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LT3470A LINER | Alldatasheet

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FEATURES

APPLICATIONS

DESCRIPTION

The L T®3470A is a micropower step-down DC/DC con- verter that integrates a 440mA power switch, catch diode and boost diode into low profi le 2mm × 3mm DFN package. The L T3470A 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 L T3470A 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 L T3470A and external components against shorted outputs, even at 40V input. The L T3470A has higher output current and improved start-up and dropout performance compared to the L T3470. Effi ciency and Power Loss vs Load Current n Low Quiescent Current: 35μA at 12VIN to 3.3VOUT n Integrated Boost and Catch Diodes n Input Range: 4V to 40V n 3.3V at 250mA from 4V to 40V Input n 5V at 250mA from 5.7V to 40V Input n Low Output Ripple: <10mV n < 1μA in Shutdown Mode n Output Voltage: 1.25V to 16V n Hysteretic Mode Control – Low Ripple Burst Mode ® Operation at Light Loads – Continuous Operation at Higher Loads n Solution Size as Small as 50mm 2 n Low Profi le (0.75mm) 2mm × 3mm Thermally Enhanced 8-Lead DFN Package n Automotive Battery Regulation n Power for Portable Products n Distributed Supply Regulation n Industrial Supplies n Wall T ransformer Regulation L, L T , L TC and L TM are registered trademarks of Linear Technology Corporation. Burst Mode is a registered trademark of Linear Technology Corporation. All other trademarks are the property of their respective owners. VIN BOOST L T3470A SWSHDN 0.22μF 22pF 22μF2.2μF VIN 5.7V TO 40V VOUT 250mA 604k 200k 33μH BIAS FB GND OFF ON 3470a TA01 LOAD CURRENT (mA) EFFICIENCY (%) POWER LOSS (mW) 0.1 10 100 300 3470a TA02 1000 100 0.1 VIN = 12V

PIN CONFIGURATION ABSOLUTE MAXIMUM RATINGS IN Maximum Junction Temperature Operating Temperature Range (Note 2) (Note 1) TOP VIEW DDB8 PACKAGE 8-LEAD (3mm × 2mm) PLASTIC DFN 1 FB BIAS BOOST SW SHDN NC VIN GND θJA = 80°C/W EXPOSED PAD (PIN 9) IS GND, MUST BE SOLDERED TO PCB ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL PART MARKING * PACKAGE DESCRIPTION TEMPERATURE RANGE L T3470AEDDB#PBF L T3470AEDDB#TRPBF LDPR 8-Lead (3mm × 2mm) Plastic DFN –40°C to 85°C L T3470AIDDB#PBF L T3470AIDDB#TRPBF LDPR 8-Lead (3mm × 2mm) Plastic DFN –40°C to 125°C Consult L TC Marketing for parts specifi ed with wider operating temperature ranges. *The temperature grade is identifi ed by a label on the shipping container . Consult L TC Marketing for information on non-standard lead based fi nish parts. For more information on lead free part marking, go to: http://www.linear .com/leadfree/ For more information on tape and reel specifi cations, go to: http://www.linear .com/tapeandreel/

