MIC23303 4MHz PWM 3A Buck Regulator with HyperLight Load™ and Power Good General Description Features The MIC23303 is a high-efficiency 4MHz 3A synchronous buck regulator with HyperLight Load™ mode, Power Good output indicator, and programmable soft-start. HyperLight Load provides very high efficiency at light loads and ultrafast transient response, which makes the MIC23303 perfectly suited for supplying processor core voltages. An additional benefit of this proprietary architecture is very low output ripple voltage throughout the entire load range with the use of small output capacitors. The tiny 3mm × 3mm DFN package saves precious board space and requires only six external components. • • • • • • • • • • • The MIC23303 is designed for use with a very small inductor, down to 0.33µH, and an output capacitor as small as 10µF that enables a total solution size less than 1mm in height. The MIC23303 has very low quiescent current of 24µA and can achieve peak efficiency of 93% in continuous conduction mode. In discontinuous conduction mode, the MIC23303 can achieve 80% efficiency at 1mA. The MIC23303 is available in a 12-pin 3mm × 3mm DFN package with an operating junction temperature range from –40°C to +125°C. Datasheets and support documentation are available on Micrel’s web site at: www.micrel.com. • • • • • Input voltage: 2.7V to 5.5V Output voltage: down to 0.65 Up to 3A output current Up to 93% peak efficiency 80% typical efficiency at 1mA Power Good output Programmable soft-start 24µA typical quiescent current 4MHz PWM operation in continuous mode Ultra-fast transient response Low ripple output voltage − 35mVpp ripple in HyperLight Load mode − 5mV output voltage ripple in full PWM mode Fully-integrated MOSFET switches 0.01µA shutdown current Thermal-shutdown and current-limit protection 12-pin 3mm × 3mm DFN –40°C to +125°C junction temperature range Applications • • • • • • Portable media/MP3 players Portable navigation devices (GPS) WiFi/WiMax/WiBro modules Digital Cameras Wireless LAN cards Portable applications Typical Application HyperLight Load 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 September 6, 2013 090613-2.0 Micrel, Inc. MIC23303 Ordering Information Part Number Marking Code Nominal Output Voltage Junction Temperature Range MIC23303YML WYA Adjustable –40°C to +125°C Package (1, 2) 12-Pin 3mm × 3mm DFN Notes: 1. DFN is a GREEN RoHS compliant package. Lead finish is NiPdAu. Mold compound is Halogen Free. 2. DFN Pin 1 identifier is ● . Pin Configuration 3mm x 3mm DFN (ML) (Top View) Pin Description Pin Number (Adjustable) Pin Name 1, 2 SW Switch (Output): Internal power MOSFET output switches. 3 PG Power Good: Open-drain output for the power good indicator. Use a pull-up resistor from this pin to a voltage source to detect a power good condition. 4 EN Enable (Input): Logic high enables operation of the regulator. Logic low shuts down the device. Do not leave floating. 5 SNS Sense: Connect to VOUT as close to output capacitor as possible to sense output voltage. 6 FB Feedback: Connect a resistor divider from the output to ground to set the output voltage. 7 SS Soft Start: Place a capacitor from this pin to ground to program the soft start time. Do not leave floating, 2.2nF minimum CSS is required. 8 AGND Analog Ground: Connect to central ground point where all high current paths meet (CIN, COUT, and PGND) for best operation. 9 AVIN Supply Voltage (Power Input): Analog control circuitry. Connect to PVIN. 10, 11 PVIN Input Voltage: Connect a capacitor to ground to decouple the noise. 