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LTC3603

3603fc

For more information www.linear.com/LTC3603

Features

applications

Description

2.5A, 15V Monolithic

Synchronous Step-Down

Regulator

The LT C

3603 is a high efﬁciency, monolithic synchronous

step-down DC/DC converter utilizing a constant-frequency,

current mode architecture. It operates from an input voltage

range of 4.5V to 15V and provides an adjustable regulated

output voltage from 0.6V to 14.5V while delivering up to

2.5A of output current. The internal synchronous power

switch with 45mΩ on-resistance increases efﬁciency

and eliminates the need for an external Schottky diode.

The switching frequency can either be set by an external

resistor or synchronized to an external clock. OPTI-LOOP

compensation allows the transient response to be optimized

over a wide range of loads and output capacitors.

The LTC3603 can be conﬁgured for either Burst Mode op

eration or forced continuous operation. Forced continuous

operation reduces noise and RF interference, while Burst

Mode operation provides the highest efﬁciency at light

loads. In Burst Mode operation, external control of the burst

clamp level allows the output voltage ripple to be adjusted

according to the requirements of the application.

3.3V, 2.5A, 1MHz Step-Down Regulator

typical application

Wide Input Voltage Range: 4.5V to 15V

2.5A Output Current

Low R

DS(ON)

Internal Switches: 45mΩ and 85mΩ

Programmable Frequency: 300kHz to 3MHz

Low Quiescent Current: 75µA

0.6V ±1% Reference Allows Precise,

Low Output Voltage

99% Maximum Duty Cycle

Adjustable Burst Mode

Clamp

Synchronizable to External Clock

Power Good Output Voltage Monitor

Overtemperature Protection

Overvoltage Protection

Available in 16-Lead Thermally Enhanced eMSOP

and 4mm × 4mm QFN Packages

Point-of-Load Supplies

Portable Instruments

Communications Infrastructure

Efﬁciency and Power Loss vs Load Current

105k

3603 TA01

22µF

100µF

0.22µF

2.2µH

1µF

1nF

RUN

PGOOD

TRACK/SS

ITH

BOOST

PGND

LTC3603

INTV

SYNC/MODE V

105k

475k

10pF

4.32k

OUT

3.3V

2.5A

4.5V TO 15V

LOAD CURRENT (A)

0.001

EFFICIENCY (%)

POWER LOSS (mW)

100

0.10.01 1 10

3603 TA01b

100

1000

10000

POWER LOSS

EFFICIENCY

= 12V

OUT

= 3.3V

L, LT, LTC, LTM, Burst Mode, OPTI-LOOP, Linear Technology and the Linear logo are registered

trademarks and ThinSOT is a trademark of Linear Technology Corporation. All other trademarks

are the property of their respective owners. Protected by U.S. Patents including 5481178,

6580258, 6498466, 6611131, 6177787, 5705919, 5847554.

Summary of content (22 pages)

