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MIC4680 1A 200kHz SuperSwitcherTM Buck Regulator General Description The MIC4680 SuperSwitcherTM is an easy-to-use fixed or adjustable output voltage step-down (buck) switch-mode voltage regulator. The 200kHz MIC4680 achieves up to 1.3A of continuous output current over a wide input range in a 8-pin SOIC. The MIC4680 is available in 3.3V and 5V fixed output versions or adjustable output down to 1.25V. The MIC4680 has an input voltage range of 4V to 34V, with excellent line, load, and transient response. The regulator performs cycle-by-cycle current limiting and thermal shutdown for protection under fault conditions. In shutdown mode, the regulator draws less than 2A of standby current. The MIC4680 SuperSwitcherTM regulator requires a minimum number of external components and can operate using a standard series of inductors and capacitors. Frequency compensation is provided internally for fast transient response and ease of use. The MIC4680 is available in the 8-pin SOIC with a -40C to +125C junction temperature range. Features * * * * * * * * * * * SOIC-8 package with up to 1.3A output current All surface mount solution Only 4 external components required Fixed 200kHz operation 3.3V, 5V, and adjustable output versions Internally compensated with fast transient response Wide 4V to 34V operating input voltage range Less than 2A typical shutdown-mode current Up to 90% efficiency Thermal shutdown Overcurrent protection Applications * * * * * * * * Simple 1A high-efficiency step-down (buck) regulator Replacement of TO-220 and TO-263 designs Efficient pre-regulator (5V to 2.5V, 12V to 3.3V, etc.) On-card switching regulators Positive-to-negative converter (inverting buck-boost) Simple battery charger Negative boost converter Higher output current regulator using external FET Typical Application +6V to +34V C1 15F 35V SHUTDOWN ENABLE MIC4680-3.3BM 2 IN SHDN GND 5-8 SW FB 3 L1 68H 3.3V/1A C2 220F 16V 1 4 +5V to +34V C1 15F 35V SHUTDOWN ENABLE 2 MIC4680BM IN SW SHDN GND 5-8 3 L1 68H R1 3.01k R2 2.94k 2.5V/1A C2 220F 16V 1 Power SOIC-8 D1 B260A or SS26 FB 4 Power SOIC-8 D1 B260A or SS26 Fixed Regulator Circuit Adjustable Regulator Circuit SuperSwitcher is a trademark of Micrel, Inc. Micrel Inc. * 2180 Fortune Drive * San Jose, CA 95131 * USA * tel +1 (408) 944-0800 * fax + 1 (408) 474-1000 * http://www.micrel.com March 2008 M9999-032808 Micrel, Inc. MIC4680 Ordering Information Part Number Standard MIC4680BM MIC4680-3.3BM MIC4680-5.0BM Pb-Free MIC4680YM MIC4680-3.3YM MIC4680-5.0YM Voltage Adj. 3.3V 5.0V Junction Temp. Range -40C to +125C -40C to +125C -40C to +125C Package 8-Pin SOIC 8-Pin SOIC 8-Pin SOIC Pin Configuration SHDN 1 IN 2 SW 3 FB 4 8-Pin SIOC (M) 8 GND 7 GND 6 GND 5 GND Pin Description Pin Number 1 2 3 4 5-8 Pin Name SHDN VIN SW FB GND Pin Function Shutdown (Input): Logic low enables regulator. Logic high (>1.6V) shuts down regulator. Supply Voltage (Input): Unregulated +4V to +34V supply voltage. Switch (Output): Emitter of NPN output switch. Connect to external storage inductor and Shottky diode. Feedback (Input): Connect to output on fixed output voltage versions, or to 1.23V-tap of voltage-divider network for adjustable version. Ground March 2008 2 M9999-032808 Micrel, Inc. MIC4680 Absolute Maximum Ratings(1) Supply Voltage (VIN)(3) ..................................................+38V Shutdown Voltage (VSHDN)............................. -0.3V to +38V Steady-State Output Switch Voltage (VSW) ....................-1V Feedback Voltage [Adjustable] (VFB) ...........................