ELECTRICAL CHARACTERISTICS

The l denotes the specifi cations which apply over the full operating temperature range, otherwise specifi cations are at TA = 25°C. VIN = 10V , VSHDN = 10V , VBOOST = 15V , VBIAS = 3V unless otherwise specifi ed. PARAMETER CONDITIONS MIN TYP MAX UNITS Minimum Input Voltage ● 4V Quiescent Current from VIN VSHDN = 0.2V VBIAS = 3V , Not Switching VBIAS = 0V , Not Switching 0.1 0.5 μA μA μA Quiescent Current from Bias V SHDN = 0.2V VBIAS = 3V , Not Switching VBIAS = 0V , Not Switching 0.1 0.1 0.5 1.5 μA μA μA FB Comparator T rip Voltage V FB Falling ● 1.228 1.250 1.265 V FB Pin Bias Current (Note 3) V FB = 1V 150 nA nA FB Voltage Line Regulation 4V < V IN < 40V 0.0006 0.02 %/V Minimum Switch Off-Time (Note 5) 500 ns Maximum Duty Cycle ● 90 95 % Switch Leakage Current 0.7 1.5 μA Switch VCESAT ISW = 100mA 150 mV Switch VCESAT Without Boost V BOOST = VSW 0.9 1.2 V Switch Top Current Limit V FB = 0V 320 440 560 mA Switch Bottom Current Limit V FB = 0V 280 mA Catch Schottky Drop I SW = 100mA 600 mV Catch Schottky Reverse Leakage V SW = 10V 0.2 2 μA Boost Schottky Drop I BIAS = 50mA 690 775 mV Boost Schottky Reverse Leakage V SW = 10V , VBIAS = 0V 0.2 2 μA Minimum Boost Voltage (Note 4) ● 1.7 2.2 V BOOST Pin Current I SW = 100mA 2.3 5 mA Bias Pin Preload V BOOST = 10V 50 mA SHDN Pin Current V SHDN = 2.5V 1 5 μA SHDN Input Voltage High 2V SHDN Input Voltage Low 0.2 V Note 1: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. Exposure to any Absolute Maximum Rating condition for extended periods may affect device reliability and lifetime. Note 2: The L T3470AE is guaranteed to meet performance specifi cations from 0°C to 85°C. Specifi cations over the –40°C to 85°C operating temperature range are assured by design, characterization and correlation with statistical process controls. The L T3470AI specifi cations are guaranteed over the –40°C to 125°C temperature range. Note 3: Bias current fl ows out of the FB pin. Note 4: This is the minimum voltage across the boost capacitor needed to guarantee full saturation of the switch. Note 5: This parameter is assured by design and correlation with statistical process controls.

TYPICAL PERFORMANCE CHARACTERISTICS Effi ciency, VOUT = 3.3V Effi ciency, V OUT = 5V V FB vs Temperature Top and Bottom Switch Current Limits (VFB = 0V) vs Temperature VIN Quiescent Current vs Temperature BIAS Quiescent Current (Bias > 3V) vs Temperature SHDN Bias Current vs Temperature TEMPERATURE (°C) –50

1.240 VFB (V)

1.245 1.250 1.255 1.260 –25 0 25 50 3470a G03 75 100 125 TEMPERATURE (°C) –50 –25 VIN CURRENT (μA)20 0 50 75 3470a G05 25 100 125 BIAS < 3V BIAS > 3V TEMPERATURE (°C) –50 BIAS CURRENT (μA) 25 75 3470a G06 –25 0 50 100 125 TEMPERATURE (°C) –50 SHDN CURRENT (μA) 3470a G07 0–25 75 10025 125

8 VSHDN = 36V

VSHDN = 2.5V LOAD CURRENT (mA) EFFICIENCY (%) 0.1 10 100 3470a G01 L = TOKO D52LC 47μH TA = 25°C VIN = 7V VIN = 36VVIN = 24V VIN = 12V LOAD CURRENT (mA) EFFICIENCY (%) 0.1 10 100 3470a G02 L = TOKO D52LC 47μH TA = 25°C VIN = 12V VIN = 36VVIN = 24V TEMPERATURE (°C) –50 CURRENT LIMIT (mA) 550 3470a G04 400 300 –25 0 50 250 200 600 500 450 350 75 100 125 TA = 25°C unless otherwise noted.

