LT3990/LT3990-3.3/LT3990-5 62V, 350mA Step-Down Regulator with 2.5µA Quiescent Current and Integrated Diodes FEATURES DESCRIPTION Low Ripple Burst Mode® Operation 2.5µA IQ at 12VIN to 3.3VOUT Output Ripple < 5mVP-P n Wide Input Voltage Range: 4.2V to 62V Operating n Adjustable Switching Frequency: 200kHz to 2.2MHz n Integrated Boost and Catch Diodes n 350mA Output Current n Fixed Output Voltages: 3.3V, 5V 2µA IQ at 12VIN n Accurate Programmable Undervoltage Lockout n FMEA Fault Tolerant (MSOP Package) Output Stays at or Below Regulation Voltage During Adjacent Pin Short or When a Pin is Left Floating n Low Shutdown Current: I = 0.7µA Q n Internal Sense Limits Catch Diode Current n Power Good Flag n Small, Thermally Enhanced 16-Pin MSOP and (3mm × 3mm) DFN Packages The LT®3990 is an adjustable frequency monolithic buck switching regulator that accepts a wide input voltage range up to 62V, and consumes only 2.5µA of quiescent current. A high efficiency switch is included on the die along with the catch diode, boost diode, and the necessary oscillator, control and logic circuitry. Low ripple Burst Mode operation maintains high efficiency at low output currents while keeping the output ripple below 5mV in a typical application. Current mode topology is used for fast transient response and good loop stability. A catch diode current limit provides protection against shorted outputs and overvoltage conditions. An accurate programmable undervoltage lockout feature is available, producing a low shutdown current of 0.7µA. A power good flag signals when VOUT reaches 90% of the programmed output voltage. The LT3990 is available in small, thermally enhanced 16-pin MSOP and 3mm × 3mm DFN packages. n APPLICATIONS 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 owners. Automotive Battery Regulation Power for Portable Products n Industrial Supplies n n TYPICAL APPLICATION Power Loss 1000 5V Step-Down Converter VIN = 12V 0.22µF VIN BOOST LT3990-5 OFF ON EN/UVLO PG RT 2.2µF 374k f = 400kHz GND 33µH SW BD VOUT VOUT 5V 350mA 22µF 3990 TA01a POWER LOSS (mW) 100 VIN 6.5V TO 62V 10 1 0.1 0.01 0.001 0.01 0.1 1 10 LOAD CURRENT (mA) 100 3990 TA01b 3990fa 1 LT3990/LT3990-3.3/LT3990-5 ABSOLUTE MAXIMUM RATINGS (Note 1) VIN, EN/UVLO Voltage................................................62V BOOST Pin Voltage....................................................75V BOOST Pin Above SW Pin..........................................30V FB/VOUT, RT Voltage.....................................................6V PG, BD Voltage..........................................................30V Operating Junction Temperature Range (Note 2) LT3990E/LT3990E-X............................ –40°C to 125°C LT3990I/LT3990I-X............................. –40°C to 125°C LT3990H/LT3990H-X........................... –40°C to 150°C Storage Temperature Range.................... –65°C to 150°C Lead Temperature (Soldering, 10 sec) MS Only............................................................. 300°C PIN CONFIGURATION TOP VIEW TOP VIEW FB 1 EN/UVLO 2 VIN 3 GND 4 GND 5 FB/VOUT* FB/VOUT* NC EN/UVLO NC VIN NC GND 10 RT 11 GND 9 PG 8 BD 7 BOOST 6 SW 1 2 3 4 5 6 7 8 17 GND 16 15 14 13 12 11 10 9 RT NC PG BD NC BOOST NC SW MSE PACKAGE 16-LEAD PLASTIC MSOP DD PACKAGE 10-LEAD (3mm × 3mm) PLASTIC DFN θJA = 45°C/W, θJC = 10°C/W EXPOSED PAD (PIN 11) IS GND, MUST BE SOLDERED TO PCB θJA = 40°C/W, θJC = 10°C/W EXPOSED PAD (PIN 17) 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 TA = 25°C. VIN = 12V, VBD = 3.3V unless otherwise noted. (Note 2) PARAMETER CONDITIONS MIN Minimum Input Voltage Quiescent Current from VIN l VEN/UVLO Low VEN/UVLO High VEN/UVLO High TYP MAX 4 4.2 V 0.7 1.9 1.2 2.8 4 µA µA µA l LT3990 Feedback Voltage l 1.195 1.185 1.21 1.21 1.225 1.235 V V l 3.26 3.234 3.3 3.3 3.34 3.366 V V l 4.94 4.9 5 5 5.06 5.1 V V 0.1 20 nA LT3990-3.3 Output Voltage LT3990-5 Output Voltage LT3990 FB Pin Bias Current (Note 3) UNITS l FB/Output Voltage Line Regulation 4.2V < VIN < 40V 0.0002 0.01 %/V Switching Frequency RT = 41.2k, VIN = 6V RT = 158k, VIN = 6V RT = 768k, VIN = 6V 1.84 672 168 2.3 840 210 2.76 1008 252 MHz kHz kHz Switch Current Limit VIN = 5V, VFB = 0V 535 700 865 mA Catch Schottky Current Limit VIN = 5V 360 450 540 mA Switch VCESAT ISW = 200mA 210 Switch Leakage Current Catch Schottky Forward Voltage 0.05 ISCH = 100mA, VIN = VBD = NC 725 Catch Schottky Reverse Leakage VSW = 12V 0.05 Boost Schottky Forward Voltage ISCH = 50mA, VIN = NC, VBOOST = 0V 900 Boost Schottky Reverse Leakage VREVERSE = 12V Minimum Boost Voltage (Note 4) VIN = 5V l BOOST Pin Current ISW = 200mA, VBOOST = 15V EN/UVLO Pin Current VEN/UVLO = 12V EN/UVLO Voltage Threshold EN/UVLO Rising, VIN ≥ 4.2V l 1.14 EN/UVLO Voltage Hysteresis PG Threshold Offset from Feedback Voltage 2 VFB Rising 6.5 2 VPG = 3V PG Sink Current 0.02 2 µA 1.4 1.8 V 8.5 12 mA 1 30 nA 1.19 1.28 10 VPG = 0.4V 0.01 l Minimum Switch On-Time VIN = 10V 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 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. l 30 µA mV V mV 13.5 % 1 µA 1.0 PG Leakage µA mV 35 PG Hysteresis as % of Output Voltage Minimum Switch Off-Time mV % 80 µA 115 ns 100 160 ns Note 3: Bias current flows into the FB pin. Note 4: This is the minimum voltage across the boost capacitor needed to guarantee full saturation of the switch. 