MIC23250 4MHz Dual 400mA Synchronous Buck Regulator with HyperLight Load™ General Description Features The MIC23250 is a high efficiency 4MHz dual 400mA • Input voltage: 2.7V to 5.5V HyperLight Load™ synchronous buck regulator with HyperLight Load™ mode. • Dual output current 400mA/400mA HyperLight Load™ provides very high efficiency at light • Up to 94% peak efficiency and 85% efficiency at 1mA loads and ultra-fast transient response which is perfectly • 33µA dual quiescent current suited for supplying processor core voltages. An additional • 1µH inductor with a 4.7µF capacitor benefit of this proprietary architecture is very low output • 4MHz in PWM operation ripple voltage throughout the entire load range with the use of small output capacitors. The fixed output MIC23250 has • Ultra fast transient response a tiny 2mm x 2mm Thin MLF® package that saves • Low voltage output ripple precious board space by requiring only 6 additional • 20mVpp in HyperLight Load™ mode external components to drive both outputs up to 400mA • 3mV output voltage ripple in full PWM mode each. • 0.01µA shutdown current The device is designed for use with a 1µH inductor and a • Fixed output:10-pin 2mm x 2mm Thin MLF® 4.7µF output capacitor that enables a sub-1mm height. • Adjustable output:12-pin 2.5mm x 2.5mm Thin MLF® The MIC23250 has a very low quiescent current of 33µA • –40°C to +125°C junction temperature range with both outputs enabled and can achieve over 85% efficiency at 1mA. At higher loads the MIC23250 provides a constant switching frequency around 4MHz while providing Applications peak efficiencies up to 94%. • Mobile handsets The MIC23250 fixed output voltage option is available in a • Portable media players ® 10-pin 2mm x 2mm Thin MLF . The adjustable output ® • Portable navigation devices (GPS) options is available in a 12-pin 2.5mm x 2.5mm Thin MLF . • WiFi/WiMax/WiBro modules The MIC23250 is designed to operate over the junction • Digital cameras operating range from –40°C to +125°C. • Wireless LAN cards Data sheets and support documentation can be found on • USB Powered Devices Micrel’s web site at: www.micrel.com. ____________________________________________________________________________________________________________ Typical Application Efficiency V OUT = 1.8V 100 VIN = 3.0V 90 VIN = 2.7V 80 70 VIN = 4.2V 60 VIN = 3.6V 50 40 30 20 10 0 11 L = 1µH COUT = 4.7µF 0 100 1000 OUTPUT CURRENT (mA) HyperLight Load is a trademark of Micrel, Inc. MLF and MicroLeadFrame are registered trademarks of Amkor Technology, 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 June 2010 M9999-061110-E Micrel, Inc. MIC23250 Ordering Information Part Number Marking Code Nominal Output Voltage 1 Nominal Output Voltage 2 Junction Temp. Range Package Lead Finish MIC23250-3BYMT WV3 0.9V 1.1V –40° to +125°C 10-Pin 2mm x 2mm Thin MLF® Pb-Free ® MIC23250-C4YMT WV2 1.2V 1.0V –40° to +125°C 10-Pin 2mm x 2mm Thin MLF Pb-Free MIC23250-W4YMT WV4 1.2V 1.6V –40° to +125°C 10-Pin 2mm x 2mm Thin MLF® Pb-Free –40° to +125°C ® Pb-Free ® MIC23250-G4YMT WV5 1.2V 1.8V 10-Pin 2mm x 2mm Thin MLF MIC23250-S4YMT 1WV 1.2V 3.3V –40° to +125°C 10-Pin 2mm x 2mm Thin MLF Pb-Free MIC23250-GFHYMT WV1 1.575V 1.8V –40° to +125°C 10-Pin 2mm x 2mm Thin MLF® Pb-Free –40° to +125°C ® MIC23250-SKYMT MIC23250-AAYMT 5WV 4WV 2.6V ADJ 3.3V ADJ –40° to +125°C 10-Pin 2mm x 2mm Thin MLF Pb-Free ® 12-Pin 2.5mm x 2.5mm Thin MLF Pb-Free Notes: 1) Additional voltage options available (0.8V to 3.3V). Contact Micrel for details. 