FB Bias Current (VFB = 1V) vs Temperature TYPICAL PERFORMANCE CHARACTERISTICS FB Bias Current (VFB = 0V) vs Temperature Switch VCESAT (ISW = 100mA) vs Temperature Boost Diode VF (IF = 50mA) vs Temperature Catch Diode VF (IF = 100mA) vs Temperature Diode Leakage (VR = 36V) vs Temperature TEMPERATURE (°C) –50 –25 FB CURRENT (nA)20 0 50 75 3470a G08 25 100 125 TEMPERATURE (°C) –50 FB CURRENT (μA) 100 120 25 75 3470a G09 –25 0 50 100 125 TEMPERATURE (°C) –50 SCHOTTKY VF (V) 0.7 3470a G11 0.4 0.2 –25 0 50 0.1 0.8 0.6 0.5 0.3 75 100 125 TEMPERATURE (°C) –50 SWITCH VCESAT (mV)200 250 300 25 75 3470a G10 150 100 –25 0 50 100 125 TEMPERATURE (°C) –50 0.4 0.5 0.7 25 75 3470a G12 0.3 0.2 –25 0 50 100 125 0.1 0.6 SCHOTTKY VF (V) TEMPERATURE (°C) –50 –25 SCHOTTKY DIODE LEAKAGE (mA) 0 50 75 3470a G13 25 100 125 CATCH BOOST TA = 25°C unless otherwise noted.

Boost Diode Forward Voltage Minimum Input Voltage, VOUT = 3.3V Minimum Input Voltage, V OUT = 5V TYPICAL PERFORMANCE CHARACTERISTICS BOOST DIODE CURRENT (mA) SCHOTTKY VF (V) 500 600 700 200 3470a G17 400 300 50 100 150 100 200 900 800 Switch VCESAT BOOST Pin Current Catch Diode Forward Voltage SWITCH CURRENT (mA) 400 500 700 300 400 3470a G14 300 200 100 200 500 100 600SWITCH VCESAT (mV) SWITCH CURRENT (mA) 300 400 3470a G15 100 200 500 BOOST PIN CURRENT (mA) CATCH DIODE CURRENT (mA) SCHOTTKY VF (V) 0.4 0.6 400 3470a G16 0.2 100 200 300 1.0 0.8 LOAD CURRENT (mA) 3.0 INPUT VOLTAGE (V) 3.5 4.0 4.5 5.0 5.5 6.0 50 100 150 200 250 3470a G18 TA = 25°C VIN TO RUN/START LOAD CURRENT (mA) INPUT VOLTAGE (V) 250 3470a G19 50 100 150 200

8 TA = 25°C

TA = 25°C unless otherwise noted.

SHDN (Pin 8): The SHDN pin is used to put the L T3470A in shutdown mode. Tie to ground to shut down the L T3470A. Apply 2V or more for normal operation. If the shutdown feature is not used, tie this pin to the V IN pin. NC (Pin 7): This pin can be left fl oating, connected to VIN, or tied to GND. VIN (Pin 6): The VIN pin supplies current to the L T3470A’s internal regulator and to the internal power switch. This pin must be locally bypassed. GND (Pin 5): Tie the GND pin to a local ground plane below the L T3470A and the circuit components. Return the feedback divider to this pin. SW (Pin 4): The SW pin is the output of the internal power switch. Connect this pin to the inductor , catch diode and boost capacitor . BOOST (Pin 3): The BOOST pin is used to provide a drive voltage, which is higher than the input voltage, to the internal bipolar NPN power switch. BIAS (Pin 2): The BIAS pin connects to the internal boost Schottky diode and to the internal regulator . Tie to VOUT when VOUT > 2.5V or to VIN otherwise. When VBIAS > 3V the BIAS pin will supply current to the internal regulator . FB (Pin 1): The L T3470A regulates its feedback pin to 1.25V . Connect the feedback resistor divider tap to this pin. Set the output voltage according to V OUT = 1.25V (1 + R1/R2) or R1 = R2 (VOUT/1.25 – 1). Exposed Pad (Pin 9): Ground. Must be soldered to PCB. PIN FUNCTIONS

RQ ʹ SQ 500ns ONE SHOT VREF 1.25V BURST MODE DETECT SW GND 3470a BD FB R2 R1 SHDN ENABLE VIN VIN NC BIAS BOOST VOUT gm

Figure 1. Operating Waveforms of the L T3470A Converting 12V to 5V Using a 33μH Inductor and 10μF Output Capacitor

section BOOST Pin Considerations. switch at too high a frequency to yield good effi ciency. tOFF-TIME possibly allowing the use of a smaller inductor . See Table 1 for an inductor value selection guide. Table 1. Recommended Inductors for Loads up to 250mA Choose an inductor that is intended for power applications. Table 2 lists several manufacturers and inductor series.