3990fa 3 LT3990/LT3990-3.3/LT3990-5 TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C, unless otherwise noted. Efficiency, VOUT = 3.3V Efficiency, VOUT = 5V 90 VIN = 24V VIN = 12V 80 70 VIN = 12V 60 EFFICIENCY (%) 70 VIN = 36V 50 VIN = 48V 40 30 10 0.01 0.1 1 10 LOAD CURRENT (mA) 60 VIN = 48V 50 1.215 VIN = 36V 40 FRONT PAGE APPLICATION VOUT = 3.3V R1 = 1M R2 = 576k 20 VIN = 24V FEEDBACK VOLTAGE (V) 80 EFFICIENCY (%) LT3990 Feedback Voltage 1.220 90 FRONT PAGE APPLICATION 20 0.01 0.1 1 10 LOAD CURRENT (mA) 100 3990 G01 1.195 –50 –25 LT3990-5 Output Voltage No-Load Supply Current 3.31 5.02 3.5 3.28 SUPPLY LEVEL (µA) 4.0 OUTPUT VOLTAGE (V) 5.04 3.29 5.00 4.98 4.96 0 4.94 –50 –25 25 50 75 100 125 150 TEMPERATURE (°C) 0 LOAD CURRENT (mA) SUPPLY CURRENT (µA) 6 3 25 50 75 100 125 150 TEMPERATURE (°C) 3990 G07 25 35 45 INPUT VOLTAGE (V) TYPICAL 550 MINIMUM 500 450 350 55 FRONT PAGE APPLICATION VOUT = 5V 600 TYPICAL 550 MINIMUM 500 450 400 400 0 15 Maximum Load Current 650 FRONT PAGE APPLICATION VOUT = 3.3V 600 9 5 3990 G06 Maximum Load Current 650 FRONT PAGE APPLICATION VIN = 12V VOUT = 3.3V R1 = 1M R2 = 576k 0 –50 –25 2.5 3990 G05 No-Load Supply Current 12 3.0 1.5 25 50 75 100 125 150 TEMPERATURE (°C) 3990 G04 15 FRONT PAGE APPLICATION VOUT = 3.3V R1 = 1M R2 = 576k LT3990-3.3 2.0 LOAD CURRENT (mA) 3.27 –50 –25 25 50 75 100 125 150 TEMPERATURE (°C) 3990 G03 3.32 3.30 0 3990 G02 LT3990-3.3 Output Voltage OUTPUT VOLTAGE (V) 1.205 1.200 30 100 1.210 5 15 25 35 45 INPUT VOLTAGE (V) 55 3990 G08 350 5 15 25 35 45 INPUT VOLTAGE (V) 55 3990 G09 3990fa 4 LT3990/LT3990-3.3/LT3990-5 TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C, unless otherwise noted. Maximum Load Current H-GRADE 400 LIMITED BY MAXIMUM JUNCTION TEMPERATURE θJA = 45°C/W 300 200 100 FRONT PAGE APPLICATION VIN = 12V VOUT = 5V 0 –50 –25 0 Switch Current Limit 800 0.20 LIMITED BY CURRENT LIMIT LOAD REGULATION (%) LOAD CURRENT (A) 500 Load Regulation 0.25 25 50 75 100 125 150 TEMPERATURE (°C) SWITCH CURRENT LIMIT (mA) 600 0.15 0.10 0.05 0 –0.05 –0.10 –0.15 FRONT PAGE APPLICATION REFERENCED FROM VOUT AT 100mA LOAD –0.20 50 100 150 200 250 300 350 0 CATCH DIODE VALLEY CURRENT LIMIT 1.6 1.4 1.2 1.0 0.8 0.6 400 0.4 0.2 0 –50 –25 25 50 75 100 125 150 TEMPERATURE (°C) 0 600 3990 G16 LOAD CURRENT = 175mA 225 200 175 MINIMUM ON-TIME 150 125 100 75 MINIMUM OFF-TIME 50 25 0 25 50 75 100 125 150 TEMPERATURE (°C) BOOST Pin Current Switch VCESAT 21 18 500 400 300 200 100 0 100 80 3990 G15 BOOST PIN CURRENT (mA) SWITCH CURRENT VCESAT (mV) SWITCH VCESAT (mV) 300 25 50 75 100 125 150 TEMPERATURE (°C) 40 60 DUTY CYCLE (%) 3990 G14 Switch VCESAT (ISW = 200mA) vs Temperature 200 20 0 –50 –25 25 50 75 100 125 150 TEMPERATURE (°C) 3990 G13 250 0 3990 G12 SWITCH ON-TIME/SWITCH OFF-TIME (ns) 1.8 500 0 300 250 2.0 FREQUENCY (MHz) SWITCH CURRENT LIMIT (mA) 800 600 CATCH DIODE VALLEY CURRENT LIMIT Minimum Switch On-Time/Switch Off-Time 2.2 150 –50 –25 400 200 2.4 0 500 Switching Frequency 900 300 –50 –25 600 3990 G11 Switch Current Limit SWITCH PEAK CURRENT LIMIT SWITCH PEAK CURRENT LIMIT LOAD CURRENT (mA) 3990 G10 700 700 15 12 9 6 3 0 100 200 300 400 SWITCH CURRENT (mA) 500 3990 G17 0 0 100 200 300 400 SWITCH CURRENT (mA) 500 3990 G18 3990fa 5 LT3990/LT3990-3.3/LT3990-5 TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C, unless otherwise noted. 6.5 FRONT PAGE APPLICATION VOUT = 3.3V TO START 4.0 TO RUN 3.5 3.0 2.5 5.5 TO RUN 5.0 4.5 0 50 100 150 200 250 LOAD CURRENT (mA) 300 4.0 350 12 0.6 0.4 –50°C 25°C 125°C 150°C 200 100 300 CATCH DIODE CURRENT (mA) 0.4 400 –50°C 25°C 125°C 150°C 0.2 0 50 100 150 200 250 LOAD CURRENT (mA) 300 0 350 0 50 100 150 BOOST DIODE CURRENT (mA) Power Good Threshold 92 VR = 12V 91 8 6 90 89 3 0 –50 –25 0 25 50 75 100 125 150 TEMPERATURE (°C) 88 –50 –25 0 25 50 75 100 125 150 TEMPERATURE (°C) 3990 G23 3990 G22 3990 G24 Transient Load Response; Load Current is Stepped from 10mA (Burst Mode Operation) to 110mA EN/UVLO Threshold 200 3990 G21 THRESHOLD (%) 0.8 CATCH DIODE LEAKAGE (µA) 15 0 0.6 Catch Diode Leakage 1.0 0.2 0.8 3990 G20 Catch Diode Forward Voltage CATCH DIODE, VF (V) 1.0 TO START 3990 G19 0 Boost Diode Forward Voltage 1.2 FRONT PAGE APPLICATION f = 600kHz 6.0 INPUT VOLTAGE (V) INPUT VOLTAGE (V) 4.5 Minimum Input Voltage, VOUT = 5V BOOST DIODE VF (V) 5.0 Minimum Input Voltage, VOUT = 3.3V Transient Load Response; Load Current is Stepped from 100mA to 200mA 1.240 VOUT 100mV/DIV VOUT 100mV/DIV 1.190 IL 100mA/DIV IL 100mA/DIV THRESHOLD VOLTAGE (V) 1.215 100µs/DIV FRONT PAGE APPLICATION VIN = 12V VOUT = 5V 1.165 1.140 –50 –25 0 3990 G26 100µs/DIV FRONT PAGE APPLICATION VIN = 12V VOUT = 5V 3990 G27 25 50 75 100 125 150 TEMPERATURE (°C) 3990 G25 3990fa 6 LT3990/LT3990-3.3/LT3990-5 TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C, unless otherwise noted. Switching Waveforms, Full Frequency Continuous Operation Switching