resistor divider tap to this pin.
ILIM: Output Current Limit Program Pin. Connect a resistor
to ground to program the regulator output current limit.
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.
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.
SW: The SW pin is the output of the internal power switch.
Connect this pin to the inductor, catch diode and boost
capacitor.
VIN: The VIN pin supplies current to the LT3663’s internal
regulator and internal power switch. Capacitively bypass
the pin to ground.
VOUT: The VOUT pin is connected to the negative terminal
of the internal output current limit sense resistor.
VOUTS (LT3663-X): Output Voltage Sense Pin. Connect to
the positive terminal of the output capacitor.
LT3663
6
3663fb
FUNCTIONAL BLOCK DIAGRAM
Σ
2.5V INTERNAL
REGULATOR,
REFERENCE,
UVLO AND OVP OSCILLATOR
SLOPE
COMPENSATION
C3
RSENSE1
VIN SWQ1
RSENSE2
R1 NOTE: RESISTOR DIVIDER
IS INTERNAL ON LT3663-X
VERSIONS.
EXPOSED PAD (GND)
3663 BD
BOOST
ISENSE
VOUT
C1
RILIM
VIN
INTERNAL
COMPENSATION
D1
D2
R
S
Q
–
+
–
+
–
+
DRIVER
L
C2
VOUT
–
+
G2
A1
0.8V
–
+
G1
ILIM
VC
R2
FB
RUN
LT3663
7
3663fb
OPERATION
The LT3663 is a constant frequency, current mode step
down regulator. A switch cycle is initiated when the os-
cillator enables the RS fl ip fl op, turning on the internal
power switch, Q1. The sense amplifi er (A1) monitors the
switch current via the voltage dropped across the current
sense resistor RSENSE1. The comparator compares the
amplifi ed current signal with the output (VC) of the error
amplifi er (G1). The switch is turned off when this current
exceeds a value determined by the VC voltage. The error
amplifi er 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.
(Refer to Block Diagram)
This allows the driver to fully saturate the internal bipolar
NPN power switch for effi cient 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
amplifi er 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, reduc-
ing 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.
LT3663
8
3663fb
2.5μs/DIV 3663 F02
VSW
20V/DIV
IL
1A/DIV
VOUT
200mV/DIV
AC-COUPLED
Figure 2. Pulse-Skip Mode
VSW
20V/DIV
IL
1A/DIV
VOUT
200mV/DIV
AC-COUPLED
2.5μs/DIV 3663 F01
APPLICATIONS INFORMATION
FB Resistor Network
The output voltage of the LT3663 is programmed with a
resistor divider. Choose the 1% resistors according to:
R1 = R2 (VOUT/0.8 – 1)
Reference designators refer to the Block Diagram.
The resistor divider is internal on the fi xed output voltage
versions, LT3663-X.
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:
VVV
DC VV
IN OUT F
MIN FSW
=+
()
+–
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.
Figure 2. illustrates switching waveforms in pulse skip
mode a 3.3V output application with VIN = 30V.
Figure 1. Normal Operation
Inductor Selection
A good fi rst choice for the inductor value is:
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 condi-
tions. For high effi ciency, 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 effi ciency.
LT3663
9
3663fb
APPLICATIONS INFORMATION
Catch Diode
The catch diode conducts current only during switch-off
time. Average forward current in normal operation is
calculated from:
II
VV
V
D AVG OUT IN OUT
IN
()
–
=
where IOUT is the maximum output load current pro-
grammed 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 volt-
age and are not recommended. If the input power source
has high impedance, or there is signifi cant inductance
due to long wires or cables, additional bulk capacitance
may be necessary. This can be provided with a low per-
formance 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).
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 re-
sistance (ESR) and provide the best ripple performance.
Use X5R or X7R types and keep in mind that a ceramic
capacitor biased with VOUT has less than its specifi ed
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 con-
nected from ILIM pin to GND programs the output current.
Table 1 details the ILIM resistor values for specifi c 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 demon-
strates how the output current limit can be adjusted:
Figure 3. Circuit for Multiple Values of Output Current Limit
LT3663
ON, RILIM = RA
OFF, RILIM = RA + RB
ILIM
3663 F03
RA
RB
LT3663
10
3663fb
APPLICATIONS INFORMATION
BOOST and BIAS Pin Considerations
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 effi ciency. 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
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
4 b). F o r l o w e r o u t p u t v o l t a g e s c o n n e c t a n e x t e r n a l S c h o t t k y
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 effi cient 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.
