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LTC3632

3632fc

TYPICAL APPLICATION

FEATURES

APPLICATIONS

DESCRIPTION

High Efﬁciency, High Voltage

20mA Synchronous

Step-Down Converter

The LTC

3632 is a high efﬁciency, high voltage step-down

DC/DC converter with internal high side and synchronous

power switches that draws only 12μA typical DC sup-

ply current at no load while maintaining output voltage

regulation.

The LTC3632 can supply up to 20mA load current and

features a programmable peak current limit that provides

a simple method for optimizing efﬁciency in lower current

applications. The LTC3632’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 50V input range and internal

overvoltage monitor capable of protecting the part through

60V surges, the LTC3632 is a robust converter suited for

regulating a wide variety of power sources. Additionally,

the LTC3632 includes a precise run threshold and soft-start

feature to guarantee that the power system start-up is

well-controlled in any environment.

The LTC3632 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 50V

Overvoltage Lockout Provides Protection Up to 60V

Internal High Side and Low Side Power Switches

No Compensation Required

20mA Output Current

Low Dropout Operation: 100% Duty Cycle

Low Quiescent Current: 12µA

Wide Output Voltage Range: 0.8V to V

0.8V ±1% Feedback Voltage Reference

Adjustable Peak Current Limit

Internal and External Soft-Start

Precise RUN Pin Threshold with Adjustable

Hysteresis

Few External Components Required

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, 20mA Step-Down Converter

LTC3632

RUN

HYST

3632 TA01a

5V TO 50V

1µF 10µF

1.47M

280k

OUT

20mA

SET

GND

1mH

LOAD CURRENT (mA)

0.1

EFFICIENCY (%)

POWER LOSS (mW)