Waveforms, Burst Mode Operation VSW 5V/DIV VSW 5V/DIV IL 100mA/DIV IL 200mA/DIV VOUT 5mV/DIV VOUT 5mV/DIV 2µs/DIV FRONT PAGE APPLICATION VIN = 12V VOUT = 5V ILOAD = 10mA f = 600kHz 3990 G28 1µs/DIV FRONT PAGE APPLICATION VIN = 12V VOUT = 5V ILOAD = 350mA f = 600kHz 3990 G29 PIN FUNCTIONS (DFN, MSOP) FB (Pin 1/Pins 1, 2 LT3990 Only): The LT3990 regulates the FB pin to 1.21V. Connect the feedback resistor divider tap to this pin. The two FB pins on the MSE package are connected internally and provide a redundant path for the feedback divider. Tie the divider to both pins. VOUT (Pins 1, 2, LT3990-X Only): The LT3990-3.3 and LT3990-5 regulate the VOUT pin to 3.3V and 5V, respectively. This pin connects to the internal feedback divider that programs the fixed output voltage. The two VOUT pins are connected internally and provide a redundant path to the output. Tie the output to both pins. 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 voltage is 1.19V going up with 35mV of hysteresis. Tie to VIN if shutdown feature is not used. The EN/UVLO threshold is accurate only when VIN is above 4.2V. If VIN is lower than 4.2V, ground EN/UVLO to place the part in shutdown. VIN (Pin 3/Pin 6): The VIN pin supplies current to the LT3990’s internal circuitry and to the internal power switch. This pin must be locally bypassed. GND (Pins 4, 5, Exposed Pad Pin 11/Pin 8, Exposed Pad Pin 17): Ground. The exposed pad must be soldered to the PCB. SW (Pin 6/Pin 9): The SW pin is the output of an internal power switch. Connect this pin to the inductor. BOOST (Pin 7/Pin 11): This pin is used to provide a drive voltage, higher than the input voltage, to the internal bipolar NPN power switch. BD (Pin 8/Pin 13): This pin connects to the anode of the boost diode. This pin also supplies current to the LT3990’s internal regulator when BD is above 3.2V. PG (Pin 9/Pin 14): The PG pin is the open-drain output of an internal comparator. PG remains low until the FB pin is within 10% of the final regulation voltage. PG is valid when VIN is above 4.2V and EN/UVLO is high. RT (Pin 10/Pin 16): A resistor is tied between RT and ground to set the switching frequency. NC (Pins 3, 5, 7, 10, 12, 15, MSOP Only): No Connects. 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 EN/UVLO – + + SHDN – BD DBOOST SLOPE COMP BOOST SWITCH LATCH R RT RT PG OSCILLATOR 200kHz TO 2.2MHz + + 1.09V ERROR AMP – VC Burst Mode DETECT – R2 FB GND R2 LT3990 ONLY Q C3 S SW DCATCH L1 VOUT C2 R1 LT3990-X ONLY* VOUT R1 *LT3990-3.3: R1 = 12.65M, R2 = 7.35M LT3990-5: R1 = 15.15M, R2 = 4.85M 3990 BD 3990fa 8 LT3990/LT3990-3.3/LT3990-5 OPERATION The LT3990 is a constant frequency, current mode stepdown regulator. An oscillator, with frequency set by RT, sets an RS flip-flop, turning on the internal power switch. An amplifier and comparator monitor the current flowing between the VIN and SW pins, turning the switch off when this current reaches a level determined by the voltage at VC (see Block Diagram). An error amplifier measures the output voltage through an external resistor divider tied to the FB pin and servos the VC node. If the error amplifier’s output increases, more current is delivered to the output; if it decreases, less current is delivered. Another comparator monitors the current flowing through the catch diode and reduces the operating frequency when the current exceeds the 450mA bottom current limit. This foldback in frequency helps to control the output current in fault conditions such as a shorted output with high input voltage. Maximum deliverable current to the output is therefore limited by both switch current limit and catch diode current limit. An internal regulator provides power to the control circuitry. The bias regulator normally draws power from the VIN pin, but if the BD pin is connected to an external voltage higher than 3.2V, bias power will be drawn from the external source (typically the regulated output voltage). This improves efficiency. If the EN/UVLO pin is low, the LT3990 is shut down and draws 0.7µA from the input. When the EN/UVLO pin exceeds 1.19V, the switching regulator will become active. The switch driver operates from either VIN or from the BOOST pin. An external capacitor is used to generate a voltage at the BOOST pin that is higher than the input supply. This allows the driver to fully saturate the internal bipolar NPN power switch for efficient operation. To further optimize efficiency, the LT3990 automatically switches to Burst Mode operation in light load situations. Between bursts, all circuitry associated with controlling the output switch is shut down reducing the input supply current to 1.8µA. The LT3990 contains a power good comparator which trips when the FB pin is at 90% of its regulated value. The PG output is an open-drain transistor that is off when the output is in regulation, allowing an external resistor to pull the PG pin high. Power good is valid when the LT3990 is enabled and VIN is above 4.2V. 3990fa 9 LT3990/LT3990-3.3/LT3990-5 APPLICATIONS INFORMATION FB Resistor Network The output voltage is programmed with a resistor divider