LT3680EMSE#PBF

LT3680 36V, 3.5A, 2.4MHz Step-Down Switching Regulator with 75µA Quiescent Current FEATURES DESCRIPTION Wide Input Voltage Range: 3.6V to 36V ■ 3.5A Maximum Output Current ® ■ Low Ripple (30V), the saturation current should be above 5A. To keep the efficiency high, the series resistance (DCR) should be less than 0.1 , 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.componenttdk.com SLF10145 Shielded Toko www.toko.com D75C D75F Shielded Open Sumida www.sumida.com CDRH74 CR75 CDRH8D43 Shielded Open Shielded NEC www.nec.com MPLC073 MPBI0755 Shielded Shielded where IL(PEAK) is the peak inductor current, IOUT(MAX) is the maximum output load current, and ΔIL is the inductor Rev C 10 For more information www.analog.com LT3680 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 3.5A, 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 LT3680 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 LT3680 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 LT3680 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 LT3680 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 LT3680. A ceramic input capacitor combined with trace or cable inductance forms a high quality (under damped) tank circuit. If the LT3680 circuit is plugged into a live supply, the input voltage can ring to twice its nominal value, possibly exceeding the LT3680’s voltage rating. This situation is easily avoided (see the Hot Plugging Safely section). For space sensitive applications, a 4.7µF ceramic capacitor can be used for local bypassing of the LT3680 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 LT3680 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 LT3680 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 LT3680’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 Rev C For more information www.analog.com 11 LT3680 APPLICATIONS INFORMATION Table 2. Capacitor Vendors VENDOR PHONE URL PART SERIES Panasonic (714) 373-7366 www.panasonic.com Ceramic, COMMANDS Polymer, EEF Series Tantalum Kemet (864) 963-6300 www.kemet.com Sanyo (408) 749-9714 www.sanyovideo.com Ceramic, Tantalum T494, T495 Ceramic, Polymer, POSCAP Tantalum Murata (408) 436-1300 AVX www.murata.com Ceramic www.avxcorp.com Ceramic, Tantalum Taiyo Yuden (864) 963-6300 www.taiyo-yuden.com capacitor. Low ESR is important, so choose one that is intended for use in switching regulators. The ESR should be specified by the supplier, and should be 0.05 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. 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. Table 3 lists several Schottky diodes and their manufacturers. TPS Series Ceramic Table 3. Diode Vendors PART NUMBER VR (V) IAVE (A) VF AT 3A (mV) On Semiconductor MBRA340 40 3 500 Diodes Inc. PDS340 B340A B340LA 40 40 40 3 3 3 500 500 450 Ceramic Capacitors Ceramic capacitors are small, robust and have very low ESR. However, ceramic capacitors can cause problems when used with the LT3680 due to their piezoelectric nature. When in Burst Mode operation, the LT3680’s switching frequency depends on the load current, and at very light loads the LT3680 can excite the ceramic capacitor at audio frequencies, generating audible noise. Since the LT3680 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. Rev C 12 For more information www.analog.com LT3680 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 LT3680 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 LT3680 CURRENT MODE POWER STAGE gm = 5.3mho SW ERROR AMPLIFIER OUTPUT R1 3M ESR 0.8V C1 VC CF CPL FB gm = 500µmho + The LT3680 uses current mode control to regulate the output. This simplifies loop compensation. In particular, the LT3680 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. 