LT3980 58V, 2A, 2.4MHz Step-Down Switching Regulator with 85µA Quiescent Current Features Description Wide Input Range: Operation from 3.6V to 58V ■ Overvoltage Lockout Protects Circuits Through 80V Transients ■ 2A Maximum Output Current ® ■ Low Ripple (<15mV P-P) Burst Mode Operation: IQ = 85µA at 12VIN to 3.3VOUT ■ Adjustable Switching Frequency: 100kHz to 2.4MHz ■ Low Shutdown Current: I < 1µA Q ■ Catch Diode Current Sense Protects Circuit Through Short-Circuit and Input Overvoltage ■ Synchronizable Between 250kHz to 2MHz ■ Power Good Flag ■ Saturating Switch Design: 200mΩ On-Resistance ■ Thermal Protection ■ Soft-Start Capability ■ Small 16-Pin Thermally Enhanced MSOP and 3mm × 4mm DFN Packages The LT®3980 is an adjustable frequency (100kHz to 2.4MHz) monolithic buck switching regulator that accepts input voltages up to 58V (80V transient). A high efficiency 200mΩ switch is included on the die along with a boost Schottky diode and the necessary oscillator, control, and logic circuitry. Current mode topology is used for fast transient response and good loop stability. Catch diode current sense (DA pin) protects the circuit during input voltage transients even when a high switching frequency is used. Low ripple Burst Mode operation maintains high efficiency at low output currents while keeping output ripple below 15mV in a typical application. In addition, the LT3980 can further enhance low output current efficiency by drawing bias current from the output when VOUT is above 3V. Shutdown reduces input supply current to less than 1µA while a resistor and capacitor on the RUN/SS pin provide a controlled output voltage ramp (soft-start). A power good flag signals when VOUT reaches 91% of the programmed output voltage. The LT3980 is available in 16-pin MSOP and 3mm × 4mm DFN packages with exposed pads for low thermal resistance. ■ Applications ■ ■ ■ ■ Automotive Battery Regulation Distributed Supply Regulation Industrial Supplies Wall Transformer Regulation L, LT, LTC, LTM, Linear Technology, Burst Mode and the Linear logo are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. Typical Application 5V Step-Down Converter Efficiency, VOUT = 5V VOUT 5V 2A 4.75k 10µF RUN/SS BOOST 0.47µF 10µH VC LT3980 SW 22pF RT 1nF 97.6k PG DA SYNC FB GND VIN = 12V 90 BD VIN OFF ON 95 EFFICIENCY (%) VIN 6.5V TO 58V TRANSIENT TO 80V 85 VIN = 24V 80 VIN = 48V 75 70 65 60 536k f = 400kHz D = DIODES, INC. SBR3U100LP 55 47µF 100k 3980 TA01 50 0 0.5 1 ILOAD (A) 1.5 2 3980 TA01b 3980fa For more information www.linear.com/LT3980 1 LT3980 Absolute Maximum Ratings (Note 1) VIN , RUN/SS Voltage (Note 5)....................................80V BOOST Pin Voltage....................................................75V BOOST Pin Above SW Pin..........................................30V FB, RT, VC Voltage........................................................5V PG, BD, SYNC Voltage...............................................25V Operating Junction Temperature Range (Note 2) LT3980E..............................................– 40°C to 125°C LT3980I...............................................– 40°C to 125°C LT3980H.............................................– 40°C to 150°C Storage Temperature Range....................–65°C to 150°C Lead Temperature (Soldering, 10 sec) (MSE Only)........................................................ 300°C pIN CONFIGURATION TOP VIEW SYNC 1 14 DA NC 2 13 NC PG 3 FB 4 12 VIN 11 SW VC 5 10 BOOST RT 6 9 BD GND 7 8 RUN/SS 15 GND TOP VIEW SYNC PG NC FB NC VC RT GND 1 2 3 4 5 6 7 8 16 15 14 13 12 11 10 9 17 GND NC DA VIN NC SW BOOST BD RUN/SS MSE PACKAGE 16-LEAD PLASTIC MSOP DE14 PACKAGE 14-LEAD (4mm × 3mm) PLASTIC DFN θJA = 45°C/W, θJC = 10°C/W EXPOSED PAD (PIN 15) IS GND, MUST BE SOLDERED TO PCB θJA = 45°C/W, θJC = 10°C/W EXPOSED PAD (PIN 17) IS GND, MUST BE SOLDERED TO PCB order information LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE LT3980EDE#PBF LT3980EDE#TRPBF 3980 14-Lead (3mm × 4mm) Plastic DFN –40°C to 125°C LT3980IDE#PBF LT3980IDE#TRPBF 3980 14-Lead (3mm × 4mm) Plastic DFN –40°C to 125°C LT3980EMSE#PBF LT3980EMSE#TRPBF 3980 16-Lead Plastic MSOP –40°C to 125°C LT3980IMSE#PBF LT3980IMSE#TRPBF 3980 16-Lead Plastic MSOP –40°C to 125°C LT3980HMSE#PBF LT3980HMSE#TRPBF 3980 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/ Electrical Characteristics The ● denotes the specifications which apply over the full operating temper- ature range, otherwise specifications are at TA = 25°C. VIN = 10V, VRUN/SS = 10V, VBOOST = 15V, VBD = 3.3V unless otherwise noted. (Note 2) PARAMETER CONDITIONS MIN Minimum Input Voltage ● VIN Overvoltage Lockout ● Quiescent Current from VIN VRUN/SS = 0.2V VBD = 3V, Not Switching VBD = 0, Not Switching TYP MAX UNITS 3 3.6 V 58 61.5 64 V 20 70 0.01 35 120 0.5 60 160 µA µA µA 3980fa 2 For more information www.linear.com/LT3980 LT3980 Electrical Characteristics The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 10V, VRUN/SS = 10V, VBOOST = 15V, VBD = 3.3V unless otherwise noted. (Note 2) PARAMETER CONDITIONS Quiescent Current from BD VRUN/SS = 0.2V VBD = 3V, Not Switching VBD = 0, Not Switching Feedback Voltage ● FB Pin Bias Current (Note 3) VFB = 0.8V, VC = 1.2V FB Voltage Line Regulation 4V < VIN < 56V MIN TYP MAX UNITS 55 0.01 82 1 0.5 115 5 µA µA µA 782 770 790 790 798 805 mV mV 10 40 nA 0.002 0.01 %/V ● Error Amp gm 500 Error Amp Gain 1800 µmho VC Source Current 60 µA VC Sink Current 60 µA 3.87 A/V VC Pin to Switch Current Gain VC Clamp Voltage Switching Frequency 2 RT = 8.66k RT = 29.4k RT = 187k 1.95 0.86 195 Minimum Switch Off-Time ● Switch Current Limit Duty Cycle = 5% Switch VCESAT ISW = 2A 3.3 2.55 1.27 255 MHz MHz kHz 140 230 nS 4 4.9 540 DA Pin Current to Pause OSC Boost Schottky Reverse Leakage V 2.25 1.07 225 1.9 VBD = 0V Minimum Boost Voltage (Note 4) ● A mV 2.4 3 A 0.02 2 µA 1.7 2.2 V BOOST Pin Current ISW = 2A 40 55 mA RUN/SS Pin Current VRUN/SS = 2.5V 6 10 µA 2.5 V RUN/SS Input Voltage High RUN/SS Input Voltage Low PG Threshold Offset from Feedback Voltage VFB Rising ● 0.4 ● 50 PG Hysteresis 65 80 14 PG Leakage VPG = 5V PG Sink Current VPG = 0.4V 0.1 ● SYNC Threshold SYNC Pin Bias Current V VSYNC = 0V 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 LT3980E is guaranteed to meet performance specifications from 0°C to 125°C. Specifications over the –40°C to 125°C operating temperature range are assured by design, characterization and correlation with statistical process controls. The LT3980I specifications are guaranteed over the –40°C to 125°C temperature range. The LT3980H 200 700 0.575 0.675 0.1 mV mV 1 µA µA 0.775 V µA specifications are guaranteed over the –40°C to 150°C operating temperature range. High junction temperatures degrade operating lifetimes. Operating lifetime is derated at junction temperatures greater than 125°C. Note 3: Bias current flows out of the FB pin. Note 4: This is the minimum voltage across the boost capacitor needed to guarantee full saturation of the switch. Note 5: Absolute Maximum at VIN and RUN/SS pins is 80V for nonrepetitive 1 minute transients, and 60V for continuous operation. 