between the output and the FB pin. Choose the 1% resistors according to: V R1= R2 OUT – 1 1.21 Reference designators refer to the Block Diagram. Note that choosing larger resistors will decrease the quiescent current of the application circuit. Setting the Switching Frequency The LT3990 uses a constant frequency PWM architecture that can be programmed to switch from 200kHz to 2.2MHz by using a resistor tied from the RT pin to ground. A table showing the necessary RT value for a desired switching frequency is in Table 1. SWITCHING FREQUENCY (MHz) RT VALUE (kΩ) 0.2 0.3 0.4 0.5 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 787 511 374 287 232 169 127 102 84.5 69.8 59 51.1 44.2 Operating Frequency Trade-Offs Selection of the operating frequency is a trade-off between efficiency, component size, minimum dropout voltage and maximum input voltage. The advantage of high frequency operation is that smaller inductor and capacitor values may be used. The disadvantages are lower efficiency, lower maximum input voltage, and higher dropout voltage. The highest acceptable switching frequency (fSW(MAX)) for a given application can be calculated as follows: Lower frequency also allows a lower dropout voltage. The input voltage range depends on the switching frequency because the LT3990 switch has finite minimum on and off times. The switch can turn off for a minimum of ~160ns but the minimum on-time is a strong function of temperature. Use the minimum switch on-time curve (see Typical Performance Characteristics) to design for an application’s maximum temperature, while adding about 30% for part-to-part variation. The minimum and maximum duty cycles that can be achieved taking these on and off times into account are: DCMIN = fSW • tON(MIN) DCMAX = 1 – fSW • tOFF(MIN) Table 1. Switching Frequency vs RT Value fSW(MAX) = where VIN is the typical input voltage, VOUT is the output voltage, VD is the integrated catch diode drop (~0.7V), and VSW is the internal switch drop (~0.5V at max load). This equation shows that slower switching frequency is necessary to accommodate high VIN/VOUT ratio. VOUT + VD tON(MIN) ( VIN – VSW + VD ) where fSW is the switching frequency, the tON(MIN) is the minimum switch on-time, and the tOFF(MIN) is the minimum switch off-time (~160ns). These equations show that duty cycle range increases when switching frequency is decreased. A good choice of switching frequency should allow adequate input voltage range (see next section) and keep the inductor and capacitor values small. Input Voltage Range The minimum input voltage is determined by either the LT3990’s minimum operating voltage of 4.2V or by its maximum duty cycle (as explained in previous section). The minimum input voltage due to duty cycle is: VIN(MIN) = VOUT + VD –V +V 1– fSW • tOFF(MIN) D SW where VIN(MIN) is the minimum input voltage, VOUT is the output voltage, VD is the catch diode drop (~0.7V), VSW is the internal switch drop (~0.5V at max load), fSW is the switching frequency (set by RT), and tOFF(MIN) is the minimum switch off-time (160ns). Note that higher switching 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 frequency should be used. The highest allowed VIN during normal operation (VIN(OP‑MAX)) is limited by minimum duty cycle and can be calculated by the following equation: VIN(OP-MAX) = VOUT + VD –V +V fSW • tON(MIN) D SW where tON(MIN) is the minimum switch on-time. However, the circuit will tolerate inputs up to the absolute maximum ratings of the VIN and BOOST pins, regardless of chosen switching frequency. During such transients where VIN is higher than VIN(OP-MAX), the switching frequency will be reduced below the programmed frequency to prevent damage to the part. The output voltage ripple and inductor current ripple may also be higher than in typical operation, however the output will still be in regulation. Inductor Selection For a given input and output voltage, the inductor value and switching frequency will determine the ripple current. The ripple current increases with higher VIN or VOUT and decreases with higher inductance and faster switching frequency. A good starting point for selecting the inductor value is: L=3 VOUT + VD fSW where VD is the voltage drop of the catch diode (~0.7V), L is in µH and fSW is in MHz. The inductor’s RMS current rating must be greater than the maximum load current and its saturation current should be about 30% higher. For robust operation in fault conditions (start-up or short circuit) and high input voltage (>30V), the saturation current should be above 800mA. To keep the efficiency high, the series resistance (DCR) should be less than 0.1Ω, and the core material should be intended for high frequency applications. Table 2 lists several vendors and suitable types. This simple design guide will not always result in the optimum inductor selection for a given application. As a general rule, lower output voltages and higher switching frequency will require smaller inductor values. If the application requires less than 350mA load current, then a lesser inductor value may be acceptable. This