Features. Applications 3.3V/1A SHUTDOWN ENABLE 16V

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1 A khz SuperSwitcher Buck Regulator General Description The SuperSwitcher is an easy-to-use fixed or adjustable output voltage step-down (buck) switch-mode voltage regulator. The khz achieves up to.a of continuous output current over a wide input range in a 8-pin SOIC. The is available in. and 5 fixed output versions or adjustable output down to.5. The has an input voltage range of to, 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 µa of standby current. The SuperSwitcher 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 is available in the 8-pin SOIC with a C to +5 C junction temperature range. Features SOIC-8 package with up to.a output current All surface mount solution Only external components required Fixed khz operation., 5, and adjustable output versions Internally compensated with fast transient response Wide to operating input voltage range Less than µa typical shutdown-mode current Up to 9% efficiency Thermal shutdown Overcurrent protection Applications Simple A high-efficiency step-down (buck) regulator Replacement of TO- and TO-6 designs Efficient pre-regulator (5 to.5, to., 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 SHUTDOWN ENABLE +6 to + C 5µF 5 Power SOIC-8 -.BM IN SW SHDN FB 5 8 L 68µH D B6A or SS6./A C µf 6 SHUTDOWN ENABLE BM C IN SW 5µF 5 SHDN FB Power SOIC to + L 68µH D B6A or SS6 R.k R.9k.5/A C µf 6 Fixed Regulator Circuit Adjustable Regulator Circuit SuperSwitcher is a trademark of Micrel, Inc. Micrel Inc. 8 Fortune Drive San Jose, CA 95 USA tel + (8) 9-8 fax + (8) 7- March 8 M

2 Ordering Information Part Number Standard Pb-Free oltage Junction Temp. Range Package BM YM Adj. C to +5 C 8-Pin SOIC -.BM -.YM. C to +5 C 8-Pin SOIC -5.BM -5.YM 5. C to +5 C 8-Pin SOIC Pin Configuration SHDN 8 IN 7 SW 6 FB 5 8-Pin SIOC (M) Pin Description Pin Number Pin Name Pin Function SHDN Shutdown (Input): Logic low enables regulator. Logic high (>.6) shuts down regulator. IN Supply oltage (Input): Unregulated + to + supply voltage. SW Switch (Output): Emitter of NPN output switch. Connect to external storage inductor and Shottky diode. FB Feedback (Input): Connect to output on fixed output voltage versions, or to.-tap of voltage-divider network for adjustable version. 5 8 Ground March 8 M

3 Absolute Maximum Ratings () Supply oltage ( IN ) ()...+8 Shutdown oltage ( SHDN ).... to +8 Steady-State Output Switch oltage ( SW )... Feedback oltage [Adjustable] ( FB )...+ Storage Temperature (T s ) C to +5 C EDS Rating (5) Operating Ratings () Supply voltage ( IN ) ()... + to + Junction Temperature (T J ) C Package Thermal Resistance (6) SIOC (θ JA )...6 C/W Electrical Characteristics IN = ; I LOAD = 5mA; T J = 5 C, bold values indicate C T J +5 C, Note 7; unless noted. Parameter Condition Min Typ Max Units [Adjustable] Feedback oltage (±%) (±%) March 8 M IN,.A I LOAD A, OUT = Maximum Duty Cycle FB = % Output Leakage Current IN =, SHDN = 5, SW = 5 5 µa IN =, SHDN = 5, SW = ma Quiescent Current FB =.5 7 ma -. Output oltage (±%) (±%) IN,.A I LOAD A Maximum Duty Cycle FB = % Output Leakage Current IN =, SHDN = 5, SW = 5 5 µa IN =, SHDN = 5, SW = ma Quiescent Current FB =. 7 ma -5. Output oltage (±%) (±%) IN,.A I LOAD A Maximum Duty Cycle FB = % Output Leakage Current IN =, SHDN = 5, SW = 5 5 µa IN =, SHDN = 5, SW = ma Quiescent Current FB = 6. 7 ma /-./-5. Frequency Fold Back 5 khz Oscillator Frequency 8 khz Saturation oltage I OUT = A..8 Short Circuit Current Limit Standby Quiescent Current FB =, see Test Circuit..8.5 A SHDN = IN.5 µa SHDN = 5 (regulator off) µa