2) Thin MLF is GREEN RoHS compliant package. Lead finish is NiPdAu. Mold compound is Halogen Free. June 2010 ® 2 M9999-061110-E Micrel, Inc. MIC23250 Pin Configuration FB1 1 12 FB2 SNS1 2 11 SNS2 AVIN EN1 3 10 EN2 7 SW2 AGND 4 9 AVIN 6 VIN SW1 5 8 SW2 PGND 6 7 VIN SNS1 1 10 SNS2 EN1 2 9 EN2 AGND 3 8 SW1 4 PGND 5 10-Pin 2mm x 2mm Thin MLF® (MT) Fixed Output (Top View) 12-Pin 2.5mmx2.5mm Thin MLF® (MT) Adjustable Output (Top View) Pin Description Pin Number (Fixed) Pin Number (Adjustable) Pin Name – 1 FB1 Feedback VOUT1 (Input): Connect resistor divider at this node to set output voltage. Resistors should be selected based on a nominal VFB of 0.72V. 1 2 SNS1 Sense 1 (Input): Error amplifier input. Connect to feedback resistor network to set output 1 voltage. 2 3 EN1 3 4 AGND Analog Ground. Must be connected externally to PGND. 4 5 SW1 Switch Node 1 (Output): Internal power MOSFET output. 5 6 PGND 6 7 VIN Supply Voltage (Power Input): Requires close bypass capacitor to PGND. 7 8 SW2 Switch Node 2 (Output): Internal power MOSFET output. 8 9 AVIN Supply Voltage (Power Input): Analog control circuitry. Connect to VIN. 9 10 EN2 Enable 2 (Input): Logic low will shut down output 2. Logic high powers up output 2. Do not leave unconnected. 10 11 SNS2 Sense 2 (Input): Error amplifier input. Connect to feedback resistor network to set output 2 voltage. – 12 FB2 Feedback VOUT2 (Input): Connect resistor divider at this node to set output voltage. Resistors should be selected based on a nominal VFB of 0.72V. June 2010 Pin Function Enable 1 (Input): Logic low will shut down output 1. Logic high powers up output 1. Do not leave unconnected. Power Ground. 3 M9999-061110-E Micrel, Inc. MIC23250 Absolute Maximum Ratings(1) Operating Ratings(2) Supply Voltage (VIN) .........................................................6V Output Switch Voltage (VSW) ............................................6V Logic Input Voltage (VEN1, VEN2) ........................ –0.3V to VIN Storage Temperature Range (Ts)..............–65°C to +150°C ESD Rating(3) .................................................................. 2kV Supply Voltage (VIN)......................................... 2.7V to 5.5V Logic Input Voltage (VEN1, VEN2) ............................. 0V to VIN Junction Temperature (TJ) ..................–40°C ≤ TJ ≤ +125°C Thermal Resistance 2mm x 2mm Thin MLF-10 (θJA) .........................70°C/W 2.5mm x 2.5mm Thin MLF-12 (θJA) ...................65°C/W Electrical Characteristics(4) TA = 25°C with VIN = VEN1 = VEN2 = 3.6V; L = 1µH; COUT = 4.7µF; IOUT = 20mA; only one channel power is enabled, unless otherwise specified. Bold values indicate –40°C< TJ < +125°C. Parameter Condition Min Typ Max Units Under-Voltage Lockout Threshold UVLO Hysteresis Quiescent Current (turn-on) 2.45 2.55 60 2.65 V mV 33 50 µA 0.01 4 +2.5 +2.5 µA % % V A %/V %/V % % Ω Ω MHz µs V µA Shutdown Current Output Voltage Accuracy Feedback Voltage (Adj only) Current Limit in PWM Mode Output Voltage Line Regulation Output Voltage Load Regulation PWM Switch ON-Resistance