+12V Storage Temperature (Ts) .........................-65C to +150C EDS Rating(5) Operating Ratings(2) Supply voltage (VIN)(4)....................................... +4V to +34V Junction Temperature (TJ) ....................................... +125C Package Thermal Resistance(6) SIOC (JA)..........................................................63C/W Electrical Characteristics VIN = 12V; ILOAD = 500mA; TJ = 25C, bold values indicate -40C TJ +125C, Note 7; unless noted. Parameter MIC4680 [Adjustable] Feedback Voltage (1%) (1%) 8V VIN 34V, 0.1A ILOAD 1A, VOUT = 5V Maximum Duty Cycle Output Leakage Current Quiescent Current MIC4680-3.3 Output Voltage (1%) (3%) 6V VIN 34V, 0.1A ILOAD 1A Maximum Duty Cycle Output Leakage Current Quiescent Current MIC4680-5.0 Output Voltage (1%) (3%) 8V VIN 34V, 0.1A ILOAD 1A Maximum Duty Cycle Output Leakage Current Quiescent Current MIC4680/-3.3/-5.0 Frequency Fold Back Oscillator Frequency Saturation Voltage Short Circuit Current Limit Standby Quiescent Current IOUT = 1A VFB = 0V, see Test Circuit VSHDN = VIN VSHDN = 5V (regulator off) 1.3 30 180 50 200 1.4 1.8 1.5 30 100 100 220 1.8 2.5 kHz kHz V A A A VFB = 4.0V VIN = 34V, VSHDN = 5V, VSW = 0V VIN = 34V, VSHDN = 5V, VSW = -1V VFB = 6.0V 4.950 4.85 4.800 4.750 93 5.0 5.0 97 50 4 7 500 20 12 5.05 5.15 5.200 5.250 V V V V % A mA mA VFB = 2.5V VIN = 34V, VSHDN = 5V, VSW = 0V VIN = 34V, VSHDN = 5V, VSW = -1V VFB = 4.0V 3.266 3.201 3.168 3.135 93 3.3 3.3 97 50 4 7 500 20 12 3.333 3.399 3.432 3.465 V V V V % A mA mA VFB = 1.0V VIN = 34V, VSHDN = 5V, VSW = 0V VIN = 34V, VSHDN = 5V, VSW = -1V VFB = 1.5V 1.217 1.205 1.193 1.180 93 1.230 1.230 97 50 4 7 500 20 12 1.243 1.255 1.267 1.280 V V V V % A mA mA Condition Min Typ Max Units March 2008 3 M9999-032808 Micrel, Inc. Parameter Shutdown Input Logic Level Shutdown Input Current Thermal Shutdown Notes: 1. Exceeding the absolute maximum rating may damage the device. 2. The device is not guaranteed to function outside its operating rating. 3. Absolute maximum rating is intended for voltage transients only, prolonged dc operation is not recommended. 4. VIN(min) = VOUT + 2.5V or 4V whichever is greater. 5. Devices are ESD sensitive. Handling precautions recommended. 6. Measured on 1" square of 1 oz. copper FR4 printed circuit board connected to the device ground leads. 7. Test at TA = +85C, guaranteed by design, and characterized to TJ = +125C. MIC4680 Condition regulator off regulator on VSHDN = 5V (regulator off) VSHDN = 0V (regulator on) -10 -10 Min 2 Typ 1.6 1.0 -0.5 -1.5 160 0.8 10 10 Max Units V V A A C Test Circuit +12V Device Under Test 2 IN SHDN GND SOIC-8 5-8 SW FB 3 68H SHUTDOWN ENABLE 1 4 I Current Limit Test Circuit Shutdown Input Behavior OFF ON 0.8V 0V 1V 1.6V 2V VIN(max) Shutdown Hysteresis March 2008 4 M9999-032808 Micrel, Inc. MIC4680 Typical Characteristics 5.06 OUTPUT VOLTAGE (V) 5.05 5.04 5.03 5.02 5.01 5.00 4.99 4.98 4.97 4.96 Line Regulation OUTPUT VOLTAGE (V) 5.04 Load Regulation 100 VIN = 12V VOUT = 5V Shutdown Current vs. Input Voltage IOUT = 1.0A 5.02 80 CURRENT (A) 60 40 20 5.00 4.98 4.96 0 5 10 15 20 25 30 INPUT VOLTAGE (V) 35 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 OUTPUT CURRENT (A) 0 0 5 10 15 20 25 30 INPUT VOLTAGE (V) 35 4.0 3.5 CURRENT (A) 3.0 2.5 2.0 1.5 1.0 0.5 Shutdown Current vs. Temperature OUTPUT VOLTAGE (V) VIN = 12V VSHDN = VIN 6 5 Current Limit Characteristic 202 201 FREQUENCY (kHz) 200 199 198 197 196 0 Frequency vs. Supply Voltage 4 3 2 1 0 VIN = 12V 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 OUTPUT CURRENT (A) 0 -50 -25 0 25 50 75 100 125 