PAGE 1
LTC3603 2.5A, 15V Monolithic Synchronous Step-Down Regulator Description Features n n n n n n n n n n n n n Wide Input Voltage Range: 4.5V to 15V 2.5A Output Current Low RDS(ON) Internal Switches: 45mΩ and 85mΩ Programmable Frequency: 300kHz to 3MHz Low Quiescent Current: 75µA 0.
PAGE 2
LTC3603 Absolute Maximum Ratings (Note 1) PVIN Supply Voltage (DC)........................... –0.3V to 16V PVIN Supply Transient Voltage (<1µs)........................21V SW............................................... –0.3V to (PVIN + 0.3V) BOOST..................................(VSW –0.3V) to (VSW + 6V) RUN............................................................ –0.3V to 16V All Other Pins................................................ –0.3V to 6V Peak SW Sink and Source Current (Note 7)........
PAGE 3
LTC3603 Electrical Characteristics The l denotes the specifications which apply over the full operating junction temperature range, otherwise specifications are at TA = 25°C. VIN = 12V unless otherwise specified (Note 2). SYMBOL PVIN VFB ITH = 0.7V (Note 3) VIN = 5V to 15V, ITH = 0.7V l DVFB(LINEREG) PARAMETER Operating Voltage Range Regulated Feedback Voltage Feedback Voltage Line Regulation DVFB(LOADREG) Feedback Voltage Load Regulation ITH = 0.36V to 0.84V l 0.02 0.
PAGE 4
LTC3603 Typical Performance Characteristics Load Step Transient Forced Continuous Burst Mode Operation OUTPUT VOLTAGE 50mV/DIV OUTPUT VOLTAGE 100mV/DIV INDUCTOR CURRENT 500mA/DIV LOAD CURRENT 1A/DIV VIN = 12V VOUT = 3.3V LOAD = 50mA 10µs/DIV 90 VIN = 12V 0.6000 0.5998 75 70 65 60 55 50 0.
PAGE 5
LTC3603 Typical Performance Characteristics Quiescent Current vs Input Voltage Frequency vs Temperature 1015 ACTIVE 1005 1000 995 990 400 300 200 100 985 980 –50 –25 0 25 50 75 100 0 125 6 5 7 TEMPERATURE (°C) 1.5 1.0 0.5 0 0.4 0.7 0.9 0.5 0.6 0.8 BURST CLAMP VOLTAGE (V) 100 4 3 2 1 0 1.0 70 VIN = 15V 80 0 70 0.001 10 20 30 40 50 60 70 80 90 100 DUTY CYCLE (%) 0.01 0.1 1 LOAD CURRENT (A) 3603 G14 Efficiency vs Frequency 100 FIGURE 6 CIRCUIT 95 ILOAD = 1A 90 ILOAD = 2.
PAGE 6
LTC3603 Typical Performance Characteristics 5V LDO Output Voltage vs Temperature Load Regulation 5.10 FIGURE 6 CIRCUIT VIN = 12V LDO OUTPUT VOLTAGE (V) 0 ∆VOUT/VOUT (%) 1.40 5.08 –0.10 1.35 5.06 TRACK/SS CURRENT (µA) 0.10 TRACK/SS Current vs Temperature 5.04 5.02 5.00 4.98 4.96 4.94 0 0.5 1 1.5 2 LOAD CURRENT (A) 2.5 3 4.90 –50 –25 50 25 0 75 TEMPERATURE (°C) 100 125 3603 G19 3603 G18 Pin Functions 1.25 1.20 1.15 4.92 –0.20 1.30 1.
PAGE 7
LTC3603 Block Diagram ITH BOOST 1.2µA 0.6V INTVCC PVIN LDO VOLTAGE REFERENCE SLOPE COMPENSATION RECOVERY TRACK/SS 1ms SOFT-START + + + – VFB + – + ERROR AMPLIFIER BURST COMPARATOR + SYNC/MODE 0.54V BCLAMP + – MAIN I-COMPARATOR – – SW SW SLOPE COMPENSATION OSCILLATOR SW OVER-CURRENT COMPARATOR + 0.66V – – LOGIC REVERSE COMPARATOR PGOOD + + – RT RUN PGND PGND PGND SYNC/MODE 3602 BD 3603fc For more information www.linear.
PAGE 8
LTC3603 Operation Main Control Loop The LTC3603 is a monolithic, constant-frequency, current mode step-down DC/DC converter. During normal operation, the internal top power switch (N-channel MOSFET) is turned on at the beginning of each clock cycle. Current in the inductor increases until the current comparator trips and turns off the top power MOSFET. The peak inductor current at which the current comparator shuts off the top power switch is controlled by the voltage on the ITH pin.