Frequency Soft Start Time Enable Threshold Enable Input Current Over-temperature Shutdown Over-temperature Shutdown Hysteresis VOUT1, 2 (both Enabled), IOUT1, 2 = 0mA , VSNS1,2 >1.2 * VOUT1, 2 Nominal VEN1, 2 = 0V; VIN = 5.5V VIN = 3.6V if VOUTNOM < 2.5V, ILOAD = 20mA VIN = 4.5V if VOUTNOM ≥ 2.5V, ILOAD = 20mA SNS = 0.9*VOUT NOM 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 < 400mA, VIN = 3.6V if VOUTNOM < 2.5V 20mA < ILOAD < 400mA, VIN = 5.0V if VOUTNOM ≥ 2.5V ISW = 100mA PMOS ISW = -100mA NMOS ILOAD = 120mA VOUT = 90% –2.5 –2.5 0.410 0.5 0.720 0.65 0.4 0.4 0.5 0.5 0.6 0.8 4 260 0.8 0.1 160 40 1 1.2 2 °C °C Notes: 1. Exceeding the absolute maximum rating may damage the device. 2. The device is not guaranteed to function outside its operating rating. 3. Devices are ESD sensitive. Handling precautions recommended. Human body model: 1.5kΩ in series with 100pF. 4. Specification for packaged product only. June 2010 4 M9999-061110-E Micrel, Inc. MIC23250 Typical Characteristics 50 45 Quiescent Current vs. Input Voltage Switching Frequency vs. Output Current 10 4MHz VIN = 3.0V 35 30 1 L = 1µH COUT = 4.7µF 0 2.7 3.2 3.7 4.2 4.7 5.2 5.7 INPUT VOLTAGE (V) Frequency vs. Temperature 1.8 1.7 1.6 20 40 60 80 TEMPERATURE (°C) Output Voltage vs. Temperature VIN = 3.6V 0 100 1000 OUTPUT CURRENT (mA) VIN = 3.0V 1.82 1.80 L = 1µH COUT = 4.7µF Load = 120mA VOUT = 1.8V L = 1µH COUT = 4.7µF Output Voltage vs. Output Current 1.90 4.0 1.9 0.01 11 1.88 1.86 1.84 4.5 3.0 VIN = 4.2V 0.1 15 3.5 1 L = 1µH 25 20 5.0 0 100 1000 OUTPUT CURRENT (mA) Enable Threshold vs. Temperature 1.2 L = 1µH COUT = 4.7µF Load = 120mA 700 VIN = 5.5V 1.90 L = 1µH 1.88 COUT = 4.7µF 1.86 1.84 Load = 10mA 1.72 1.70 2.7 3.2 3.7 4.2 4.7 5.2 5.7 INPUT VOLTAGE (V) Enable Threshold vs. Input Voltage 1.000 0.950 0.925 0.6 0.900 Enable ON Enable OFF 0.875 0.4 L = 1µH COUT = 4.7µF 0 20 40 60 80 TEMPERATURE (°C) Current Limit vs. Input Voltage 20 40 60 80 TEMPERATURE (°C) 100 VIN = 3.0V 90 VIN = 2.7V 80 70 VIN = 3.6V 60 VIN = 4.2V 50 40 30 L = 1µH COUT = 4.7µF 5.7 20 10 0 11 L = 1µH COUT = 4.7µF 0 100 1000 OUTPUT CURRENT (mA) 5 VIN = 3.6V VOUT = 1.8V Load = 150mA 0.825 0.800 2.7 3.2 3.7 4.2 4.7 5.2 5.7 INPUT VOLTAGE (V) Efficiency V OUT = 1.2V 600 Load = 1mA 1.78 Load = 300mA 1.76 Load = 50mA Load = 400mA 1.74 0.850 650 June 2010 Output Voltage vs. Input Voltage 0.8 VIN = 2.7V VOUT1 = 1.575V 550 2.7 3.2 3.7 4.2 4.7 5.2 INPUT VOLTAGE (V) 0 100 1000 OUTPUT CURRENT (mA) 0.975 1.0 VIN = 3.6V VOUT2 = 1.8V 0.01 11 VIN = 3.6V VOUT = 1.8V COUT = 4.7µF Load = 150mA VIN = 3.6V 1.72 1.70 11 L = 2.2µH 0.1 1.82 1.80 VIN = 4.2V 1.78 1.76 1.74 0.2 1.5 L = 4.7µH 4MHz 40 10 5 10 Switching Frequency vs. Output Current Efficiency V OUT = 1.575V 100 90 VIN = 2.7V 80 70 VIN = 4.2V 60 50 40 30 20 10 0 11 VIN = 3.0V VIN = 3.6V L = 1µH COUT = 4.7µF 0 100 1000 OUTPUT CURRENT (mA) M9999-061110-E Micrel, Inc. MIC23250 Typical Characteristics (Continued) Efficiency V OUT = 1.8V 100 VIN = 3.0V 90 VIN = 2.7V 80 Efficiency V OUT = 2.5V 100 90 VIN = 2.7V 80 VIN = 3.6V 70 VIN = 4.2V 60 VIN = 3.6V 70 VIN = 4.2V VIN = 3.0V 60 Efficiency V OUT = 3.3V 100 90 80 70 60 50 40 50 40 50 40 30 30 20 10 20 10 30 20 L = 1µH COUT = 4.7µF 0 11 100 90 0 100 1000 OUTPUT CURRENT (mA) Efficiency V OUT = 1.8V With Various Inductors