12 PGND Power Ground. EP ePad Thermal pad: Connect to Ground plane for improved heat sinking. September 6, 2013 Pin Function 2 090613-2.0 Micrel, Inc. MIC23303 Absolute Maximum Ratings(3) Operating Ratings(4) Supply Voltage (VIN) .......................................... −0.3V to 6V Sense Voltage (VSNS) ........................................ −0.3V to VIN Output Switch Voltage (VSW) ............................. −0.3V to VIN Enable Input Voltage (VEN) .. ..............................−0.3V to VIN Power Good Voltage (VPG) ................................ −0.3V to VIN Storage Temperature Range .................... −65°C to +150°C Lead temperature (soldering, 10s) ............................. 260°C (5) ESD Rating ................................................. ESD Sensitive Supply Voltage (VIN) ........................................ .2.7V to 5.5V Enable Input Voltage (VEN) .................................... 0V to VIN Sense Voltage (VSNS) ..................................... 0.65V to 5.5V Junction Temperature Range (TJ)...... .−40°C ≤ TJ ≤ +125°C Thermal Resistance 3mm × 3mm DFN-12 (θJA) ................................. 61°C/W 3mm × 3mm DFN-12 (θJC) ................................. 27°C/W Electrical Characteristics(6) TA = 25°C; VIN = VEN = 3.6V; VOUT=1.8V; L = 0.33µH; COUT = 44µF unless otherwise specified. Bold values indicate –40°C ≤ TJ ≤ +125°C, unless otherwise noted. Parameter Condition Min. 2.7 Supply Voltage Range Undervoltage Lockout Threshold 2.3 (turn-on) Undervoltage Lockout Hysteresis IOUT = 0mA, SNS > 1.2 × VOUT Nominal Shutdown Current VEN = 0V; VIN = 5.5V VIN = 3.6V if VOUTNOM < 2.5V, ILOAD = 20mA VIN = 4.5V if VOUTNOM ≥ 2.5V, ILOAD = 20mA Feedback Regulation Voltage ILOAD = 20mA Current Limit SNS = 0.9 × VOUTNOM Output Voltage Line Regulation Switching Frequency Maximum Duty Cycle V 2.8 V mV 40 µA 0.01 5 µA +2.5 % 0.62 0.635 V 3.5 6.5 10 A VIN = 3.6V to 5.5V if VOUTNOM < 2.5V, ILOAD = 20mA VIN = 4.5V to 5.5V if VOUTNOM ≥ 2.5V, ILOAD = 20mA 20mA < ILOAD < 500mA, VIN = 5.0V if VOUTNOM ≥ 2.5V 20mA < ILOAD < 1A, VIN = 3.6V if VOUTNOM < 2.5V 0.3 %/V 0.3 % 0.7 % ISW = 100mA PMOS 0.075 ISW = −100mA NMOS 0.055 IOUT = 300mA (7, 8) Soft Start Time 5.5 0.604 20mA < ILOAD < 1A, VIN = 5.0V if VOUTNOM ≥ 2.5V PWM Switch ON-Resistance Units 24 −2.5 20mA < ILOAD < 500mA, VIN = 3.6V if VOUTNOM < 2.5V Output Voltage Load Regulation 2.53 Max. 275 Quiescent Current Output Voltage Accuracy Typ. 80 VOUT = 90%, CSS = 2.2nF Ω 4 MHz 85 % 1.26 ms Notes: 3. Exceeding the absolute maximum rating may damage the device. 4. The device is not guaranteed to function outside its operating rating. 5. Devices are ESD sensitive. Handling precautions recommended. Human body model, 1.5kΩ in series with 100pF. 6. Specification for packaged product only. 7. The maximum duty cycle is limited by the fixed mandatory off time of 300ns. 8. Guaranteed by design. September 6, 2013 3 090613-2.0 Micrel, Inc. MIC23303 Electrical Characteristics(6) (Continued) TA = 25°C; VIN = VEN = 3.6V; VOUT=1.8V; L = 0.33µH; COUT = 44µF unless otherwise specified. Bold values indicate –40°C ≤ TJ ≤ +125°C, unless noted. Parameter Condition Power Good Threshold (Rising) Moving FB from Low to High relative to 0.62V (VFB) Power Good Threshold Hysteresis Moving FB from High to Low relative to 0.62V (VFB) Power Good Delay Time Rising 160 µs Power Good Pull-Down RPG = 5.1k from PG to VOUT 200 mV Enable Threshold The voltage on Enable that ensures the part is ON 0.9 1.2 V Enable Input Current 0.1 2 µA Overtemperature Shutdown 160 °C Overtemperature Shutdown Hysteresis 20 °C September 6, 2013 4 Min. Typ. Max. Units 85 90 95 % 20 0.4 % 090613-2.0 Micrel, Inc. MIC23303 Typical Characteristics Efficiency vs. Load 1.2 VOUT Efficiency vs. Load 1.8 VOUT 100 100 90 100000 80 VIN = 3.6V 60 50 40 30 20 70 0 0.0001 50 40 30 1000 100 0.001 0.01 0.1 1 10 L = 0.33µH