4 Parameter Condition Min Typ Max Units Shutdown Input Logic Level regulator off.6 regulator on..8 Shutdown Input Current SHDN = 5 (regulator off).5 µa SHDN = (regulator on).5 µa Thermal Shutdown 6 C Notes:. Exceeding the absolute maximum rating may damage the device.. The device is not guaranteed to function outside its operating rating.. Absolute maximum rating is intended for voltage transients only, prolonged dc operation is not recommended.. IN(min) = OUT +.5 or whichever is greater. 5. Devices are ESD sensitive. Handling precautions recommended. 6. Measured on " square of oz. copper FR printed circuit board connected to the device ground leads. 7. Test at T A = +85 C, guaranteed by design, and characterized to T J = +5 C. Test Circuit + Device Under Test IN SW 68µH SHUTDOWN ENABLE SHDN FB I SOIC Current Limit Test Circuit Shutdown Input Behavior OFF ON.8.6 IN(max) Shutdown Hysteresis March 8 M

5 Typical Characteristics OUTPUT OLTAGE () CURRENT (µa) FREQUENCY (khz) EFFICIENCY (%) Line Regulation I OUT =.A INPUT OLTAGE () TEMPERATURE ( C) 9 Shutdown Current vs. Temperature IN = SHDN = IN TEMPERATURE ( C) Frequency vs. Temperature. Output Efficiency OUTPUT CURRENT (A) OUTPUT OLTAGE () FEEDBACK OLTAGE () OUTPUT OLTAGE () Load Regulation IN = OUT = OUTPUT CURRENT (A) 6 5 Current Limit Characteristic IN = OUTPUT CURRENT (A) Feedback oltage vs. Temperature IN = OUT =5 I OUT =A TEMPERATURE ( C) EFFICIENCY (%) Output Efficiency OUTPUT CURRENT (A) CURRENT (µa) FREQUENCY (khz) SATURATION OLTAGE () EFFICIENCY (%) Shutdown Current vs. Input oltage INPUT OLTAGE () Frequency vs. Supply oltage SUPPLY OLTAGE () Saturation oltage vs. Temperature IN = OUT =5 I LOAD =A TEMPERATURE ( C) Output Efficiency OUTPUT CURRENT (A) March 8 5 M

6 OUTPUT CURRENT (A) Safe Operating Area OUT =5 T A =6 C Demonstration board layout Minimum Current Limit Note INPUT OLTAGE () Functional Characteristics Frequency Foldback The folds the switching frequency back during a hard short-circuit condition to reduce the energy per cycle and protect the device. March 8 6 M

7 Bode Plots The following bode plots show that the is stable over all conditions using a 68µF inductor (L) and a µf output capacitor (C OUT ). To assure stability, it is a good practice to maintain a phase margin of greater than 5. March 8 7 M

8 Functional Diagrams IN IN SHDN Internal Regulator khz Oscillator Thermal Shutdown Current Limit Comparator Reset Driver A Switch SW OUT C OUT FB -x.x Error Amp. Bandgap Reference Fixed Regulator IN IN SHDN Internal Regulator R OUT = REF + R khz Oscillator Thermal Shutdown Current Limit R R = OUT - REF REF =. Comparator Reset Driver A Switch SW OUT C OUT [adj.] Error Amp. Bandgap Reference FB R R Adjustable Regulator March 8 8 M

9 Functional Description The is a variable duty cycle switch-mode regulator with an internal power switch. Refer to the block diagrams. Supply oltage The operates from a + to + unregulated input. Highest efficiency operation is from a supply voltage around +5. 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.5µa when SHDN = IN = and µa when SHDN = 5. 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. bandgap voltage reference. The resulting error amplifier output voltage is compared to a khz 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 uses a voltagemode control architecture. Output Switching When the internal switch is on, an increasing current flows from the supply IN, through external storage inductor L, to output capacitor C OUT 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 L forces current to flow through fast recovery diode D, charging C OUT. Output Capacitor External output capacitor C OUT 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 L, which means that D is part of the high-current return path. March 8 9 M

10 Applications Information Adjustable Regulators Adjustable regulators require a. feedback signal. Recommended voltage-divider resistor values for common output voltages are included in Figure b. For other voltages, the resistor values can be determined using the following formulas: OUT R = REF + R OUT R R = R, R = REF OUT REF =. REF SHUTDOWN ENABLE IN C IN BM IN SW SHDN FB 5 8 L R D R Figure a. Adjustable Regulator Circuit OUT C OUT OUT R* R* C IN D L C OUT.8.k 6.95k.5.k.95k..k.788k 5..k 98Ω 6..k 776Ω 5µF 5 AX TPSE565R * All resistors % ** Shielded magnetics for low RFI applications *** ishay-diode, Inc. (85) 6-86 Nearest available resistor values A 6 Schottky B6A ishay-diode, Inc*** or SS6 General Semiconductor 68µH.5A Coiltronics UPB-68 or Sumida CDRH5-68MC** or Sumida CDRH-68MC** Figure b. Recommended Components for Common Output oltages µf AX TPSE7R6 March 8 M