L = 1.5µH 80 70 60 L = 1.0µH L = 0.47µH 50 40 30 20 10 0 11 June 2010 VIN = 3.6V COUT = 4.7µF 0 100 1000 OUTPUT CURRENT (mA) 0 11 L = 1µH COUT = 4.7µF 0 100 1000 OUTPUT CURRENT (mA) 10 0 11 VIN = 4.2V VIN = 5.0V VIN = 5.5V L = 1µH COUT = 4.7µF 0 100 1000 OUTPUT CURRENT (mA) Dual Output Efficiency 100 90 80 70 60 50 VIN = 3.3V VIN = 4.2V VIN = 3.6V 40 VOUT1 = 1.575V 30 VOUT2 = 1.8V 20 Load1 = Load2 L1 = L2 = 1µH 10 COUT1 = COUT2 = 4.7µF 0 11 0 100 1000 OUTPUT CURRENT (mA) 6 M9999-061110-E Micrel, Inc. MIC23250 Functional Characteristics June 2010 7 M9999-061110-E Micrel, Inc. MIC23250 Functional Characteristics (Continued) June 2010 8 M9999-061110-E Micrel, Inc. MIC23250 Functional Characteristics (Continued) June 2010 9 M9999-061110-E Micrel, Inc. MIC23250 Functional Diagram MIC23250 Simplified Fixed Output Block Diagram VIN AVIN ENABLE LOGIC ENABLE LOGIC EN1 GATE DRIVES SW1 ISENSE CONTROL LOGIC TON TIMER & SOFT START Zero X GATE DRIVES CONTROL LOGIC TON TIMER & SOFT START Current Limit - SW2 Zero X ISENSE Current Limit + FB1 EN2 UVLO UVLO REF1 REF2 + ERROR COMPARATOR ERROR COMPARATOR SNS1 FB2 SNS2 PGND AGND MIC23250 Simplified Adjustable Output Block Diagram June 2010 10 M9999-061110-E Micrel, Inc. MIC23250 Functional Description VIN The VIN provides power to the internal MOSFETs for the switch mode regulator along with the current limit sensing. The VIN operating range is 2.7V to 5.5V so an input capacitor with a minimum of 6.3V voltage rating is recommended. Due to the high switching speed, a minimum of 2.2µF bypass capacitor placed close to VIN and the power ground (PGND) pin is required. Based upon size, performance and cost, a TDK C1608X5R0J475K, size 0603, 4.7µF ceramic capacitor is highly recommended for most applications. Refer to the layout recommendations for details. SNS1/SNS2 The SNS pin (SNS1 or SNS2) is connected to the output of the device to provide feedback to the control circuitry. A minimum of 2.2µF bypass capacitor should be connected in shunt with each output. Based upon size, performance and cost, a TDK C1608X5R0J475K, size 0603, 4.7µF ceramic capacitor is highly recommended for most applications. In order to reduce parasitic inductance, it is good practice to place the output bypass capacitor as close to the inductor as possible. The SNS connection should be placed close to the output bypass capacitor. Refer to the layout recommendations for more details. AVIN The analog VIN (AVIN) provides power to the analog supply circuitry. AVIN and VIN must be tied together. Careful layout should be considered to ensure high frequency switching noise caused by VIN is reduced before reaching AVIN. A 0.01µF bypass capacitor placed as close to AVIN as possible is recommended. See layout recommendations for details. PGND The power ground (PGND) 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. Refer to the layout recommendations for more details. EN1/EN2 The enable pins (EN1 and EN2) control the on and off states of outputs 1 and 2, respectively. A logic high signal on the enable pin activates the output voltage of the device. A logic low signal on each enable pin deactivates the output. MIC23250 features built-in soft-start circuitry that reduces in-rush current and prevents the output voltage from overshooting at start