COUT = 44µF 10 0 0.0001 10 6.00 5.00 VOUT = 1.8V L = 0.33µH COUT = 44µF 3.0 3.5 4.0 4.5 10 5.0 30 1.25 28 1.24 26 1.23 24 22 20 18 16 14 1.22 TCASE = 25°C 2.5 3 INPUT VOLTAGE (V) 1.20 1.19 1.17 3.5 4 4.5 5 2.5 Output Voltage (HLL) vs. Load Current 1.23 1.23 IOUT=500mA 1.21 1.20 1.19 IOUT=2A 1.17 L = 0.33µH COUT = 44µF OUTPUT VOLTAGE (V) 1.24 1.23 OUTPUT VOLTAGE (V) 1.25 1.24 1.22 1.22 1.21 1.20 1.19 1.18 1.17 VIN=3.6V L = 33µH COUT = 44µF 1.16 1.15 4 4.5 INPUT VOLTAGE (V) September 6, 2013 5 5.5 4 4.5 5 5.5 1.22 1.21 1.20 1.19 1.18 1.17 VIN=3.6V L = 33µH COUT = 44µF 1.16 1.15 3.5 3.5 Output Voltage (CCM) vs. Load Current 1.25 3 3 INPUT VOLTAGE (V) 1.24 2.5 L = 0.33µH COUT = 44µF 1.15 5.5 1.25 1.16 IOUT=1mA 1.18 INPUT VOLTAGE (V) Output Voltage vs. Input Voltage 1.18 IOUT=20mA 1.21 1.16 10 1000000 Output Voltage vs. Input Voltage 12 5.5 100000 10000 CSS (pF) OUTPUT VOLTAGE (V) QUIESCENT CURRENT (µA) 7.00 2.5 1 Quiscent Current vs. Input Voltage 8.00 3.00 0.1 VIN=3.6V 1 1000 LOAD CURRENT (A) Current Limit vs. Input Voltage 4.00 0.01 0.001 LOAD CURRENT(A) CURRENT LIMIT (A) 10000 60 20 L = 0.33µH COUT = 44µF 10 OUTPUT VOLTAGE (V) VIN = 5V VIN = 3.6V RISE TIME (µs) VIN = 5V 70 EFFICIENCY (%) EFFICIENCY (%) 1000000 VIN = 3V 90 80 VOUT Rise Time vs Css 1.15 0 0.05 0.1 0.15 0.2 0.25 0.3 LOAD CURRENT (A) 5 0.35 0.4 0.4 0.8 1.2 1.6 2 2.4 2.8 3.2 LOAD CURRENT (A) 090613-2.0 Micrel, Inc. MIC23303 Typical Characteristics (Continued) Output Voltage vs. Temperature PG Thresholds vs. Input Voltage PG Delay Time vs. Input Voltage 1.85 160 95 PG Rising PG THRESHOLD (% of V REF) 140 1.83 1.82 PG DELAY (µs) OUTPUT VOLTAGE (V) 1.84 1.81 1.80 1.79 1.78 VIN = 3.6V L = 0.33µH COUT = 44µF IOUT = 20mA 1.77 1.76 120 PG Rising 100 80 PG Falling 60 -40 -20 0 20 40 60 80 100 2.5 120 85 80 75 PG Falling 70 65 40 1.75 90 3.0 3.5 4.0 4.5 5.0 2.5 5.5 3.0 Undervoltage Lockout vs. Temperature 4.0 4.5 5.0 5.5 Enable Thresholds vs. Temperature Enable Threshold vs. Input Voltage 2.6 3.5 INPUT VOLTAGE (V) INPUT VOLTAGE (V) TEMPERATURE (°C) 1.1 1 1.0 0.95 EN THRESHOLD (V) 2.5 UVLO (V) 2.4 2.3 UVLO OFF 2.2 2.1 EN THRESHOLD (V) UVLO ON 0.9 0.8 0.7 0.9 0.85 0.8 0.75 0.6 TCASE=25°C 2.0 0.5 -40 -20 0 20 40 60 80 100 120 0.7 2.5 3.0 TEMPERATURE (°C) Feedback Voltage vs. Temperature 4.0 4.5 5.0 5.5 -40 10000 1000 0.63 VIN = 5V 0.62 0.61 VIN = 2.7V 0.6 0.59 100 10 VIN=5.5V VEN=0V 1 -40 -20 0 20 40 60 80 TEMPERATURE (°C) September 6, 2013 100 120 0 -40 -20 0 20 40 60 80 TEMPERATURE (°C) 6 20 40 60 80 100 120 140 Switching Frequency vs. Load Current VIN = 5V 1000 SW FREQUENCY (kHz) SHUTDOWN CURRENT (nA) 0.64 -20 TEMPERATURE (°C) Shutdown Current vs. Temperature 0.65 FEEDBACK VOLTAGE (V) 3.5 INPUT VOLTAGE (V) 100 120 100 VIN = 3V 10 1 0.1 0.0001 VOUT = 1.8V L = 0.33µH COUT = 44µF 0.001 0.01 0.1 1 10 LOAD CURRENT (A) 090613-2.0 Micrel, Inc. MIC23303 Functional Characteristics September 6, 2013 7 090613-2.0 Micrel, Inc. MIC23303 Functional Characteristics (Continued) September 6, 2013 8 090613-2.0 Micrel, Inc. MIC23303 Functional Characteristics (Continued) September 6, 2013 9 090613-2.0 Micrel, Inc. MIC23303 Functional Diagram Figure 1. Simplified MIC23303 Functional Block Diagram September 6, 2013 10 090613-2.0 Micrel, Inc. MIC23303 Functional Description PVIN The input supply (PVIN) provides power to the internal MOSFETs for the switch mode regulator section. The VIN operating range is 2.7V to 5.5V so an input capacitor, with a minimum voltage rating of 6.3V, is recommended. Due to the high switching speed, a minimum 4.7µF bypass capacitor placed close to PVIN and the power ground (PGND) pin is required. Refer to the PCB Layout Recommendations for details. AVIN Analog VIN (AVIN) provides power to the