3980fa For more information www.linear.com/LT3980 3 LT3980 Typical Performance Characteristics Efficiency, VOUT = 5V VIN = 12V 85 EFFICIENCY (%) 70 65 60 VIN = 24V 80 VIN = 48V 75 70 65 f = 400kHz D = DIODES, INC. SBR3U100LP 0.5 1 50 2 ILOAD (A) 130 400 VOUT = 3.3V 0.5 1 ILOAD (A) 1.5 SUPPLY CURRENT (µA) 70 50 30 3980 G02 0 10 20 30 40 INPUT VOLTAGE (V) 50 82 2.5 80 2.0 78 1.5 3980 G03 3.5 Maximum Load Current, VOUT = 3.3V TYPICAL INCREASED SUPPLY CURRENT DUE TO CATCH DIODE LEAKAGE AT HIGH TEMPERATURE 250 200 150 3.0 MINIMUM 2.5 100 0 –50 –25 60 0 Maximum Load Current, VOUT = 5V MINIMUM 5 10 15 20 25 30 35 40 45 50 55 60 INPUT VOLTAGE (V) 3980 G07 Switch Current Limit 5 10 15 20 25 30 35 40 45 50 55 60 INPUT VOLTAGE (V) 3980 G06 Switch Current Limit 6.5 5.0 6.0 4.5 4.0 SWITCH CURRENT LIMIT (A) 3.0 2.0 25 50 75 100 125 150 TEMPERATURE (°C) 3980 G05 SWITCH CURRENT LIMIT (A) LOAD CURRENT (A) 3.0 50 TYPICAL 2.0 84 VIN = 12V VOUT = 3.3V 300 3980 G04 2.5 2 CATCH DIODE: DIODES, INC. PDS360 350 90 3.5 3.5 No-Load Supply Current 110 SUPPLY CURRENT (µA) 0 3980 G01 No-Load Supply Current 10 f = 400kHz D = DIODES, INC. SBR3U100LP 55 1.5 86 1.0 VIN = 12V 0.5 74 VOUT = 5V IOUT = 2A 0 72 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 1.80 2.00 SWITCHING FREQUENCY (MHz) LOAD CURRENT (A) 0 4.0 76 60 55 50 85 88 POWER LOSS (W) VIN = 48V 75 Efficiency vs Switching Frequency VIN = 12V 90 VIN = 24V 80 EFFICIENCY (%) 95 EFFICIENCY (%) Efficiency, VOUT = 3.3V 90 TA = 25°C unless otherwise noted. TYPICAL 3.5 MINIMUM 3.0 2.5 2.0 5.5 5.0 4.5 DUTY CYCLE = 10% 4.0 3.5 3.0 2.5 0 20 60 40 DUTY CYCLE (%) 80 100 2.0 –50 –25 0 25 50 75 100 125 150 TEMPERATURE (°C) 3980 G09 3980 G08 3980fa 4 For more information www.linear.com/LT3980 LT3980 Typical Performance Characteristics Boost Pin Current vs Switch Current 120 600 105 500 400 300 200 100 Feedback Voltage 840 FEEDBACK VOLTAGE (mV) 700 BOOST PIN CURRENT (mA) VOLTAGE DROP (mV) Switch Voltage Drop 0 TA = 25°C unless otherwise noted. 90 75 60 45 30 820 800 780 15 0 1 2 SWITCH CURRENT (A) 0 3 0 1 2 SWITCH CURRENT (A) 3980 G10 760 –50 –25 3 0 25 50 75 100 125 150 TEMPERATURE (°C) 3980 G12 3980 G11 Switching Frequency Frequency Foldback 1.05 1.00 0.95 0.90 0.85 RF = 32.4k 0.80 –50 –25 0 800 600 400 200 0 25 50 75 100 125 150 TEMPERATURE (°C) 3880 G13 Minimum Switch On-Time 2500 2000 1500 1000 500 0 0 100 200 300 400 500 600 700 800 900 FB PIN VOLTAGE (mV) 3980 G14 Soft-Start 24 220 6 20 SWITCH CURRENT LIMIT (A) 7 180 160 140 ILOAD = 1A 100 –50 –25 0 5 4 3 2 25 50 75 100 125 150 TEMPERATURE (°C) 3980 G16 0 1000 3980 G15 16 12 8 4 1 120 10 100 RESISTANCE (kΩ) 1 RUN/SS Pin Current 240 200 RT vs Frequency 3000 RUN/SS PIN CURRENT (µA) FREQUENCY (MHz) 1.10 1000 SWITCHING FREQUENCY (kHz) SWITCHING FREQUENCY (kHz) 1.15 MINIMUM SWITCH ON-TIME (ns) 3500 1200 1.20 0 0.5 2.5 2 1.5 RUN/SS PIN VOLTAGE (V) 1 3 3.5 3980 G17 0 0 10 20 30 40 50 RUN/SS PIN VOLTAGE (V) 60 3980 G18 3980fa For more information www.linear.com/LT3980 5 LT3980 Typical Performance Characteristics Boost Diode 50 0.8 0.6 0.4 5 20 INPUT VOLTAGE (V) VC PIN CURRENT (µA) 10 0 –10 –20 –30 4 TO RUN 3 –40 0 0.5 1.0 1.5 BOOST DIODE CURRENT (A) –50 –200 2.0 3980 G19 Minimum Input Voltage, VOUT = 5V 8 2.50 f = 400kHz 2 –100 100 0 FB PIN ERROR VOLTAGE (mV) 200 VC VOLTAGE (V) 7 5 10 100 ILOAD (mA) 1000 2000 1.50 1.00 SWITCHING THRESHOLD 0 –50 –25 0 25 50 75 100 125 150 TEMPERATURE (°C) VOUT 10mV/DIV 5µs/DIV 85 80 75 –50 –25 Switching Waveforms: Transition from Burst Mode Operation to Full Frequency 3980 G25 0 25 50 75 100 125 150 TEMPERATURE (°C) 3980 G24 Switching Waveforms: Full Frequency Continuous Operation VSW 5V/DIV VSW 5V/DIV VIN = 12V VOUT = 3.3V ILOAD = 10mA 90 3980 G23 Switching Waveforms: Burst Mode Operation IL 0.2A/DIV 3980 G21 Power Good Threshold 3980 G22 VSW 5V/DIV 1000 2000 95 0.50 1 100 ILOAD (mA) VC Voltages 2.00 TO RUN 10 CURRENT LIMIT CLAMP TO START 6 1 3980 G20 THRESHOLD VOLTAGE (%) BOOST DIODE VF (V) f = 400kHz TO START 30 1.0 0.2 INPUT VOLTAGE (V) 6 40 1.2 4 Minimum Input Voltage, VOUT = 3.3V Error Amp Output Current 1.4 0 TA = 25°C, unless otherwise noted. IL 0.2A/DIV IL 0.5A/DIV VOUT 10mV/DIV VOUT 10mV/DIV VIN = 12V VOUT = 3.3V ILOAD = 110mA 1µs/DIV 3980 G26 VIN = 12V VOUT = 3.3V ILOAD = 1A 1µs/DIV 3980 G27 3980fa 6 For more information www.linear.com/LT3980 LT3980 Pin Functions (DFN, MSOP) SYNC (Pin 1/Pin 1): This is the external clock synchronization input. Ground this pin for low ripple Burst Mode operation at low output loads. Tie to a voltage above 0.8V to select pulse-skipping mode. Tie to a clock source for synchronization. Clock edges should have rise and fall times faster than 1µs. Tie pin to GND if not used. See the Synchronization section in Applications Information. NC (Pins 2, 13/Pins 3, 5, 13, 16): No Connect. These pins are not connected to internal circuitry. PG (Pin 3/Pin 2): The PG pin is the open collector output of an internal comparator. PG remains low until the FB pin is within 9% of the final regulation voltage. PG output is valid when VIN is above 3.6V and RUN/SS is high. FB (Pin 4/Pin 4): The LT3980 regulates the FB pin to 0.790V. Connect the feedback resistor divider tap to this pin. VC (Pin 5/Pin 6): The VC pin is the output of the internal error amplifier. The voltage on this pin controls