Figure 4. Three Circuits to Generate BOOST Pin Voltage
LT3663
(4c) For VOUT < 2.5V; VIN(MAX) = 25V
VIN
VIN
3663 F04
BOOST
SW
D3
C3
ISENSE
VOUT VOUT
LT3663
(4b) For 2.5V < VOUT < 2.8V
VIN
VIN BOOST
SW
D3
C3
ISENSE
VOUT VOUT
LT3663
(4a) For VOUT > 2.8V
VIN
VIN BOOST
SW
C3
ISENSE
VOUT VOUT
LT3663
11
3663fb
APPLICATIONS INFORMATION
PCB Layout
Proper operation and minimum EMI, requires careful
printed circuit board layout. Figure 5 shows the recom-
mended component placement with trace, ground plane
and via locations. Note that large, switched currents fl ow
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
the ambient temperature is above 85°C. For higher tem-
peratures, 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 tempera-
ture 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 effi ciency 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.
3663 F05
VIN
RUN
RILIM C2
VOUT
GND
L
D1
C3
C1
R2
R1
3
4
2
1
6
5
7
8
LT3663
Figure 5. LT3663 PCB Layout
LT3663
12
3663fb
TYPICAL APPLICATIONS
2.5V Step-Down Converter
1.2V Step-Down Converter
5V Step-Down Converter
3663 TA02
LT3663
VIN
VIN
7.5V TO 36V
TRANSIENT
TO 60V
RUN
ILIM
BOOST
SW
GND
C3
0.1μF
C1
4.7μF
D1: DIODES INC, DFLS260
L: TDK, VLCF5020T-6R8N1R3-1
C2
22μF
R1
59k
RILIM
28.7k
R2
11k
L
6.8μH
D1
ISENSE
VOUT VOUT
5V
1.2A
FB
ON OFF
3663 TA04
LT3663
VIN
VIN
7.5V TO 36V
TRANSIENT
TO 60V
RUN
ILIM
BOOST
SW
GND
C3
1μF
C1
4.7μF
D1: DIODES INC, DFLS260
D3: ON SEMI, MBR0560
L: TDK, VLCF5020T-3R3N2R0-1
C2
22μF
R1
210k
RILIM
28.7k
R2
100k
L
3.3μH
D1
ISENSE
VOUT VOUT
2.5V
1.2A
D3
FB
ON OFF
3663 TA05
LT3663
VIN
VIN
7.5V TO 23V
RUN
ILIM
BOOST
SW
GND
C3
0.22μF
C1
4.7μF
D1: DIODES INC, DFLS240
D3: ON SEMI, MBR0540
L: TDK, VLCF5020T-3R3N2R0-1
C2
22μF
R1
49.9k
RILIM
28.7k
R2
100k
L
3.3μH
D1
ISENSE
VOUT VOUT
1.2V
1.2A
D3
FB
ON OFF
•
•
3663 TA07
LT3663-5
VIN
RUN
ILIM
SW
BOOST
GND
C2
0.1μF
16V
C1
2.2μF
50V
1206
C3
47μF
1206
10V
20%
L16-0017
BH ELECTRONICS
1761ES5-3.3
R1
10k
D1
DFLS260
60V
2A
ISENSE
VOUT
C5
2.2μF
0603
10V
T1
4
2
3
1
10μH
10μH
1
2
34
5
D2
13
2
R3
100
0805
C4
47pF
50V
0603
CMPSH-3E
SOT-23
VOUTS
R2
100k
NOTE: 60V MAX
TRANSIENT VOLTAGE
RILIM
75k
VIN
7.5V TO 36V
HVBUCK
5V
600mA
IN
GND
SHDN
OUT
BYP
C6
0.01μF
10V
0403
C7
10μF
6.3V
0603
3.3V
50mA
RTN
LT3663-5 5V Step-Down Regulator
with Isolated 3.3V Output
LT3663
13
3663fb
PACKAGE DESCRIPTION
3.00 ±0.10
(2 SIDES)
2.00 ±0.10
(2 SIDES)
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
0.40 ± 0.10
BOTTOM VIEW—EXPOSED PAD
0.75 ±0.05
R = 0.115
TYP
R = 0.05
TYP
1.35 REF
1
4
85
PIN 1 BAR
TOP MARK
(SEE NOTE 6)
0.200 REF
0.00 – 0.05
(DCB8) DFN 0106 REV A
0.23 ± 0.05
0.45 BSC
PIN 1 NOTCH
R = 0.20 OR 0.25