internal control and analog supply circuitry. AVIN and PVIN must be tied together. Careful layout should be considered to ensure high frequency switching noise caused by PVIN is reduced before reaching AVIN. A 1µF capacitor as close to AVIN as possible is recommended. See PCB Layout Recommendations for details. EN A logic high signal on the enable pin activates the output voltage of the device. A logic low signal on the enable pin deactivates the output and reduces supply current to nominal 0.01µA. MIC23303 features external soft-start circuitry via the soft start (SS) pin that reduces in-rush current and prevents the output voltage from overshooting when EN is driven logic high. Do not leave the EN pin floating. SW The switch (SW) connects directly to one end of the inductor and provides the current path during switching cycles. The other end of the inductor is connected to the load, SNS pin, and output capacitor. Due to the high speed switching on this pin, the switch node should be routed away from sensitive nodes whenever possible. SNS The sense (SNS) pin is connected to the output of the device to provide feedback to the control circuitry. The SNS connection should be placed close to the output capacitor. Refer to the PCB Layout Recommendations for more details. AGND The analog ground (AGND) is the ground path for the biasing and control circuitry. The current loop for the signal ground should be separate from the power ground (PGND) loop. Refer to the PCB Layout Recommendations for more details. September 6, 2013 11 PGND The power ground pin is the ground path for the high current in PWM mode. The current loop for the power ground should be as small as possible and separate from the analog ground (AGND) loop as applicable. Refer to the PCB Layout Recommendations for more details. PG The power good (PG) pin is an open-drain output that indicates logic high when the output voltage is typically above 90% of its steady state voltage. A pull-up resistor of more than 5kΩ should be connected from PG to VOUT. SS The soft start (SS) pin is used to control the output voltage ramp-up time. The approximate equation for the ramp time 3 in seconds is 250 × 10 × ln(10) × CSS. For example, for CSS = 2.2nF, Trise ~ 1.26ms. See the Typical Characteristics curve for a graphical guide. The minimum recommended value for CSS is 2.2nF. FB The feedback (FB) pin is provided for the adjustable voltage option (no internal connection for fixed options). This is the control input for programming the output voltage. A resistor divider network is connected to this pin from the output and is compared to the internal 0.62V reference within the regulation loop. The output voltage can be programmed between 0.65V and 3.6V using the following equation: R3 VOUT = VREF ⋅ 1 + R4 Where: R3 is the top resistor, R4 is the bottom resistor. Example feedback resistor values: VOUT R3 R4 1.2V 274k 294k 1.5V 316k 221k 1.8V 560k 294k 2.5V 324k 107k 3.3V 464k 107k 090613-2.0 Micrel, Inc. MIC23303 Application Information The MIC23303 is a high-performance DC-to-DC step down regulator offering a small solution size. Supporting an output current up to 3A inside a tiny 3mm x 3mm DFN package, the IC requires only six external components while meeting today’s miniature portable electronic device needs. Using the HyperLight Load switching scheme, the MIC23303 is able to maintain high efficiency throughout the entire load range while providing ultra-fast load transient response. The following sections provide additional device application information. Input Capacitor A 4.7µF ceramic capacitor or greater should be placed close to the PVIN pin and PGND pin for bypassing. A Murata GRM188R60J475ME19D, size 