LT3990/LT3990-3.3/LT3990-5 62V, 350mA Step-Down Regulator with 2.5µA Quiescent Current and Integrated Diodes FEATURES DESCRIPTION n Low Ripple Burst Mode® Operation The LT®3990 is an adjustable frequency monolithic buck 2.5µA IQ at 12VIN to 3.3VOUT switching regulator that accepts a wide input voltage Output Ripple < 5mVP-P range up to 62V, and consumes only 2.5µA of quiescent n Wide Input Voltage Range: 4.2V to 62V Operating current. A high efficiency switch is included on the die n Adjustable Switching Frequency: 200kHz to 2.2MHz along with the catch diode, boost diode, and the neces- n Integrated Boost and Catch Diodes sary oscillator, control and logic circuitry. Low ripple Burst n 350mA Output Current Mode operation maintains high efficiency at low output n Fixed Output Voltages: 3.3V, 5V currents while keeping the output ripple below 5mV in a 2µA IQ at 12VIN typical application. Current mode topology is used for fast n Accurate Programmable Undervoltage Lockout transient response and good loop stability. A catch diode n FMEA Fault Tolerant (MSOP Package) current limit provides protection against shorted outputs Output Stays at or Below Regulation Voltage During and overvoltage conditions. An accurate programmable Adjacent Pin Short or When a Pin is Left Floating undervoltage lockout feature is available, producing a low n Low Shutdown Current: IQ = 0.7µA shutdown current of 0.7µA. A power good flag signals when n Internal Sense Limits Catch Diode Current V reaches 90% of the programmed output voltage. The OUT n Power Good Flag LT3990 is available in small, thermally enhanced 16-pin n Small, Thermally Enhanced 16-Pin MSOP MSOP and 3mm × 3mm DFN packages. and (3mm × 3mm) DFN Packages L, LT, LTC, LTM, Burst Mode, Linear Technology and the Linear logo are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective APPLICATIONS owners. n Automotive Battery Regulation n Power for Portable Products n Industrial Supplies TYPICAL APPLICATION Power Loss 1000 5V Step-Down Converter VIN = 12V 100 VIN 6.5V TO 62V 0.22µF W) m VIN BOOST S ( 10 LT3990-5 33µH VOUT LOS OFF ON EN/UVLO SW 5V R PG BD 350mA WE 1 O P 2.2µF RT VOUT 22µF 0.1 GND 374k 0.01 f = 400kHz 3990 TA01a 0.001 0.01 0.1 1 10 100 LOAD CURRENT (mA) 3990 TA01b 3990fa 1

LT3990/LT3990-3.3/LT3990-5 ABSOLUTE MAXIMUM RATINGS (Note 1) V , EN/UVLO Voltage ...............................................62V Operating Junction Temperature Range (Note 2) IN BOOST Pin Voltage ...................................................75V LT3990E/LT3990E-X ...........................–40°C to 125°C BOOST Pin Above SW Pin .........................................30V LT3990I/LT3990I-X ............................–40°C to 125°C FB/V , RT Voltage ....................................................6V LT3990H/LT3990H-X ..........................–40°C to 150°C OUT PG, BD Voltage .........................................................30V Storage Temperature Range ...................–65°C to 150°C Lead Temperature (Soldering, 10 sec) MS Only ............................................................300°C PIN CONFIGURATION TOP VIEW TOP VIEW FB/VOUT* 1 16 RT FB 1 10 RT FB/VOUT* 2 15 NC NC 3 14 PG EN/UVLO 2 9 PG EN/UVLO 4 17 13 BD GVNIDN 43 G1N1D 78 BBDOOST VNNICCN 567 GND 111210 NBNOCCOST GND 5 6 SW GND 8 9 SW MSE PACKAGE DD PACKAGE 16-LEAD PLASTIC MSOP 10-LEAD (3mm × 3mm) PLASTIC DFN θJA = 40°C/W, θJC = 10°C/W θJA = 45°C/W, θJC = 10°C/W EXPOSED PAD (PIN 17) IS GND, MUST BE SOLDERED TO PCB EXPOSED PAD (PIN 11) IS GND, MUST BE SOLDERED TO PCB *FB FOR LT3990, VOUT FOR LT3990-3.3, LT3990-5 ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE LT3990EDD#PBF LT3990EDD#TRPBF LFWJ 10-Lead (3mm × 3mm) Plastic DFN –40°C to 125°C LT3990IDD#PBF LT3990IDD#TRPBF LFWJ 10-Lead (3mm × 3mm) Plastic DFN –40°C to 125°C LT3990EMSE#PBF LT3990EMSE#TRPBF 3990 16-Lead Plastic MSOP –40°C to 125°C LT3990IMSE#PBF LT3990IMSE#TRPBF 3990 16-Lead Plastic MSOP –40°C to 125°C LT3990HMSE#PBF LT3990HMSE#TRPBF 3990 16-Lead Plastic MSOP –40°C to 150°C LT3990EMSE-3.3#PBF LT3990EMSE-3.3#TRPBF 399033 16-Lead Plastic MSOP –40°C to 125°C LT3990IMSE-3.3#PBF LT3990IMSE-3.3#TRPBF 399033 16-Lead Plastic MSOP –40°C to 125°C LT3990HMSE-3.3#PBF LT3990HMSE-3.3#TRPBF 399033 16-Lead Plastic MSOP –40°C to 150°C LT3990EMSE-5#PBF LT3990EMSE-5#TRPBF 39905 16-Lead Plastic MSOP –40°C to 125°C LT3990IMSE-5#PBF LT3990IMSE-5#TRPBF 39905 16-Lead Plastic MSOP –40°C to 125°C LT3990HMSE-5#PBF LT3990HMSE-5#TRPBF 39905 16-Lead Plastic MSOP –40°C to 150°C Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container. Consult LTC Marketing for information on non-standard lead based finish parts. For more information on lead free part marking, go to: http://www.linear.com/leadfree/ For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/ 3990fa 2