TEMPERATURE (C) 5 10 15 20 25 30 SUPPLY VOLTAGE (V) 35 220 Frequency vs. Temperature FEEDBACK VOLTAGE (V) 1.242 1.240 1.238 1.236 1.234 1.232 1.230 Feedback Voltage vs. Temperature SATURATION VOLTAGE (V) 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 Saturation Voltage vs. Temperature FREQUENCY (kHz) 210 200 190 180 -50 -25 0 25 50 75 100 125 TEMPERATURE (C) VIN = 12V VOUT = 5V IOUT = 1A VIN = 12V VOUT = 5V ILOAD = 1A 1.228 -50 -25 0 25 50 75 100 125 150 TEMPERATURE (C) 0 -50 -25 0 25 50 75 100 125 TEMPERATURE (C) 80 70 EFFICIENCY (%) 3.3V Output Efficiency 90 80 EFFICIENCY (%) 70 60 50 40 30 20 10 0 12V 5V Output Efficiency EFFICIENCY (%) 60 50 40 30 20 10 0 0 12V 24V 6V 24V 7V 100 90 80 70 60 12V Output Efficiency 15V 24V 0.2 0.4 0.6 0.8 1.0 1.2 1.4 OUTPUT CURRENT (A) 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 OUTPUT CURRENT (A) 50 40 30 20 10 0 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 OUTPUT CURRENT (A) March 2008 5 M9999-032808 Micrel, Inc. MIC4680 1.5 1.4 1.3 1.2 1.1 OUTPUT CURRENT (A) 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 0 5 Safe Operating Area Minimum Current Limit Note VOUT = 5V TA = 60C Demonstration board layout 10 15 20 25 INPUT VOLTAGE (V) 30 35 Functional Characteristics Frequency Foldback The MIC4680 folds the switching frequency back during a hard short-circuit condition to reduce the energy per cycle and protect the device. March 2008 6 M9999-032808 Micrel, Inc. MIC4680 Bode Plots The following bode plots show that the MIC4680 is stable over all conditions using a 68F inductor (L) and a 220F output capacitor (COUT). To assure stability, it is a good practice to maintain a phase margin of greater than 35. March 2008 7 M9999-032808 Micrel, Inc. MIC4680 Functional Diagrams V IN IN SHDN Internal Regulator 200kHz Oscillator Thermal Shutdown Current Limit Comparator Driver Reset 1A Switch SW VOUT COUT FB Error Amp MIC4680-x.x 1.23V Bandgap Reference GND Fixed Regulator VIN IN SHDN Internal Regulator 200kHz Oscillator Thermal Shutdown Current Limit R1 VOUT = VREF + 1 R2 V R1 = R2 OUT - 1 VREF VREF = 1.23V Comparator Driver Reset 1A Switch R1 FB Error Amp MIC4680 [adj.] 1.23V Bandgap Reference R2 SW VOUT COUT Adjustable Regulator March 2008 8 M9999-032808 Micrel, Inc. MIC4680 Functional Description The MIC4680 is a variable duty cycle switch-mode regulator with an internal power switch. Refer to the block diagrams. Supply Voltage The MIC4680 operates from a +4V to +34V unregulated input. Highest efficiency operation is from a supply voltage around +15V. See the efficiency curves. Enable/Shutdown The shutdown (SHDN) input is TTL compatible. Ground the input if unused. A logic-low enables the regulator. A logic-high shuts down the internal regulator which reduces the current to typically 1.5A when VSHDN = VIN = 12V and 30A when VSHDN = 5V. See "Shutdown Input Behavior: Shutdown Hysteresis." Feedback Fixed-voltage versions of the regulator have an internal resistive divider from the feedback (FB) pin. Connect FB directly to the output voltage. Adjustable versions require an external resistive voltage divider from the output voltage to ground, center tapped to the FB pin. See Figure 6b for recommended resistor values Duty Cycle Control A fixed-gain error amplifier compares the feedback signal with a 1.23V bandgap voltage reference. The resulting error amplifier output voltage is compared to a 200kHz sawtooth waveform to produce a voltage controlled variable duty cycle output. A higher feedback voltage increases the error amplifier output voltage. A higher error amplifier voltage (comparator inverting input) causes the comparator to detect only the peaks of the sawtooth, reducing the duty cycle of the comparator output. A lower feedback voltage increases the duty cycle. The MIC4680 uses a voltagemode control architecture. Output Switching When the internal switch is on, an increasing current flows from the supply VIN, through external storage inductor L1, to output capacitor COUT and the load. Energy is stored in the inductor as the current increases with time. When the internal switch is turned off, the collapse of the magnetic field in L1 forces current to flow through fast recovery diode D1, charging COUT. Output Capacitor External output capacitor COUT provides stabilization and reduces ripple. See "Bode Plots" for additional information. Return Paths During the on portion of the cycle, the output capacitor and load currents return to the supply ground. During the off portion of the cycle, current is being supplied to the output capacitor and load by storage inductor L1, which means that D1 is part of the high-current return path. March 2008 9 M9999-032808 Micrel, Inc. MIC4680 Applications Information Adjustable Regulators Adjustable regulators require a 1.23V feedback signal. Recommended voltage-divider resistor values for common output voltages are included in Figure 1b. For other voltages, the resistor values can be determined using the following formulas: R1 VOUT = VREF + 1 R2 V R1 R1 = R2 OUT - 1 , R2 = V VOUT REF -1 VREF VREF = 1.23V SHUTDOWN ENABLE V IN CIN 2 MIC4680BM IN SW SHDN GND 5-8 3 L1 R1 VOUT 1 FB 4 D1 R2 COUT Figure 1a. Adjustable Regulator Circuit VOUT 1.8V 2.5V 3.3V 5.0V 6.0V * ** *** R1* 3.01k 3.01k 3.01k 3.01k 3.01k R2* 6.495k 2.915k 1.788k 982 776 CIN D1 2A 60V Schottky L1 68H 1.5A COUT 15F 35V AVX TPSE156035R0200 B260A Vishay-Diode, Inc*** or SS26 General Semiconductor Coiltronics UP2B-680 or Sumida CDRH125-680MC** or Sumida CDRH124-680MC** 220F 10V AVX TPSE227010R0060 All resistors 1% Shielded magnetics for low RFI applications Vishay-Diode, Inc. (805) 446-48600 Nearest available resistor values Figure 1b. Recommended Components for Common Output Voltages March 2008 10 M9999-032808 Micrel, Inc. MIC4680 Thermal Considerations The MIC4680 SuperSwitcher features the power-SOIC8. This package has a standard 8-pin small-outline package profile but with much higher power dissipation than a standard SOIC-8. The MIC4680 SuperSwitcher is the first dc-to-dc converter to take full advantage of this package. The reason that the power SOIC-8 has higher power dissipation (lower thermal resistance) is that pins 5 though 8 and the die-attach paddle are a single piece of metal. The die is attached to the paddle with thermally conductive adhesive. This provides a low thermal resistance path from the junction of the die to the ground pins. This design significantly improves package power dissipation by allowing excellent heat transfer through the ground leads to the printed circuit board. One of the limitation of the maximum output current on any MIC4680 design is the junction-to-ambient thermal resistance (JA) of the design (package and ground plane).Examining JA in more detail: JA = (JC + CA) where: JC = junction-to-case thermal resistance CA = case-to-ambient thermal resistance JC is a relatively constant 20C/W for a power SOIC-8. CA is dependent on layout and is primarily governed by the connection of pins 5 though 8 to the ground plane. The purpose of the ground plane is to function as a heat sink. JA is ideally 63C/W but will vary depending on the size of the ground plane to which the power SOIC-8 