MIC4690 Micrel MIC4690 500kHz 1A SuperSwitcher™ Buck Regulator General Description Features The MIC4690 SuperSwitcher™ is an easy-to-use, 500kHz step-down PWM voltage regulator. The MIC4690 achieves over 1A of continuous output current over a wide input voltage range in an 8-lead SO (small outline) package. The high switching frequency of the MIC4690 allows the smallest surface-mount inductors and capacitors to be used. Internal compensation ensures fast transient response and a minimum amount of external components. The MIC4690 features a power SO-8 package with a special lead frame that allows over 1A of continuous current. The MIC4690, housed in an SO-8, can replace larger TO-220 and TO-263 packages in many applications. The MIC4690 allows for a high degree of safety. It has a wide input voltage range of 4V to 34V, allowing for it to be used in applications where input voltage transients may be present. Built-in safety features include over-current protection, frequency foldback protection, and thermal shutdown. The MIC4690 is available in an 8-lead SO package with a junction temperature range of –40°C to +125°C. • • • • • • • • • • SO-8 package with over 1A output current Fixed 500kHz operation Wide 4V to 34Vinput voltage range Output voltage adjustable to 1.23V All surface mount solution Internally compensated with fast transient response Up to 85% efficiency Overcurrent protection Frequency foldback short-circuit protection Thermal shutdown Applications • • • • • • • • • Simple 1A step-down (buck) regulator Replacement of TO-220 and TO-263 designs 12V to 5V/3.3V/2.5V/1.8V/1.5V conversion 5V to 2.5V/1.8V/1.5V conversion On-card switching regulators Hard disk drives Cable modems Positive-to-negative converters Simple battery chargers Typical Application MIC4690BM Power SOP-8 2.5V Adjustable Converter !"#$!% µ &' ( ( MIC4690BM Power SOP-8 )* µ µ 1.8V Adjustable Converter 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 April 2005 1 MIC4690 MIC4690 Micrel Ordering Information Part Number Standard Lead-Free Voltage Temperature Range Package MIC4690BM MIC4690YM Adjustable –40°C to +125°C 8-lead SOP Pin Configuration SHDN 1 8 GND VIN 2 7 GND SW 3 6 GND FB 4 5 GND SOP-8 (M) Pin Description Pin Number Pin Name 1 SHDN 2 VIN Supply Voltage (Input): Unregulated +4V to +30V continuous supply voltage, with a maximum +34V transient voltage. 3 SW Switch (Output): Emitter of NPN output switch. Connect to external storage inductor and Schottky diode. 4 FB Feedback (Input): Connect to output on fixed output voltage versions, or to 1.23V-tap of voltage-divider network for adjustable version. 5-8 GND MIC4690 Pin Function Shutdown (Input): Logic low enables regulator. Logic high (>1.5V) shuts down regulator. Ground 2 April 2005 MIC4690 Micrel Absolute Maximum Ratings (Note 1) Operating Ratings (Note 2) Supply Voltage (VIN), Note 3 ...................................... +34V Shutdown Voltage (VSHDN) ............................. –0.3V to VIN Steady-State Output Switch Voltage (VSW) ....... –1V to VIN Feedback Voltage (VFB) .............................................. +12V Storage Temperature (TS) ....................... –65°C to +150°C ESD Rating .............................................................. Note 4 Supply Voltage (VIN) ....................................... +4V to +30V Junction Temperature Range (TJ) ........... –40°C to +125°C Package Thermal Resistance (θJA), Note 5 ........................................................ 