LT3990/LT3990-3.3/LT3990-5 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at T = 25°C. V = 12V, V = 3.3V unless otherwise noted. (Note 2) A IN BD PARAMETER CONDITIONS MIN TYP MAX UNITS Minimum Input Voltage l 4 4.2 V Quiescent Current from V V Low 0.7 1.2 µA IN EN/UVLO V High 1.9 2.8 µA EN/UVLO V High l 4 µA EN/UVLO LT3990 Feedback Voltage 1.195 1.21 1.225 V l 1.185 1.21 1.235 V LT3990-3.3 Output Voltage 3.26 3.3 3.34 V l 3.234 3.3 3.366 V LT3990-5 Output Voltage 4.94 5 5.06 V l 4.9 5 5.1 V LT3990 FB Pin Bias Current (Note 3) l 0.1 20 nA FB/Output Voltage Line Regulation 4.2V < V < 40V 0.0002 0.01 %/V IN Switching Frequency R = 41.2k, V = 6V 1.84 2.3 2.76 MHz T IN R = 158k, V = 6V 672 840 1008 kHz T IN R = 768k, V = 6V 168 210 252 kHz T IN Switch Current Limit V = 5V, V = 0V 535 700 865 mA IN FB Catch Schottky Current Limit V = 5V 360 450 540 mA IN Switch V I = 200mA 210 mV CESAT SW Switch Leakage Current 0.05 2 µA Catch Schottky Forward Voltage I = 100mA, V = V = NC 725 mV SCH IN BD Catch Schottky Reverse Leakage V = 12V 0.05 2 µA SW Boost Schottky Forward Voltage I = 50mA, V = NC, V = 0V 900 mV SCH IN BOOST Boost Schottky Reverse Leakage V = 12V 0.02 2 µA REVERSE Minimum Boost Voltage (Note 4) V = 5V l 1.4 1.8 V IN BOOST Pin Current I = 200mA, V = 15V 8.5 12 mA SW BOOST EN/UVLO Pin Current V = 12V 1 30 nA EN/UVLO EN/UVLO Voltage Threshold EN/UVLO Rising, V ≥ 4.2V l 1.14 1.19 1.28 V IN EN/UVLO Voltage Hysteresis 35 mV PG Threshold Offset from Feedback Voltage V Rising 6.5 10 13.5 % FB PG Hysteresis as % of Output Voltage 1.0 % PG Leakage V = 3V 0.01 1 µA PG PG Sink Current V = 0.4V l 30 80 µA PG Minimum Switch On-Time 115 ns Minimum Switch Off-Time V = 10V l 100 160 ns IN Note 1: Stresses beyond those listed under Absolute Maximum Ratings Note 3: Bias current flows into the FB pin. may cause permanent damage to the device. Exposure to any Absolute Note 4: This is the minimum voltage across the boost capacitor needed to Maximum Rating condition for extended periods may affect device guarantee full saturation of the switch. reliability and lifetime. Note 2: The LT3990E is guaranteed to meet performance specifications from 0°C to 125°C junction temperature. Specifications over the –40°C to 125°C operating junction temperature range are assured by design, characterization, and correlation with statistical process controls. The LT3990I is guaranteed over the full –40°C to 125°C operating junction temperature range. The LT3990H is guaranteed over the full –40°C to 150°C operating junction temperature range. High junction temperatures degrade operating lifetimes. Operating lifetime is derated at junction temperatures greater than 125°C. 3990fa 3

LT3990/LT3990-3.3/LT3990-5 TYPICAL PERFORMANCE CHARACTERISTICS T = 25°C, unless otherwise noted. A Efficiency, V = 3.3V Efficiency, V = 5V LT3990 Feedback Voltage OUT OUT 90 90 1.220 80 VIN = 24V VIN = 12V 80 VIN = 24V 1.215 CY (%) 6700 VIN = 36V CY (%) 6700 VIN = 12V VIN = 36V OLTAGE (V)1.210 CIEN 50 VIN = 48V CIEN 50 VIN = 48V CK V FFI 40 FFI BA1.205 E E D 30 FRONT PAGE APPLICATION 40 FEE 1.200 20 VRO1U =T 1=M 3.3V 30 R2 = 576k FRONT PAGE APPLICATION 10 20 1.195 0.01 0.1 1 10 100 0.01 0.1 1 10 100 –50 –25 0 25 50 75 100 125 150 LOAD CURRENT (mA) LOAD CURRENT (mA) TEMPERATURE (°C) 3990 G01 3990 G02 3990 G03 LT3990-3.3 Output Voltage LT3990-5 Output Voltage No-Load Supply Current 3.32 5.04 4.0 FRONT PAGE APPLICATION VOUT = 3.3V R1 = 1M 3.31 5.02 3.5 R2 = 576k OUTPUT VOLTAGE (V)33..2390 OUTPUT VOLTAGE (V)45..9080 SUPPLY LEVEL (µA) 23..50 LT3990-3.3 3.28 4.96 2.0 3.27 4.94 1.5 –50 –25 0 25 50 75 100 125 150 –50 –25 0 25 50 75 100 125 150 5 15 25 35 45 55 TEMPERATURE (°C) TEMPERATURE (°C) INPUT VOLTAGE (V) 3990 G04 3990 G05 3990 G06 No-Load Supply Current Maximum Load Current Maximum Load Current 15 650 650 FRONT PAGE APPLICATION FRONT PAGE APPLICATION FRONT PAGE APPLICATION VIN = 12V VOUT = 3.3V VOUT = 5V 12 VOUT = 3.3V 600 600 TYPICAL R1 = 1M URRENT (µA) 9 R2 = 576k RRENT (mA)550500 MTYINPIIMCAULM RRENT (mA)550500 MINIMUM C U U SUPPLY 6 LOAD C450 LOAD C450 3 400 400 0 350 350 –50 –25 0 25 50 75 100 125 150 5 15 25 35 45 55 5 15 25 35 45 55 TEMPERATURE (°C) INPUT VOLTAGE (V) INPUT VOLTAGE (V) 3990 G07 3990 G08 3990 G09 3990fa 4