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 1A to 3A and back to 1A. – Frequency Compensation POLYMER OR TANTALUM GND RC C1 + CERAMIC R2 CC 3680 F02 Figure 2. Model for Loop Response VOUT 100mV/DIV IL 1A/DIV VIN = 12V VOUT = 3.3V 10µs/DIV 3680 F03 Figure 3. Transient Load Response of the LT3680 Front Page Application as the Load Current is Stepped from 1A to 3A. VOUT = 5V Rev C For more information www.analog.com 13 LT3680 APPLICATIONS INFORMATION Low-Ripple Burst Mode and Pulse-Skip Mode The LT3680 is capable of operating in either Low-Ripple Burst Mode or pulse-skipping mode which are selected using the SYNC pin. See the Synchronization section for details. To enhance efficiency at light loads, the LT3680 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 LT3680 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 LT3680 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 30µA and 90µA respectively during the sleep time. As the load current decreases towards a no load condition, the percentage of time that the LT3680 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 LT3680 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. If low quiescent current is not required the LT3680 can operate in Pulse-Skip mode. The benefit of this mode is that the LT3680 will enter full frequency standard PWM VSW 5V/DIV IL 0.2A/DIV VOUT 10mV/DIV VIN = 12V VOUT = 3.3V ILOAD = 10mA 5µs/DIV Figure 4. Burst Mode Operation 3680 F04 operation at a lower output load current than when in Burst Mode. The front page application circuit will switch at full frequency at output loads higher than about 60mA. Select pulse-skipping mode by applying a clock signal or a DC voltage higher than 0.8V to the SYNC pin. 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 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. The minimum operating voltage of an LT3680 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 LT3680 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 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 Rev C 14 For more information www.analog.com LT3680 APPLICATIONS INFORMATION 6.0 VOUT BD 5.5 BOOST VIN LT3680 GND 4.7µF C3 INPUT VOLTAGE (V) VIN SW TO START (WORST CASE) 5.0 4.5 4.0 TO RUN 3.5 3.0 (5a) For VOUT > 2.8V VOUT = 3.3V TA = 25°C L = 8.2µH f = 700kHz 2.5 2.0 VOUT BD BOOST VIN LT3680 GND 4.7µF VOUT 5.0 TO RUN 4.0 VOUT = 5V TA = 25°C L = 8.2µH f = 700kHz 2.0 BOOST LT3680 6.0 3.0 BD VIN 10000 TO START (WORST CASE) 7.0 SW (5b) For 2.5V < VOUT < 2.8V VIN 100 1000 LOAD CURRENT (mA) 8.0 C3 INPUT VOLTAGE (V) VIN 10 1 D2 1 C3 10 100 1000 LOAD CURRENT (mA) 10000 3680 F06 4.7µF GND SW Figure 6. The Minimum Input Voltage Depends on Output Voltage, Load Current and Boost Circuit 3680 FO5 (5c) For VOUT < 2.5V; VIN(MAX) = 30V Figure 5. Three Circuits For Generating The Boost Voltage 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 LT3680, requiring a higher input voltage to maintain regulation. Soft-Start The RUN/SS pin can be used to soft-start the LT3680, reducing the maximum input current during start-up. The RUN/SS pin is driven through an external RC filter to create a voltage ramp at this pin. Figure 7 shows the startup and shut-down 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 0.3V (this can be ground or a logic output). Rev C For more information www.analog.com 15 LT3680 APPLICATIONS INFORMATION IL 1A/DIV RUN 15k RUN/SS 0.22µF VRUN/SS 2V/DIV GND VOUT 2V/DIV 2ms/DIV 3680 F07 Figure 7. To Soft-Start the LT3680, Add a Resisitor and Capacitor to the RUN/SS Pin Synchronizing the LT3680 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). applications or in battery backup systems where a battery or some other supply is diode OR-ed with the LT3680’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 LT3680’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 LT3680 can pull large currents from the output through the SW pin and the 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 MBRS140 VIN The LT3680 will not enter Burst Mode at low output loads while synchronized to an external clock, but instead will skip pulses to maintain regulation. The LT3680 may be synchronized over a 250kHz to 2MHz range. The RT resistor should be chosen to set the LT3680 switching frequency 20% 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 LT3680 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 