63°C/W (θJC), ................................................................... 20°C/W Electrical Characteristics VIN = 12V, VOUT = 5V; ILOAD = 500mA; VSHDN = 0V, TJ = 25°C, unless otherwise noted. Bold values indicate –40°C ≤ TJ ≤ +125°C. Parameter Condition Min Typ Max Units Feedback Voltage (±1%) (±2%) 1.217 1.205 1.230 1.243 1.255 V V 8V ≤ VIN ≤ 30V, 0.1A ≤ ILOAD ≤ 1A, VOUT = 5V 1.193 1.180 1.230 1.267 1.280 V V 90 93 Maximum Duty Cycle VFB = 1.0V Quiescent Current VFB = 1.5V 7 12 mA Standby Quiescent Current VSHDN = 5V (regulator off) 30 100 µA VSHDN = 12V (regulator off) 1.5 VFB = 0V 220 300 KHz 500 550 kHz Frequency Foldback Oscillator Frequency 450 % µA Saturation Voltage IOUT = 1A 1.2 Output Leakage Current VIN = 30V, VSHDN = 5V, VSW = 0V 50 500 µA VIN = 30V, VSHDN = 5V, VSW = –1V 4 20 mA 1.3 2.5 3.0 A 2 1.5 Short Circuit Current Limit VFB = 0V, VOUT = 0V, See Test Circuit Shutdown Pin Input Logic Level regulator off regulator on Shutdown Pin Input Current V V 1.25 0.8 V VSHDN = 5V (regulator off) –10 –0.7 10 µA VSHDN = 0V (regulator on) –10 –1.5 10 µA Thermal Shutdown @ TJ 160 °C Note 1. Exceeding the absolute maximum rating may damage the device. Note 2. With input voltages above the operating rating, the device may be damaged if a short-circuit is applied to the output. The device will otherwise not be damaged up to its absolute maximum voltage rating. Note 3. Absolute maximum rating is intended for voltage transients only, prolonged dc operation is not recommended. Note 4. Devices are ESD sensitive. Handling precautions recommended. Note 5. Measured on 1" square of 1 oz. copper FR4 printed circuit board connected to the device ground leads. April 2005 3 MIC4690 MIC4690 Micrel Test Circuit +12V 2 1 Device Under Test 3 VIN SW SHDN 18µH 4 FB I GND SOP-8 5–8 Current Limit Test Circuit Shutdown Input Behavior OFF ON GUARANTEED ON 0V TYPICAL ON 0.8V 1.25V 2V 1.5V GUARANTEED OFF TYPICAL OFF VIN(max) Shutdown Hysteresis MIC4690 4 April 2005 MIC4690 Micrel Typical Characteristics Quiescent Current vs. Temperature 8.6 1.241 1.239 1.237 1.235 1.233 1.231 VIN = 12V 1.229 VOUT = 5V 1.227 IOUT = 100mA 1.225 1.223 -40 -20 0 20 40 60 80 100120140 TEMPERTURE (°C) 8.5 VIN = 12.0V 8.4 VOUT = 5.0V 8.3 IOUT = 0 8.2 8.1 8 7.9 7.8 7.7 7.6 -40 -20 0 20 40 60 80 100120140 TEMPERATURE (°C) 80 Efficiency vs. Input Voltage 50 40 30 20 VOUT = 5V = 1A I 10 OUT 5 250 400 300 VIN = 12V VOUT = 5V IOUT = 100mA 0 -50 10 15 20 25 30 35 40 INPUT VOLTAGE (V) 0 50 100 Temperature (°C) 150 100 5.005 OUTPUT VOLTAGE (V) 5.010 0 -50 150 0.2 0.4 0.6 0.8 1 1.2 1.4 OUTPUT CURRENT (A) 0 50 100 Temperature (°C) 150 Shutdown Current vs. Temperature 3.5 5.04 5.02 5.00 VIN = 12V VOUT = 5V IOUT = 500mA 4.98 4.96 0 VIN = 12V VOUT = 5V IOUT = 100mA 50 5.06 5.015 0.2 0.4 0.6 0.8 1 1.2 1.4 