Datasheet

ManualsBrandsLinear Technology ManualsDC / DC Adjustable Switching RegulatorsSwitching Regulator IC Boost/Buck SOT-23-1.3 ... 16V

LT3470

3470fd

Typical applicaTion

FeaTures

applicaTions

DescripTion

Micropower Buck Regulator

with Integrated Boost and

Catch Diodes

The LT

3470 is a micropower step-down DC/DC con-

verter that integrates a 300mA power switch, catch diode

and boost diode into low profile 3mm × 2mm DD and

ThinSOT™ packages. The LT3470 combines Burst Mode

and continuous operation to allow the use of tiny induc-

tor and capacitors while providing a low ripple output to

loads of up to 200mA.

With its wide input range of 4V to 40V, the LT3470 can

regulate a wide variety of power sources, from 2-cell Li-Ion

batteries to unregulated wall transformers and lead-acid

batteries. Quiescent current in regulation is just 26µA in

a typical application while a zero current shutdown mode

disconnects the load from the input source, simplifying

power management in battery-powered systems. Fast

current limiting and hysteretic control protects the LT3470

and external components against shorted outputs, even

at 40V input.

L, LT, LTC, LTM, Linear Technology, the Linear logo and Burst Mode are registered trademarks

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

property of their respective owners.

Efficiency and Power Loss vs Load Current

Low Quiescent Current: 26µA at 12V

to 3.3V

OUT

Integrated Boost and Catch Diodes

Input Range: 4V to 40V

Low Output Ripple: <10mV

<1µA in Shutdown Mode

Output Voltage: 1.25V to 16V

200mA Output Current

Hysteretic Mode Control

– Low Ripple Burst Mode

Operation at Light Loads

– Continuous Operation at Higher Loads

Solution Size as Small as 50mm

Low Profile (0.75mm) 3mm × 2mm Thermally

Enhanced 8-Lead DD and 1mm ThinSOT Packages

Automotive Battery Regulation

Power for Portable Products

Distributed Supply Regulation

Industrial Supplies

Wall Transformer Regulation

LOAD CURRENT (mA)

EFFICIENCY (%)

POWER LOSS (mW)

0.1 10 100

3470 TA02

1000

100

0.1

= 12V

BOOST

LT3470

SWSHDN

0.22µF

22pF

22µF

2.2µF

3470 TA01a

7V TO 40V

OUT

200mA

604k

200k

33µH

BIAS

GND

OFF ON

Summary of content (20 pages)