0603, 4.7µF ceramic capacitor is recommended based upon performance, size, and cost. A X5R or X7R temperature rating is recommended for the input capacitor. Y5V temperature rating capacitors, aside from losing most of their capacitance over temperature, can also become resistive at high frequencies. This reduces their ability to filter out high frequency noise. Output Capacitor The MIC23303 is designed for use with a 10µF or greater ceramic output capacitor. Increasing the output capacitance will lower output ripple and improve load transient response but could also increase solution size or cost. A low equivalent series resistance (ESR) ceramic output capacitor such as the Murata GRM21BR60J226ME39L, size 0805, 22µF ceramic capacitor is recommended based upon performance, size and cost. Two of these capacitors in parallel will decrease ESR, resulting in decreased output voltage ripple. Both the X7R or X5R temperature rating capacitors are recommended. The Y5V and Z5U temperature rating capacitors are not recommended due to their wide variation in capacitance over temperature and increased resistance at high frequencies. Inductor Selection When selecting an inductor, it is important to consider the following factors (not necessarily in the order of importance): • Inductance • Rated current value • Size requirements • DC resistance (DCR) September 6, 2013 12 The MIC23303 is designed for use with a 0.33µH to 1.0µH inductor. For faster transient response and greater efficiency, a 0.33µH inductor will yield the best result. To achieve lower output voltage ripple, a higher value inductor such as a 1µH can be used. However, a greater value inductor, when operating in low load mode will result in a higher operating frequency. This effect with increased DCR will result in a less efficient design. Maximum current ratings of the inductor are generally given in two methods; permissible DC current and saturation current. Permissible DC current can be rated either for a 40°C temperature rise or a 10% to 20% loss in inductance. Ensure that the inductor selected can handle the maximum operating current. When saturation current is specified, make sure that there are enough margins that the peak current does not cause the inductor to saturate. Peak current can be calculated as follows: 1 − VOUT /VIN IPEAK = IOUT + VOUT 2× f ×L As shown by the calculation above, the peak inductor current is inversely proportional to the switching frequency and the inductance; the lower the switching frequency or the inductance the higher the peak current. As input voltage increases, the peak current is somewhat limited by constant off time control. The size of the inductor depends on the requirements of the application. Refer to the Typical Application Schematic and Bill of Materials for details. DC resistance (DCR) is also important. While DCR is inversely proportional to size, DCR can represent a significant efficiency loss. Refer to the Efficiency Considerations. The transition between high loads (CCM) to HyperLight Load (HLL) mode is determined by the inductor ripple current and the load current. 090613-2.0 Micrel, Inc. MIC23303 Maintaining high efficiency serves two purposes. It reduces power dissipation in the power supply, reducing the need for heat sinks and thermal design considerations, and it reduces consumption of current for battery-powered applications. Reduced current draw from a battery increases the devices operating time and is critical in handheld devices. There are two types of losses in switching converters; DC losses and switching losses. DC losses are simply the 2 power dissipation of I R. Power is dissipated in the highside switch during the on cycle. Power loss is