the peak switch current. Tie an RC network from this pin to ground to compensate the control loop. RT (Pin 6/Pin 7): Oscillator Resistor Input. Connecting a resistor to ground from this pin sets the switching frequency. must be soldered to the PCB. RUN/SS (Pin 8/Pin 9): The RUN/SS pin is used to put the LT3980 in shutdown mode. Tie to ground to shut down the LT3980. Tie to 2.5V or more for normal operation. If the shutdown feature is not used, tie this pin to the VIN pin. RUN/SS also provides a soft-start function; see the Applications Information section. BD (Pin 9/Pin 10): This pin connects to the anode of the boost Schottky diode. BD also supplies current to the internal regulator. BOOST (Pin 10/Pin 11): This pin is used to provide a drive voltage, higher than the input voltage, to the internal bipolar NPN power switch. SW (Pin 11/Pin 12): The SW pin is the output of the internal power switch. Connect this pin to the inductor, catch diode and boost capacitor. VIN (Pin 12/Pin 14): The VIN pin supplies current to the LT3980’s internal regulator and to the internal power switch. This pin must be locally bypassed. DA (Pin 14/Pin 15): This pin measures catch diode current and pauses the oscillator during overcurrent conditions. GND (Pin 7, 15/Pin 8, 17): Ground. The exposed pads Block Diagram VIN VIN C1 – + INTERNAL 0.79V REF RUN/SS Σ RT SLOPE COMP OSCILLATOR 100kHzTO2.4MHz RT BD SWITCH LATCH BOOST C3 R S Q L1 SW VOUT DISABLE SYNC BurstMode DETECT SOFT-START C2 D1 DA PG ERROR AMP + – + – 0.725V GND VC CLAMP CC RC FB R2 VC CF R1 3680 BD 3980fa For more information www.linear.com/LT3980 7 LT3980 Operation The LT3980 is a constant frequency, current mode stepdown regulator. An oscillator, with frequency set by RT, enables 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 . An error amplifier measures the output voltage through an external resistor divider tied to the FB pin and servos the VC pin. If the error amplifier’s output increases, more current is delivered to the output; if it decreases, less current is delivered. An active clamp on the VC pin provides current limit. The VC pin is also clamped to the voltage on the RUN/SS pin; soft-start is implemented by generating a voltage ramp at the RUN/SS pin using an external resistor and capacitor. the input supply. This allows the driver to fully saturate the internal bipolar NPN power switch for efficient operation. 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 3V bias power will be drawn from the external source (typically the regulated output voltage). This improves efficiency. The RUN/SS pin is used to place the LT3980 in shutdown, disconnecting the output and reducing the input current to less than 0.5µA. The LT3980 contains a power good comparator which trips when the FB pin is at 91% of its regulated value. The PG output is an open-collector 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 LT3980 is enabled and VIN is above 3.6V. The switch driver operates from either the input or from the BOOST pin. An external capacitor and diode are used to generate a voltage at the BOOST pin that is higher than To further optimize efficiency, the LT3980 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 75µA in a typical application. The oscillator reduces the LT3980’s operating frequency when the voltage at the FB pin is low. This frequency foldback helps to control the output current during startup and overload. In addition, the LT3980 monitors the catch diode current flowing through the DA pin and pauses the oscillator during overcurrent conditions to keep inductor current at safe levels. The LT3980 has an overvoltage protection feature which disables switching action when the VIN goes above 61.5V typical (58V minimum). When switching is disabled, the LT3980 can safely sustain input voltages up to 62V. 3980fa 8 For more information www.linear.com/LT3980 LT3980 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 0.79 V Reference designators refer to the Block Diagram. Setting the Switching Frequency The LT3980 uses a constant frequency PWM architecture that can be programmed to switch from 100kHz to 2.4MHz 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 Figure 1. SWITCHING FREQUENCY (MHz) RT VALUE (kΩ) 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.2 1.4 1.6 1.8 2.0 432 215 137 97.6 76.8 60.4 51.1 43.2 35.7 32.4 24.9 20 16.2 14 11 Figure 1. Switching Frequency vs RT Value 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: VD + VOUT fSW(MAX ) = tON(MIN) ( VD + VIN – VSW ) where VIN is the typical input voltage, VOUT is the output voltage, VD is the catch diode drop (~0.5V) and VSW is the internal switch drop (~0.5V at max load). This equation shows that slower switching frequency is necessary to safely accommodate high VIN / VOUT ratio. Also, as shown in the next section, lower frequency allows a lower dropout voltage. The reason input voltage range depends on the switching frequency is because the LT3980 switch has finite minimum on and off times. The switch can turn on for a minimum of ~200ns and turn off for a minimum of ~200ns. This means that the minimum and maximum duty cycles are: DCMIN = fSW tON(MIN) DCMAX = 1– fSW tOFF(MIN) where fSW is the switching frequency, the tON(MIN) is the minimum switch on time (~200ns), and the tOFF(MIN) is the minimum switch off time (~200ns). 