Datasheet

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LTC3631

3631fe

For more information www.linear.com/LTC3631

Typical applicaTion

FeaTures

applicaTions

DescripTion

High Efficiency, High Voltage

100mA Synchronous

Step-Down Converter

The LT C

3631 is a high voltage, high efﬁciency step-down

DC/DC converter with internal high side and synchronous

power switches that draws only 12μA typical DC supply

current at no load while maintaining output voltage

regulation.

The LTC3631 can supply up to 100mA load current and

features a programmable peak current limit that provides

a simple method for optimizing efﬁciency in lower current

applications. The LTC3631’s combination of Burst Mode

operation, integrated power switches, low quiescent cur

rent, and programmable peak current limit provides high

efﬁciency over a broad range of load currents.

With its wide 4.5V to 45V input range and internal overvolt

age monitor capable of protecting the part from 60V surges,

the LTC3631 is a robust converter suited for regulating a

wide variety of power sources. Additionally, the LTC3631

includes a precise run threshold and a soft-start feature

to guarantee that power system start-up is well-controlled

in any environment.

The LTC3631 is available in the thermally enhanced

3mm × 3mm DFN and MS8E packages.

Efﬁciency and Power Loss vs Load Current

Wide Input Voltage Range: Operation from 4.5V to 45V

Overvoltage Lockout Provides Protection Up to 60V

Internal High Side and Low Side Power Switches

No Compensation Required

100mA Output Current

Low Dropout Operation: 100% Duty Cycle

Low Quiescent Current: 12µA

0.8V ±1% Feedback Voltage Reference

Adjustable Peak Current Limit

Internal and External Soft-Start

Precise RUN Pin Threshold with Adjustable

Hysteresis

3.3V, 5V and Adjustable Output Versions

Only Three External Components Required for Fixed

Output Versions

Low Proﬁle (0.75mm) 3mm × 3mm DFN and

Thermally-Enhanced MS8E Packages

4mA to 20mA Current Loops

Industrial Control Supplies

Distributed Power Systems

Portable Instruments

Battery-Operated Devices

Automotive Power Systems

5V, 100mA Step-Down Converter

LTC3631-5

RUN

HYST

3631 TA01a

5V TO 45V

2.2µF 10µF

OUT

100mA

OUT

SET

GND

100µH

LOAD CURRENT (mA)

0.1

EFFICIENCY (%)

POWER LOSS (mW)

100

1 10 100

3631 TA01b

100

1000

= 12V

= 36V

EFFICIENCY

POWER LOSS

L, LT, LTC, LTM, Burst Mode, 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.

Summary of content (22 pages)