LT3990/LT3990-3.3/LT3990-5 TYPICAL PERFORMANCE CHARACTERISTICS T = 25°C, unless otherwise noted. A Maximum Load Current Load Regulation Switch Current Limit 600 0.25 800 H-GRADE 0.20 LOAD CURRENT (A)345200000000 LIMITEJDU NBLYCIM TCIIUOTRNEDR T EEBθNMYJT APM LE=AIR M4XA5IITTM°UCUR/WME LOAD REGULATION (%)––00000.....11100050055 WITCH CURRENT LIMIT (mA)456700000000 CATCH DIODE VCASULWLRERITYEC NCHUT P RLERIMAEKINTT LIMIT 100 FRONT PAGE APPLICATION S300 VIN = 12V –0.15 FRONT PAGE APPLICATION VOUT = 5V REFERENCED FROM VOUT AT 100mA LOAD 0 –0.20 200 –50 –25 0 25 50 75 100 125 150 0 50 100 150 200 250 300 350 0 20 40 60 80 100 TEMPERATURE (°C) LOAD CURRENT (mA) DUTY CYCLE (%) 3990 G10 3990 G11 3990 G12 Minimum Switch Current Limit Switching Frequency Switch On-Time/Switch Off-Time 900 2.4 250 LOAD CURRENT = 175mA 2.2 ns) 225 A)800 2.0 ME ( 200 MIT (m700 SWITCH PEAK CURRENT LIMIT Hz) 11..86 OFF-TI 175 MINIMUM ON-TIME H CURRENT LI650000 REQUENCY (M 0111....8204 TIME/SWITCH 111502005 SWITC400 CATCH DIODE VALLEY CURRENT LIMIT F 00..46 TCH ON- 7550 MINIMUM OFF-TIME 0.2 SWI 25 300 0 0 –50 –25 0 25 50 75 100 125 150 –50 –25 0 25 50 75 100 125 150 –50 –25 0 25 50 75 100 125 150 TEMPERATURE (°C) TEMPERATURE (°C) TEMPERATURE (°C) 3990 G13 3990 G14 3990 G15 Switch V (I = 200mA) CESAT SW vs Temperature Switch V BOOST Pin Current CESAT 300 600 21 V)500 18 m A) mV)250 (SAT400 T (m 15 H V (CESAT RRENT VCE300 N CURREN 129 WITC200 H CU200 ST PI S C O 6 T O WI B S100 3 150 0 0 –50 –25 0 25 50 75 100 125 150 0 100 200 300 400 500 0 100 200 300 400 500 TEMPERATURE (°C) SWITCH CURRENT (mA) SWITCH CURRENT (mA) 3990 G16 3990 G17 3990 G18 3990fa 5

LT3990/LT3990-3.3/LT3990-5 TYPICAL PERFORMANCE CHARACTERISTICS T = 25°C, unless otherwise noted. A Minimum Input Voltage, Minimum Input Voltage, V = 3.3V V = 5V Boost Diode Forward Voltage OUT OUT 5.0 6.5 1.2 FRONT PAGE APPLICATION FRONT PAGE APPLICATION VOUT = 3.3V f = 600kHz 1.0 4.5 6.0 TO START TAGE (V) 4.0 TO START TO RUN TAGE (V) 5.5 TO RUN DE V (V)F0.8 L L O 0.6 NPUT VO 3.5 NPUT VO 5.0 OOST DI 0.4 I I B –50°C 3.0 4.5 0.2 25°C 125°C 150°C 2.5 4.0 0 0 50 100 150 200 250 300 350 0 50 100 150 200 250 300 350 0 50 100 150 200 LOAD CURRENT (mA) LOAD CURRENT (mA) BOOST DIODE CURRENT (mA) 3990 G19 3990 G20 3990 G21 Catch Diode Forward Voltage Catch Diode Leakage Power Good Threshold 1.0 15 92 VR = 12V 0.8 µA) 12 91 DIODE, V (V)F 0.6 DE LEAKAGE ( 8 SHOLD (%) 90 CATCH 0.4 TCH DIO 6 THRE 89 –50°C A 0.2 25°C C 3 125°C 150°C 0 0 88 0 100 200 300 400 –50 –25 0 25 50 75 100 125 150 –50 –25 0 25 50 75 100 125 150 CATCH DIODE CURRENT (mA) TEMPERATURE (°C) TEMPERATURE (°C) 3990 G22 3990 G23 3990 G24 Transient Load Response; Load Transient Load Response; Load Current is Stepped from 10mA Current is Stepped from 100mA EN/UVLO Threshold (Burst Mode Operation) to 110mA to 200mA 1.240 VOUT VOUT V)1.215 100mV/DIV 100mV/DIV E ( G A D VOLT1.190 100mA/DIIVL 100mA/DIIVL L O H ES 100µs/DIV 3990 G26 100µs/DIV 3990 G27 R TH1.165 FRONT PAGE APPLICATION FRONT PAGE APPLICATION VIN = 12V VIN = 12V VOUT = 5V VOUT = 5V 1.140 –50 –25 0 25 50 75 100 125 150 TEMPERATURE (°C) 3990 G25 3990fa 6

LT3990/LT3990-3.3/LT3990-5 TYPICAL PERFORMANCE CHARACTERISTICS T = 25°C, unless otherwise noted. A Switching Waveforms, Switching Waveforms, Full Burst Mode Operation Frequency Continuous Operation VSW VSW 5V/DIV 5V/DIV IL IL 100mA/DIV 200mA/DIV VOUT VOUT 5mV/DIV 5mV/DIV 2µs/DIV 3990 G28 1µs/DIV 3990 G29 FRONT PAGE APPLICATION FRONT PAGE APPLICATION VIN = 12V VIN = 12V VOUT = 5V VOUT = 5V ILOAD = 10mA ILOAD = 350mA f = 600kHz f = 600kHz PIN FUNCTIONS (DFN, MSOP) FB (Pin 1/Pins 1, 2 LT3990 Only): The LT3990 regulates GND (Pins 4, 5, Exposed Pad Pin 11/Pin 8, Exposed the FB pin to 1.21V. Connect the feedback resistor divider Pad Pin 17): Ground. The exposed pad must be soldered tap to this pin. The two FB pins on the MSE package are to the PCB. connected internally and provide a redundant path for the SW (Pin 6/Pin 9): The SW pin is the output of an internal feedback divider. Tie the divider to both pins. power switch. Connect this pin to the inductor. V (Pins 1, 2, LT3990-X Only): The LT3990-3.3 and OUT BOOST (Pin 7/Pin 11): This pin is used to provide a drive LT3990-5 regulate the V pin to 3.3V and 5V, respec- OUT voltage, higher than the input voltage, to the internal bipolar tively. This pin connects to the internal feedback divider NPN power switch. that programs the fixed output voltage. The two V pins OUT are connected internally and provide a redundant path to BD (Pin 8/Pin 13): This pin connects to the anode of the the output. Tie the output to both pins. boost diode. This pin also supplies current to the LT3990’s internal regulator when BD is above 3.2V. EN/UVLO (Pin 2/Pin 4): The part is in shutdown when this pin is low and active when this pin is high. The threshold PG (Pin 9/Pin 14): The PG pin is the open-drain output of voltage is 1.19V going up with 35mV of hysteresis. Tie to an internal comparator. PG remains low until the FB pin V if shutdown feature is not used. The EN/UVLO threshold is within 10% of the final regulation voltage. PG is valid IN is accurate only when VIN is above 4.2V. If VIN is lower when VIN is above 4.2V and EN/UVLO is high. than 4.2V, ground EN/UVLO to place the part in shutdown. RT (Pin 10/Pin 16): A resistor is tied between RT and V (Pin 3/Pin 6): The V pin supplies current to the ground to set the switching frequency. IN IN LT3990’s internal circuitry and to the internal power switch. NC (Pins 3, 5, 7, 10, 12, 15, MSOP Only): No Connects. This pin must be locally bypassed. These pins are not connected to internal circuitry and must be left floating to ensure fault tolerance. 3990fa 7