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 maximum input voltage for LT3980 applications depends on switching frequency, Absolute Maximum Ratings of the VIN and BOOST pins, and the operating mode. The LT3980 can operate from input voltages of up to 58V, and withstand voltages up to 80V. Note that while VIN is above 61V typical (58V minimum and 64V maximum) the part will keep the switch off and the output will not be in regulation. The switching frequency should be chosen according to the following equation: VIN(MAX ) = VOUT + VD –V +V fSW tON(MIN) D SW where VIN(MAX) is the maximum typical operating input voltage, VOUT is the output voltage, VD is the catch diode 3980fa For more information www.linear.com/LT3980 9 LT3980 Applications Information drop (~0.5V), VSW is the internal switch drop (~0.5V at max load), fSW is the switching frequency (set by RT), and tON(MIN) is the minimum switch on time (~200ns). Note that a higher switching frequency will depress the maximum operating input voltage. Conversely, a lower switching frequency will be necessary to achieve safe operation at high input voltages. where IL(PEAK) is the peak inductor current, IOUT(MAX) is the maximum output load current, and ΔIL is the inductor ripple current. The LT3980’s switch current limit (ILIM) is 4A at low duty cycles and decreases linearly to 3A at DC = 0.8. The maximum output current is a function of the inductor ripple current: Input voltages up to 58V are acceptable regardless of the switching frequency. In this mode, the LT3980 may enter pulse-skipping operation where some switching pulses are skipped to maintain safe inductor current. Be sure to pick an inductor ripple current that provides sufficient maximum output current (IOUT(MAX)). The minimum input voltage is determined by either the LT3980’s minimum operating voltage of ~3.6V or by its maximum duty cycle (see equation in previous section). The minimum input voltage due to duty cycle is: VIN(MIN) = VOUT + VD –V +V 1– fSW tOFF(MIN) D SW The largest inductor ripple current occurs at the highest VIN . To guarantee that the ripple current stays below the specified maximum, the inductor value should be chosen according to the following equation: where VIN(MIN) is the minimum input voltage, and tOFF(MIN) is the minimum switch off time (200ns). Note that higher switching frequency will increase the minimum input voltage. If a lower dropout voltage is desired, a lower switching frequency should be used. Inductor Selection For a given input and output voltage, the inductor value and switching frequency will determine the ripple current. The ripple current ΔIL increases with higher VIN or VOUT and decreases with higher inductance and faster switching frequency. A reasonable starting point for selecting the ripple current is: ΔIL = 0.4(IOUT(MAX)) where IOUT(MAX) is the maximum output load current. To guarantee sufficient output current, peak inductor current must be lower than the LT3980’s switch current limit (ILIM). The peak inductor current is: IL(PEAK) = IOUT(MAX) + ΔIL/2 IOUT(MAX) = ILIM – ΔIL/2 V +V V +V L = OUT D 1– OUT D VIN(MAX ) fSW∆ IL where VD is the voltage drop of the catch diode (~0.4V), VIN(MAX) is the maximum input voltage, VOUT is the output voltage, fSW is the switching frequency (set by RT), and L is in the inductor value. The inductor’s RMS and saturation current rating must be greater than the maximum load current. For robust operation in fault conditions (start-up or short circuit) and high input voltage (>40V), the saturation current should be above 3.5A. 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 1 lists several vendors and suitable types. Table 1. Inductor Vendors VENDOR URL PART SERIES TYPE Murata www.murata.com LQH55D Open TDK www.component.tdk.com SLF10145 Shielded Toko www.toko.com D75C D75F Shielded Open Sumida www.sumida.com CDRH74 CR75 CDRH8D43 Shielded Open Shielded NEC www.nec-tokin.com MPLC073 MPBI0755 Shielded Shielded Vishay www.vishay.com IHLP2525CE01 Shielded 3980fa 10 For more information www.linear.com/LT3980 LT3980 Applications Information Of course, such a simple design guide will not always result in the optimum inductor for your application. A larger value inductor provides a slightly higher maximum load current and will reduce the output voltage ripple. If your load is lower than 2A, then you can decrease the value of the inductor and operate with higher ripple current. This allows you to use 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 and inductor value for several popular output voltages. Low inductance may result in discontinuous mode operation, which is okay but further 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 AN19. Input Capacitor Bypass the input of the LT3980 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 10µF to 22µF ceramic capacitor is adequate to bypass the LT3980 and will easily handle the ripple current. Note that larger input capacitance is required when a lower switching frequency is used. 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 lower performance electrolytic capacitor. 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 LT3980 and to force this very high frequency switching current into a tight local loop, minimizing EMI. A 10µF capacitor is capable of this task, but only if it is placed close to the LT3980 and the catch diode (see the PCB Layout section). A second precaution regarding the ceramic input capacitor concerns the maximum input voltage rating of the LT3980. A ceramic input capacitor combined with trace or cable inductance forms a high quality (under damped) tank circuit. If the LT3980 circuit is plugged into a live supply, the input voltage can ring to twice its nominal value, possibly exceeding the LT3980’s voltage rating. This situation is easily avoided (see the Hot Plugging Safety section). For space sensitive applications, a 4.7µF ceramic capacitor can be used for local bypassing of the LT3980 input. However, the lower input capacitance will result in increased input current ripple and input voltage ripple, and may couple noise into other circuitry. Also, the increased voltage ripple will raise the minimum operating voltage of the LT3980 to ~3.7V. Output Capacitor and Output Ripple The output capacitor has two essential functions. Along with the inductor, it filters the square wave generated by the LT3980 to produce the DC output. In this role it determines the output ripple, and low impedance at the switching frequency is important. The second function is to store energy in order to satisfy transient loads and stabilize the LT3980’s control loop. Ceramic capacitors have very low equivalent series resistance (ESR) and provide the best ripple performance. A good starting value is: COUT = 100 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 the compensation network is also adjusted to maintain the loop bandwidth. A lower value of output capacitor can be used to save space and cost but transient performance will suffer. See the Frequency Compensation section to choose an appropriate compensation network. 