PAGE 9
LTC3603 Operation resistor should be chosen to correspond to a frequency that is 25% lower than the synchronization frequency. When synchronized, the LTC3603 will operate in pulseskipping mode. Dropout Operation When the input supply voltage decreases toward the output voltage, the duty cycle increases toward the maximum on-time. Further reduction of the supply voltage forces the top switch to remain on for more than one cycle until it attempts to stay on continuously.
PAGE 10
LTC3603 Applications Information The basic LTC3603 application circuit is shown on the front page of this data sheet. External component selection is determined by the maximum load current and begins with the selection of the inductor value and operating frequency followed by CIN and COUT. Operating Frequency Selection of the operating frequency is a trade-off between efficiency and component size. High frequency operation allows the use of smaller inductor and capacitor values.
PAGE 11
LTC3603 Applications Information characteristics. The choice of which style inductor to use mainly depends on the price vs size requirements and any radiated field/EMI requirements. New designs for surface mount inductors are available from Coiltronics, Coilcraft, Toko and Sumida. CIN and COUT Selection The input capacitance, CIN, is needed to filter the trapezoidal current at the source of the top MOSFET.
PAGE 12
LTC3603 Applications Information Burst Clamp Programming If the voltage on the SYNC/MODE pin is in the range of 0.42V to 1V, Burst Mode operation is enabled. During Burst Mode operation, the voltage on the SYNC/MODE pin determines the burst clamp level. This level sets the minimum peak inductor current, IBURST, for each switching cycle according to the following equation: IBURST V BURST = + 0.42V 6A/V VBURST is the voltage on the SYNC/MODE pin. IBURST can be programmed in the range of 0A to 3.
PAGE 13
LTC3603 Applications Information In order to turn on the topside MOSFET, the voltage on the BOOST pin is then applied to its gate. As the topside MOSFET turns on, the SW pin rises to the PVIN voltage and the BOOST pin rises to PVIN + INTVCC , thereby keeping the MOSFET fully enhanced. For most applications, a 0.22µF ceramic capacitor is appropriate for CBST. Schottky diode DBST should have a reverse breakdown voltage that is greater than PVIN(MAX). INTVCC DBST LTC3603 CBST SW 3603 F03 Figure 3.
PAGE 14
LTC3603 Applications Information OUTPUT VOLTAGE VX VOUT TIME Figure 5b. Ratiometric Tracking OUTPUT VOLTAGE VX VOUT TIME 3603 F05b,c Figure 5c. Coincident Tracking Efficiency Considerations The efficiency of a switching regulator is equal to the output power divided by the input power times 100%. It is often useful to analyze individual losses to determine what is limiting the efficiency and which change would produce the most improvement.
PAGE 15
LTC3603 Applications Information To prevent the LTC3603 from exceeding the maximum junction temperature, the user will need to do some thermal analysis. The goal of the thermal analysis is to determine whether the power dissipated exceeds the maximum junction temperature of the part. The temperature rise is given by: TR = (PD) • (qJA) where PD is the power dissipated by the regulator and qJA is the thermal resistance from the junction of the die to the ambient temperature.