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 the inductor is chosen so that it won’t saturate excessively, an LT3680 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 LT3680 is absent. This may occur in battery charging VIN BOOST LT3680 RUN/SS VOUT SW VC GND FB BACKUP 3680 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 LT3680 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 LT3680’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 Rev C 16 For more information www.analog.com LT3680 APPLICATIONS INFORMATION L1 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 LT3680 to additional ground planes within the circuit board and on the bottom side. C2 VOUT CC RRT RC Hot Plugging Safely R2 R1 D1 C1 RPG GND 3680 F09 VIAS TO LOCAL GROUND PLANE VIAS TO VOUT VIAS TO VIN VIAS TO RUN/SS OUTLINE OF LOCAL GROUND PLANE VIAS TO PG VIAS TO SYNC Figure 9. A Good PCB Layout Ensures Proper, Low EMI Operation CLOSING SWITCH SIMULATES HOT PLUG IIN VIN + LOW IMPEDANCE ENERGIZED 24V SUPPLY VIN 20V/DIV DANGER RINGING VIN MAY EXCEED ABSOLUTE MAXIMUM RATING LT3680 4.7µF IIN 10A/DIV STRAY INDUCTANCE DUE TO 6 FEET (2 METERS) OF TWISTED PAIR 0.7W + The small size, robustness and low impedance of ceramic capacitors make them an attractive option for the input bypass capacitor of LT3680 circuits. However, these capacitors can cause problems if the LT3680 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, 0.1µF 20µs/DIV (10a) LT3680 VIN 20V/DIV 4.7µF IIN 10A/DIV (10b) + 22µF 35V AI.EI. + LT3680 20µs/DIV VIN 20V/DIV 4.7µF IIN 10A/DIV (10c) 20µs/DIV 3680 F10 Figure 10. A Well Chosen Input Network Prevents Input Voltage Overshoot and Ensures Reliable Operation when the LT3680 Is Connected to a Live Supply Rev C For more information www.analog.com 17 LT3680 APPLICATIONS INFORMATION and the voltage at the VIN pin of the LT3680 can ring to twice the nominal input voltage, possibly exceeding the LT3680’s rating and damaging the part. If the input supply is poorly controlled or the user will be plugging the LT3680 into an energized supply, the input network should be designed to prevent this overshoot. Figure 10 shows the waveforms that result when an LT3680 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 0.7 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. (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 LT3680, 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. High Temperature Considerations 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. The PCB must provide heat sinking to keep the LT3680 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 LT3680. Place additional vias can reduce thermal resistance further. With these steps, the thermal resistance from die Power dissipation within the LT3680 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 LT3680 power dissipation by the thermal resistance from junction to ambient. Other Linear Technology Publications TYPICAL APPLICATIONS 5V Step-Down Converter VOUT 5V 3.5A VIN 6.3V TO 36V BD VIN RUN/SS ON OFF BOOST 0.47µF VC 10µF LT3680 SW D RT 15k PG SYNC 63.4k 680pF L 4.7µH GND 536k FB f = 600kHz 47µF 100k 3680 TA02 D: ON SEMI MBRA340 L: NEC MPLC0730L4R7 Rev C 18 For more information www.analog.com LT3680 TYPICAL APPLICATIONS 3.3V Step-Down Converter VOUT 3.3V 3.5A VIN 4.4V TO 36V BD VIN RUN/SS ON OFF BOOST L 3.3µH 0.47µF VC 4.7µF SW LT3680 D RT 19k PG SYNC 63.4k 680pF 316k FB GND 22µF 100k f = 600kHz 3680 TA03 D: ON SEMI MBRA340 L: NEC MPLC0730L3R3 2.5V Step-Down Converter VOUT 2.5V 3.5A VIN 4V TO 36V BD VIN RUN/SS ON OFF D2 BOOST 1µF VC 4.7µF LT3680 SW D1 RT 15.4k PG SYNC 63.4k 680pF GND L 3.3µH 215k FB f = 600kHz 47µF 100k 3680 TA04 D1: ON SEMI MBRA340 D2: MBR0540 L: NEC MPLC0730L3R3 Rev C For more information www.analog.com 19 LT3680 TYPICAL APPLICATIONS 5V, 2MHz Step-Down Converter VIN 8.6V TO 22V TRANSIENT TO 36V BD VIN RUN/SS ON OFF VOUT 5V 2.5A BOOST 0.47µF VC 4.7µF SW LT3680 D RT 15k PG SYNC 12.7k 680pF L 2.2µH 536k FB GND 22µF 100k f = 2MHz 3680 TA05 D: ON SEMI MBRA340 L: NEC MPLC0730L2R2 12V Step-Down