is attached. Determining Ground-Plane Heat-Sink Area There are two methods of determining the minimum ground plane area required by the MIC4680. Quick Method Make sure that MIC4680 pins 5 though 8 are connected to a ground plane with a minimum area of 6cm2. This ground plane should be as close to the MIC4680 as possible. The area maybe distributed in any shape around the package or on any pcb layer as long as there is good thermal contact to pins 5 though 8. This ground plane area is more than sufficient for most designs. SOIC-8 JA JC CA AM BIE N ground plane heat sink area T printed circuit board Figure 2. Power SOIC-8 Cross Section Minimum Copper/Maximum Current Method Using Figure 3, for a given input voltage range, determine the minimum ground-plane heat-sink area required for the application's maximum output current. Figure 3 assumes a constant die temperature of 75C above ambient. 1.5 8V OUTPUT CURRENT (I) 1.0 12V 24V 34V 0.5 TA = 50C Minimum Current Limit = 1.3A 0 0 5 10 15 20 25 AREA (cm 2) Figure 3. Output Current vs. Ground Plane Area When designing with the MIC4680, it is a good practice to connect pins 5 through 8 to the largest ground plane that is practical for the specific design. Checking the Maximum Junction Temperature: For this example, with an output power (POUT) of 5W, (5V output at 1A maximum with VIN = 12V) and 65C maximum ambient temperature, what is the maximum junction temperature? Referring to the "Typical Characteristics: 5V Output Efficiency" graph, read the efficiency () for 1A output current at VIN = 12V or perform you own measurement. = 79% The efficiency is used to determine how much of the output power (POUT) is dissipated in the regulator circuit (PD). March 2008 11 M9999-032808 Micrel, Inc. PD = POUT - POUT MIC4680 PD = 5W - 5W 0.79 PD = 1.33W Calculate the worst-case junction temperature: TJ = PD(IC)JC + (TC - TA) + TA(max) where: TJ = MIC4680 junction temperature PD(IC) = MIC4680 power dissipation JC = junction-to-case thermal resistance. The JC for the MIC4680's power-SOIC-8 is approximately 20C/W. (Also see Figure 1.) TC = "pin" temperature measurement taken at the entry point of pins 6 or 7 into the plastic package at the ambient temperature (TA) at which TC is measured. TA = ambient temperature at which TC is measured. TA(max) = maximum ambient operating temp. for the specific design. Calculating the maximum junction temperature given a maximum ambient temperature of 65C: TJ = 1.064 x 20C/W + (45C - 25C) + 65C TJ = 106.3C This value is less than the allowable maximum operating junction temperature of 125C as listed in "Operating Ratings." Typical thermal shutdown is 160C and is listed in "Electrical Characteristics." Increasing the Maximum Output Current The maximum output current at high input voltages can be increased for a given board layout. The additional three components shown in Figure 4 will reduce the overall loss in the MIC4680 by about 20% at high VIN and high IOUT. Even higher output current can be achieved by using the MIC4680 to switch an external FET. See Figure 9 for a 5A supply with current limiting. J1 VIN 4V to +34V C2 0.1F 50V S1 NKK G12AP Layout Considerations Layout is very important when designing any switching regulator. Rapidly changing switching currents through the printed circuit board traces and stray inductance can generate voltage transients which can cause problems. To minimize stray inductance and ground loops, keep trace lengths, indicated by the heavy lines in Figure 5, as short as possible. For example, keep D1 close to pin 3 and pins 5 through 8, keep