× 45° CHAMFER
0.25 ± 0.05
1.35 REF
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED
2.10 ±0.05
0.70 ±0.05
3.50 ±0.05
PACKAGE
OUTLINE
0.45 BSC
1.35 ±0.10
1.35 ±0.05
1.65 ± 0.10
1.65 ± 0.05
DCB Package
8-Lead Plastic DFN (2mm × 3mm)
(Reference LTC DWG # 05-08-1718 Rev A)
LT3663
14
3663fb
MS8E Package
8-Lead Plastic MSOP, Exposed Die Pad
(Reference LTC DWG # 05-08-1662 Rev E)
MSOP (MS8E) 0908 REV E
0.53 p 0.152
(.021 p .006)
SEATING
PLANE
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
0.18
(.007)
0.254
(.010)
1.10
(.043)
MAX
0.22 – 0.38
(.009 – .015)
TYP
0.86
(.034)
REF
0.65
(.0256)
BSC
0o – 6o TYP
DETAIL “A”
DETAIL “A”
GAUGE PLANE
12
34
4.90 p 0.152
(.193 p .006)
8
8
1
BOTTOM VIEW OF
EXPOSED PAD OPTION
765
3.00 p 0.102
(.118 p .004)
(NOTE 3)
3.00 p 0.102
(.118 p .004)
(NOTE 4)
0.52
(.0205)
REF
1.83 p 0.102
(.072 p .004)
2.06 p 0.102
(.081 p .004)
5.23
(.206)
MIN
3.20 – 3.45
(.126 – .136)
2.083 p 0.102
(.082 p .004)
2.794 p 0.102
(.110 p .004)
0.889 p 0.127
(.035 p .005)
RECOMMENDED SOLDER PAD LAYOUT
0.42 p 0.038
(.0165 p .0015)
TYP
0.65
(.0256)
BSC
0.1016 p 0.0508
(.004 p .002)
DETAIL “B”
DETAIL “B”
CORNER TAIL IS PART OF
THE LEADFRAME FEATURE.
FOR REFERENCE ONLY
NO MEASUREMENT PURPOSE
0.05 REF
0.29
REF
LT3663
15
3663fb
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corpor ation makes no representa-
t i o n t h a t t h e i n t e r c o n n e c t i o n o f i t s c i r c u i t s a s d e s c r i b e d h e r e i n w i l l n o t i n f r i n g e o n e x i s t i n g p a t e n t r i g h t s .
REVISION HISTORY
REV DATE DESCRIPTION PAGE NUMBER
B 11/09 Additions to Features
Text Changes to Description
Addition of MSE Package to Pin Confi guration
Additions Made to Order Information
Changes to Electrical Characteristics
Expanded Temperature Range of Typical Performance Curves
Addition of Note to Functional Block Diagram
Text Changes to Applications Information
Addition of Typical Applications Drawing
Addition of MS8E Package Drawing
1
1
2
2, 3
3
4, 5
6
8, 11
12
14
(Revision history begins at Rev B)
LT3663
16
3663fb
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com
© LINEAR TECHNOLOGY CORPORATION 2009
LT 1109 REV B • PRINTED IN USA
RELATED PARTS
TYPICAL APPLICATION
3.3V Step-Down Converter
3663 TA03
LT3663
VIN
VIN
7.5V TO 36V
RUN
ILIM
BOOST
SW
GND
C3
0.1μF
C1
4.7μF
D1: DIODES INC, DFLS240
L: TDK, VLCF5020T-4R7N1R7-1
C2
22μF
R1
316k
RILIM
28.7k
R2
100k
L
4.7μH
D1
ISENSE
VOUT VOUT
3.3V
1.2A
FB
ON OFF
Effi ciency
OUTPUT CURRENT (A)
0.1
EFFICIENCY (%)
100
90
80
70
60
50
30
40
0.5 0.90.3 0.7 1.1
3663 TA06
1.3
VIN = 15V
VIN = 8V
VIN = 30V
PART NUMBER DESCRIPTION COMMENTS