LT3990/LT3990-3.3/LT3990-5 BLOCK DIAGRAM VIN VIN C1 INTERNAL 1.21V REF – 1.19V + BD EN/UVLO SHDN + – DBOOST SLOPE COMP SWITCH LATCH BOOST R RT 200OkSHCzI LTLOA 2T.O2RMHz Q C3 RT S PG + 1.09V + SW L1 ERROR VC Burst Mode VOUT AMP DETECT DCATCH C2 – – R2 R1 GND FB LOT3N9L9Y0 LTO3N9L9Y0*-X VOUT R2 R1 3990 BD *LT3990-3.3: R1 = 12.65M, R2 = 7.35M LT3990-5: R1 = 15.15M, R2 = 4.85M 3990fa 8

LT3990/LT3990-3.3/LT3990-5 OPERATION The LT3990 is a constant frequency, current mode step- If the EN/UVLO pin is low, the LT3990 is shut down and down regulator. An oscillator, with frequency set by RT, draws 0.7µA from the input. When the EN/UVLO pin ex- sets an RS flip-flop, turning on the internal power switch. ceeds 1.19V, the switching regulator will become active. An amplifier and comparator monitor the current flowing The switch driver operates from either V or from the IN between the V and SW pins, turning the switch off when IN BOOST pin. An external capacitor is used to generate a this current reaches a level determined by the voltage at voltage at the BOOST pin that is higher than the input V (see Block Diagram). An error amplifier measures the C supply. This allows the driver to fully saturate the internal output voltage through an external resistor divider tied to bipolar NPN power switch for efficient operation. the FB pin and servos the V node. If the error amplifier’s C output increases, more current is delivered to the output; To further optimize efficiency, the LT3990 automatically if it decreases, less current is delivered. switches to Burst Mode operation in light load situations. Between bursts, all circuitry associated with controlling Another comparator monitors the current flowing through the output switch is shut down reducing the input supply the catch diode and reduces the operating frequency when current to 1.8µA. the current exceeds the 450mA bottom current limit. This foldback in frequency helps to control the output current The LT3990 contains a power good comparator which in fault conditions such as a shorted output with high trips when the FB pin is at 90% of its regulated value. The input voltage. Maximum deliverable current to the output PG output is an open-drain transistor that is off when the is therefore limited by both switch current limit and catch output is in regulation, allowing an external resistor to pull diode current limit. the PG pin high. Power good is valid when the LT3990 is enabled and V is above 4.2V. IN An internal regulator provides power to the control cir- cuitry. The bias regulator normally draws power from the V pin, but if the BD pin is connected to an external IN voltage higher than 3.2V, bias power will be drawn from the external source (typically the regulated output voltage). This improves efficiency. 3990fa 9

LT3990/LT3990-3.3/LT3990-5 APPLICATIONS INFORMATION FB Resistor Network where V is the typical input voltage, V is the output IN OUT voltage, V is the integrated catch diode drop (~0.7V), The output voltage is programmed with a resistor divider D and V is the internal switch drop (~0.5V at max load). between the output and the FB pin. Choose the 1% resis- SW This equation shows that slower switching frequency is tors according to: necessary to accommodate high V /V ratio. IN OUT  V  R1=R2 OUT –1 Lower frequency also allows a lower dropout voltage.  1.21  The input voltage range depends on the switching fre- quency because the LT3990 switch has finite minimum Reference designators refer to the Block Diagram. Note on and off times. The switch can turn off for a minimum that choosing larger resistors will decrease the quiescent of ~160ns but the minimum on-time is a strong function current of the application circuit. of temperature. Use the minimum switch on-time curve (see Typical Performance Characteristics) to design for Setting the Switching Frequency an application’s maximum temperature, while adding The LT3990 uses a constant frequency PWM architecture about 30% for part-to-part variation. The minimum and that can be programmed to switch from 200kHz to 2.2MHz maximum duty cycles that can be achieved taking these by using a resistor tied from the RT pin to ground. A table on and off times into account are: showing the necessary R value for a desired switching T DC = f • t frequency is in Table 1. MIN SW ON(MIN) DC = 1 – f • t MAX SW OFF(MIN) Table 1. Switching Frequency vs R Value T SWITCHING FREQUENCY (MHz) RT VALUE (kΩ) where fSW is the switching frequency, the tON(MIN) is the minimum switch on-time, and the t is the minimum 0.2 787 OFF(MIN) 0.3 511 switch off-time (~160ns). These equations show that 0.4 374 duty cycle range increases when switching frequency is 0.5 287 0.6 232 decreased. 0.8 169 1.0 127 A good choice of switching frequency should allow ad- 1.2 102 equate input voltage range (see next section) and keep 1.4 84.5 the inductor and capacitor values small. 1.6 69.8 1.8 59 2.0 51.1 Input Voltage Range 2.2 44.2 The minimum input voltage is determined by either the Operating Frequency Trade-Offs LT3990’s minimum operating voltage of 4.2V or by its Selection of the operating frequency is a trade-off between maximum duty cycle (as explained in previous section). efficiency, component size, minimum dropout voltage and The minimum input voltage due to duty cycle is: maximum input voltage. The advantage of high frequency V +V operation is that smaller inductor and capacitor values may V = OUT D –V +V IN(MIN) D SW 1–f •t be used. The disadvantages are lower efficiency, lower SW OFF(MIN) maximum input voltage, and higher dropout voltage. The where V is the minimum input voltage, V is the highest acceptable switching frequency (f ) for a IN(MIN) OUT SW(MAX) output voltage, V is the catch diode drop (~0.7V), V given application can be calculated as follows: D SW is the internal switch drop (~0.5V at max load), f is SW f = VOUT+VD the switching frequency (set by RT), and tOFF(MIN) is the SW(MAX) t (V –V +V ) minimum switch off-time (160ns). Note that higher switch- ON(MIN) IN SW D ing frequency will increase the minimum input voltage. 3990fa 10