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. High performance tantalum or electrolytic capacitors can be used for the output capacitor. Low ESR is important, so choose one that is intended for 3980fa For more information www.linear.com/LT3980 11 LT3980 Applications Information use in switching regulators. The ESR should be specified by the supplier, and should be 0.05Ω or less. Such a capacitor will be larger than a ceramic capacitor and will have a larger capacitance, because the capacitor must be large to achieve low ESR. Table 2 lists several capacitor vendors. loads the LT3980 can excite the ceramic capacitor at audio frequencies, generating audible noise. Since the LT3980 operates at a lower current limit during Burst Mode operation, the noise is nearly silent to a casual ear. If this is unacceptable, use a high performance tantalum or electrolytic capacitor at the output. Table 2. Capacitor Vendors Frequency Compensation PART SERIES Ceramic, Polymer, Tantalum Kemet www.kemet.com Ceramic, Tantalum Sanyo www.sanyovideo.com Ceramic, Polymer, Tantalum Murata www.murata.com Ceramic AVX www.avxcorp.com Ceramic, Tantalum Taiyo Yuden www.taiyo-yuden.com Ceramic COMMANDS EEF Series T494, T495 POSCAP SOT-23 SOT-23 TPS Series Catch Diode The catch diode conducts current only during switch off time. Average forward current in normal operation can be calculated from: ID(AVG) = IOUT (VIN – VOUT)/VIN where IOUT is the output load current. The only reason to consider a diode with a larger current rating than necessary for nominal operation is for the worst-case condition of shorted output. The diode current will then increase to the typical peak switch current. Peak reverse voltage is equal to the regulator input voltage. Use a Schottky diode with a reverse voltage rating greater than the input voltage. The overvoltage protection feature in the LT3980 will keep the switch off when VIN > 64V which allows the use of 64V rated Schottky even when VIN ranges up to 80V. The LT3980 uses current mode control to regulate the output. This simplifies loop compensation. In particular, the LT3980 does not require the ESR of the output capacitor for stability, so you are free to use ceramic capacitors to achieve low output ripple and small circuit size. Frequency compensation is provided by the components tied to the VC pin, as shown in Figure 2. Generally a capacitor (CC) and a resistor (RC) in series to ground are used. In addition, there may be lower value capacitor in parallel. This capacitor (CF) is not part of the loop compensation but is used to filter noise at the switching frequency, and is required only if a phase-lead capacitor is used or if the output capacitor has high ESR. LT3980 CURRENT MODE POWER STAGE gm = 5.3mho ERROR AMPLIFIER OUTPUT R1 3M VC CF ESR 0.79V C1 C1 + POLYMER OR TANTALUM GND RC CPL FB gm = 500µmho Ceramic Capacitors Ceramic capacitors are small, robust and have very low ESR. However, ceramic capacitors can cause problems when used with the LT3980 due to their piezoelectric nature. When in Burst Mode operation, the LT3980’s switching frequency depends on the load current, and at very light SW + URL www.panasonic.com – VENDOR Panasonic CERAMIC R2 CC 3980 F02 Figure 2. Model for Loop Response 3980fa 12 For more information www.linear.com/LT3980 LT3980 Applications Information Loop compensation determines the stability and transient performance. Designing the compensation network is a bit complicated and the best values depend on the application and in particular the type of output capacitor. A practical approach is to start with one of the circuits in this data sheet that is similar to your application and tune the compensation network to optimize the performance. Stability should then be checked across all operating conditions, including load current, input voltage and temperature. The LT1375 data sheet contains a more thorough discussion of loop compensation and describes how to test the stability using a transient load. Figure 2 shows an equivalent circuit for the LT3980 control loop. The error amplifier is a transconductance amplifier with finite output impedance. The power section, consisting of the modulator, power switch and inductor, is modeled as a transconductance amplifier generating an output current proportional to the voltage at the VC pin. Note that the output capacitor integrates this current, and that the capacitor on the VC pin (CC) integrates the error amplifier output current, resulting in two poles in the loop. In most cases a zero is required and comes from either the output capacitor ESR or from a resistor RC in series with CC. This simple model works well as long as the value of the inductor is not too high and the loop crossover frequency is much lower than the switching frequency. A phase lead capacitor (CPL) across the feedback divider may improve the transient response. Figure 3 shows the transient response when the load current is stepped from 0.5A to 1.5A and back to 0.5A. VOUT 100mV/DIV Low Ripple Burst Mode Operation and Pulse-Skipping Mode The LT3980 is capable of operating in either low ripple Burst Mode operation or pulse-skipping mode which are selected using the SYNC pin. See the Synchronization section for details. To enhance efficiency at light loads, the LT3980 can be operated 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 LT3980 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 LT3980 delivers power to the output with single, low current pulses, the output ripple is kept below 15mV for a typical application. In addition, VIN and BD quiescent currents are reduced to typically 35µA and 82µA respectively during the sleep time. As the load current decreases towards a no-load condition, the percentage of time that the LT3980 operates in sleep mode increases and the average input current is greatly reduced resulting in high efficiency even at very low loads. See Figure 4. At higher output loads (above 140mA for the front page application) the LT3980 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 operation is seamless, and will not disturb the output voltage. VSW 