vendors for more information. capacitor satisfi es these requirements. between the output and the feedback pin. Table 2. Inductor Vendors

capacitor and a low cost electrolytic capacitor . the Hot-Plugging Safely section. 3.3V and above, the standard circuit (Figure 2a) is best. Figure 2. T wo Circuits for Generating the Boost Voltage Table 2. Capacitor Vendors

and BIAS pins are not exceeded. voltage such that the switch is allowed to fully saturate. protects against a shorted or reversed input. Figure 3. The Minimum Input Voltage Depends on Output Figure 4. Diode D1 Prevents a Shorted Input from Discharging

ideally at the ground terminal of the output capacitor C2. Figure 5. A Good PCB Layout Ensures Proper , Low EMI Operation

The small size, robustness and low impedance of ceramic capacitors make them an attractive option for the input bypass capacitor of L T3470A. However , these capacitors can cause problems if the L T3470A is plugged into a live supply (see Linear Technology Application Note 88 for a complete discussion). The low loss ceramic capacitor combined with stray inductance in series with the power source forms an under damped tank circuit, and the volt- age at the V IN pin of the L T3470A can ring to twice the nominal input voltage, possibly exceeding the L T3470A’s rating and damaging the part. If the input supply is poorly controlled or the user will be plugging the L T3470A into an energized supply, the input network should be designed to prevent this overshoot. Figure 6 shows the waveforms that result when an L T3470A circuit is connected to a 24V supply through six feet of 24-gauge twisted pair . The fi rst plot is the response with a 2.2μF ceramic capacitor at the input. The input voltage rings as high as 35V and the input current peaks at 20A. One method of damping the tank circuit is to add another capacitor with a series resistor to the circuit. In Figure 6b an aluminum electrolytic capacitor has been added. This capacitor’s high equivalent series resistance damps the circuit and eliminates the voltage overshoot. The extra capacitor improves low frequency ripple fi ltering and can slightly improve the effi ciency of the circuit, though it is likely to be the largest component in the circuit. An alternative solution is shown in Figure 6c. A 1Ω resistor is added in series with the input to eliminate the voltage overshoot (it also reduces the peak input current). A 0.1μF capacitor improves high frequency fi ltering. This solution is smaller and less expensive than the electrolytic capacitor . For high input voltages its impact on effi ciency is minor , reducing effi ciency less than one half percent for a 5V output at full load operating from 24V . High Temperature Considerations The die junction temperature of the L T3470A must be lower than the maximum rating of 125°C. This is generally not a concern unless the ambient temperature is above 85°C. For higher temperatures, care should be taken in the layout of the circuit to ensure good heat sinking of the L T3470A. The maximum load current should be derated as the ambient temperature approaches the maximum junction rating. The die temperature is calculated by multiplying the L T3470A power dissipation by the thermal resistance from junction to ambient. Power dissipation within the L T3470A can be estimated by calculating the total power loss from an effi ciency measurement. Thermal resistance depends on the layout of the circuit board and choice of package. The DFN package with the exposed pad has a thermal resistance of approximately 80°C/W . Finally, be aware that at high ambient temperatures the internal Schottky diode will have signifi cant leakage current (see Typical Performance Characteristics) increasing the quiescent current of the L T3470A converter .