up. SW1/SW2 The switching pin (SW1 or SW2) connects directly to one end of the inductor (L1 or L2) and provides the current path during switching cycles. The other end of the inductor is connected to the load and SNS pin. Due to the high speed switching on this pin, the switch node should be routed away from sensitive nodes. AGND The signal 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 layout recommendations for more details. FB1/FB2 (Adjustable Output Only) The feedback pins (FB1/FB2) are two extra pins that can only be found on the MIC23250-AAYMT devices. It allows the regulated output voltage to be set by applying an external resistor network. The internal reference voltage is 0.72V and the recommended value of RBOTTOM is within 10% of 442kΩ. The RTOP resistor is the resistor from the FB pin to the output of the device and RBOTTOM is the resistor from the FB pin to ground. The output voltage is calculated from the equation below. See Compensation under the Applications Information section for recommended feedback component values. ⎛ RTOP ⎞ VOUT = 0.72V ⎜⎜ + 1⎟⎟ ⎝ R BOTTOM ⎠ June 2010 11 M9999-061110-E Micrel, Inc. MIC23250 Applications Information The MIC23250 is designed for high performance with a small solution size. With a dual 400mA output inside a tiny 2mm x 2mm Thin MLF® package and requiring only six external components, the MIC23250 meets today’s miniature portable electronic device needs. While small solution size is one of its advantages, the MIC23250 is big in performance. Using the HyperLight Load™ switching scheme, the MIC23250 is able to maintain high efficiency throughout the entire load range while providing ultra-fast load transient response. Even with all the given benefits, the MIC23250 can be as easy to use as linear regulators. The following sections provide an over view of implementing MIC23250 into related applications Input Capacitor A minimum of 2.2µF ceramic capacitor should be placed close to the VIN pin and PGND pin for bypassing. A TDK C1608X5R0J475K, 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 MIC23250 was designed for use with a 2.2µF or greater ceramic output capacitor. Increasing the output capacitance will lower output ripple and improve load transient response but could increase solution size or cost. A low equivalent series resistance (ESR) ceramic output capacitor such as the TDK C1608X5R0J475K, size 0603, 4.7µF ceramic capacitor is recommended based upon performance, size and cost. Either the X7R or X5R temperature rating capacitors are recommended. The Y5V and Z5U temperature rating capacitors, aside from the undesirable effect of their wide variation in capacitance over temperature, become resistive at high frequencies. Inductor Selection Inductor selection will be determined by the following (not necessarily in the order of importance); • Inductance • Rated current value • Size requirements 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 the inductor selected can handle the maximum operating current. When saturation current is specified, make sure that there is enough margin so that the peak current of the inductor does not cause it to saturate. Peak current can be calculated as follows: ⎡ ⎛ 1 − VOUT / VIN ⎞⎤ I PEAK = ⎢I OUT + VOUT ⎜⎜ ⎟⎟⎥ ⎝ 2 × f × L ⎠⎦ ⎣ As shown