LT3990/LT3990-3.3/LT3990-5 APPLICATIONS INFORMATION If a lower dropout voltage is desired, a lower switching where V is the voltage drop of the catch diode (~0.7V), D frequency should be used. L is in µH and f is in MHz. The inductor’s RMS current SW rating must be greater than the maximum load current The highest allowed V during normal operation IN and its saturation current should be about 30% higher. (V ) is limited by minimum duty cycle and can IN(OP-MAX) For robust operation in fault conditions (start-up or short be calculated by the following equation: circuit) and high input voltage (>30V), the saturation V = VOUT+VD –V +V current should be above 800mA. To keep the efficiency IN(OP-MAX) D SW f •t high, the series resistance (DCR) should be less than SW ON(MIN) 0.1Ω, and the core material should be intended for high where t is the minimum switch on-time. frequency applications. Table 2 lists several vendors and ON(MIN) suitable types. However, the circuit will tolerate inputs up to the absolute maximum ratings of the V and BOOST pins, regardless of This simple design guide will not always result in the IN chosen switching frequency. During such transients where optimum inductor selection for a given application. As a V is higher than V , the switching frequency will general rule, lower output voltages and higher switching IN IN(OP-MAX) be reduced below the programmed frequency to prevent frequency will require smaller inductor values. If the ap- damage to the part. The output voltage ripple and inductor plication requires less than 350mA load current, then a current ripple may also be higher than in typical operation, lesser inductor value may be acceptable. This allows use however the output will still be in regulation. of a physically smaller inductor, or one with a lower DCR resulting in higher efficiency. There are several graphs in Inductor Selection the Typical Performance Characteristics section of this data sheet that show the maximum load current as a function For a given input and output voltage, the inductor value of input voltage for several popular output voltages. Low and switching frequency will determine the ripple current. inductance may result in discontinuous mode operation, The ripple current increases with higher V or V and IN OUT which is acceptable but reduces maximum load current. decreases with higher inductance and faster switching For details of maximum output current and discontinu- frequency. A good starting point for selecting the induc- ous mode operation, see Linear Technology Application tor value is: Note 44. Finally, for duty cycles greater than 50% (V /V OUT IN V +V L=3 OUT D > 0.5), there is a minimum inductance required to avoid f subharmonic oscillations. See Application Note 19. SW Table 2. Inductor Vendors Input Capacitor VENDOR URL Bypass the input of the LT3990 circuit with a ceramic Coilcraft www.coilcraft.com capacitor of X7R or X5R type. Y5V types have poor Sumida www.sumida.com performance over temperature and applied voltage, and Toko www.tokoam.com should not be used. A 1µF to 4.7µF ceramic capacitor Würth Elektronik www.we-online.com is adequate to bypass the LT3990 and will easily handle Coiltronics www.cooperet.com the ripple current. Note that larger input capacitance Murata www.murata.com is required when a lower switching frequency is used 3990fa 11

LT3990/LT3990-3.3/LT3990-5 APPLICATIONS INFORMATION (due to longer on-times). If the input power source has the output ripple, so low impedance (at the switching high impedance, or there is significant inductance due to frequency) is important. The output ripple decreases with long wires or cables, additional bulk capacitance may be increasing output capacitance, down to approximately necessary. This can be provided with a low performance 1mV. See Figure 1. Note that a larger phase lead capacitor electrolytic capacitor. should be used with a large output capacitor. Step-down regulators draw current from the input sup- 18 FRONT PAGE APPLICATION ply in pulses with very fast rise and fall times. The input 16 f = 600kHz capacitor is required to reduce the resulting voltage ripple mV) CLEAD = 47pF FOR COUT ≥ 47µF E ( 14 at the LT3990 and to force this very high frequency switch- PL P 12 ing current into a tight local loop, minimizing EMI. A 1µF UT RI 10 capacitor is capable of this task, but only if it is placed TP OU 8 close to the LT3990 (see the PCB Layout section). A second E AS 6 precaution regarding the ceramic input capacitor concerns T-C the maximum input voltage rating of the LT3990. A ceramic ORS 4 VIN = 24V input capacitor combined with trace or cable inductance W 2 VIN = 12V 0 forms a high quality (under damped) tank circuit. If the 0 20 40 60 80 100 LT3990 circuit is plugged into a live supply, the input volt- COUT (µF) age can ring to twice its nominal value, possibly exceeding 3990 F01 the LT3990’s voltage rating. This situation is easily avoided Figure 1. Worst-Case Output Ripple Across Full Load Range (see the Hot Plugging Safely section). When choosing a capacitor, look carefully through the data sheet to find out what the actual capacitance is under Output Capacitor and Output Ripple operating conditions (applied voltage and temperature). The output capacitor has two essential functions. It stores A physically larger capacitor or one with a higher voltage energy in order to satisfy transient loads and stabilize the rating may be required. Table 3 lists several capacitor LT3990’s control loop. Ceramic capacitors have very low vendors. equivalent series resistance (ESR) and provide the best ripple performance. A good starting value is: Table 3. Recommended Ceramic Capacitor Vendors MANUFACTURER WEBSITE 50 C = AVX www.avxcorp.com OUT V •f OUT SW Murata www.murata.com Taiyo Yuden www.t-yuden.com where f is in MHz and C is the recommended output SW OUT Vishay Siliconix www.vishay.com capacitance in μF. Use X5R or X7R types. This choice will TDK www.tdk.com provide low output ripple and good transient response. Transient performance can be improved with a higher value Ceramic Capacitors capacitor if combined with a phase lead capacitor (typically Ceramic capacitors are small, robust and have very low 22pF) between the output and the feedback pin. A lower ESR. However, ceramic capacitors can cause problems value of output capacitor can be used to save space and when used with the LT3990 due to their piezoelectric nature. cost but transient performance will suffer. When in Burst Mode operation, the LT3990’s switching The second function is that the output capacitor, along frequency depends on the load current, and at very light with the inductor, filters the square wave generated by the loads the LT3990 can excite the ceramic capacitor at audio LT3990 to produce the DC output. In this role it determines frequencies, generating audible noise. Since the LT3990 3990fa 12