PAGE 1
LT3470 Micropower Buck Regulator with Integrated Boost and Catch Diodes Description Features n n n n n n n n n n Low Quiescent Current: 26µA at 12VIN to 3.3VOUT Integrated Boost and Catch Diodes Input Range: 4V to 40V Low Output Ripple: <10mV < 1µA in Shutdown Mode Output Voltage: 1.25V to 16V 200mA Output Current Hysteretic Mode Control – Low Ripple Burst Mode® Operation at Light Loads – Continuous Operation at Higher Loads Solution Size as Small as 50mm2 Low Profile (0.
PAGE 2
LT3470 Absolute Maximum Ratings (Note 1) VIN, SHDN Voltage.................................................... 40V BOOST Pin Voltage................................................... 47V BOOST Pin Above SW Pin......................................... 25V FB Voltage................................................................... 5V BIAS Voltage..............................................................25V SW Voltage.................................................................
PAGE 3
LT3470 Electrical Characteristics The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 10V, VSHDN = 10V, VBOOST = 15V, VBIAS = 3V unless otherwise specified. PARAMETER CONDITIONS MIN Minimum Input Voltage TYP ● MAX UNITS 4 V Quiescent Current from VIN VSHDN = 0.2V VBIAS = 3V, Not Switching VBIAS = 0V, Not Switching ● 0.1 10 35 0.5 18 50 µA µA µA Quiescent Current from Bias VSHDN = 0.
PAGE 4
LT3470 Typical Performance Characteristics 90 80 Efficiency, VOUT = 3.3V 90 L = TOKO D52LC 47µH TA = 25°C VIN = 12V VIN = 7V 80 Efficiency, VOUT = 5V VFB vs Temperature 1.260 L = TOKO D52LC 47µH TA = 25°C VIN = 12V 60 50 70 VIN = 36V VIN = 24V VFB (V) EFFICIENCY (%) VIN = 36V VIN = 24V EFFICIENCY (%) 1.255 70 1.250 60 50 1.245 40 40 30 0.1 1 10 LOAD CURRENT (mA) 30 0.1 100 1 10 LOAD CURRENT (mA) 3470 G01 400 1.
PAGE 5
LT3470 Typical Performance Characteristics 120 300 100 250 60 40 0.8 0.7 0.6 200 SCHOTTKY VF (V) 80 20 150 100 0 0 –50 –25 25 50 75 100 125 150 TEMPERATURE (°C) 0 60 0.4 0.3 0.2 0.1 25 50 75 100 125 150 TEMPERATURE (°C) Switch VCESAT 700 50 600 45 SWITCH VCESAT (mV) SCHOTTKY DIODE LEAKAGE (µA) 0.5 0 3470 G11 CATCH BOOST 55 0.
PAGE 6
LT3470 Typical Performance Characteristics Boost Diode Forward Voltage 6.0 900 800 Minimum Input Voltage, VOUT = 5V TA = 25°C VIN TO START VIN TO START 600 500 400 300 200 INPUT VOLTAGE (V) 7 INPUT VOLTAGE (V) SCHOTTKY VF (V) TA = 25°C 8 5.5 700 5.0 4.5 4.0 VIN TO RUN 6 VIN TO RUN 5 3.5 100 0 Minimum Input Voltage, VOUT = 3.3V 0 100 50 150 BOOST DIODE CURRENT (mA) 200 3.
PAGE 7
LT3470 Block Diagram VIN VIN BIAS C1 + – BOOST 500ns ONE SHOT R Q′ S Q C3 SW – SHDN VREF 1.
PAGE 8
LT3470 Operation The LT3470 uses a hysteretic control scheme in conjunction with Burst Mode operation to provide low output ripple and low quiescent current while using a tiny inductor and capacitors. Operation can best be understood by studying the Block Diagram. An error amplifier measures the output voltage through an external resistor divider tied to the FB pin.
PAGE 9
LT3470 Applications Information Input Voltage Range The minimum input voltage required to generate a particular output voltage in an LT3470 application is limited by either its 4V undervoltage lockout or by its maximum duty cycle. The duty cycle is the fraction of time that the internal switch is on and is determined by the input and output voltages: VOUT + VD DC = VIN – VSW + VD where VD is the forward voltage drop of the catch diode (~0.
PAGE 10
LT3470 Applications Information Table 2. Inductor Vendors VENDOR URL PART SERIES INDUCTANCE RANGE (µH) SIZE (mm) Coilcraft www.coilcraft.com DO1605 ME3220 DO3314 10 to 47 10 to 47 10 to 47 1.8 × 5.4 × 4.2 2.0 × 3.2 × 2.5 1.4 × 3.3 × 3.3 Sumida www.sumida.com CR32 CDRH3D16/HP CDRH3D28 CDRH2D18/HP 10 to 47 10 to 33 10 to 47 10 to 15 3.0 × 3.8 × 4.1 1.8 × 4.0 × 4.0 3.0 × 4.0 × 4.0 2.0 × 3.2 × 3.2 Toko www.tokoam.com DB320C D52LC 10 to 27 10 to 47 2.0 × 3.8 × 3.8 2.0 × 5.0 × 5.
PAGE 11