OUTPUT CURRENT (A) 200 Line Regulation 5.025 5.000 0 EFFICIENCY (%) 500 200 VIN = 12.0V VOUT = 5.0V Frequency Foldback vs. Temperature 300 Load Regulation 5.020 72 600 100 VIN = 12V VOUT = 5V 74 68 0 5 10 15 20 25 30 35 40 INPUT VOLTAGE (V) SHUTDOWN CURRENT (µA) 0 0 76 70 FREQUENCY (kHz) FREQUENCY (kHz) EFFICIENCY (%) 70 60 78 Frequency vs. Temperature 80 OUTPUT VOLTAGE (V) Efficiency vs. Output Current 1.243 CURRENT (mA) VOLTAGE (V) Reference Voltage vs. Temperature 3.0 VSHDN = V = 12V IN V = 5V OUT 2.5 2.0 1.5 1.0 0.5 0 -40 -20 0 20 40 60 80 100120140 TEMPERATURE (°C) SHUTDOWN PIN VOLTAGE (V) Shutdown Hysteresis vs. Temperature April 2005 1.6 OFF 1.4 ON 1.2 1 0.8 0.6 VIN = 12.0V VOUT = 5.0V IOUT = 100mA 0.4 0.2 0 -40 0 40 80 120 160 TEMPERATURE (°C) 5 MIC4690 MIC4690 Micrel Functional Characteristics Switching Frequency Foldback VSW (NORMAL) 12V IN, 5V/1A OUT Load Transient IOUT (1A/div) 1.5A 0A 500kHz VSW (SHORTED) 12V IN, 0V OUT VOUT (100mV/div) 100mV Normal Operation VIN = 12V VOUT = 5V Short Circuit Operation 190kHz TIME CONTINUOUS OUTPUT CURRENT (A) TIME (100µs/div) SOA for MIC4690* 1.4 1.2 TA = 25°C 1.0 0.8 0.6 0.4 VOUT = 5V TA = 50°C TJ = 125°C 0.2 0 0 5 10 15 20 25 30 INPUT VOLTAGE (V) MIC4690BM IN SW 3 1N4148 82‰ SHDN 35 D1 FB 2.2nF GND 5 6 7 8 Snubber Circuit MIC4690 6 April 2005 MIC4690 Micrel Block Diagrams VIN IN SHDN Internal Regulator 500kHz Oscillator Thermal Shutdown ⎛ R1 ⎞ VOUT = VREF ⎜ + 1⎟ ⎝ R2 ⎠ ⎛V ⎞ R1 = R2 ⎜ OUT − 1⎟ ⎝ VREF ⎠ Current Limit VREF = 1.23V Comparator VOUT SW Driver COUT Reset R1 FB Error Amp 1.23V Bandgap Reference R2 MIC4690 [adj.] Adjustable Regulator 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 MIC4690 uses a voltage-mode 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. 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. Functional Description The MIC4690 is a variable duty cycle switch-mode regulator with an internal power switch. Refer to the block diagrams. Supply Voltage The MIC4690 operates from a +4V to +30V (transients to 34V) unregulated input. Highest efficiency operation is from a supply voltage around +12V. See the efficiency curve on page 5. Enable/Shutdown The shutdown (SHDN) input is TTL compatible. A logic-low enables the regulator. A logic-high shuts down the internal regulator which reduces the current to typically 1.5µA when VSHDN = VIN = 12V and 30µA 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 1b 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 500kHz sawtooth April 2005 7 MIC4690 MIC4690 Micrel Applications Information µ 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: !! Power MIC4690BM #$ " µ µ Figure 1a. Adjustable Regulator Circuit ⎛ R1 ⎞ VOUT = VREF ⎜ + 1⎟ ⎝ R2 ⎠ ⎛V ⎞ R1 = R2 ⎜ OUT − 1⎟ ⎝ VREF ⎠ VREF = 1.23V Bill of Material Matrix VOUT R1(1) R2(1) VIN CIN D1 L1 COUT IOUT 5.0V 3.01k 976Ω 6.8V-30V 22µF, 35V Vishay-Dale 595D226X0035D2T Micro Commercial 2A, 40V Schotty SS24 18µH Sumida CDRH6D38-180ML 220µF, 10V Vishay-Dale 594D227X0010D2T see SOA 5.0V 3.01k 976Ω 6.8V-14V 47µF, 20V Vishay-Dale 595D476X0020C2T Micro Commercial 2A, 20V Schotty SS22 18µH Sumida CDRH6D38-180ML 100µF, 6.3V