allows use of a physically smaller inductor, or one with a lower DCR resulting in higher efficiency. There are several graphs in the Typical Performance Characteristics section of this data sheet that show the maximum load current as a function of input voltage for several popular output voltages. Low inductance may result in discontinuous mode operation, which is acceptable but reduces maximum load current. For details of maximum output current and discontinuous mode operation, see Linear Technology Application Note 44. Finally, for duty cycles greater than 50% (VOUT/VIN > 0.5), there is a minimum inductance required to avoid subharmonic oscillations. See Application Note 19. Input Capacitor Table 2. Inductor Vendors VENDOR URL Coilcraft www.coilcraft.com Sumida www.sumida.com Toko www.tokoam.com Würth Elektronik www.we-online.com Coiltronics www.cooperet.com Murata www.murata.com Bypass the input of the LT3990 circuit with a ceramic capacitor of X7R or X5R type. Y5V types have poor performance over temperature and applied voltage, and should not be used. A 1µF to 4.7µF ceramic capacitor is adequate to bypass the LT3990 and will easily handle the ripple current. Note that larger input capacitance is required when a lower switching frequency is used 3990fa 11 LT3990/LT3990-3.3/LT3990-5 APPLICATIONS INFORMATION Step-down regulators draw current from the input supply in pulses with very fast rise and fall times. The input capacitor is required to reduce the resulting voltage ripple at the LT3990 and to force this very high frequency switching current into a tight local loop, minimizing EMI. A 1µF capacitor is capable of this task, but only if it is placed close to the LT3990 (see the PCB Layout section). A second precaution regarding the ceramic input capacitor concerns the maximum input voltage rating of the LT3990. A ceramic input capacitor combined with trace or cable inductance forms a high quality (under damped) tank circuit. If the LT3990 circuit is plugged into a live supply, the input voltage can ring to twice its nominal value, possibly exceeding the LT3990’s voltage rating. This situation is easily avoided (see the Hot Plugging Safely section). Output Capacitor and Output Ripple The output capacitor has two essential functions. It stores energy in order to satisfy transient loads and stabilize the LT3990’s control loop. Ceramic capacitors have very low equivalent series resistance (ESR) and provide the best ripple performance. A good starting value is: 50 COUT = VOUT • fSW where fSW is in MHz and COUT is the recommended output capacitance in μF. Use X5R or X7R types. This choice will provide low output ripple and good transient response. Transient performance can be improved with a higher value capacitor if combined with a phase lead capacitor (typically 22pF) between the output and the feedback pin. A lower value of output capacitor can be used to save space and cost but transient performance will suffer. The second function is that the output capacitor, along with the inductor, filters the square wave generated by the LT3990 to produce the DC output. In this role it determines the output ripple, so low impedance (at the switching frequency) is important. The output ripple decreases with increasing output capacitance, down to approximately 1mV. See Figure 1. Note that a larger phase lead capacitor should be used with a large output capacitor. 18 WORST-CASE OUTPUT RIPPLE (mV) (due to longer on-times). If the input power source has high impedance, or there is significant inductance due to long wires or cables, additional bulk capacitance may be necessary. This can be provided with a low performance electrolytic capacitor. FRONT PAGE APPLICATION f = 600kHz CLEAD = 47pF FOR COUT ≥ 47µF 16 14 12 10 8 6 4 VIN = 24V 2 0 VIN = 12V 0 20 60 40 COUT (µF) 80 100 3990 F01 Figure 1. Worst-Case Output Ripple Across Full Load Range When choosing a capacitor, look carefully through the data sheet to find out what the actual capacitance is under operating conditions (applied voltage and temperature). A physically larger capacitor or one with a higher voltage rating may be required. Table 3 lists several capacitor vendors. Table 3. Recommended Ceramic Capacitor Vendors MANUFACTURER WEBSITE AVX www.avxcorp.com Murata www.murata.com Taiyo Yuden www.t-yuden.com Vishay Siliconix www.vishay.com TDK www.tdk.com Ceramic Capacitors Ceramic capacitors are small, robust and have very low ESR. However, ceramic capacitors can cause problems when used with the LT3990 due to their piezoelectric nature. When in Burst Mode operation, the LT3990’s switching frequency depends on the load current, and at very light loads the LT3990 can excite the ceramic capacitor at audio frequencies, generating audible noise. Since the LT3990 3990fa 12 LT3990/LT3990-3.3/LT3990-5 APPLICATIONS INFORMATION A final precaution regarding ceramic capacitors concerns the maximum input voltage rating of the LT3990. As previously mentioned, a ceramic input capacitor combined with trace or cable inductance forms a high quality (under damped) tank circuit. If the LT3990 