by the previous calculation, 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 also increases. The size of the inductor depends on the requirements of the application. Refer to the Application Circuit and Bill of Material 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. Compensation The MIC23250 is designed to be stable with a 0.47µH to 4.7µH inductor with a minimum of 2.2µF ceramic (X5R) output capacitor. For the adjustable MIC23250, the total feedback resistance should be kept around 1MΩ to reduce current loss down the feedback resistor network. This helps to improve efficiency. A feed-forward capacitor (CFF) of 120pF must be used in conjunction with the external feedback resistors to reduce the effects of parasitic capacitance that is inherent of most circuit board layouts. Figure 1 and Table 1 shows the recommended feedback resistor values along with the recommended feed-forward capacitor values for the MIC23250 adjustable device. RTOP • DC resistance (DCR) The MIC23250 was designed for use with an inductance range from 0.47µH to 4.7µH. Typically, a 1µH inductor is recommended for a balance of transient response, efficiency and output ripple. For faster transient response a 0.47µH inductor may be used. For lower output ripple, a 4.7µH is recommended. June 2010 CFF RBOTTOM Figure 1. Feedback Resistor Network 12 M9999-061110-E Micrel, Inc. MIC23250 There are two types of losses in switching converters; DC losses and switching losses. DC losses are simply the power dissipation of I2R. Power is dissipated in the high side 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 is another DC loss. The current required driving the gates on and off at a constant 4MHz frequency and the switching transitions make up the switching losses. VOUT (V) RTOP (kΩ) RBOTTOM (kΩ) CFF (pF) 0.8 49 442 120 0.9 111 442 120 1 172 442 120 1.1 233 442 120 1.2 295 442 120 1.3 356 442 120 1.4 417 442 120 1.5 479 442 120 1.6 540 442 120 1.7 602 442 120 1.8 663 442 120 1.9 724 442 120 80 2 786 442 120 60 2.1 847 442 120 2.2 909 442 120 2.3 970 442 120 2.4 1031 442 120 2.5 1093 442 120 2.6 1154 442 120 2.7 1216 442 120 2.8 1277 442 120 2.9 1338 442 120 3 1400 442 120 3.1 1461 442 120 3.2 1522 442 120 3.3 1584 442 120 Table 1. Recommended Feedback Component Values Efficiency Considerations Efficiency is defined as the amount of useful output power, divided by the amount of power supplied. ⎛V × I OUT Efficiency % = ⎜⎜ OUT ⎝ V IN × I IN ⎞ ⎟⎟ × 100 ⎠ 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 hand held devices. June 2010 Efficiency V OUT = 1.8V 100 VIN = 2.7V VIN = 3.6V VIN = 3.3V 40 20 0 0.1 VOUT = 1.8V L = 1µH 11 0 100 LOAD (mA) 1000 The Figure above shows an efficiency curve. From no load to 100mA, efficiency losses are dominated by quiescent current losses, gate drive and transition losses. By using the HyperLight Load™ mode the MIC23250 is able to maintain high efficiency at low output currents. Over 100mA, efficiency loss is dominated by MOSFET RDSON and inductor losses. Higher input supply voltages will increase the Gate-to-Source threshold 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. In which case, inductor selection becomes increasingly critical in efficiency calculations. As the inductors are reduced in size, the DC resistance (DCR) can become quite significant. The DCR losses can be calculated as follows: DCR Loss = IOUT2 × DCR From that, the loss in efficiency due to inductor resistance can be calculated as follows: ⎡ ⎛ VOUT × I OUT Efficiency Loss = ⎢1 − ⎜⎜ ⎣ ⎝ VOUT × I OUT + L _ PD ⎞⎤ ⎟⎟⎥ × 100 ⎠⎦ 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. 