5V/DIV IL 0.2A/DIV IL 0.5A/DIV VOUT 10mV/DIV VIN = 12V VOUT = 5V 50µs/DIV 3980 F03 Figure 3. Transient Load Response of the LT3980 Front Page Application as the Load Current Is Stepped from 0.5A to 1.5A VIN = 12V VOUT = 3.3V ILOAD = 10mA 5µs/DIV 3980 F04 Figure 4. Burst Mode Operation 3980fa For more information www.linear.com/LT3980 13 LT3980 Applications Information If low quiescent current is not required the LT3980 can operate in pulse-skipping mode. The benefit of this mode is that the LT3980 will enter full frequency standard PWM operation at a lower output load current than when in Burst Mode operation. The front page application circuit will switch at full frequency at output loads higher than about 60mA. outputs of 3V and above, the standard circuit (Figure 5a) is best. For outputs between 2.8V and 3V, use a 1µF boost capacitor. A 2.5V output presents a special case because it is marginally adequate to support the boosted drive stage while using the internal boost diode. For reliable BOOST pin operation with 2.5V outputs use a good external Schottky diode (such as the ON Semi MBR0540), and a 1µF boost capacitor (see Figure 5b). For lower output voltages the boost diode can be tied to the input (Figure 5c), or to another supply greater than 2.8V. Tying BD to VIN reduces the maximum input voltage to 28V. The circuit in Figure 5a is more efficient because the BOOST pin current and BD pin quiescent current comes from a lower voltage source. You must also be sure that the maximum voltage ratings of the BOOST and BD pins are not exceeded. BOOST and BIAS 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 2 shows three ways to arrange the boost circuit. The BOOST pin must be more than 2.3V above the SW pin for best efficiency. For VOUT VOUT BD BOOST VIN 4.7µF VIN D2 BD LT3980 GND BOOST VIN C3 SW VIN LT3980 GND 4.7µF (5a) For VOUT > 2.8V C3 SW (5b) For 2.5V < VOUT < 2.8V VOUT BD BOOST VIN 4.7µF VIN LT3980 GND C3 SW 3980 FO5 (5c) For VOUT < 2.5V; VIN(MAX) = 30V Figure 5. Three Circuits for Generating the Boost Voltage 3980fa 14 For more information www.linear.com/LT3980 LT3980 Applications Information While operating with high boost voltages (>10V), it is important to ensure that the power dissipation from the boost circuit is not too high. See the Typical Performance Characteristics section for the plot, BOOST Pin Current vs Switch Current. Boost circuit power dissipation is calculated as follows: PBOOST = IBOOST VBOOST – SWDC Where DC is the switch duty cycle, IBOOST is the boost pin current, and VBOOST – VSW is the voltage between the boost pin and switch pin. If the PBOOST > 0.5W, a Zener can be put between the boost pin and the boost capacitor such that the power is dissipated in the Zener instead of the LT3980. The minimum operating voltage of an LT3980 application is limited by the minimum input voltage (3.6V) and by the maximum duty cycle as outlined in a previous section. For proper startup, the minimum input voltage is also limited by the boost circuit. If the input voltage is ramped slowly, or the LT3980 is turned on with its RUN/SS pin when the output is already in regulation, then the boost capacitor may not be fully charged. Because 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 6 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 6 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. At light loads, the inductor current becomes discontinuous and the effective duty cycle can be very high. This reduces the minimum input voltage to approximately 300mV above VOUT. At higher load currents, the inductor current is continuous and the duty cycle is limited by the maximum duty cycle of the LT3980, requiring a higher input voltage to maintain regulation. Soft-Start The RUN/SS pin can be used to soft-start the LT3980, reducing the maximum input current during start-up. The RUN/SS pin is driven through an external RC filter to 8 f = 400kHz f = 400kHz TO START TO START 7 4 INPUT VOLTAGE (V) INPUT VOLTAGE (V) 5 TO RUN 3 2 6 TO RUN 5 4 1 10 100 ILOAD (mA) 1000 2000 1 3980 F06a 10 100 ILOAD (mA) 1000 2000 3980 F06b Figure 6. The Minimum Input Voltage Depends on Output Voltage, Load Current and Boost Circuit 3980fa For more information www.linear.com/LT3980 15 LT3980 Applications Information create a voltage ramp at this pin. Figure 7 shows the startup and shutdown waveforms with the soft-start circuit. By choosing a large RC time constant, the peak start-up current can be reduced to the current that is required to regulate the output, with no overshoot. Choose the value of the resistor so that it can supply 20µA when the RUN/ SS pin reaches 2.5V. Synchronization To select low ripple Burst Mode operation, tie the SYNC pin below 0.5V (this can be ground or a logic output). Tie to a voltage above 0.8V to select pulse-skipping mode. Synchronizing the LT3980 oscillator to an external frequency can be done by connecting a square wave (with 20% to 80% duty cycle) to the SYNC pin. The square wave amplitude should have valleys that are below 0.3V and peaks that are above 0.8V (up to 6V). The LT3980 will not enter Burst Mode operation at low output loads while synchronized to an external clock, but instead will skip pulses to maintain regulation. The LT3980 may be synchronized over a 150kHz to 2MHz range. The RT resistor should be chosen to set the LT3980 switching frequency 25% below the lowest synchronization input. For example, if the synchronization signal will be 250kHz and higher, the RT should be chosen for 200kHz. To assure reliable and safe operation the LT3980 will only synchronize when the output voltage is near regulation as indicated by the PG flag. It is therefore necessary to choose a large enough inductor value to supply the required output current at the frequency set by the RT resistor. See the Inductor Selection section. It is also important to note that slope compensation is set by the RT value: When the sync frequency is much higher than the one set by RT, the slope compensation will be significantly reduced which may require a larger inductor value to prevent subharmonic oscillation. Shorted and Reversed Input Protection If an inductor is chosen that will not saturate