LT3990/LT3990-3.3/LT3990-5 APPLICATIONS INFORMATION operates at a lower current limit during Burst Mode op- 500 FRONT PAGE APPLICATION eration, the noise is typically very quiet to a casual ear. If this is unacceptable, use a high performance tantalum or Hz)400 k electrolytic capacitor at the output. Y ( C N E300 A final precaution regarding ceramic capacitors concerns QU E R the maximum input voltage rating of the LT3990. As pre- G F200 N viously mentioned, a ceramic input capacitor combined HI C T with trace or cable inductance forms a high quality (under WI100 S damped) tank circuit. If the LT3990 circuit is plugged into a live supply, the input voltage can ring to twice its nominal 0 0 50 100 150 200 250 300 350 value, possibly exceeding the LT3990’s rating. This situation LOAD CURRENT (mA) is easily avoided (see the Hot Plugging Safely section). 3990 F03 Figure 3. Switching Frequency in Burst Mode Operation Low Ripple Burst Mode Operation At higher output loads (above ~35mA for the front page To enhance efficiency at light loads, the LT3990 operates application) the LT3990 will be running at the frequency in low ripple Burst Mode operation which keeps the output programmed by the R resistor, and will be operating in capacitor charged to the proper voltage while minimizing T standard PWM mode. The transition between PWM and the input quiescent current. During Burst Mode opera- low ripple Burst Mode is seamless, and will not disturb tion, the LT3990 delivers single cycle bursts of current to the output voltage. the output capacitor followed by sleep periods where the output power is delivered to the load by the output capaci- BOOST and BD Pin Considerations tor. Because the LT3990 delivers power to the output with single, low current pulses, the output ripple is kept below Capacitor C3 and the internal boost Schottky diode (see the 5mV for a typical application. See Figure 2. Block Diagram) are used to generate a boost voltage that is higher than the input voltage. In most cases a 0.22µF As the load current decreases towards a no load condition, capacitor will work well. Figure 4 shows two ways to ar- the percentage of time that the LT3990 operates in sleep range the boost circuit. The BOOST pin must be more than mode increases and the average input current is greatly 1.9V above the SW pin for best efficiency. For outputs of reduced resulting in high efficiency even at very low loads. 2.2V and above, the standard circuit (Figure 4a) is best. Note that during Burst Mode operation, the switching For outputs between 2.2V and 2.5V, use a 0.47µF boost frequency will be lower than the programmed switching capacitor. For output voltages below 2.2V, the boost diode frequency. See Figure 3. can be tied to the input (Figure 4b), or to another external supply greater than 2.2V. However, the circuit in Figure 4a is more efficient because the BOOST pin current and BD VSW 5V/DIV pin quiescent current come from a lower voltage source. Also, be sure that the maximum voltage ratings of the IL 100mA/DIV BOOST and BD pins are not exceeded. VOUT 5mV/DIV The minimum operating voltage of an LT3990 application 2µs/DIV 3990 G28 is limited by the minimum input voltage (4.2V) and by the FRONT PAGE APPLICATION maximum duty cycle as outlined in a previous section. For VIN = 12V VOUT = 5V proper start-up, the minimum input voltage is also limited fI L=O A6D0 0=k H10zmA by the boost circuit. If the input voltage is ramped slowly, Figure 2. Burst Mode Operation the boost capacitor may not be fully charged. Because 3990fa 13

LT3990/LT3990-3.3/LT3990-5 APPLICATIONS INFORMATION VOUT 5.0 FRONT PAGE APPLICATION BD VOUT = 3.3V VIN VIN BOOST 4.5 LT3990 C3 V) TO START SW GE ( 4.0 TO RUN A GND T L O V T 3.5 U P N I (4a) For VOUT ≥ 2.2V 3.0 BD 2.5 0 50 100 150 200 250 300 350 VIN VIN BOOST LOAD CURRENT (mA) LT3990 C3 6.5 SW VOUT FRONT PAGE APPLICATION GND VOUT = 5V, f = 600kHz 6.0 TO START V) (4b) For VOUT < 2.2V; VIN < 30V 3990 F04 TAGE ( 5.5 TO RUN L O V Figure 4. Two Circuits for Generating the Boost Voltage T 5.0 U P N I the boost capacitor is charged with the energy stored 4.5 in the inductor, the circuit will rely on some minimum load current to get the boost circuit running properly. 4.0 0 50 100 150 200 250 300 350 This minimum load will depend on input and output volt- LOAD CURRENT (mA) 3990 F05 ages, and on the arrangement of the boost circuit. The minimum load generally goes to zero once the circuit has Figure 5. The Minimum Input Voltage Depends on Output Voltage, Load Current and Boost Circuit started. Figure 5 shows a plot of minimum load to start and to run as a function of input voltage. In many cases source resistance. A switching regulator draws constant the discharged output capacitor will present a load to the power from the source, so source current increases as switcher, which will allow it to start. The plots show the source voltage drops. This looks like a negative resistance worst-case situation where V is ramping very slowly. IN load to the source and can cause the source to current limit For lower start-up voltage, the boost diode can be tied to or latch low under low source voltage conditions. UVLO V ; however, this restricts the input range to one-half of IN prevents the regulator from operating at source voltages the absolute maximum rating of the BOOST pin. where the problems might occur. The UVLO threshold can be adjusted by setting the values R3 and R4 such that they Enable and Undervoltage Lockout satisfy the following equation: The LT3990 is in shutdown when the EN/UVLO pin is low R3+R4 and active when the pin is high. The rising threshold of the V = •1.19V UVLO EN/UVLO comparator is 1.19V, with a 35mV hysteresis. R4 This threshold is accurate when V is above 4.2V. If V IN IN where switching should not start until V is above V . IN UVLO is lower than 4.2V, tie EN/UVLO pin to GND to place the Note that due to the comparator’s hysteresis, switching part in shutdown. will not stop until the input falls slightly below V . UVLO Figure 6 shows how to add undervoltage lockout (UVLO) Undervoltage lockout is functional only when VUVLO is to the LT3990. Typically, UVLO is used in situations where greater than 5V. the input supply is current limited, or has a relatively high 3990fa 14

LT3990/LT3990-3.3/LT3990-5 APPLICATIONS INFORMATION VIN VIN LT3990 D4 BD VIN VIN BOOST R3 1.19V + LT3990 EN/UVLO SHDN – EN/UVLO SW VOUT R4 GND FB + 3990 F06 BACKUP Figure 6. Undervoltage Lockoout 3990 F07 Shorted and Reversed Input Protection Figure 7. Diode D4 Prevents a Shorted Input from Discharging a If the inductor is chosen so that it won’t saturate exces- Backup Battery Tied to the Output. It Also Protects the Circuit from sively, a LT3990 buck regulator will tolerate a shorted a Reversed Input. The LT3990 Runs Only when the Input Is Present output. There is another situation to consider in systems where the output will be held high when the input to the GND GND LT3990 is absent. This may occur in battery charging ap- plications or in battery backup systems where a battery 1 10 or some other supply is diode ORed with the LT3990’s EN/UVLO 2 9 PG output. If the V pin is allowed to float and the EN/UVLO IN VIN 3 8 pin is held high (either by a logic signal or because it is 4 7 tied to V ), then the LT3990’s internal circuitry will pull 5 6 IN its quiescent current through its SW pin. This is fine if the system can tolerate a few µA in this state. If the EN/UVLO pin is grounded, the SW pin current will drop to 0.7µA. GND VOUT However, if the V pin is grounded while the output is held IN VIAS TO LOCAL GROUND PLANE 3990 F08 high, regardless of EN/UVLO, parasitic diodes inside the VIAS TO VOUT LT3990 can pull current from the output through the SW Figure 8. A Good PCB Layout Ensures Proper, Low EMI Operation pin and the V pin. Figure 7 shows a circuit that will run IN only when the input voltage is present and that protects output capacitor, should be placed on the same side of against a shorted or reversed input. the circuit board, and their connections should be made on that layer. Place a local, unbroken ground plane below PCB Layout these components. The SW and BOOST nodes should be For proper operation and minimum EMI, care must as small as possible. Finally, keep the FB nodes small so be taken during printed circuit board layout. Figure 8 that the ground traces will shield them from the SW and shows the recommended component placement with BOOST nodes. The exposed pad on the bottom must be trace, ground plane and via locations. Note that large, soldered to ground so that the pad acts as a heat sink. To switched currents flow in the LT3990’s V and SW pins, keep thermal resistance low, extend the ground plane as IN the internal catch diode and the input capacitor. The loop much as possible, and add thermal vias under and near formed by these components should be as small as pos- the LT3990 to additional ground planes within the circuit sible. These components, along with the inductor and board and on the bottom side. 3990fa 15