Converter VOUT 12V 3.5A VIN 15V TO 36V BD VIN RUN/SS ON OFF BOOST 0.47µF VC 10µF SW LT3680 D RT 17.4k PG SYNC 63.4k 680pF L 8.2µH 715k FB GND 47µF 50k f = 600kHz 3680 TA06 D: ON SEMI MBRA340 L: NEC MBP107558R2P 1.8V Step-Down Converter VOUT 1.8V 3.5A VIN 3.5V TO 27V BD VIN RUN/SS ON OFF BOOST 0.47µF VC 4.7µF LT3680 SW D RT 16.9k PG SYNC 78.7k 680pF L 3.3µH GND 127k FB f = 500kHz 47µF 100k 3680 TA08 D: ON SEMI MBRA340 L: NEC MPLC0730L3R3 Rev C 20 For more information www.analog.com LT3680 PACKAGE DESCRIPTION Please refer to http://www.linear.com/product/LT3680#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 Rev C For more information www.analog.com 21 LT3680 PACKAGE DESCRIPTION Please refer to http://www.linear.com/product/LT3680#packaging for the most recent package drawings. MSE Package 10-Lead Plastic MSOP, Exposed Die Pad (Reference LTC DWG # 05-08-1664 Rev I) BOTTOM VIEW OF EXPOSED PAD OPTION 1.88 ±0.102 (.074 ±.004) 5.10 (.201) MIN 1 0.889 ±0.127 (.035 ±.005) 1.68 ±0.102 (.066 ±.004) 0.05 REF 10 0.305 ± 0.038 (.0120 ±.0015) TYP RECOMMENDED SOLDER PAD LAYOUT 3.00 ±0.102 (.118 ±.004) (NOTE 3) DETAIL “B” CORNER TAIL IS PART OF DETAIL “B” THE LEADFRAME FEATURE. FOR REFERENCE ONLY NO MEASUREMENT PURPOSE 10 9 8 7 6 DETAIL “A” 0° – 6° TYP 1 2 3 4 5 GAUGE PLANE 0.53 ±0.152 (.021 ±.006) DETAIL “A” 0.18 (.007) 0.497 ±0.076 (.0196 ±.003) REF 3.00 ±0.102 (.118 ±.004) (NOTE 4) 4.90 ±0.152 (.193 ±.006) 0.254 (.010) 0.29 REF 1.68 (.066) 3.20 – 3.45 (.126 – .136) 0.50 (.0197) BSC 1.88 (.074) SEATING PLANE 0.86 (.034) REF 1.10 (.043) MAX 0.17 – 0.27 (.007 – .011) TYP 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. 0.1016 ±0.0508 (.004 ±.002) MSOP (MSE) 0213 REV I Rev C 22 For more information www.analog.com LT3680 REVISION HISTORY (Revision history begins at Rev C) REV DATE DESCRIPTION C 04/18 Clarified Switch Current Limit Max to 6.6A. PAGE NUMBER 3 Rev C Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. Specifications subject to change without notice. No license For is granted implication or otherwise under any patent or patent rights of Analog Devices. moreby information www.analog.com 23 LT3680 TYPICAL APPLICATION 1.2V Step-Down Converter VOUT 1.2V 3.5A VIN 3.6V TO 27V BD VIN RUN/SS ON OFF BOOST 0.47µF VC 4.7µF LT3680 SW D RT 17k PG SYNC 78.7k 470pF L 3.3µH GND 52.3k FB 100k f = 500kHz 100µF 3680 TA09 D: ON SEMI MBRA340 L: NEC MPLC0730L3R3 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LT1766 60V, 1.2A (IOUT), 200kHz, High Efficiency Step-Down DC/DC Converter VIN: 5.5V to 60V, VOUT(MIN) = 1.2V, IQ = 2.5mA, ISD = 25µA, TSSOP16/E Package LT1767 25V, 1.2A (IOUT), 1.2MHz, High Efficiency Step-Down DC/DC Converter VIN: 3V to 25V, VOUT(MIN) = 1.2V, IQ = 1mA, ISD < 6µA, MS8E Package LT1933 500mA (IOUT), 500kHz Step-Down Switching Regulator in SOT-23 VIN: 3.6V to 36V, VOUT(MIN) = 1.2V, IQ = 1.6mA, ISD < 1µA, ThinSOTTM 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 LT1940 Dual 25V, 1.4A (IOUT), 1.1MHz, High Efficiency Step-Down DC/DC Converter VIN: 3.6V to 25V, VOUT(MIN) = 1.2V, IQ = 3.8mA, ISD < 30µA, TSSOP16E Package 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) = 1.2V, IQ = 100µA, ISD < 1µA, TSSOP16E 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, TSSOP16 Package LT3437 60V, 400mA (IOUT), Micropower Step-Down DC/DC Converter with Burst Mode Operation VIN: 3.3V to 60V, VOUT(MIN) = 1.25V, IQ = 100µA, ISD < 1µA, 3mm × 3mm DFN10 and TSSOP16E 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 DFN10 and MSOP10E 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 DFN10 and MSOP10E Packa ges 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 x 3mm DFN6 Package 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 DFN8 and MSOP8E 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 QFN24 and TSSOP16E 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 DFN10 and MSOP10E 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 DFN10 and MSOP10E Packages Rev C 24 D16845-0-4/18(C) For more information www.analog.com www.analog.com  ANALOG DEVICES, INC. 2007-2018