excessively, an LT3980 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 LT3980 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 LT3980’s output. If the VIN pin is allowed to float and the RUN/SS pin is held high (either by a logic signal or because it is tied to VIN), then the LT3980’s internal circuitry will pull its quiescent current through its SW pin. This is fine if your system can tolerate a few mA in this state. If you ground the RUN/ SS pin, the SW pin current will drop to essentially zero. However, if the VIN pin is grounded while the output is held high, then parasitic diodes inside the LT3980 can pull large currents from the output through the SW pin and the RUN IL 1A/DIV 15k RUN/SS 0.22µF VRUN/SS 2V/DIV GND VOUT 2V/DIV 2ms/DIV 3680 F07 Figure 7. To Soft-Start the LT3980, Add a Resistor and Capacitor to the RUN/SS Pin 3980fa 16 For more information www.linear.com/LT3980 LT3980 Applications Information VIN pin. Figure 8 shows a circuit that will run only when the input voltage is present and that protects against a shorted or reversed input. D4 MBRS360 VIN VIN BOOST LT3980 RUN/SS VOUT SW VC GND FB BACKUP 3980 F08 Figure 8. 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 LT3980 Runs Only When the Input Is Present PCB Layout For proper operation and minimum EMI, care must be taken during printed circuit board layout. Figure 9 shows the recommended component placement with trace, ground plane and via locations. Note that large, switched currents flow in the LT3980’s VIN and SW pins, the catch diode (D1) and the input capacitor (C1). The loop formed by these components should be as small as possible. These components, along with the inductor and 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 and VC nodes small so that the ground traces will shield them from the SW and BOOST nodes. The Exposed Pad on the bottom of the package 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 LT3980 to additional ground planes within the circuit board and on the bottom side. pacitors can cause problems if the LT3980 is plugged into a live supply (see Linear Technology Application Note 88 for a complete discussion). The low loss ceramic capacitor, combined with stray inductance in series with the power source, forms an under damped tank circuit, and the voltage at the VIN pin of the LT3980 can ring to twice the nominal input voltage, possibly exceeding the LT3980’s rating and damaging the part. If the input supply is poorly controlled or the user will be plugging the LT3980 into an energized supply, the input network should be designed to prevent this overshoot. Figure 10 shows the waveforms that result when an LT3980 circuit is connected to a 24V supply through six feet of 24-gauge twisted pair. The first plot is the response with a 4.7µF ceramic capacitor at the input. The input voltage rings as high as 50V and the input current peaks at 26A. A good solution is shown in Figure 10b. A 0.7Ω resistor is added in series with the input to eliminate the voltage overshoot (it also reduces the peak input current). A 0.1µF capacitor improves high frequency filtering. For high input voltages its impact on efficiency is minor, reducing efficiency by 1.5 percent for a 5V output at full load operating from 24V. L1 C2 VOUT RRT CC RC R2 R1 D1 C1 GND RPG 3980 F09 Hot Plugging Safely VIAS TO LOCAL GROUND PLANE The small size, robustness and low impedance of ceramic capacitors make them an attractive option for the input bypass capacitor of LT3980 circuits. However, these ca- VIAS TO VOUT VIAS TO SYNC VIAS TO RUN/SS VIAS TO PG VIAS TO VIN OUTLINE OF LOCAL GROUND PLANE Figure 9. A Good PCB Layout Ensures Proper, Low EMI Operation 3980fa For more information www.linear.com/LT3980 17 LT3980 Applications Information CLOSING SWITCH SIMULATES HOT PLUG IIN VIN + LOW IMPEDANCE ENERGIZED 24V SUPPLY DANGER RINGING VIN MAY EXCEED ABSOLUTE MAXIMUM RATING LT3980 4.7µF IIN 10A/DIV STRAY INDUCTANCE DUE TO 6 FEET (2 METERS) OF TWISTED PAIR 0.7Ω + VIN 20V/DIV 0.1µF 20µs/DIV (10a) LT3980 VIN 20V/DIV 4.7µF IIN 10A/DIV (10b) + 22µF AI.EI. + LT3980 20µs/DIV VIN 20V/DIV 4.7µF IIN 10A/DIV (10c) 20µs/DIV 3980 F10 Figure 10. A Well Chosen Input Network Prevents Input Voltage Overshoot and Ensures Reliable Operation When the LT3980 Is Connected to a Live Supply High Temperature Considerations The PCB must provide heat sinking to keep the LT3980 cool. The Exposed Pad on the bottom of the package 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 LT3980. Place additional vias can reduce thermal resistance further. With these steps, the thermal resistance from die (or junction) to ambient can be reduced to JA = 35°C/W or less. With 100 LFPM airflow, this resistance can fall by another 25%. Further increases in airflow will lead to lower thermal resistance. Because of the large output current capability of the LT3980, it is possible to dissipate enough heat to raise the junction temperature beyond the absolute maximum of 125°C. When operating at high ambient temperatures, the maximum load current should be derated as the ambient temperature approaches 125°C. 18 Power dissipation within the LT3980 can be estimated by calculating the total power loss from an efficiency measurement and subtracting the catch diode loss and inductor loss. The die temperature is calculated by multiplying the LT3980 power dissipation by the thermal resistance from junction to ambient. 