L1 away from sensitive node FB, and keep CIN close to pin 2 and pins 5 though 8. See "Applications Information: Thermal Considerations" for ground plane layout. The feedback pin should be kept as far way from the switching elements (usually L1 and D1) as possible. A circuit with sample layouts is provided. See Figure 6a through 6e. MIC4680BM IN SW SHDN GND 5678 3 FB 1N4148 2.2nF D1 Figure 4. Increasing Maximum Output Current at High Input Voltages V IN +4V to +34V CIN Power SOIC-8 MIC4680BM 2 IN SHDN GND 5678 SW FB 3 L1 68H COUT VOUT R1 R2 GND Load 1 4 D1 Figure 5. Critical Traces for Layout U1 MIC4680BM 2 IN SHDN GND SOIC-8 5-8 SW FB 3 L1 68H R1 3.01k R2 6.49k 1 J2 VOUT 1A C3* optional R3 2.94k 3 C1 15F 35V J3 GND OFF ON 1 4 D1 B260A or SS26 R6 optional R4 1.78k 5 R5 7 C4 220F 10V C5 0.1F 50V J4 GND JP1a 1.8V JP1b 2.5V JP1c 3.3V * C3 can be used to provide additional stability and improved transient response. 2 4 6 8 JP1d 5.0V Figure 6a. Evaluation Board Schematic Diagram March 2008 12 M9999-032808 Micrel, Inc. MIC4680 Printed Circuit Board Layouts Figure 6b. Top-Side Silk Screen Figure 6d. Bottom-Side Silk Screen Figure 6c. Top-Side Copper Figure 6e. Bottom-Side Copper Abbreviated Bill of Materials (Critical Components) Reference C1 C4 D1 L1 Part Number TPSD156M035R0300 ECE-A1HFS470 TPSD227M010R0150 B260A SS26 UP2B-680 CDH115-680MC CDRH124-680MC U1 Notes: 1. AVX: www.avxcorp.com 2. Panasonic: www.maco.panasonic.co.jp/eccd/index.html 3. Vishay-Diodes, Inc.: www.diodes.com 4. Coiltronics: www.coiltronics.com 5. Sumida: www.sumida.com 6. Micrel, Inc.: www.micrel.com Manufacturer AVX1 Panasonic AVX Vishay-Diodes, Inc.3 General Semiconductor Coiltronics4 Sumida Micrel 5 2 Description 15F 35V 47F 50V, 8mm x 11.5mm 220F 10V Schottky 68H, 1.5A, nonshielded 68H, 1.5A, nonshielded 68H, 1.5A, shielded 1A 200kHz power-SO-8 buck regulator Qty. 1 1 1 1 Sumida (6) MIC4680BM 1 March 2008 13 M9999-032808 Micrel, Inc. MIC4680 Application Circuits For continuously updated circuits using the MIC4680, see Application Hint 37 at www.micrel.com. J1 +34V max. Figure 7. Constant Current and Constant Voltage Battery Charger Figure 8. +12V to -12V/150mA Buck-Boost Converter +4.5V to +17V U1 MIC4680BM MIC4417BM4 2 IN SHDN GND SOIC-8 5-8 SW FB 3 Si4425DY 3.3V/5A 1 4 * I SAT = 8A GND Figure 9. 5V to 3.3V/5A Power Supply March 2008 14 M9999-032808 Micrel, Inc. MIC4680 Package Information 8-Pin SOIC (M) MICREL, INC. 2180 FORTUNE DRIVE SAN JOSE, CA 95131 USA TEL +1 (408) 944-0800 FAX +1 (408) 474-1000 WEB http:/www.micrel.com The information furnished by Micrel in this data sheet is believed to be accurate and reliable. However, no responsibility is assumed by Micrel for its use. Micrel reserves the right to change circuitry and specifications at any time without notification to the customer. Micrel Products are not designed or authorized for use as components in life support appliances, devices or systems where malfunction of a product can reasonably be expected to result in personal injury. Life support devices or systems are devices or systems that (a) are intended for surgical implant into the body or (b) support or sustain life, and whose failure to perform can be reasonably expected to result in a significant injury to the user. A Purchaser's use or sale of Micrel Products for use in life support appliances, devices or systems is a Purchaser's own risk and Purchaser agrees to fully indemnify Micrel for any damages resulting from such use or sale. (c) 2000 Micrel, Incorporated. March 2008 15 M9999-032808 |
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