circuit is plugged into a live supply, the input voltage can ring to twice its nominal value, possibly exceeding the LT3990’s rating. This situation is easily avoided (see the Hot Plugging Safely section). FRONT PAGE APPLICATION 400 300 200 100 0 0 50 100 150 200 250 LOAD CURRENT (mA) 300 350 3990 F03 Figure 3. Switching Frequency in Burst Mode Operation Low Ripple Burst Mode Operation To enhance efficiency at light loads, the LT3990 operates in low ripple Burst Mode operation which keeps the output capacitor charged to the proper voltage while minimizing the input quiescent current. During Burst Mode operation, the LT3990 delivers single cycle bursts of current to the output capacitor followed by sleep periods where the output power is delivered to the load by the output capacitor. Because the LT3990 delivers power to the output with single, low current pulses, the output ripple is kept below 5mV for a typical application. See Figure 2. As the load current decreases towards a no load condition, the percentage of time that the LT3990 operates in sleep mode increases and the average input current is greatly reduced resulting in high efficiency even at very low loads. Note that during Burst Mode operation, the switching frequency will be lower than the programmed switching frequency. See Figure 3. VSW 5V/DIV IL 100mA/DIV VOUT 5mV/DIV 2µs/DIV FRONT PAGE APPLICATION VIN = 12V VOUT = 5V ILOAD = 10mA f = 600kHz 500 SWITCHING FREQUENCY (kHz) operates at a lower current limit during Burst Mode operation, the noise is typically very quiet to a casual ear. If this is unacceptable, use a high performance tantalum or electrolytic capacitor at the output. 3990 G28 Figure 2. Burst Mode Operation At higher output loads (above ~35mA for the front page application) the LT3990 will be running at the frequency programmed by the RT resistor, and will be operating in standard PWM mode. The transition between PWM and low ripple Burst Mode is seamless, and will not disturb the output voltage. BOOST and BD Pin Considerations Capacitor C3 and the internal boost Schottky diode (see the Block Diagram) are used to generate a boost voltage that is higher than the input voltage. In most cases a 0.22µF capacitor will work well. Figure 4 shows two ways to arrange the boost circuit. The BOOST pin must be more than 1.9V above the SW pin for best efficiency. For outputs of 2.2V and above, the standard circuit (Figure 4a) is best. For outputs between 2.2V and 2.5V, use a 0.47µF boost capacitor. For output voltages below 2.2V, the boost diode 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 pin quiescent current come from a lower voltage source. Also, be sure that the maximum voltage ratings of the BOOST and BD pins are not exceeded. The minimum operating voltage of an LT3990 application is limited by the minimum input voltage (4.2V) and by the maximum duty cycle as outlined in a previous section. For proper start-up, the minimum input voltage is also limited by the boost circuit. If the input voltage is ramped slowly, 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 VOUT = 3.3V BD VIN 4.5 BOOST C3 LT3990 INPUT VOLTAGE (V) VIN SW GND (4a) For VOUT ≥ 2.2V VIN 3.5 2.5 BOOST C3 LT3990 SW TO RUN 3.0 BD VIN TO START 4.0 6.5 VOUT GND 0 50 INPUT VOLTAGE (V) (4b) For VOUT < 2.2V; VIN < 30V Figure 4. Two Circuits for Generating the Boost Voltage the boost capacitor is charged with the energy stored in the inductor, the circuit will rely on some minimum load current to get the boost circuit running properly. This minimum load will depend on input and output voltages, and on the arrangement of the boost circuit. The minimum load generally goes to zero once the circuit has started. Figure 5 shows a plot of minimum load to start and to run as a function of input voltage. In many cases the discharged output capacitor will present a load to the switcher, which will allow it to start. The plots show the worst-case situation where VIN is ramping very slowly. For lower start-up voltage, the boost diode can be tied to VIN; however, this restricts the input range to one-half of the absolute maximum rating of the BOOST pin. Enable and Undervoltage Lockout The LT3990 is in shutdown when the EN/UVLO pin is low and active when the pin is high. The rising threshold of the EN/UVLO comparator is 1.19V, with a 35mV hysteresis. This threshold is accurate when VIN is above 4.2V. If VIN is lower than 4.2V, tie EN/UVLO pin to GND to place the part in shutdown. Figure 6 shows how to add undervoltage lockout (UVLO) to the LT3990. Typically, UVLO is used in situations where the input supply is current limited, or has a relatively high 300 350 300 350 FRONT PAGE APPLICATION VOUT = 5V, f = 600kHz 6.0 3990 F04 100 150 200 250 LOAD CURRENT (mA) TO START 5.5 TO RUN 5.0 4.5 4.0 0 50 100 150 200 250 LOAD CURRENT (mA) 3990 F05 Figure 5. The Minimum Input Voltage Depends on Output Voltage, Load Current and Boost Circuit source resistance. A switching regulator draws constant power from the source, so source current increases as source voltage drops. This looks like a negative resistance