equal to the high side MOSFET RDSON multiplied by the switch current squared. During the off cycle, the low side N-channel MOSFET conducts, also dissipating power. Device operating current also reduces efficiency. The product of the quiescent (operating) current and the supply voltage represents another DC loss. Figure 2 shows the signals for high-side switch drive (HSD) for Ton control, the inductor current and the lowside switch drive (LSD) for Toff control. In HLL mode, the inductor is charged with a fixed Ton pulse on the high-side switch (HSD). After this, the LSD is switched on and current falls at a rate VOUT/L. The controller remains in HLL mode while the inductor falling current is detected to cross approximately 300mA. When the LSD (or Toff) time reaches its minimum and the inductor falling current is no longer able to reach this 300mA threshold, the part is in CCM mode and switching at a virtually constant frequency. Compensation The MIC23303 is designed to be stable with a 0.33µH to 1.0µH inductor with a minimum 10µF ceramic (X5R) output capacitor. The total feedback resistance should be kept 2 around 500kΩ to reduce the I R losses through the feedback resistor network, improving efficiency. A feedforward capacitor (CFF) of 33pF is recommended across the top feedback resistor to reduce the effects of parasitic capacitance and improve transient performance. Duty Cycle The typical maximum duty cycle of the MIC23303 is 85%. Efficiency Considerations Efficiency is defined as the amount of useful output power, divided by the amount of power supplied. V ×I Efficiency % = OUT OUT V × IN IIN September 6, 2013 × 100 13 The current required to drive the gates on and off at a constant 4MHz frequency and the switching transitions make up the switching losses. 100 Efficiency vs. Load 1.8 VOUT 90 80 EFFICIENCY (%) Figure 2. HyperLight Load (HLL) and Continuous Conduction Mode (CCM) Switching Diagram VIN = 5V 70 VIN = 3.6V 60 50 40 30 20 L = 0.33µH COUT = 44µF 10 0 0.0001 0.001 0.01 0.1 1 10 LOAD CURRENT(A) Figure 3. Efficiency under Load Figure 3 shows an efficiency curve. From no load to 100mA, efficiency losses are dominated by quiescent current losses, gate drive, and transition losses. By using HyperLight Load mode, the MIC23303 is able to maintain high efficiency at low output currents. Over 300mA, efficiency loss is dominated by MOSFET RDSON and inductor losses. Higher input supply voltages will increase the Gate-to-Source voltage on the internal MOSFETs, thereby reducing the internal RDSON. This improves efficiency by reducing DC losses in the device. All but the inductor losses are inherent to the device. When dealing with inductor losses, inductor selection becomes increasingly critical in efficiency calculations. 090613-2.0 Micrel, Inc. MIC23303 As the inductors are reduced in size, the DC resistance (DCR) can become quite significant. The DCR losses can be calculated as follows: 2 PDCR = IOUT × DCR From that, the loss in efficiency due to inductor resistance can be calculated as follows: VOUT × IOUT Efficiency Loss = 1 − VOUT × IOUT + PDCR As shown in the previous equation, the load at which the MIC23303 transitions from HyperLight Load mode to PWM mode is a function of the input voltage (VIN), output voltage (VOUT), duty cycle (D), efficiency (η), inductance (L) and frequency (f). As shown in Figure 4, as the output current increases, the switching frequency also increases until the MIC23303 goes from HyperLight Load mode to PWM mode at approximately 300mA. The MIC23303 will switch at a relatively constant frequency around 4MHz once the output current is over 300mA. × 100 10000 Switching Frequency vs. Load Current Efficiency loss due to DCR is