LT3990/LT3990-3.3/LT3990-5 APPLICATIONS INFORMATION Hot Plugging Safely Power dissipation within the LT3990 can be estimated by calculating the total power loss from an efficiency measure- The small size, robustness and low impedance of ceramic ment and subtracting inductor loss. The die temperature capacitors make them an attractive option for the input is calculated by multiplying the LT3990 power dissipation bypass capacitor of LT3990 circuits. However, these ca- by the thermal resistance from junction to ambient. pacitors can cause problems if the LT3990 is plugged into a live supply. The low loss ceramic capacitor, combined Finally, be aware that at high ambient temperatures the with stray inductance in series with the power source, internal Schottky diode will have significant leakage current forms an under damped tank circuit, and the voltage at (see Typical Performance Characteristics) increasing the the V pin of the LT3990 can ring to twice the nominal quiescent current of the LT3990 converter. IN input voltage, possibly exceeding the LT3990’s rating and damaging the part. If the input supply is poorly controlled Fault Tolerance or the user will be plugging the LT3990 into an energized The LT3990 regulator in the MSOP package is designed to supply, the input network should be designed to prevent tolerate single fault conditions. Shorting any two adjacent this overshoot. See Linear Technology Application Note 88 pins together or leaving any one single pin floating does for a complete discussion. not raise V above the programmed value or cause OUT damage to the part. High Temperature Considerations The NC pins are not connected to internal circuitry and For higher ambient temperatures, care should be taken in must be left floating to ensure fault tolerance. the layout of the PCB to ensure good heat sinking of the LT3990. The exposed pad on the bottom must be soldered Other Linear Technology Publications to a ground plane. This ground should be tied to large Application Notes 19, 35 and 44 contain more detailed copper layers below with thermal vias; these layers will descriptions and design information for buck regulators spread the heat dissipated by the LT3990. Placing additional and other switching regulators. The LT1376 data sheet vias can reduce thermal resistance further. The maximum has a more extensive discussion of output ripple, loop load current should be derated as the ambient temperature compensation and stability testing. Design Note 100 approaches the maximum junction rating. shows how to generate a bipolar output supply using a buck regulator. 3990fa 16

LT3990/LT3990-3.3/LT3990-5 TYPICAL APPLICATIONS 3.3V Step-Down Converter 5V Step-Down Converter VIN VIN 4.2V TO 62V C3 6.5V TO 62V C3 0.22µF 0.22µF VIN BOOST L1 VIN BOOST L1 LT3990 33µH VOUT LT3990 33µH VOUT OFF ON EN/UVLO SW 3.3V OFF ON EN/UVLO SW 5V PG BD 350mA PG BD 350mA R1 R1 22pF 22pF 1M 1M C1 RT FB C2 C1 RT FB C2 2.2µF GND R2 22µF 2.2µF GND R2 22µF 374k 374k 576k 316k f = 400kHz 3990 TA02 f = 400kHz 3990 TA03 3.3V Step-Down Converter 5V Step-Down Converter VIN VIN 4.2V TO 62V 6.5V TO 62V 0.22µF 0.22µF VIN BOOST VIN BOOST LT3990-3.3 33µH VOUT LT3990-5 33µH VOUT OFF ON EN/UVLO SW 3.3V OFF ON EN/UVLO SW 5V PG BD 350mA PG BD 350mA 2.2µF RT VOUT 22µF 2.2µF RT VOUT 22µF GND GND 374k 374k f = 400kHz 3990 TA10 f = 400kHz 3990 TA11 2.5V Step-Down Converter 1.8V Step-Down Converter VIN VIN 4.2V TO 62V C3 4.2V TO 30V C3 0.47µF 0.22µF VIN BOOST L1 VIN BOOST L1 LT3990 33µH VOUT LT3990 22µH VOUT OFF ON EN/UVLO SW 2.5V OFF ON EN/UVLO SW 1.8V PG BD 350mA BD 350mA R1 R1 47pF PG 47pF 1M 487k C1 RT FB C2 C1 RT FB C2 2.2µF GND R2 47µF 2.2µF GND R2 47µF 511k 374k 931k 1M f = 300kHz 3990 TA04 f = 400kHz 3990 TA05 3990fa 17

LT3990/LT3990-3.3/LT3990-5 TYPICAL APPLICATIONS 12V Step-Down Converter 5V, 2MHz Step-Down Converter VIN VIN 15V TO 62V C3 8.5V TO 16V 0.1µF TRANSIENTS C3 OFF ON EVNI/NULLTV3O9B9O0OSSWT 33Lµ1H V12OVUT TO 62V VINLT39B9O0OST 01.10Lµµ1FH VOUT PG BD 350mA OFF ON EN/UVLO SW 5V R1 PG BD 350mA 22pF C1 RT FB 1M C2 22pF R1M1 2.2µF GND R2 22µF C1 RT FB C2 127k 113k 1µF GND R2 10µF 51.1k 316k f = 1MHz 3990 TA06 f = 2MHz 3990 TA07 5V Step-Down Converter with Undervoltage Lockout VIN kΩ 6.5V TO 62V + 0.22µF VIN BOOST – 5.6M LT3990 33µH VOUT EN/UVLO SW 5V 1.3M PG BD 350mA 22pF 1M 2.2µF RT FB 22µF GND 374k 316k f = 400kHz 3990 TA08a Input Current During Start-Up Start-Up from High Impedance Input Source 4.5 4.0 UVLO PROGRAMMED TO 6.5V 3.5 INPUT CURRENT VIN A) 3.0 DCORNODPOITUIOTNS 5V/DIV m RRENT ( 22..50 FARPOPNLITC APTAIGOEN 2VV/ODUIVT U T C 1.5 FRONT PAGE NPU 1.0 AWPITPHLI CUAVTLIOON 5ms/DIV 3990 TA08c I FRONT PAGE APPLICATION 0.5 PTOR O6G.5RVAMMED VIN = 12V 0 VOUT = 5V 1k INPUT SOURCE RESISTANCE –0.5 2.5mA LOAD 0 2 4 6 8 10 12 INPUT VOLTAGE (V) 3990 TA08b 3990fa 18

