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LT3470A

3470afb

TYPICAL APPLICATION

FEATURES

APPLICATIONS

DESCRIPTION

Micropower Buck Regulator

with Integrated Boost and

Catch Diodes

The LT

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

verter that integrates a 440mA power switch, catch diode

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

package. The LT3470A combines Burst Mode and

continuous operation to allow the use of tiny inductor

and capacitors while providing a low ripple output to

loads of up to 250mA.

With its wide input range of 4V to 40V, the LT3470A 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 35µA 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 cur-

rent limiting and hysteretic control protects the LT3470A

and external components against shorted outputs, even

at 40V input. The LT3470A has higher output current and

improved start-up and dropout performance compared

to the LT3470.

Efficiency and Power Loss vs Load Current

Low Quiescent Current: 35μA at 12V

to 3.3V

OUT

Integrated Boost and Catch Diodes

Input Range: 4V to 40V

3.3V at 250mA from 4V to 40V Input

5V at 250mA from 5.7V to 40V Input

Low Output Ripple: <10mV

<1µA in Shutdown Mode

Output Voltage: 1.25V to 16V

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) 2mm × 3mm Thermally

Enhanced 8-Lead DFN Package

Automotive Battery Regulation

Power for Portable Products

Distributed Supply Regulation

Industrial Supplies

Wall Transformer Regulation

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

of Linear Technology Corporation. All other trademarks are the property of their respective

owners.

BOOST

LT3470A

SWSHDN

0.22µF

22pF

22µF

2.2µF

5.7V TO 40V

OUT

250mA

604k

200k

33µH

BIAS

GND

OFF ON

3470a TA01a

LOAD CURRENT (mA)

EFFICIENCY (%)

POWER LOSS (mW)

0.1 10 100 300

3470a TA01b

1000

100

0.1

= 12V

Summary of content (20 pages)