minimal at light loads and gains significance as the load is increased. Inductor selection becomes a trade-off between efficiency and size in this case. HyperLight Load Mode MIC23303 uses a minimum on and off time proprietary control loop (patented by Micrel). When the output voltage falls below the regulation threshold, the error comparator begins a switching cycle that turns the PMOS on and keeps it on for the duration of the minimum-on-time. This increases the output voltage. If the output voltage is over the regulation threshold, then the error comparator turns the PMOS off for a minimum-off-time until the output drops below the threshold. The NMOS acts as an ideal rectifier that conducts when the PMOS is off. Using a NMOS switch instead of a diode allows for lower voltage drop across the switching device when it is on. The asynchronous switching combination between the PMOS and the NMOS allows the control loop to work in discontinuous mode for light load operations. In discontinuous mode, the MIC23303 works in pulse frequency modulation (PFM) to regulate the output. As the output current increases, the off-time decreases, thus provides more energy to the output. This switching scheme improves the efficiency of MIC23303 during light load currents by only switching when it is needed. As the load current increases, the MIC23303 goes into continuous conduction mode (CCM) and switches at a frequency centered at 4MHz. The equation to calculate the load when the MIC23303 goes into continuous conduction mode may be approximated by the following formula: SW FREQUENCY (kHz) 1000 VIN =5V 100 VIN=3.3V 10 1 0.1 0.0001 VOUT = 1.8V L = 0.33µH COUT = 44µF 0.001 0.01 0.1 1 10 LOAD CURRENT (A) Figure 4. SW Frequency vs. Output Current Power Dissipation Considerations As with all power devices, the ultimate current rating of the output is limited by the thermal properties of the package and the PCB it is mounted on. There is a simple, Ohm’s law type relationship between thermal resistance, power dissipation and temperature which are analogous to an electrical circuit: Figure 5. Ohm’s Law Description (V − VOUT ) × D × η ILOAD > IN 2L × f September 6, 2013 14 090613-2.0 Micrel, Inc. MIC23303 From this simple circuit we can calculate VX if we know ISOURCE, VZ, and the resistor values, RXY and RYZ, using the equation: Since effectively all of the power losses (minus the inductor losses) in the converter are dissipated within the MIC23303 package, PDISS can be calculated thus: V X = I SOURCE × (R XY + R YZ ) + VZ 1 2 PDISS = POUT × ( − 1) − I OUT × DCR η Thermal circuits can be considered using these same rules and can be drawn similarly replacing current sources with power dissipation (in Watts), resistance with thermal resistance (in °C/W) and voltage sources with temperature (in °C). Where: η = Efficiency taken from efficiency curves and DCR = Inductor DCR. RθJC and RθJA are found in the Operating Ratings section of the datasheet. Where the reel board area differs from 1in square, RθCA (the PCB thermal resistance) values for various PCB copper areas can be taken from Figure 7 below. This graph is taken from Designing with Low Dropout Voltage Regulators, which is available from the Micrel website (LDO Application Hints). Example: A MIC23303 is intended to drive a 2A load at 1.8V and is placed on a printed circuit board which has a ground plane area of at least 25mm square. Figure 6. Thermal Circuit Description Now replacing the variables in the equation for VX, we can find the junction temperature (TJ) from power dissipation, ambient temperature, and the known thermal resistance of the PCB (RθCA) and the package (RθJC). The voltage source is a Li-ion battery with a