load to the source and can cause the source to current limit or latch low under low source voltage conditions. UVLO prevents the regulator from operating at source voltages where the problems might occur. The UVLO threshold can be adjusted by setting the values R3 and R4 such that they satisfy the following equation: VUVLO = R3+R4 •1.19V R4 where switching should not start until VIN is above VUVLO. Note that due to the comparator’s hysteresis, switching will not stop until the input falls slightly below VUVLO. Undervoltage lockout is functional only when VUVLO is greater than 5V. 3990fa 14 LT3990/LT3990-3.3/LT3990-5 APPLICATIONS INFORMATION VIN VIN R3 1.19V EN/UVLO LT3990 + – D4 BD VIN VIN BOOST LT3990 SHDN R4 EN/UVLO SW GND FB VOUT + 3990 F06 BACKUP Figure 6. Undervoltage Lockoout Shorted and Reversed Input Protection If the inductor is chosen so that it won’t saturate excessively, a LT3990 buck regulator will tolerate a shorted output. There is another situation to consider in systems where the output will be held high when the input to the LT3990 is absent. This may occur in battery charging applications or in battery backup systems where a battery or some other supply is diode ORed with the LT3990’s output. If the VIN pin is allowed to float and the EN/UVLO pin is held high (either by a logic signal or because it is tied to VIN), then the LT3990’s internal circuitry will pull 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. However, if the VIN pin is grounded while the output is held high, regardless of EN/UVLO, parasitic diodes inside the LT3990 can pull current from the output through the SW pin and the VIN pin. Figure 7 shows a circuit that will run only when the input voltage is present and that protects against a shorted or reversed input. PCB Layout For proper operation and minimum EMI, care must be taken during printed circuit board layout. Figure 8 shows the recommended component placement with trace, ground plane and via locations. Note that large, switched currents flow in the LT3990’s VIN and SW pins, the internal catch diode and the input capacitor. The loop formed by these components should be as small as possible. These components, along with the inductor and 3990 F07 Figure 7. Diode D4 Prevents a Shorted Input from Discharging a Backup Battery Tied to the Output. It Also Protects the Circuit from a Reversed Input. The LT3990 Runs Only when the Input Is Present GND GND 1 10 EN/UVLO 2 9 VIN 3 8 4 7 5 6 PG VOUT GND VIAS TO LOCAL GROUND PLANE VIAS TO VOUT 3990 F08 Figure 8. A Good PCB Layout Ensures Proper, Low EMI Operation output capacitor, should be placed on the same side of the circuit board, and their connections should be made on that layer. Place a local, unbroken ground plane below these components. The SW and BOOST nodes should be as small as possible. Finally, keep the FB nodes small so that the ground traces will shield them from the SW and BOOST nodes. The exposed pad on the bottom must be soldered to ground so that the pad acts as a heat sink. To keep thermal resistance low, extend the ground plane as much as possible, and add thermal vias under and near the LT3990 to additional ground planes within the circuit board and on the bottom side. 3990fa 15 LT3990/LT3990-3.3/LT3990-5 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 LT3990 circuits. However, these capacitors can cause problems if the LT3990 is plugged into a live supply. The low loss ceramic capacitor, combined with stray inductance in series with the power source, forms an under damped tank circuit, and the voltage at the VIN pin of the LT3990 can ring to twice the nominal input voltage, possibly exceeding the LT3990’s rating and damaging the part. If the input supply is poorly controlled or the user will be plugging the LT3990 into an energized supply, the input network should be designed to prevent this overshoot. See Linear Technology Application Note 88 for a complete discussion. High Temperature Considerations For higher ambient temperatures, care should be taken in the layout of the PCB to ensure good heat sinking of the LT3990. The exposed pad on the bottom must be soldered to a ground plane. This ground should be tied to large copper layers below with thermal vias; these layers will spread the heat dissipated by the LT3990. Placing additional vias can reduce thermal resistance further. The maximum load current should be derated as the ambient temperature approaches the maximum junction rating. Power dissipation within the LT3990 can be estimated by calculating the total power loss from an efficiency measurement and subtracting inductor loss. The die temperature is calculated by multiplying the LT3990 power dissipation by the thermal resistance from junction to ambient. Finally, be aware that at high ambient temperatures the internal Schottky diode will have significant leakage current (see Typical Performance Characteristics) increasing the quiescent current of the LT3990 converter. Fault Tolerance The LT3990 regulator in the MSOP package is designed to tolerate single fault conditions. Shorting any two adjacent