LT1766 60V, 1.2A (IOUT), 200kHz, High Effi ciency Step-Down DC/DC Converter VIN: 5.5V to 60V, VOUTMAX = 1.20V, IQ = 2.5mA, ISD = 25μA,
TSSOP16/TSSOP16E Packages
LT1933 500mA(IOUT), 500kHz Step-Down Switching Regulator in SOT-23 VIN: 3.6V to 36V, VOUTMAX = 1.2V, IQ = 1.6mA, ISD <1μA,
ThinSOT Package
LT1936 36V, 1.4A(IOUT) , 500kHz High Effi ciency Step-Down DC/DC Converter VIN: 3.6V to 36V, VOUTMAX = 1.2V, IQ = 1.9mA, ISD <1μA,
MS8E Package
LT1940 Dual 25V, 1.4A (IOUT), 1.1MHz, High Effi ciency Step-Down DC/DC
Converter
VIN: 3.6V to 25V, VOUTMAX = 1.20V, IQ = 3.8mA, ISD <30μA,
TSSOP16E Package
LT1976/LT1977 60V, 1.2A (IOUT), 200/500kHz, High Effi ciency Step-Down DC/DC Converter
with BurstMode
®
Operation
VIN: 3.3V to 60V, VOUTMAX = 1.20V, IQ = 100μA, ISD <1μA,
TSSOP16E Package
LTC3407/
LTC3407-2
Dual 600mA/800mA, 1.5/2.25 MHz Syncronous Step-Down DC/DC
Converter
VIN: 2.5V to 5.5V, VOUTMAX = 0.6V, IQ = 40μA, ISD <1μA,
3mm × 3mm DFN, MS10E Packages
LT3434/LT3435 60V, 2.4A (IOUT), 200/500kHz, High Effi ciency Step-Down DC/DC Converter
with BurstMode Operation
VIN: 3.3V to 60V, VOUTMAX = 1.20V, IQ = 100μA, ISD <1μA,
TSSOP16E Package
LT3437 60V, 400mA (IOUT),MicroPower Step-Down DC/DC Converter with
BurstMode Operation
VIN: 3.3V to 60V, VOUTMAX = 1.25V, IQ = 100μA, ISD <1μA,
3mm × 3mm DFN, TSSOP16E Packages
LT3493 36V, 1.4A(IOUT), 750kHz High Effi ciency Step-Down DC/DC Converter VIN: 3.6V to 36V, VOUTMAX = 0.8V, IQ = 1.9mA, ISD <1μA,
2mm × 3mm DFN Package
LT3501 Dual 25V, 3A (IOUT), 1.5MHz, High Effi ciency Step-Down DC/DC Converter VIN: 3.3V to 25V, VOUTMAX = 0.8V, IQ = 3.7mA, ISD <10μA,
TSSOP-20E Package
LT3503 20V, 1A (IOUT), 2.2MHz, High Effi ciency Step-Down DC/DC Converter VIN: 3.6V to 20V, VOUTMAX = 0.78V, IQ = 1.9mA, ISD <1μA,
2mm × 3mm DFN, Package
LT3505 36V, 1.2A (IOUT), 3MHz, High Effi ciency Step-Down DC/DC Converter VIN: 3.6V to 36V, VOUTMAX = 0.78V, IQ = 2mA, ISD <2μA,
3mm × 3mm DFN, MS8E Packages
LT3506/A Dual 25V, 1.6A (IOUT), 575kHz/1.1MHz, High Effi ciency Step-Down DC/DC
Converter
VIN: 3.6V to 25V, VOUTMAX = 0.8V, IQ = 3.8mA, ISD <30μA,
4mm × 5mm DFN Package
LT3508 Dual 36V, 1.4A (IOUT), 2.5MHz, High Effi ciency Step-Down DC/DC
Converter
VIN: 3.6V to 36V, VOUTMAX = 0.8V, IQ = 4.3mA, ISD <1μA,
4mm × 4mm QFN, TSSOP16E Packages
LT3510 Dual 25V, 2A (IOUT), 1.5MHz, High Effi ciency Step-Down DC/DC Converter VIN: 3.3V to 25V, VOUTMAX = 0.8V, IQ = 3.7mA, ISD <10μA,
TSSOP-20E Package
LTC3548 Dual 400mA + 800mA, 2.25 MHz Syncronous Step-Down DC/DC Converter VIN: 2.5V to 5.5V, VOUTMAX = 0.6V, IQ = 40μA, ISD <1μA,
3mm × 3mm DFN, MS10E Packages
BurstMode is a registered trademark of Linear Technology Corporation.