11 Thermal Considerations The SuperSwitcher features the power-soic- 8. This package has a standard 8-pin small-outline package profile but with much higher power dissipation than a standard SOIC-8. The 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 design is the junction-to-ambient thermal resistance (θ JA ) of the design (package and ground plane).examining θ JA in more detail: where: θ JA = (θ JC + θ CA ) θ JC = junction-to-case thermal resistance θ CA = case-to-ambient thermal resistance θ JC is a relatively constant C/W for a power SOIC-8. θ 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. θ JA is ideally 6 C/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. Quick Method Make sure that pins 5 though 8 are connected to a ground plane with a minimum area of 6cm. This ground plane should be as close to the 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 JC JA CA printed circuit board AMBIENT ground plane heat sink area Figure. Power SOIC-8 Cross Section Minimum Copper/Maximum Current Method Using Figure, for a given input voltage range, determine the minimum ground-plane heat-sink area required for the application s maximum output current. Figure assumes a constant die temperature of 75 C above ambient. OUTPUT CURRENT (I) Minimum Current Limit =.A AREA (cm ) T A =5 C Figure. Output Current vs. Ground Plane Area When designing with the, 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 (P OUT ) of 5W, (5 output at A maximum with IN = ) and 65 C maximum ambient temperature, what is the maximum junction temperature? Referring to the Typical Characteristics: 5 Output Efficiency graph, read the efficiency (η) for A output current at IN = or perform you own measurement. η = 79% The efficiency is used to determine how much of the output power (P OUT ) is dissipated in the regulator circuit (P D ). March 8 M

12 P D P D P = η = OUT 5W.79 P OUT 5W P D =.W Calculate the worst-case junction temperature: T J = P D(IC) θ JC + (T C T A ) + T A(max) where: T J = junction temperature P D(IC) = power dissipation θ JC = junction-to-case thermal resistance. The θ JC for the s power-soic-8 is approximately C/W. (Also see Figure.) T C = pin temperature measurement taken at the entry point of pins 6 or 7 into the plastic package at the ambient temperature (T A ) at which T C is measured. T A = ambient temperature at which T C is measured. T A(max) = maximum ambient operating temp. for the specific design. Calculating the maximum junction temperature given a maximum ambient temperature of 65 C: TJ =.6 C/W + (5 C 5 C) + 65 C TJ = 6. C This value is less than the allowable maximum operating junction temperature of 5 C as listed in Operating Ratings. Typical thermal shutdown is 6 C 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 will reduce the overall loss in the by about % at high IN and high I OUT. Even higher output current can be achieved by using the to switch an external FET. See Figure 9 for a 5A supply with current limiting. 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 D close to pin and pins 5 through 8, keep L away from sensitive node FB, and keep C IN close to pin 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 L and D) as possible. A circuit with sample layouts is provided. See Figure 6a through 6e. BM IN SW IN + to + SHDN FB N8.nF D Figure. Increasing Maximum Output Current at High Input oltages C IN BM IN SW SHDN FB Power SOIC D L 68µH C OUT Figure 5. Critical Traces for Layout R R OUT Load J IN to + C.µF 5 U BM IN SW C OFF 5µF SHDN ON 5 S J NKK GAP SOIC * C can be used to provide additional stability and improved transient response. FB D B6A or SS6 L 68µH R6 optional March 8 M R.k R 6.9k JPa.8 C* optional R.9k 5 JPb.5 6 Figure 6a. Evaluation Board Schematic Diagram R.78k 7 JPc. 8 R5 JPd 5. C µf J OUT A C5.µF 5 J

13 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 Part Number Manufacturer Description Qty. C TPSD56M5R AX 5µF 5 ECE-AHFS7 Panasonic 7µF 5, 8mm.5mm C TPSD7MR5 AX µf D B6A ishay-diodes, Inc. Schottky SS6 General Semiconductor L UPB-68 Coiltronics 68µH,.5A, nonshielded CDH5-68MC Sumida 5 68µH,.5A, nonshielded CDRH-68MC Sumida 68µH,.5A, shielded U BM Micrel (6) A khz power-so-8 buck regulator Notes:. AX: Panasonic: ishay-diodes, Inc.: Coiltronics: 5. Sumida: 6. Micrel, Inc.: March 8 M

14 Application Circuits For continuously updated circuits using the, see Application Hint 7 at J + max. Figure 7. Constant Current and Constant oltage Battery Charger Figure 8. + to /5mA Buck-Boost Converter +.5 to +7 U BM MIC7BM IN SW Si5DY./5A SHDN SOIC FB * I SAT = 8A Figure 9. 5 to./5a Power Supply March 8 M

15 Package Information 8-Pin SOIC (M) MICREL, INC. 8 FORTUNE DRIE SAN JOSE, CA 95 USA TEL + (8) 9-8 FAX + (8) 7- WEB 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. Micrel, Incorporated. March 8 5 M