pins together or leaving any one single pin floating does not raise VOUT above the programmed value or cause damage to the part. The NC pins are not connected to internal circuitry and must be left floating to ensure fault tolerance. Other Linear Technology Publications Application Notes 19, 35 and 44 contain more detailed descriptions and design information for buck regulators and other switching regulators. The LT1376 data sheet has a more extensive discussion of output ripple, loop compensation and stability testing. Design Note 100 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 VIN 4.2V TO 62V VIN BOOST C1 2.2µF EN/UVLO PG VIN 6.5V TO 62V C3 0.22µF VIN L1 33µH LT3990 OFF ON 5V Step-Down Converter BD R1 1M 22pF RT FB GND 374k C2 22µF R2 576k f = 400kHz OFF ON 374k LT3990-3.3 RT 2.2µF 33µH 0.22µF VOUT 22µF OFF ON RT BOOST OFF ON C1 2.2µF EN/UVLO PG 511k f = 300kHz GND BD VOUT 22µF 3990 TA11 VIN 4.2V TO 30V VIN R1 1M R2 931k 3990 TA04 C2 47µF BOOST LT3990 VOUT 2.5V 350mA SW FB VOUT 5V 350mA 1.8V Step-Down Converter L1 33µH BD 33µH SW f = 400kHz C3 0.47µF 47pF RT GND 374k 3990 TA10 LT3990 EN/UVLO PG 2.2µF 2.5V Step-Down Converter VIN BOOST LT3990-5 VOUT 3.3V 350mA BD VIN 4.2V TO 62V C2 22µF R2 316k 3990 TA03 VIN f = 400kHz R1 1M FB GND VIN 6.5V TO 62V SW GND 374k BD 5V Step-Down Converter BOOST EN/UVLO PG VOUT 5V 350mA SW f = 400kHz 0.22µF OFF ON EN/UVLO PG RT 3.3V Step-Down Converter VIN L1 33µH 22pF C1 2.2µF 3990 TA02 VIN 4.2V TO 62V BOOST LT3990 VOUT 3.3V 350mA SW C3 0.22µF OFF ON C1 2.2µF EN/UVLO BD PG RT 374k f = 400kHz GND C3 0.22µF L1 22µH VOUT 1.8V 350mA SW 47pF FB R1 487k R2 1M C2 47µF 3990 TA05 3990fa 17 LT3990/LT3990-3.3/LT3990-5 TYPICAL APPLICATIONS 12V Step-Down Converter VIN 15V TO 62V VIN BOOST EN/ULVO PG VIN 8.5V TO 16V TRANSIENTS TO 62V C3 0.1µF L1 33µH LT3990 OFF ON 5V, 2MHz Step-Down Converter VOUT 12V 350mA SW BD R1 1M 22pF C1 2.2µF RT 127k GND FB f = 1MHz VIN BOOST LT3990 OFF ON C2 22µF R2 113k C3 0.1µF EN/UVLO PG L1 10µH BD 22pF C1 1µF RT 51.1k VOUT 5V 350mA SW GND FB R1 1M R2 316k C2 10µF 3990 TA06 f = 2MHz 3990 TA07 5V Step-Down Converter with Undervoltage Lockout VIN 6.5V TO 62V kΩ + 0.22µF – VIN 5.6M BOOST LT3990 1.3M EN/UVLO PG 2.2µF RT 33µH BD 22pF 374k GND 1M FB 22µF 316k 3990 TA08a f = 400kHz Input Current During Start-Up VOUT 5V 350mA SW Start-Up from High Impedance Input Source 4.5 UVLO PROGRAMMED TO 6.5V 4.0 INPUT CURRENT (mA) 3.5 3.0 2.5 2.0 VIN 5V/DIV FRONT PAGE APPLICATION VOUT 2V/DIV FRONT PAGE APPLICATION WITH UVLO PROGRAMMED TO 6.5V 1.5 1.0 0.5 0 –0.5 INPUT CURRENT DROPOUT CONDITIONS 0 2 6 8 4 INPUT VOLTAGE (V) 10 12 5ms/DIV FRONT PAGE APPLICATION VIN = 12V VOUT = 5V 1k INPUT SOURCE RESISTANCE 2.5mA LOAD 3990 TA08c 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 3.00 ±0.10 (4 SIDES) R = 0.125 TYP 6 0.40 ± 0.10 10 1.65 ± 0.10 (2 SIDES) PIN 1 NOTCH R = 0.20 OR 0.35 × 45° CHAMFER PIN 1 TOP MARK (SEE NOTE 6) 0.200 REF 0.75 ±0.05 0.00 – 0.05 5 1 (DD) DFN REV C 0310 0.25 ± 0.05 0.50 BSC 2.38 ±0.10 (2 SIDES) 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 (.112 ±.004) 5.23 (.206) MIN 2.845 ±0.102 (.112 ±.004) 0.889 ±0.127 (.035 ±.005) 8 1 1.651 ±0.102 (.065 ±.004) 1.651 ±0.102 3.20 – 3.45 (.065 ±.004) (.126 – .136) 0.305 ±0.038 (.0120 ±.0015) TYP 16 0.50 (.0197) BSC 4.039 ±0.102 (.159 ±.004) (NOTE 3) RECOMMENDED SOLDER PAD LAYOUT 0.254 (.010) 0.35 REF 0.12 REF DETAIL “B” CORNER TAIL IS PART OF DETAIL “B” THE LEADFRAME FEATURE. FOR REFERENCE ONLY 9 NO MEASUREMENT PURPOSE 0.280 ±0.076 (.011 ±.003) REF 16151413121110 9 DETAIL “A” 0° – 6° TYP 3.00 ±0.102 (.118 ±.004) (NOTE 4) 4.90 ±0.152 (.193 ±.006) GAUGE PLANE 0.53 ±0.152 (.021 ±.006) DETAIL “A” 1.10 (.043) MAX 0.18 (.007) SEATING PLANE 0.17 – 0.27 (.007 – .011) TYP 1234567 8 0.50 (.0197) BSC NOTE: 1. DIMENSIONS IN MILLIMETER/(INCH) 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. 0.86 (.034) REF 0.1016 ±0.0508 (.004 ±.002) MSOP (MSE16) 0911 REV E 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 Clarified Typical Applications 14, 15 17 3990fa 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. 21 LT3990/LT3990-3.3/LT3990-5 TYPICAL APPLICATION 1.21V Step-Down Converter VIN 4.2V TO 30V VIN BOOST LT3990 OFF ON C1 2.2µF 374k C3 0.22µF L1 15µH EN/UVLO SW BD FB PG RT GND f = 400kHz VOUT 1.2V 350mA C2 47µF 3990 TA09 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LT3970/LT3970-3.3/ 40V, 350mA, 2.2MHz High Efficiency Micropower Step-Down DC/DC LT3970-5 Converter with IQ = 2.5µA VIN: 4.2V to 40V, VOUT(MIN) = 1.21V, IQ = 2.5µA, ISD < 1µA, 3mm × 2mm DFN-10, MSOP-10 LT3971 38V, 1.2A, 2.2MHz High Efficiency Micropower Step-Down DC/DC Converter with IQ = 2.8µA VIN: 4.3V to 38V, VOUT(MIN) = 1.2V, IQ = 2.8µA, ISD < 1µA, 3mm × 3mm DFN-10, MSOPE-10 LT3991 55V, 1.2A, 2.2MHz High Efficiency Micropower Step-Down DC/DC Converter with IQ = 2.8µA VIN: 4.3V to 55V, VOUT(MIN) = 1.2V, IQ = 2.8µA, ISD < 1µA, 3mm × 3mm DFN-10, MSOPE-10 LT3682 36V, 60VMAX, 1A, 2.2MHz High Efficiency Micropower Step-Down DC/DC Converter VIN: 3.6V to 36V, VOUT(MIN) = 0.8V, IQ = 75µA, ISD < 1µA, 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