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. For more information www.linear.com/LT3980 3980fa LT3980 Typical Applications 5V Step-Down Converter VIN 6.5V TO 58V TRANSIENT TO 80V BD VIN ON OFF VOUT 5V 2A RUN/SS BOOST L 8.2µH 0.47µF VC 4.7µF SW LT3980 RT 4.75k PG 97.6k 1nF 22pF D DA SYNC 536k FB GND 100k f = 400kHz 47µF 3980 TA02 3.3V Step-Down Converter VIN 4.3V TO 58V TRANSIENT TO 80V BD VIN ON OFF VOUT 3.3V 2A RUN/SS BOOST L 6.8µH 0.47µF VC 4.7µF SW LT3980 RT 4.75k DA PG 97.6k 2.2nF 22pF D SYNC 316k FB GND 47µF 100k f = 400kHz 3980 TA03 2.5V Step-Down Converter VIN 4V TO 58V TRANSIENT TO 80V BD VIN ON OFF RUN/SS D2 BOOST L 4.7µH 1µF VC 4.7µF LT3980 SW 2.2nF DA PG 137k SYNC 22pF D1 RT 8.45k VOUT 2.5V 2A GND FB f = 300kHz 215k 47µF 100k 3980 TA04 3980fa For more information www.linear.com/LT3980 19 LT3980 Typical Applications 5V, 1.2MHz Step-Down Converter VIN 8.6V TO 40V TRANSIENT TO 80V BD VIN ON OFF VOUT 5V 2A RUN/SS BOOST L 4.7µH 0.47µF VC 4.7µF SW LT3980 4.75k PG 24.9k DA SYNC 1nF 22pF D RT 536k FB GND 22µF 100k f = 1.2MHz 3980 TA05 12V Step-Down Converter VIN 15V TO 58V TRANSIENT TO 80V BD VIN RUN/SS ON OFF VOUT 12V 2A BOOST L 15µH 0.47µF VC 10µF LT3980 SW D RT 12k PG 60.4k 1nF DA SYNC GND 715k FB 22µF 50k f = 600kHz 3980 TA06 1.8V Step-Down Converter VOUT 1.8V 2A VIN 3.5V TO 32V BD VIN ON OFF RUN/SS BOOST L 3.3µH 0.47µF VC 4.7µF LT3980 SW 2.49k DA PG 97.6k 680pF SYNC 22pF D RT GND FB f = 400kHz 127k 100µF 100k 3980 TA08 3980fa 20 For more information www.linear.com/LT3980 LT3980 Package Description Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. DE Package 14-Lead Plastic DFN (4mm × 3mm) (Reference LTC DWG # 05-08-1708 Rev B) 0.70 ±0.05 3.30 ±0.05 3.60 ±0.05 2.20 ±0.05 1.70 ± 0.05 PACKAGE OUTLINE 0.25 ± 0.05 0.50 BSC 3.00 REF RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED 4.00 ±0.10 (2 SIDES) R = 0.05 TYP 3.00 ±0.10 (2 SIDES) R = 0.115 TYP 8 0.40 ± 0.10 14 3.30 ±0.10 1.70 ± 0.10 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 (DE14) DFN 0806 REV B 7 1 0.25 ± 0.05 0.50 BSC 3.00 REF 0.00 – 0.05 BOTTOM VIEW—EXPOSED PAD NOTE: 1. DRAWING PROPOSED TO BE MADE VARIATION OF VERSION (WGED-3) IN JEDEC PACKAGE OUTLINE MO-229 2. DRAWING NOT TO SCALE 3. ALL DIMENSIONS ARE IN MILLIMETERS 4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE 5. EXPOSED PAD SHALL BE SOLDER PLATED 6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE 3980fa For more information www.linear.com/LT3980 21 LT3980 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 F) BOTTOM VIEW OF EXPOSED PAD OPTION 2.845 ±0.102 (.112 ±.004) 5.10 (.201) 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) 0213 REV F 3980fa 22 For more information www.linear.com/LT3980 LT3980 Revision History REV DATE DESCRIPTION A 10/13 Clarified Efficiency graph PAGE NUMBER 1 Clarified graphs 6 Clarified SYNC pin description 7 Clarified graph 15 Clarified graph 16 Clarified Synchronization description 16 3980fa 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 Forof more information www.linear.com/LT3980 that the interconnection its circuits as described herein will not infringe on existing patent rights. 23 LT3980 Typical Application 1.2V Step-Down Converter VIN 3.6V TO 32V ON OFF RUN/SS VIN BD BOOST VC 4.7µF RT 14k SYNC 1nF L 3.3µH SW LT3980 D DA PG 97.6k 0.47µF VOUT 1.2V 2A GND 52.3k FB 100k f = 400kHz 100µF 3980 TA09 Related Parts PART NUMBER DESCRIPTION LT3689 36V, 60V Transient Protection, 800mA, 2.2MHz High Efficiency Micropower VIN: 3.6V to 36V (Transient to 60V), VOUT(MIN) = 0.8V, Step-Down DC/DC Converter with POR Reset and Watchdog Timer IQ = 75µA, ISD < 1µA, 3mm × 3mm QFN-16 Package COMMENTS LT3682 36V, 60VMAX, 1A, 2.2MHz High Efficiency Micropower Step-Down DC/DC VIN: 3.6V to 36V, VOUT(MIN) = 0.8V, IQ = 75µA, ISD < 1µA, Converter 3mm × 3mm DFN-12 LT3970 40V, 350mA (IOUT), 2.2MHz High Efficiency Step-Down DC/DC Converter with Only 2.5µA of Quiescent Current VIN: 4.2V to 40V, VOUT(MIN) = 1.21V, IQ = 2.5µA, ISD < 1µA, 3mm × 3mm DFN-10 and MSOP-10 Packages LT3480 36V with Transient Protection to 60V, 2A (IOUT), 2.4MHz, High Efficiency Step-Down DC/DC Converter with Burst Mode Operation VIN: 3.6V to 38V, VOUT(MIN) = 0.78V, IQ = 70µA, ISD < 1µA, 3mm × 3mm DFN-10 and MSOP-10E Packages LT3685 36V with Transient Protection to 60V, Dual 2A (IOUT), 2.4MHz, High Efficiency Step-Down DC/DC Converter VIN: 3.6V to 38V, VOUT(MIN) = 0.78V, IQ = 70µA, ISD < 1µA, 3mm × 3mm DFN-10 and MSOP-10E Packages LT3481 34V with Transient Protection to 36V, 2A (IOUT), 2.8MHz, High Efficiency Step-Down DC/DC Converter with Burst Mode Operation VIN: 3.6V to 34V, VOUT(MIN) = 1.26V, IQ = 50µA, ISD < 1µA, 3mm × 3mm DFN-10 and MSOP-10E Packages LT3684 34V with Transient Protection to 36V, 2A (IOUT), 2.8MHz, High Efficiency Step-Down DC/DC Converter VIN: 3.6V to 34V, VOUT(MIN) = 1.26V, IQ = 850µA, ISD < 1µA, 3mm × 3mm DFN-10 and MSOP-10E Packages LT3508 36V with Transient Protection to 40V, Dual 1.4A (IOUT), 3MHz, High Efficiency Step-Down DC/DC Converter VIN: 3.7V to 37V, VOUT(MIN) = 0.8V, IQ = 4.6mA, ISD = 1µA, 4mm × 4mm QFN-24 and TSSOP-16E Packages LT3505 36V with Transient Protection to 40V, 1.4A (IOUT), 3MHz, High Efficiency Step-Down DC/DC Converter VIN: 3.6V to 34V, VOUT(MIN) = 0.78V, IQ = 2mA, ISD = 2µA, 3mm × 3mm DFN-8 and MSOP-8E Packages LT3500 36V, 40VMAX, 2.5MHz High Efficiency Step-Down DC/DC Converter and LDO Controller VIN: 3.6V to 36V, VOUT(MIN) = 0.8V, IQ = 2.5mA, ISD = 10µA, 3mm × 3mm DFN-10 Package LT3507 36V, 2.5MHz, Triple (2.4A + 1.5A + 1.5A (IOUT)) with LDO Controller High VIN: 4V to 36V, VOUT(MIN) = 0.8V, IQ = 7mA, ISD < 1µA, Efficiency Step-Down DC/DC Converter 5mm × 7mm QFN-38 Package LT3437 60V, 400mA (IOUT), Micropower Step-Down DC/DC Converter with Burst VIN: 3.3V to 60V, VOUT(MIN) = 1.25V, IQ = 100µA, ISD < 1µA, Mode Operation 3mm × 3mm DFN-10 and TSSOP-16E Packages LT1976/LT1977 60V, 1.2A (IOUT), 200kHz/500kHz, High Efficiency Step-Down DC/DC Converters with Burst Mode Operation VIN: 3.3V to 60V, VOUT(MIN) = 1.20V, IQ = 100µA, ISD < 1µA, TSSOP-16E Package LT3434/LT3435 60V, 2.4A (IOUT), 200kHz/500kHz, High Efficiency Step-Down DC/DC Converters with Burst Mode Operation VIN: 3.3V to 60V, VOUT(MIN) = 1.2V, IQ = 100µA, ISD < 1µA, TSSOP-16E Package LT1936 36V, 1.4A (IOUT), 500kHz, High Efficiency Step-Down DC/DC Converter VIN: 3.6V to 36V, VOUT(MIN) = 1.2V, IQ = 1.9mA, ISD < 1µA, MS8E Package LT3493 36V, 1.4A (IOUT), 750kHz High Efficiency Step-Down DC/DC Converter VIN: 3.6V to 36V, VOUT(MIN) = 0.8V, IQ = 1.9mA, ISD < 1µA, 2mm × 3mm DFN-6 Package LT1766 60V, 1.2A (IOUT), 200kHz, High Efficiency Step-Down DC/DC Converter VIN: 5.5V to 60V, VOUT(MIN) = 1.20V, IQ = 2.5mA, ISD < 25µA, TSSOP-16 and TSSOP-16E Packages 3980fa 24 Linear Technology Corporation 1630 McCarthy Blvd., Milpitas, CA 95035-7417 For more information www.linear.com/LT3980 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com/LT3980 LT 1013 REV A • PRINTED IN USA LINEAR TECHNOLOGY CORPORATION 2009