LT3470 applications information Ceramic Capacitors BOOST and BIAS Pin Considerations Ceramic capacitors are small, robust and have very low ESR. However, ceramic capacitors can cause problems when used with the LT3470. Not all ceramic capacitors are suitable. X5R and X7R types are stable over temperature and applied voltage and give dependable service. Other types, including Y5V and Z5U have very large temperature and voltage coefficients of capacitance.
PAGE 12
LT3470 Applications Information (Figure 2b). The circuit in Figure 2a is more efficient because the BOOST pin current and BIAS pin quiescent current comes from a lower voltage source. You must also be sure that the maximum voltage ratings of the BOOST and BIAS pins are not exceeded. The minimum operating voltage of an LT3470 application is limited by the undervoltage lockout (4V) and by the maximum duty cycle as outlined in a previous section.
PAGE 13
LT3470 applications information PCB Layout For proper operation and minimum EMI, care must be taken during printed circuit board layout. Note that large, switched currents flow in the power switch, the internal catch diode and the input capacitor. The loop formed by these components should be as small as possible. Furthermore, the system ground should be tied to the regulator ground in only one place; this prevents the switched current from injecting noise into the system ground.
PAGE 14
LT3470 Applications Information Hot-Plugging Safely The small size, robustness and low impedance of ceramic capacitors make them an attractive option for the input bypass capacitor of LT3470. However, these capacitors can cause problems if the LT3470 is plugged into a live supply (see Linear Technology Application Note 88 for a complete discussion).
PAGE 15
LT3470 applications information CLOSING SWITCH SIMULATES HOT PLUG IIN VIN + LOW IMPEDANCE ENERGIZED 24V SUPPLY LT3470 VIN 10V/DIV 2.2µF IIN 10A/DIV STRAY INDUCTANCE DUE TO 6 FEET (2 METERS) OF TWISTED PAIR 10µs/DIV (6a) 10µF 35V AI.EI. LT3470 + 2.2µF (6b) 1Ω 0.1µF LT3470 2.2µF 3470 F06 (6c) Figure 6.
PAGE 16
LT3470 Typical Applications 3.3V Step-Down Converter VIN 5.5V TO 40V VIN BOOST LT3470 OFF ON SHDN 5V Step-Down Converter VIN R1 324k 22pF FB GND OFF ON SHDN C3 0.22µF, 6.3V L1 33µH 22pF C1 1µF FB GND C1: TDK C3216JB1H105M C2: CE JMK316 BJ226ML-T L1: TOKO A914BYW-330M=P3 1.8V Step-Down Converter 2.5V Step-Down Converter VIN 4.7V TO 40V BOOST LT3470 SHDN VIN 4V TO 23V C3 0.47µF, 6.3V L1 33µH VIN GND FB OFF ON SHDN C1 1µF C2 22µF R2 200k C3 0.
PAGE 17
LT3470 Package Description Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. TS8 Package 8-Lead Plastic TSOT-23 (Reference LTC DWG # 05-08-1637 Rev A) 0.40 MAX 2.90 BSC (NOTE 4) 0.65 REF 1.22 REF 1.4 MIN 3.85 MAX 2.62 REF 2.80 BSC 1.50 – 1.75 (NOTE 4) PIN ONE ID RECOMMENDED SOLDER PAD LAYOUT PER IPC CALCULATOR 0.22 – 0.36 8 PLCS (NOTE 3) 0.65 BSC 0.80 – 0.90 0.20 BSC 0.01 – 0.10 1.00 MAX DATUM ‘A’ 0.30 – 0.50 REF 0.09 – 0.20 (NOTE 3) 1.
PAGE 18
LT3470 Package Description Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. DDB Package 8-Lead Plastic DFN (3mm × 2mm) (Reference LTC DWG # 05-08-1702 Rev B) 0.61 ±0.05 (2 SIDES) 3.00 ±0.10 (2 SIDES) 0.70 ±0.05 2.55 ±0.05 1.15 ±0.05 PACKAGE OUTLINE 0.25 ± 0.05 0.50 BSC 2.20 ±0.05 (2 SIDES) PIN 1 BAR TOP MARK (SEE NOTE 6) 0.200 REF RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS R = 0.115 TYP 5 R = 0.05 TYP 0.40 ± 0.10 8 2.00 ±0.10 (2 SIDES) 0.56 ± 0.
PAGE 19
LT3470 Revision History (Revision history begins at Rev D) REV DATE DESCRIPTION D 09/11 Corrected lead-based tape and reel part numbers in the Order Information section. PAGE NUMBER 2 3470fd Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
PAGE 20
LT3470 Related Parts PART NUMBER DESCRIPTION COMMENTS LT1616 25V, 500mA (IOUT), 1.4MHz, High Efficiency Step-Down DC/DC Converter VIN = 3.6V to 25V, VOUT = 1.25V, IQ = 1.9mA, ISD < 1µA, ThinSOT Package LT1676 60V, 440mA (IOUT), 100kHz, High Efficiency Step-Down DC/DC Converter VIN = 7.4V to 60V, VOUT = 1.24V, IQ = 3.2mA, ISD = 2.5µA, S8 Package LT1765 25V, 2.75A (IOUT), 1.25MHz, High Efficiency Step-Down DC/DC Converter VIN = 3V to 25V, VOUT = 1.