PAGE 1
LT3470A Micropower Buck Regulator with Integrated Boost and Catch Diodes DESCRIPTION FEATURES n n n n n n n n n n n Low Quiescent Current: 35μA at 12VIN to 3.3VOUT Integrated Boost and Catch Diodes Input Range: 4V to 40V 3.3V at 250mA from 4V to 40V Input 5V at 250mA from 5.7V to 40V Input Low Output Ripple: <10mV < 1μA in Shutdown Mode Output Voltage: 1.
PAGE 2
LT3470A ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION (Note 1) VIN, SHDN Voltage ................................................... 40V BOOST Pin Voltage .................................................. 47V BOOST Pin Above SW Pin........................................ 25V FB Voltage .................................................................. 5V BIAS Voltage .............................................................15V SW Voltage ................................................................
PAGE 3
LT3470A 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 TYP ● Minimum Input Voltage MAX UNITS 4 V Quiescent Current from VIN VSHDN = 0.2V VBIAS = 3V, Not Switching VBIAS = 0V, Not Switching ● 0.1 10 40 0.5 18 55 μA μA μA Quiescent Current from Bias VSHDN = 0.
PAGE 4
LT3470A TYPICAL PERFORMANCE CHARACTERISTICS Efficiency, VOUT = 3.3V Efficiency, VOUT = 5V VFB vs Temperature 90 90 80 TA = 25°C unless otherwise noted. L = TOKO D52LC 47μH TA = 25°C VIN = 12V 1.260 L = TOKO D52LC 47μH TA = 25°C VIN = 7V VIN = 12V 80 60 50 70 VIN = 24V VIN = 36V VFB (V) VIN = 24V VIN = 36V EFFICIENCY (%) EFFICIENCY (%) 1.255 70 60 1.250 50 1.245 40 40 30 0.1 1 10 LOAD CURRENT (mA) 100 30 0.1 1 10 LOAD CURRENT (mA) 1.
PAGE 5
LT3470A TYPICAL PERFORMANCE CHARACTERISTICS FB Bias Current (VFB = 0V) vs Temperature FB Bias Current (VFB = 1V) vs Temperature 60 120 50 100 FB CURRENT (μA) FB CURRENT (nA) TA = 25°C unless otherwise noted. 40 30 20 80 60 40 20 10 0 –50 –25 0 0 –50 –25 25 50 75 100 125 150 TEMPERATURE (°C) 0 25 50 75 100 125 150 TEMPERATURE (°C) 3470a G09 3470a G08 Boost Diode VF (IF = 50mA) vs Temperature Switch VCESAT (ISW = 100mA) vs Temperature 0.8 300 0.7 0.
PAGE 6
LT3470A TYPICAL PERFORMANCE CHARACTERISTICS BOOST Pin Current 700 14 600 12 BOOST PIN CURRENT (mA) SWITCH VCESAT (mV) Switch VCESAT TA = 25°C unless otherwise noted. 500 400 300 200 100 10 8 6 4 2 0 0 100 0 200 300 400 SWITCH CURRENT (mA) 500 0 100 200 300 400 SWITCH CURRENT (mA) 3470a G14 500 3470a G15 Catch Diode Forward Voltage Boost Diode Forward Voltage 1.0 900 800 700 SCHOTTKY VF (V) SCHOTTKY VF (V) 0.8 0.6 0.4 600 500 400 300 200 0.
PAGE 7
LT3470A PIN FUNCTIONS SHDN (Pin 8): The SHDN pin is used to put the LT3470A in shutdown mode. Tie to ground to shut down the LT3470A. Apply 2V or more for normal operation. If the shutdown feature is not used, tie this pin to the VIN pin. NC (Pin 7): This pin can be left floating, connected to VIN, or tied to GND. VIN (Pin 6): The VIN pin supplies current to the LT3470A’s internal regulator and to the internal power switch. This pin must be locally bypassed.
PAGE 8
LT3470A OPERATION The LT3470A 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
LT3470A APPLICATIONS INFORMATION Input Voltage Range The minimum input voltage required to generate a particular output voltage in an LT3470A application is limited by either its 4V undervoltage lockout or by its maximum duty cycle.
PAGE 10
LT3470A 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
LT3470A 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 LT3470A. 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
LT3470A 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 LT3470A monitors the boost capacitor for sufficient voltage such that the switch is allowed to fully saturate. When boost voltage falls below adequate levels (1.
PAGE 13
LT3470A 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
LT3470A 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 LT3470A. However, these capacitors can cause problems if the LT3470A is plugged into a live supply (see Linear Technology Application Note 88 for a complete discussion).
PAGE 15
LT3470A APPLICATIONS INFORMATION CLOSING SWITCH SIMULATES HOT PLUG IIN VIN LT3470A + VIN 10V/DIV 2.2μF LOW IMPEDANCE ENERGIZED 24V SUPPLY IIN 10A/DIV STRAY INDUCTANCE DUE TO 6 FEET (2 METERS) OF TWISTED PAIR 10μs/DIV (6a) LT3470A 10μF 35V AI.EI. + VIN 10V/DIV 2.2μF IIN 10A/DIV 10μs/DIV (6b) 1Ω LT3470A 0.1μF VIN 10V/DIV 2.2μF IIN 10A/DIV 10μs/DIV 3470a F06 (6c) Figure 6.
PAGE 16
LT3470A APPLICATIONS INFORMATION 3.3V Step-Down Converter VIN 4V TO 40V VIN BOOST LT3470A OFF ON SHDN C3 0.22μF, 6.3V L1 33μH BIAS 22pF C1 1μF VOUT 3.3V 250mA SW R1 324k FB GND R2 200k C2 22μF 3470a TA02 C1: TDK C3216JB1H105M C2: CE JMK316 BJ226ML-T L1: TOKO A993AS-270M=P3 5V Step-Down Converter VIN 5.7V TO 40V VIN BOOST LT3470A OFF ON SHDN C3 0.22μF, 6.
PAGE 17
LT3470A TYPICAL APPLICATIONS 1.8V Step-Down Converter VIN 4V TO 23V VIN BOOST LT3470A OFF ON SHDN VOUT 1.8V 250mA SW BIAS C1 1μF C3 0.22μF, 25V L1 22μH 22pF R1 147k FB GND R2 332k C2 22μF 3470a TA05 C1: TDK C3216JB1H105M C2: TDK C2012JB0J226M L1: MURATA LQH32CN150K53 12V Step-Down Converter VIN 15V TO 34V VIN BOOST LT3470A OFF ON SHDN C3 0.
PAGE 18
LT3470A PACKAGE DESCRIPTION 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) R = 0.115 TYP 5 R = 0.05 TYP 0.40 ± 0.10 8 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 2.00 ±0.10 (2 SIDES) 0.56 ± 0.05 (2 SIDES) 0.75 ±0.05 0 – 0.05 4 0.25 ± 0.05 1 PIN 1 R = 0.20 OR 0.
PAGE 19
LT3470A REVISION HISTORY (Revision history begins at Rev B) REV DATE DESCRIPTION PAGE NUMBER B 01/11 Added H-grade part information. 2 to 5, 15 3470afb 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
LT3470A 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.