Figure 6: A Well Chosen Input Network Prevents Input Voltage Overshoot and Ensures Reliable Operation When the L T3470A is Connected to a Live Supply L T3470A 2.2μF VIN 10V/DIV IIN 10A/DIV 10μs/DIV VIN 10V/DIV IIN 10A/DIV 10μs/DIV VIN 10V/DIV IIN 10A/DIV 10μs/DIV VIN CLOSING SWITCH SIMULATES HOT PLUG IIN (6a) (6b) (6c) LOW IMPEDANCE ENERGIZED 24V SUPPL Y STRAY INDUCTANCE DUE TO 6 FEET (2 METERS) OF TWISTED PAIR L T3470A 2.2μF 10μF 35V AI.EI. L T3470A 2.2μF0.1μF 3470a F06

3.3V Step-Down Converter 5V Step-Down Converter 2.5V Step-Down Converter VIN BOOST L T3470A SWSHDN 0.22μF , 6.3V 22pF 22μF 3470a TA03 1μF V IN 4V TO 40V VOUT 3.3V 250mA 324k 200k C1: TDK C3216JB1H105M C2: CE JMK316 BJ226ML-T L1: TOKO A993AS-270M=P3 33μH BIAS FB GND OFF ON VIN BOOST L T3470A SWSHDN 0.22μF , 6.3V 22pF 22μF 3470a TA04 1μF V IN 5.7V TO 40V VOUT 250mA 604k 200k 33μH BIAS FB GND OFF ON C1: TDK C3216JB1H105M C2: CE JMK316 BJ226ML-T L1: TOKO A914BYW-330M=P3 VIN BOOST L T3470A SWSHDN 0.47μF , 6.3V 22pF 22μF 3470a TA07 1μF V IN 4V TO 40V VOUT 2.5V 250mA 200k 200k C1: TDK C3216JB1H105M C2: TDK C2012JB0J226M L1: SUMIDA CDRH3D28 33μH BIAS FB GND OFF ON

1.8V Step-Down Converter 12V Step-Down Converter VIN BOOST L T3470A SWSHDN BIAS 0.22μF , 25V 22pF 22μF 3470a TA05 1μF V IN 4V TO 23V VOUT 1.8V 250mA 147k 332k 22μH FB GND OFF ON C1: TDK C3216JB1H105M C2: TDK C2012JB0J226M L1: MURATA LQH32CN150K53 VIN BOOST L T3470A SWSHDN 0.22μF , 16V 22pF 10μF 3470a TA06 1μF V IN 15V TO 34V VOUT 12V 250mA 866k 100k C1: TDK C3216JB1H105M C2: TDK C3216JB1C106M L1: MURATA LQH32CN150K53 33μH BIAS FB GND OFF ON

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 representa- tion that the interconnection of its circuits as described herein will not infringe on existing patent rights. PACKAGE DESCRIPTION 8-Lead Plastic DFN (3mm × 2mm) (Reference L TC DWG # 05-08-1702 Rev B) 2.00 ±0.10 (2 SIDES) NOTE: 1. DRAWING CONFORMS TO VERSION (WECD-1) IN JEDEC PACKAGE OUTLINE M0-229 2. DRAWING NOT TO SCALE 3. ALL DIMENSIONS ARE IN MILLIMETERS 4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE 5. EXPOSED PAD SHALL BE SOLDER PLATED 6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE 0.40 ± 0.10 BOTTOM VIEW—EXPOSED PAD 0.56 ± 0.05 (2 SIDES) 0.75 ±0.05 R = 0.115 TYPR = 0.05 TYP 2.15 ±0.05 (2 SIDES) 3.00 ±0.10 (2 SIDES) PIN 1 BAR TOP MARK (SEE NOTE 6)

0.200 REF

0 – 0.05 (DDB8) DFN 0905 REV B 0.25 ± 0.05 2.20 ±0.05 (2 SIDES) RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS 0.61 ±0.05 (2 SIDES) 1.15 ±0.05 0.70 ±0.05 2.55 ±0.05 PACKAGE OUTLINE 0.25 ± 0.05