lower operating threshold of 3V and the ambient temperature of the assembly can be up to 50°C. Summary of variables: IOUT = 2A VOUT = 1.8V TJ = PDISS × (Rθ JC + Rθ CA ) + TAMB VIN = 3V to 4.2V TAMB = 50°C As can be seen in the diagram, total thermal resistance RθJA = RθJC + RθCA. Hence this can also be written: RθJA = 61°C/W from datasheet η @ 2A = 85% (worst case @ 5V from Figure 3) TJ = PDISS × (RθJA ) + TAMB September 6, 2013 15 090613-2.0 Micrel, Inc. MIC23303 Figure 7. PCB Thermal Resistance versus PCB Copper Area ( ) 1 − 1) − 22 × 20mΩ = 0.56W PDISS = 1.8 × 2 × ( 0.85 The worst case switch and inductor resistance will increase at higher temperatures, so a margin of 20% can be added to account for this. PDISS = 0.56 × 1.2 = 0.67W Therefore: TJ = 0.67W. (61°C/W) + 50°C TJ = 91°C This is well below the maximum 125°C. September 6, 2013 16 090613-2.0 Micrel, Inc. MIC23303 Typical Application Schematic Bill of Materials Item Part Number 06036D475KAT2A C1 GRM188R60J475ME19D C1608X5R0J475M 06035C222KAT2A C2 C3, C8 GRM188R71H222MA01D Manufacturer Murata (10) 4.7µF/6.3V, X5R, 0603 1 2.2nF/50V, X7R, 0603 1 22µF/6.3V, X5R, 0805 1 (11) TDK AVX Murata TDK 08056D226MAT2A AVX C2012X5R0J226M Qty. AVX C1608X7R1H222K GRM21BR60J226ME39L Description (9) Murata TDK Notes: 9. AVX: www.avx.com . 10. Murata: www.murata.com. 11. TDK: www.tdk.com. September 6, 2013 17 090613-2.0 Micrel, Inc. MIC23303 Bill of Materials (Continued) Item C4 Part Number 06035A330KAT2A GRM1885C1H330JA01D 06036D105KAT2A C6 C7 GRM188R60J105KA01D AVX Murata Murata TDK 06035D104KAT2A AVX GRM188R71H104KA930 0520CDMCDSNP-R33MC 744373240033 Description Qty. 33pF/50V, 0603 1 1µF/6.3V, X5R, 0603 1 0.1µF/6.3V, X5R, 0603 1 AVX C1608X5R0J105K C1608X5R1H104K L1 Manufacturer Murata TDK Sumida Wurth (12) Vishay/Dale 0.33µH/5.6A, 8mΩ 0.33µH/8.0A, 8.6mΩ (13) (14) 1 R1, R2 CRCW060310K0FKEA 10K,1%, 1/10W, 0603 2 R3 CRCW0603560KFKEA Vishay/Dale 560K,1%, 1/10W, 0603 1 R4 CRCW0603294KFKEA Vishay/Dale 294K,1%, 1/10W, 0603 1 R5 CRCW060310R0FKEA Vishay/Dale 10Ω,1%, 1/10W, 0603 1 IC1 MIC23303YML 4MHz 3A Buck Regulator with HyperLight Load Mode and Power Good 1 (15) Micrel, Inc Notes: 12. Sumida: www.Sumida.com. 13. Wurth: www.we-online.com. 14. Vishay: www.vishay.com. 15. Micrel, Inc.: www.micrel.com. September 6, 2013 18 090613-2.0 Micrel, Inc. MIC23303 PCB Layout Recommendations Top Layer Bottom Layer September 6, 2013 19 090613-2.0 Micrel, Inc. MIC23303 Package Information (16) 12-Pin 3mm x 3mm DFN (ML) Note: 16. Package information is correct as of the publication date. For updates and most current information, go to www.micrel.com. September 6, 2013 20 090613-2.0 Micrel, Inc. MIC23303 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 Micrel makes no representations or warranties with respect to the accuracy or completeness of the information furnished in this data sheet. This information is not intended as a warranty and Micrel does not assume responsibility for its use. Micrel reserves the right to change circuitry, specifications and descriptions at any time without notice. No license, whether express, implied, arising by estoppel or otherwise, to any intellectual property rights is granted by this document. Except as provided in Micrel’s terms and conditions of sale for such products, Micrel assumes no liability whatsoever, and Micrel disclaims any express or implied warranty relating to the sale and/or use of Micrel products including liability or warranties relating to fitness for a particular purpose, merchantability, or infringement of any patent, copyright or other intellectual property right. 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. © 2002 Micrel, Incorporated. September 6, 2013 21 090613-2.0