PAGE 1
LTC3631 High Efficiency, High Voltage 100mA Synchronous Step-Down Converter Description Features n n n n n n n n n n n n n n Wide Input Voltage Range: Operation from 4.5V to 45V Overvoltage Lockout Provides Protection Up to 60V Internal High Side and Low Side Power Switches No Compensation Required 100mA Output Current Low Dropout Operation: 100% Duty Cycle Low Quiescent Current: 12µA 0.
PAGE 2
LTC3631 Absolute Maximum Ratings (Note 1) VIN Supply Voltage...................................... –0.3V to 60V SW Voltage (DC)............................ –0.3V to (VIN + 0.3V) RUN Voltage............................................... –0.3V to 60V HYST, ISET, SS Voltages................................ –0.3V to 6V VFB................................................................ –0.3V to 6V VOUT (Fixed Output Versions)........................ –0.3V to 6V Operating Junction Temperature Range (Note 2)...
PAGE 3
LTC3631 Electrical Characteristics The l denotes the specifications which apply over the full operating junction temperature range, otherwise specifications are for TA = 25°C (Note 2). VIN = 10V, unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS Input Supply (VIN) VIN Input Voltage Operating Range 4.
PAGE 4
LTC3631 Typical Performance Characteristics Efficiency vs Load Current, VOUT = 5V 90 VOUT = 5V FIGURE 10 CIRCUIT 95 VIN = 12V VOUT = 2.5V 85 FIGURE 10 CIRCUIT VIN = 12V VIN = 36V 80 VIN = 24V 75 80 70 65 65 60 0.1 1 10 LOAD CURRENT (mA) VIN = 36V 75 70 VIN = 24V ILOAD = 100mA 1 10 LOAD CURRENT (mA) ILOAD = 1mA ILOAD = 100mA FIGURE 10 CIRCUIT 5.03 0 5.02 5.01 5.00 4.99 4.98 4.97 10 15 30 25 35 20 INPUT VOLTAGE (V) 40 45 –0.
PAGE 5
LTC3631 Typical Performance Characteristics Peak Current Trip Threshold vs Input Voltage 250 200 180 160 140 120 100 80 60 40 20 200 0 400 600 800 RISET (kΩ) 1000 14 ISET OPEN 225 12 200 175 150 RSET = 500k 125 100 75 ISET = GND 50 0 1200 0 5 SHUTDOWN 4 0 10 15 20 25 30 35 40 45 50 INPUT VOLTAGE (V) 5 15 25 35 45 INPUT VOLTAGE (V) 3631 G12 Switch On-Resistance vs Temperature 5 4.5 VIN = 10V VIN = 10V SLEEP 10 8 6 4 SHUTDOWN 2 SWITCH 0N-RESISTANCE (Ω) 4.
PAGE 6
LTC3631 Typical Performance Characteristics Soft-Start Waveform Load Step Transient Response Short-Circuit Response OUTPUT VOLTAGE 50mV/DIV OUTPUT VOLTAGE 2V/DIV LOAD CURRENT 50mA/DIV INDUCTOR CURRENT 100mA/DIV OUTPUT VOLTAGE 1V/DIV CSS = 0.047µF 5ms/DIV 3631 G19 VIN = 24V VOUT = 5V 1ms/DIV 3631 G20 VIN = 10V VOUT = 5V 200µs/DIV 3631 G21 Pin Functions SW (Pin 1): Switch Node Connection to Inductor. This pin connects to the drains of the internal power MOSFET switches.
PAGE 7
LTC3631 Block Diagram VIN 1µA ISET 2 C2 3 PEAK CURRENT COMPARATOR – + RUN + 5 1.2V LOGIC AND SHOOTTHROUGH PREVENTION – SW L1 VOUT 1 C1 HYST 7 + REVERSE CURRENT COMPARATOR FEEDBACK COMPARATOR GND GND 8 9 – VOLTAGE REFERENCE + + – 0.800V 5µA SS 4 R1 R2 PART NUMBER R1 R2 LTC3631 LTC3631-3.3 LTC3631-5 0 2.5M 4.2M ∞ 800k 800k VOUT/VFB 6 3631 BD IMPLEMENT DIVIDER EXTERNALLY FOR ADJUSTABLE VERSION 3631fe For more information www.linear.
PAGE 8
LTC3631 Operation (Refer to Block Diagram) The LTC3631 is a step-down DC/DC converter with internal power switches that uses Burst Mode control, combining low quiescent current with high switching frequency, which results in high efficiency across a wide range of load currents.
PAGE 9
LTC3631 Operation (Refer to Block Diagram) then the output voltage will be limited by the ramp rate on the SS pin instead. The internal and external soft-start functions are reset on start-up and after an undervoltage or overvoltage event on the input supply. from the ISET pin to ground. The 1µA current sourced out of this pin through the resistor generates a voltage that is translated into an offset in the peak current comparator, which limits the peak inductor current.
PAGE 10
LTC3631 Applications Information The basic LTC3631 application circuit is shown on the front page of this data sheet. External component selection is determined by the maximum load current requirement and begins with the selection of the peak current programming resistor, RISET. The inductor value L can then be determined, followed by capacitors CIN and COUT.
PAGE 11
LTC3631 Applications Information SWITCHING FREQUENCY (kHz) 700 VOUT = 5V ISET OPEN 600 L = 22µH where board area is not a limiting factor, inductors with larger cores can be used, which extends the recommended range of Figure 4 to larger values. L = 47µH Inductor Core Selection 500 400 300 L = 100µH 200 L = 220µH 100 0 5 10 15 20 25 30 35 INPUT VOLTAGE (V) 40 45 3631 F02 Figure 2. Switching Frequency for VOUT = 5V 500 SWITCHING FREQUENCY (kHz) 450 L = 22µH 400 VOUT = 3.
PAGE 12