PAGE 16
LTC3603 Applications Information CVCC 1µF RPG 200k SYNC/MODE PGOOD PGOOD ROSC 105k CITH 1nF PVIN ITH R1 105k R2 475k INTVCC PVIN RT RITH 4.32k CFB 10pF VIN 12V CIN 22µF BOOST LTC3603 D1 CBST 0.22µF SW VFB SW RUN SW TRACK/SS PGND PGND PGND L1 2.2µH L1: VISHAY IHLP2525CZER2R2MO1 CIN: TAIYO YUDEN TMK325BJ226MM-T COUT: TDK C3225X5ROJ107M VOUT 3.3V 2.5A COUT 100µF 3603 F06 Figure 6. 12V to 3.3V, 2.5A Regulator at 1MHz, Burst Mode Operation Choose a standard value of R2 = 475k.
PAGE 17
LTC3603 Typical Applications 1.8V, 2.5A Regulator at 1MHz, Burst Mode Operation CVCC 1µF RPG 200k R3 845k INTVCC SYNC/MODE PGOOD R4 ROSC 137k 105k CITH 1nF PGOOD RT ITH R1 105k CFB 10pF PVIN PVIN RITH 4.32k R2 210k VIN 12V CIN 22µF BOOST LTC3603 D1 CBST 0.22µF SW VFB SW RUN SW TRACK/SS PGND PGND PGND L1 1µH VOUT 1.8V 2.5A COUT 100µF ×2 L1: VISHAY IHLP2525CZER1R0MO1 CIN: TAIYO YUDEN TMK325BJ226MM-T COUT: TAIYO YUDEN AMK316BJ107ML 3603 TA02 1.2V, 2.
PAGE 18
LTC3603 Typical Applications Efficiency vs Load Current, 1.8V Regulator at 1MHz, Burst Mode Operation Efficiency vs Load Current, 1.2V Regulator at 750kHz, Burst Mode Operation 100 100 EFFICIENCY (%) 90 85 95 VIN = 7.2V VIN = 12V 80 75 70 85 VIN = 12V 80 75 70 65 60 65 60 0.001 VIN = 7.2V 90 EFFICIENCY (%) 95 55 0.01 0.1 1 LOAD CURRENT (A) 50 0.001 10 0.01 0.1 1 LOAD CURRENT (A) 3603 TA04a 10 3603 TA04b 3.3V, 2.5A Regulator, Synchronized to 1.8MHz, Small Size 1.8MHz EXT.
PAGE 19
LTC3603 Package Description MSE Package 16-Lead Plastic MSOP, Exposed Die Pad (Reference LTC DWG # 05-08-1667 Rev E) BOTTOM VIEW OF EXPOSED PAD OPTION 2.845 ±0.102 (.112 ±.004) 5.23 (.206) MIN 2.845 ±0.102 (.112 ±.004) 0.889 ±0.127 (.035 ±.005) 8 1 1.651 ±0.102 (.065 ±.004) 1.651 ±0.102 3.20 – 3.45 (.065 ±.004) (.126 – .136) 0.305 ±0.038 (.0120 ±.0015) TYP 16 0.50 (.0197) BSC 4.039 ±0.102 (.159 ±.004) (NOTE 3) RECOMMENDED SOLDER PAD LAYOUT 0.254 (.010) 0.35 REF 0.
PAGE 20
LTC3603 Package Description UF Package 20-Lead Plastic QFN (4mm × 4mm) (Reference LTC DWG # 05-08-1710 Rev A) 0.70 ±0.05 4.50 ± 0.05 3.10 ± 0.05 2.00 REF 2.45 ± 0.05 2.45 ± 0.05 PACKAGE OUTLINE 0.25 ±0.05 0.50 BSC RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED 4.00 ± 0.10 0.75 ± 0.05 R = 0.05 TYP R = 0.115 TYP 19 20 0.40 ± 0.10 PIN 1 TOP MARK (NOTE 6) 4.00 ± 0.10 PIN 1 NOTCH R = 0.20 TYP OR 0.35 × 45° CHAMFER BOTTOM VIEW—EXPOSED PAD 1 2.00 REF 2.
PAGE 21
LTC3603 Revision History REV DATE DESCRIPTION A 11/09 Changes to Absolute Maximum Ratings PAGE NUMBER 2 Changes to Pin Configuration 2 Change to Electrical Characteristics 3 Text Changes to Pin Functions 6 Change to Block Diagram 7 Text Changes to Operation Section 8 Text Changes to Applications Information Section B C 08/10 04/13 10, 12, 15 “How to Reduce SW Ringing” Section Added 16 Additions to Related Parts 22 Updated Temperature Range in Absolute Maximum Ratings and Order Inf
PAGE 22
LTC3603 Typical Application 12V to 3.3V, 2.5A Regulator at 1MHz, Burst Mode Operation PGOOD CVCC 1µF RPG 200k ROSC 105k CITH 1nF INTVCC PVIN RT BOOST ITH R1 105k CFB 10pF LTC3603 CIN 22µF D1 PVIN RITH 4.32k R2 475k SYNC/MODE PGOOD VIN 12V CBST 0.22µF SW VFB SW RUN SW TRACK/SS PGND PGND PGND L1 2.2µH VOUT 3.3V 2.