0.50 BSC

R = 0.20 OR 0.25 × 45° CHAMFER

Linear Technology Corporation 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear .com © LINEAR TECHNOLOGY CORPORATION 2008 LT 1108 REV A • PRINTED IN USA RELATED PARTS PART NUMBER DESCRIPTION COMMENTS L T1616 25V , 500mA (I OUT), 1.4MHz, High Effi ciency Step-Down DC/DC Converter VIN = 3.6V to 25V , VOUT = 1.25V , IQ = 1.9mA, ISD = <1μA, ThinSOT Package L T1676 60V , 440mA (I OUT), 100kHz, High Effi ciency Step-Down DC/DC Converter VIN = 7.4V to 60V , VOUT = 1.24V , IQ = 3.2mA, ISD = 2.5μA, L T1765 25V , 2.75A (I OUT), 1.25MHz, High Effi ciency Step-Down DC/DC Converter VIN = 3V to 25V , VOUT = 1.2V , IQ = 1mA, ISD = 15μA, S8, TSSOP16E Packages L T1766 60V , 1.2A (I OUT), 200kHz, High Effi ciency Step-Down DC/DC Converter VIN = 5.5V to 60V , VOUT = 1.2V , IQ = 2.5mA, ISD = 25μA, TSSOP16/E Package L T1767 25V , 1.2A (I OUT), 1.25MHz, High Effi ciency Step-Down DC/DC Converter VIN = 3V to 25V; VOUT = 1.2V , IQ = 1mA, ISD = 6μA, MS8/E Packages L T1776 40V , 550mA (I OUT), 200kHz, High Effi ciency Step-Down DC/DC Converter VIN = 7.4V to 40V; VOUT = 1.24V , IQ = 3.2mA, ISD = 30μA, N8, S8 Packages LT C 1877 600mA (I OUT), 550kHz, Synchronous Step-Down DC/DC Converter VIN = 2.7V to 10V; VOUT = 0.8V , IQ = 10μA, ISD = <1μA, L TC1879 1.2A (I OUT), 550kHz, Synchronous Step-Down DC/DC Converter VIN = 2.7V to 10V; VOUT = 0.8V , IQ = 15μA, ISD = <1μA, L T1933 36V , 600mA, 500kHz, High Effi ciency Step-Down DC/DC Converter VIN = 3.6V to 36V; VOUT = 1.25V , IQ = 2.5μA, ISD = <1μA, ThinSOT and 2mm × 3mm DFN-6 Package L T1934 34V , 250mA (I OUT), Micropower , Step-Down DC/DC Converter VIN = 3.2V to 34V; VOUT = 1.25V , IQ = 12μA, ISD = <1μA, ThinSOT and 2mm × 3mm DFN-6 Package L T1956 60V , 1.2A (I OUT), 500kHz, High Effi ciency Step-Down DC/DC Converter VIN = 5.5V to 60V , VOUT = 1.2V , IQ = 2.5mA, ISD = 25μA, TSSOP16/E Package L TC3405/L TC3405A 300mA (I OUT), 1.5MHz, Synchronous Step-Down DC/DC Converter VIN = 2.7V to 6V , VOUT = 0.8V , IQ = 20μA, ISD = <1μA, ThinSOT Package L TC3406/L TC3406B 600mA (I OUT), 1.5MHz, Synchronous Step-Down DC/DC Converter VIN = 2.5V to 5.5V , VOUT = 0.6V , IQ = 20μA, ISD = <1μA, ThinSOT Package L TC3411 1.25A (I OUT), 4MHz, Synchronous Step-Down DC/DC Converter VIN = 2.5V to 5.5V , VOUT = 0.8V , IQ = 60μA, ISD = <1μA, L TC3412 2.5A (I OUT), 4MHz, Synchronous Step-Down DC/DC Converter VIN = 2.5V to 5.5V , VOUT = 0.8V , IQ = 60μA, ISD = <1μA, L T3430 60V , 2.75A (I OUT), 200kHz, High Effi ciency Step-Down DC/DC Converter VIN = 5.5V to 60V , VOUT = 1.2V , IQ = 2.5mA, ISD = 30μA, L T3470 40V , 200mA, Micropower Step-Down DC/DC Converter V IN = 4V to 40V , VOUT = 1.25V , IQ = 35μA, ISD = <1μA, DFN-8, ThinSOT Packages