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LT3663

3663fc

For more information For more information www.linear.com/LT3663

OUTPUT CURRENT (A)

0.1

EFFICIENCY (%)

100

0.5 0.90.3 0.7 1.1

3663 TA01b

1.3

= 15V

= 8V

= 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 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.

5V Step-Down Converter

FeaTures

applicaTions

Wide Input Range:

Operation from 7.5V to 36V

Overvoltage Lockout Protects Circuit through 60V

Transients

Programmable Output Current Limit (0.4A to 1.2A)

3.3V and 5V Fixed Output Voltage Options

Integrated Boost Diode

Fixed Frequency, Peak Current Mode Control

LT3663 f

= 1.5MHz

LT3663-X f

= 1MHZ

Low Switch V

CESAT

: 275mV at 1A

Internally Compensated

Thermal Protection

Thermally Enhanced 8-Pin 2mm × 3mm DFN and

MSOP Packages

Distributed Supply Regulation

Automotive Battery Regulation

Industrial Supplies

Wall Transformer Regulation

Efﬁciency

3663 TA01

LT3663

RUN

LIM

BOOST

GND

0.1µF

2.2µF

22µF59k28.7k

11k

6.8µH

SENSE

OUT

ON OFF

Summary of content (16 pages)

PAGE 1
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.
PAGE 2
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..............................................
PAGE 3
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.
PAGE 4
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.
PAGE 5
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.
PAGE 6
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 For more information www.linear.
PAGE 7
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).
PAGE 8
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.
PAGE 9
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.
PAGE 10
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.
PAGE 11
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.
PAGE 12
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.
PAGE 13
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.
PAGE 14
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.
PAGE 15
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 Ad
PAGE 16
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.