Vishay-Dale 595D107X06R3C2T 1.0A 3.3V 3.01k 1.78k 4.9V-14V 47µF, 20V Vishay-Dale 595D476X0020C2T Micro Commercial 2A, 20V Schotty SS22 15µH Sumida CDRH6D38-150ML 120µF, 4.0V Vishay-Dale 595D127X0004C2T 1.0A 2.5V 3.01k 2.94k 4.25V-14V 47µF, 20V Vishay-Dale 595D476X0020C2T Micro Commercial 2A, 20V Schotty SS22 10µH Sumida CDRH6D38-100ML 120µF, 4.0V Vishay-Dale 595D127X0004C2T 1.0A 1.8V 3.01k 6.49k 4.0V-14V 2A, 20V Schotty SS22 10µH Sumida CDRH6D38-100ML 120µF, 4.0V Vishay-Dale 595D127X0004C2T 1.0A Note 1. 47µF, 20V Vishay-Dale 595D476X0020C2T Micro Commercial All resistors 1% Figure 1b. Recommended Components for Common Ouput Voltages MIC4690 8 April 2005 MIC4690 Micrel When designing with the MIC4690, it is a good practice to connect pins 5 through 8 to the largest ground plane that is practical for the specific design. Thermal Considerations The MIC4690 SuperSwitcher™ features the power-SOP-8. This package has a standard 8-lead small-outline package profile, but with much higher power dissipation than a standard SOP-8. Micrel's MIC4690 SuperSwitcher™ family are the first dc-to-dc converters to take full advantage of this package. The reason that the power SOP-8 has higher power dissipation (lower thermal resistance) is that pins 5 through 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 limitation of the maximum output current on any MIC4690 design is the junction-to-ambient thermal resistance (θJA) of the design (package and ground plane). Examining θJA in more detail: θJA = (θJC + θCA) where: θJC = junction-to-case thermal resistance θCA = case-to-ambient thermal resistance θJC is a relatively constant 20°C/W for a power SOP-8. θCA 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. θJA is ideally 63°C/W, but will vary depending on the size of the ground plane to which the power SOP-8 is attached. Checking the Maximum Junction Temperature: For this example, with an output power (POUT) of 5W, (5V output at 1A maximum with VIN = 12V) and 50°C maximum ambient temperature, what is the maximum junction temperature? Referring to the “Typical Characteristics: 5V Output Efficiency” graph, read the efficiency (η) for 1A output current at VIN = 12V or perform you own measurement. η = 75% The efficiency is used to determine how much of the output power (POUT) is dissipated in the regulator circuit (PD). PD = Quick Method Make sure that MIC4690 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 MIC4690 as possible. The area may be 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. SOP-8 θJA ground plane heat sink area AM BIE NT printed circuit board Figure 2. Power SOP-8 Cross Section April 2005 − POUT 5W − 5W 0.75 PD = 1.67W A worst-case rule of thumb is to assume that 80% of the total output power dissipation is in the MIC4690 (PD(IC)) and 20% is in the diode-inductor-capacitor circuit. PD(IC) = 0.8 PD PD(IC) = 0.8 × 1.67W PD(IC) = 1.336W Calculate the worst-case junction temperature: TJ = PD(IC) θJC + (TC – TA) + TA(max) where: TJ = MIC4690 junction temperature PD(IC) = MIC4690 power dissipation θJC = junction-to-case thermal resistance. The θJC for the MIC4690’s power-SOP-8 is approximately 