100

1 10

3632 TA01b

100

1000

EFFICIENCY

POWER LOSS

= 10V

= 48V

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
LTC3632 High Efficiency, High Voltage 20mA Synchronous Step-Down Converter FEATURES n n n n n n n n n n n n n n DESCRIPTION Wide Input Voltage Range: Operation from 4.5V to 50V Overvoltage Lockout Provides Protection Up to 60V Internal High Side and Low Side Power Switches No Compensation Required 20mA Output Current Low Dropout Operation: 100% Duty Cycle Low Quiescent Current: 12µA Wide Output Voltage Range: 0.8V to VIN 0.
PAGE 2
LTC3632 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 VFB, HYST, ISET, SS Voltages......................... –0.3V to 6V Operating Junction Temperature Range (Note 2)................................................... –40°C to 125°C Storage Temperature Range....................
PAGE 3
LTC3632 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
LTC3632 TYPICAL PERFORMANCE CHARACTERISTICS 100 95 VIN = 24V 90 100 95 VIN = 12V VIN = 36V 70 65 90 80 75 VIN = 48V 70 VIN = 36V 65 60 60 VOUT = 5V FIGURE 11 CIRCUIT 55 50 0.1 1 LOAD CURRENT (mA) VOUT = 3.3V FIGURE 11 CIRCUIT 50 0.1 1 LOAD CURRENT (mA) 3632 G01 ILOAD = 5mA 75 70 10 15 20 25 30 35 40 INPUT VOLTAGE (V) 45 50 0.10 0 –0.10 –0.20 0.798 –40 –10 20 50 80 TEMPERATURE (°C) 5.02 5.00 4.99 4.98 4.97 –0.40 4.96 –0.
PAGE 5
LTC3632 TYPICAL PERFORMANCE CHARACTERISTICS 40 30 20 10 0 200 400 600 800 RISET (kΩ) 1000 50 14 ISET OPEN 12 40 30 RSET = 500k 20 ISET = GND 10 0 1200 VIN = 10V VIN SUPPLY CURRENT (µA) 60 VIN = 10V 50 0 0 5 SLEEP 8 6 SHUTDOWN 20 50 80 TEMPERATURE (°C) 8 7 7 6 TOP 5 4 3 1 110 BOTTOM RUN COMPARATOR THRESHOLD (V) SWITCH LEAKAGE CURRENT (µA) 4 BOTTOM 3 2 1 0 10 20 30 50 40 0 –40 –10 20 50 80 TEMPERATURE (°C) 110 3632 G15 Operating Waveforms 1.30 0.20 0.
PAGE 6
LTC3632 TYPICAL PERFORMANCE CHARACTERISTICS Soft-Start Waveforms Load Step Transient Response OUTPUT VOLTAGE 2V/DIV OUTPUT VOLTAGE 100mV/DIV OUTPUT VOLTAGE 1V/DIV LOAD CURRENT 20mA/DIV CSS = 0.047µF 5ms/DIV 3632 G19 Short-Circuit Response INDUCTOR CURRENT 20mA/DIV VIN = 10V VOUT = 5V 1ms/DIV 3632 G20 VIN = 10V VOUT = 5V 200µs/DIV 3632 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
LTC3632 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 5.
PAGE 8
LTC3632 OPERATION (Refer to Block Diagram) The LTC3632 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
LTC3632 OPERATION (Refer to Block Diagram) 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. through the resistor generates a voltage that is translated into an offset in the peak current comparator, which limits the peak inductor current. In order to ensure a smooth start-up transition in any application, the internal soft‑start also ramps the peak inductor current from 10mA during its 0.
PAGE 10
LTC3632 APPLICATIONS INFORMATION The basic LTC3632 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
LTC3632 APPLICATIONS INFORMATION 350 VOUT = 5V ISET OPEN SWITCHING FREQUENCY (kHz) 300 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 = 220µH 250 200 Inductor Core Selection L = 470µH 150 100 L = 1000µH 50 L = 2200µH 0 5 10 15 20 25 30 35 40 INPUT VOLTAGE (V) 45 50 3632 F02 Figure 2. Switching Frequency for VOUT = 5V SWITCHING FREQUENCY (kHz) 250 L = 220µH VOUT = 3.
PAGE 12
LTC3632 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
LTC3632 APPLICATIONS INFORMATION Output Voltage Programming The output voltage is set by an external resistive divider according to the following equation:  R1  VOUT = 0.8V • 1+   R2  VSUPPLY VIN 4.7M LTC3632 RUN The resistive divider allows the VFB pin to sense a fraction of the output voltage as shown in Figure 6. Output voltage adjustment range is from 0.8V to VIN. VOUT R1 VFB LTC3632 controller is enabled. Figure 7 shows examples of configurations for driving the RUN pin from logic.
PAGE 14
LTC3632 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 LTC3632, and care should be taken to minimize the impact of this current on the overall efficiency of the application circuit.
PAGE 15
LTC3632 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
LTC3632 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:   1.21V  • R1= 224k R2 =   – 1.21V V  IN(RISING)    1.1V  • R1– R2 = 90.8k R3 =   – 1.1V V  IN(FALLING)  3. Keep the switching node, SW, away from all sensitive small-signal nodes.
PAGE 17
LTC3632 TYPICAL APPLICATIONS L1 1mH VIN 5V TO 50V VIN CIN 4.7µF SW LTC3632 RUN HYST ISET R1 4.2M VFB COUT 100µF VOUT 5V 20mA R2 800k SS CSS 470nF GND 3632 F11 CIN: TDK C5750X7R2A475MT COUT: AVX 1812D107MAT L1: COILCRAFT LPS6235-105ML Figure 11. High Efficiency 5V Regulator 3.3V, 20mA Regulator with Peak Current Soft-Start, Small Size VIN 4.5V TO 24V L1 470µH VIN CIN 1µF SW R1 294k LTC3632 RUN ISET SS CSS 0.1µF VFB COUT 10µF VOUT 3.3V 20mA R2 93.
PAGE 18
LTC3632 TYPICAL APPLICATIONS Small Size, Limited Peak Current, 4mA Regulator VIN 7V TO 50V L1 2.2mH CIN 1µF R3 470k R4 100k R5 33k VIN SW R1 470k LTC3632 RUN VFB COUT 10µF VOUT 5V 4mA R2 88.
PAGE 19
LTC3632 PACKAGE DESCRIPTION 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 ± 0.10 (2 SIDES) 0.75 ±0.05 4 0.25 ± 0.05 1 (DD8) DFN 0509 REV C 0.50 BSC 2.38 ±0.10 0.00 – 0.
PAGE 20
LTC3632 PACKAGE DESCRIPTION MS8E Package 8-Lead Plastic MSOP, Exposed Die Pad (Reference LTC DWG # 05-08-1662 Rev I) 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 (.
PAGE 21
LTC3632 REVISION HISTORY (Revision history begins at Rev B) REV DATE DESCRIPTION B 6/10 Text updates in Description PAGE NUMBER Updates to Electrical Characteristics Updates to graphs G08, G09, G17, G18, G19 Updated description for Pins 8 and 9 in Pin Functions C 10/10 1 3 4, 5, 6 6 Text updates in Operation section 8, 9 Text updates in Applications Information section 13 Figure 10 graphic added 16 Asterisk and related text added to Typical Application 22 Related Parts updated 22 Upda
PAGE 22
LTC3632 TYPICAL APPLICATION 5V, 20mA Regulator for Automotive Applications VBATT 4.5V TO 50V TRANSIENTS UP TO 60V L1 1mH CIN 1µF VIN SW LTC3632 RUN ISET SS VFB HYST GND CIN: TDK C3225X7R2A105M COUT: KEMET C1210C106K4RAC L1: COILTRONICS DRA73-102-R R1 470k COUT 10µF VOUT* 5V 20mA R2 88.7k 3632 TA06a *VOUT = VBATT FOR VBATT < 5V RELATED PARTS PART NUMBER LTC3631/LTC3631-3.3/ LTC3631-5 LTC3642/LTC3642-3.