LT3990/LT3990-3.3/LT3990-5 PACKAGE DESCRIPTION Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. DD Package 10-Lead Plastic DFN (3mm × 3mm) (Reference LTC DWG # 05-08-1699 Rev C) 0.70 ±0.05 3.55 ±0.05 1.65 ±0.05 2.15 ±0.05 (2 SIDES) PACKAGE OUTLINE 0.25 ± 0.05 0.50 BSC 2.38 ±0.05 (2 SIDES) RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS R = 0.125 0.40 ± 0.10 TYP 6 10 3.00 ±0.10 1.65 ± 0.10 (4 SIDES) (2 SIDES) PIN 1 NOTCH PIN 1 R = 0.20 OR TOP MARK 0.35 × 45° (SEE NOTE 6) CHAMFER (DD) DFN REV C 0310 5 1 0.200 REF 0.75 ±0.05 0.25 ± 0.05 0.50 BSC 2.38 ±0.10 (2 SIDES) 0.00 – 0.05 BOTTOM VIEW—EXPOSED PAD NOTE: 1. DRAWING TO BE MADE A JEDEC PACKAGE OUTLINE M0-229 VARIATION OF (WEED-2). CHECK THE LTC WEBSITE DATA SHEET FOR CURRENT STATUS OF VARIATION ASSIGNMENT 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 3990fa 19

LT3990/LT3990-3.3/LT3990-5 PACKAGE DESCRIPTION Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. MSE Package 16-Lead Plastic MSOP, Exposed Die Pad (Reference LTC DWG # 05-08-1667 Rev E) BOTTOM VIEW OF EXPOSED PAD OPTION 2.845 ±0.102 2.845 ±0.102 (.112 ±.004) 0.889 ±0.127 (.112 ±.004) (.035 ±.005) 1 8 0.35 REF 5.23 1.651 ±0.102 3.20 – 3.45 1.651 ±0.102 (.M20IN6) (.065 ±.004) (.126 – .136) (.065 ±.004) 0.12 REF DETAIL “B” CORNER TAIL IS PART OF DETAIL “B” THE LEADFRAME FEATURE. FOR REFERENCE ONLY 16 9 0.305 ±0.038 0.50 NO MEASUREMENT PURPOSE (.0120 ±.0015) (.0197) 4.039 ±0.102 TYP BSC (.159 ±.004) (NOTE 3) 0.280 ±0.076 RECOMMENDED SOLDER PAD LAYOUT 16151413121110 9 (.011 ±.003) REF DETAIL “A” 0.254 (.010) 3.00 ±0.102 0° – 6° TYP 4.90 ±0.152 (.118 ±.004) (.193 ±.006) GAUGE PLANE (NOTE 4) 0.53 ±0.152 (.021 ±.006) 1234567 8 DETAIL “A” 1.10 0.86 0.18 (.043) (.034) (.007) MAX REF SEATING PLANE 0.17 – 0.27 0.1016 ±0.0508 (.007 – .011) (.004 ±.002) TYP 0.50 NOTE: (.0197) MSOP (MSE16) 0911 REV E 1. DIMENSIONS IN MILLIMETER/(INCH) BSC 2. DRAWING NOT TO SCALE 3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.152mm (.006") PER SIDE 4. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS. INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.152mm (.006") PER SIDE 5. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.102mm (.004") MAX 6. EXPOSED PAD DIMENSION DOES INCLUDE MOLD FLASH. MOLD FLASH ON E-PAD SHALL NOT EXCEED 0.254mm (.010") PER SIDE. 3990fa 20

LT3990/LT3990-3.3/LT3990-5 REVISION HISTORY (Revision history begins at Rev B) REV DATE DESCRIPTION PAGE NUMBER B 08/12 Title, Features, Typical Application clarified to add fixed output versions 1 Clarified Absolute Maximum Ratings, added H-grade option 2 Clarified pinout for fixed voltage options, clarified Ordering Information for fixed output and H-grades 2 Clarified Electrical Characteristics table 3 Clarified Typical Performance Characteristics 4, 6 Clarified Pin Functions and Block Diagram 7, 8 Clarified EN/UVLO text and formula 14, 15 Clarified Typical Applications 17 3990fa Information furnished by Linear Technology Corporation is believed to be accurate and reliable. 21 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.

LT3990/LT3990-3.3/LT3990-5 TYPICAL APPLICATION 1.21V Step-Down Converter VIN 4.2V TO 30V C3 0.22µF VIN BOOST L1 LT3990 15µH VOUT OFF ON EN/UVLO SW 1.2V BD FB 350mA PG C1 RT C2 2.2µF GND 47µF 374k f = 400kHz 3990 TA09 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LT3970/LT3970-3.3/ 40V, 350mA, 2.2MHz High Efficiency Micropower Step-Down DC/DC V : 4.2V to 40V, V = 1.21V, I = 2.5µA, I < 1µA, IN OUT(MIN) Q SD LT3970-5 Converter with IQ = 2.5µA 3mm × 2mm DFN-10, MSOP-10 LT3971 38V, 1.2A, 2.2MHz High Efficiency Micropower Step-Down DC/DC V : 4.3V to 38V, V = 1.2V, I = 2.8µA, I < 1µA, IN OUT(MIN) Q SD Converter with IQ = 2.8µA 3mm × 3mm DFN-10, MSOPE-10 LT3991 55V, 1.2A, 2.2MHz High Efficiency Micropower Step-Down DC/DC V : 4.3V to 55V, V = 1.2V, I = 2.8µA, I < 1µA, IN OUT(MIN) Q SD Converter with IQ = 2.8µA 3mm × 3mm DFN-10, MSOPE-10 LT3682 36V, 60V , 1A, 2.2MHz High Efficiency Micropower Step-Down V : 3.6V to 36V, V = 0.8V, I = 75µA, I < 1µA, MAX IN OUT(MIN) Q SD DC/DC Converter 3mm × 3mm DFN-12 3990fa 22 Linear Technology Corporation LT 0812 REV A • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com  LINEAR TECHNOLOGY CORPORATION 2010