20°C/W. TC = “pin” temperature measurement taken at the entry point of pins 6 or 7 TA = ambient temperature TA(max) = maximum ambient operating temperature for the specific design. Calculating the maximum junction temperature given a maximum ambient temperature of 50°C: TJ = 1.336W × 20°C/W + (63°C – 25°C) + 50°C TJ = 114.72°C This value is within the allowable maximum operating junction temperature of 125°C as listed in “Operating Ratings.” Typical thermal shutdown is 160°C and is listed in “Electrical Characteristics.” Layout Considerations Layout is very important when designing any switching regulator. Rapidly changing currents through the printed circuit board traces and stray inductance can generate voltage transients which can cause problems. There are two methods of determining the minimum ground plane area required by the MIC4690. θCA η PD = Determining Ground-Plane Heat-Sink Area θJC POUT 9 MIC4690 MIC4690 Micrel ! The feedback pin should be kept as far way from the switching elements (usually L1 and D1) as possible. A circuit with sample layouts are provided. See Figures 6a though 6e. Gerber files are available upon request. MIC4690BM Power SOP-8 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. " # $ % Figure 5. Critical Traces for Layout !"# !$ µ µ % MIC4690BM %& ' µ , - ,. )" + ( 3 2# 6!#4 )7"4# 44"" + !2"+"8 4 "9)7#4 !"# #!) !# ( ) * )" + , , , , ./- /- 0- /0.1 0 % %2 %3 %4 . µ µ Figure 6a. Evaluation Board Schematic Diagram MIC4690 10 April 2005 MIC4690 Micrel Printed Circuit Board Layouts Figure 6b. Top-Side Silk Screen Figure 6d. Bottom-Side Silk Screen Figure 6e. Bottom-Side Copper Figure 6c. Top-Side Copper Abbreviated Bill of Material (Critical Components) Reference Part Number Manufacturer Description Sprague1 Qty C1 595D2260035D2T ECE-A1HFS470 TPSD226M035R0300 Vishay Panasonic AVX2 22µF, 35V 47µF, 50V, 8mm X 11.5mm 22µF, 35V 1 C2, C6 VJ0805Y104KXAMB Vishay Vitramon2 0.1µF 50V 2 220µF, 10V 1 Schottky 2A, 40A 1 18µH, 1.5A ISAT 1 1A 200kHz power-SO-8 buck regulator 1 C4 594D227X0010D2T Vishay Sprague1 D1 SS24 B240A Micro Commercial Diode Inc L1 CDRH6D38-180MC Sumida4 U1 MIC4690BM Micrel 1 Vishay Dale, Inc., tel: 1 877-847-4291, http://www.vishay.com 2 Diodes Inc, tel: (805) 446-4800, http://www.diodes.com 3 Micro Corp3 Semiconductor5 Commercial Corp., tel: (800) 346-3371 4 Sumida, tel: (408) 982-9960, http://www.sumida.com 5 Micrel, tel: (408) 944-0800, http://www.micrel.com April 2005 11 MIC4690 MIC4690 Micrel Package Information 0.026 (0.65) MAX) PIN 1 0.157 (3.99) 0.150 (3.81) DIMENSIONS: INCHES (MM) 0.020 (0.51) 0.013 (0.33) 0.050 (1.27) TYP 0.064 (1.63) 0.045 (1.14) 45° 0.0098 (0.249) 0.0040 (0.102) 0.197 (5.0) 0.189 (4.8) 0°–8° SEATING PLANE 0.010 (0.25) 0.007 (0.18) 0.050 (1.27) 0.016 (0.40) 0.244 (6.20) 0.228 (5.79) 8-Lead SOP (M) MICREL, INC. 2180 FORTUNE DRIVE SAN JOSE, CA 95131 TEL + 1 (408) 944-0800 FAX + 1 (408) 474-1000 WEB USA 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 at Purchaser’s own risk and Purchaser agrees to fully indemnify Micrel for any damages resulting from such use or sale. © 2005 Micrel, Incorporated. MIC4690 12 April 2005