LTC3631 Applications Information This formula has a maximum at VIN = 2VOUT, where IRMS = IOUT/2. This simple worst-case condition is commonly used for design because even significant deviations do not offer much relief. Note that ripple current ratings from capacitor manufacturers are often based only on 2000 hours of life which makes it advisable to further derate the capacitor, or choose a capacitor rated at a higher temperature than required.
PAGE 13
LTC3631 Applications Information Output Voltage Programming For the adjustable version, the output voltage is set by an external resistive divider according to the following equation: controller is enabled. Figure 7 shows examples of configurations for driving the RUN pin from logic. VSUPPLY VIN 4.7M LTC3631  R1  VOUT = 0.8V • 1+   R2  RUN LTC3631 RUN 3631 F07 The resistive divider allows the VFB pin to sense a fraction of the output voltage as shown in Figure 6.
PAGE 14
LTC3631 Applications Information The minimum value of these thresholds is limited to the internal VIN UVLO thresholds that are shown in the Electrical Characteristics table. The current that flows through this divider will directly add to the shutdown, sleep and active current of the LTC3631, and care should be taken to minimize the impact of this current on the overall efficiency of the application circuit.
PAGE 15
LTC3631 Applications Information The gate charge current results from switching the gate capacitance of the internal power MOSFET switches. Each time the gate is switched from high to low to high again, a packet of charge, dQ, moves from VIN to ground. The resulting dQ/dt is the current out of VIN that is typically larger than the DC bias current. 2. I2R losses are calculated from the resistances of the internal switches, RSW, and external inductor RL.
PAGE 16
LTC3631 Applications Information The undervoltage lockout requirement on VIN can be satisfied with a resistive divider from VIN to the RUN and HYST pins. Choose R1 = 2M and calculate R2 and R3 as follows: R2 = R3 = 1.21V • R1= 224k VIN(RISING) – 1.21V 1.1V • R1– R2 = 94.8k VIN(FALLING) – 1.1V Choose standard values for R2 = 226k and R3 = 95.3k. The ISET pin should be left open in this example to select maximum peak current (225mA). Figure 9 shows a complete schematic for this design example.
PAGE 17
LTC3631 TYPICAL APPLICATIONS L1 100µH VIN 5V TO 45V CIN 4.7µF VIN SW LTC3631 RUN HYST ISET R1 1.47M VFB SS GND VOUT 5V COUT 100µF R2 280k CSS 47nF 3631 F10a CIN: TDK C5750X7R2A475MT COUT: AVX 1812D107MAT L1: TDK SLF7045T-101MR50-PF Figure 10. High Efficiency 5V Regulator 3.3V, 100mA Regulator with Peak Current Soft-Start, Small Size VIN 4.5V TO 24V L1 22µH CIN 1µF VIN SW RUN ISET SS CSS 22nF R1 294k LTC3631 VFB VOUT 3.3V COUT 100mA 10µF R2 93.
PAGE 18
LTC3631 TYPICAL APPLICATIONS Small Size, Limited Peak Current, 20mA Regulator VIN 7V TO 45V L1 470µH CIN 1µF R3 470k R4 100k R5 33k VIN SW R1 470k LTC3631 RUN VFB COUT 10µF VOUT 5V 20mA R2 88.7k HYST SS ISET GND 3631 TA05a CIN: TDK C3225X7R1H105KT COUT: AVX 08056D106KAT2A L1: MURATA LQH43CN471K03 High Efficiency 15V, 20mA Regulator 100 L1 1000µH CIN 1µF VIN SW LTC3631 RUN ISET SS VFB HYST GND CIN: AVX 18125C105KAT2A COUT: TDK C3216X7R1E475KT L1: TDK SLF7045T-102MR14 R1 3M COUT 4.
PAGE 19
LTC3631 Package Description Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. DD Package 8-Lead Plastic DFN (3mm × 3mm) (Reference LTC DWG # 05-08-1698 Rev C) 0.70 ±0.05 3.5 ±0.05 1.65 ±0.05 2.10 ±0.05 (2 SIDES) PACKAGE OUTLINE 0.25 ± 0.05 0.50 BSC 2.38 ±0.05 RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED PIN 1 TOP MARK (NOTE 6) 0.200 REF 3.00 ±0.10 (4 SIDES) R = 0.125 TYP 5 0.40 ± 0.10 8 1.65 ± 0.
PAGE 20
LTC3631 Package Description Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. MS8E Package 8-Lead Plastic MSOP, Exposed Die Pad (Reference LTC DWG # 05-08-1662 Rev K) 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 5.10 (.201) 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 (.
PAGE 21
LTC3631 Revision History (Revision history begins at Rev B) REV DATE DESCRIPTION B 05/10 Updated Absolute Maximum Ratings and Order Information Sections PAGE NUMBER Updated Note 2 3 Updated Graphs G09, G18 and G19 C D E 10/10 08/11 05/13 2 4, 5, 6 Updated GND pin text in Pin Functions 6 Text added to “Output Voltage Programming” section 12 “Example Layout” Art added 16 Updated Typical Application 22 Updated Related Parts 22 Updated CIN and COUT Selection section 12 Updated Efficie
PAGE 22
LTC3631 Typical Application 5V, 100mA Regulator for Automotive Applications VBATT 4.5V TO 45V AND SURVIVES TRANSIENTS UP TO 60V L1 100µH CIN 2.2µF VIN SW LTC3631 RUN ISET SS VFB HYST GND CIN: TDK C3225X7R2A225M COUT: KEMET C1210C106K4RAC L1: COILTRONICS DRA73-101-R R1 470k COUT 10µF VOUT* 5V 100mA R2 88.7k 3631 TA06a *VOUT = VBATT FOR VBATT < 5V Related Parts PART NUMBER LTC3632 DESCRIPTION 50V, 20mA Synchronous Micropower Step-Down DC/DC Converter COMMENTS VIN: 4.