13 M9999-061110-E Micrel, Inc. HyperLight Load Mode™ The MIC23250 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 minimumon-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 MIC23250 works in pulse frequency modulation (PFM) to regulate the output. As the output current increases, the off-time decreases, thus providing more energy to the output. This switching scheme improves the efficiency of MIC23250 during light load currents by only switching when it is needed. As the load current increases, the MIC23250 goes into continuous conduction mode (CCM) and switches at a frequency centered at 4MHz. The equation to calculate the load when the MIC23250 goes into continuous conduction mode may be approximated by the following formula: MIC23250 As shown in the previous equation, the load at which MIC23250 transitions from HyperLight Load™ mode to PWM mode is a function of the input voltage (VIN), output voltage (VOUT), duty cycle (D), inductance (L) and frequency (f). This is illustrated in the graph below. Since the inductance range of MIC23250 is from 0.47µH to 4.7µH, the device may then be tailored to enter HyperLight Load™ mode or PWM mode at a specific load current by selecting the appropriate inductance. For example, in the graph below, when the inductance is 4.7µH the MIC23250 will transition into PWM mode at a load of approximately 5mA. Under the same condition, when the inductance is 1µH, the MIC23250 will transition into PWM mode at approximately 70mA. 10 L = 4.7µH 4MHz 1 L = 1µH L = 2.2µH 0.1 0.01 11 ⎛ (V − VOUT ) × D ⎞ ⎟⎟ I LOAD > ⎜⎜ IN 2L × f ⎝ ⎠ June 2010 Switching Frequency vs. Output Current 14 VIN = 3.6V VOUT = 1.8V COUT = 4.7µF 0 100 1000 OUTPUT CURRENT (mA) M9999-061110-E Micrel, Inc. MIC23250 MIC23250 Typical Application Circuit (Fixed Output) Bill of Materials Item C1, C2, C3 Part Number C1608X5R0J475K Manufacturer (1) TDK Description 4.7µF Ceramic Capacitor, 6.3V, X5R, Size 0603 (2) C4 VJ0603Y103KXXAT Vishay 0.01µF Ceramic Capacitor, 25V, X7R, Size 0603 R1, R2 CRCW06031002FKEA Vishay(2) 10kΩ, 1%, 1/16W, Size 0603 LQM21PN1R0MC0D Murata(3) 1µH, 0.8A, 190mΩ, L2mm x W1.25mm x H0.5mm L1, L2 LQH32CN1R0M33 Murata 1µH, 1A, 60mΩ, L3.2mm x W2.5mm x H2.0mm LQM31PN1R0M00 Murata(3) 1µH, 1.2A, 120mΩ, L3.2mm x W1.6mm x H0.95mm GLF251812T1R0M LQM31PNR47M00 MIPF2520D1R5 EPL2010-102 U1 (3) MIC23250-xxYMT TDK (1) 1µH, 0.8A, 100mΩ, L2.5mm x W1.8mm x H1.35mm (3) Murata FDK (4) Coilcraft Qty 3 1 Optional 2 0.47µH, 1.4A, 80mΩ, L3.2mm x W1.6mm x H0.85mm 1.5µH, 1.5A, 70mΩ, L2.5mm x W2mm x H1.0mm (5) Micrel, Inc.(6) 1.0µH, 1.0A, 86mΩ, L2.0mm x W1.8mm x H1.0mm 4MHz Dual 400mA Fixed Output Buck Regulator with HyperLight Load™ Mode 1 Notes: 1. TDK: www.tdk.com. 2. Vishay: www.vishay.com. 3. Murata: www.murata.com. 4. FDK: www.fdk.co.jp. 5. Coilcraft: www.coilcraft.com. 6. Micrel, Inc: www.micrel.com. June 2010 15 M9999-061110-E Micrel, Inc. MIC23250 PCB Layout Recommendations (Fixed Output) Top Layer Bottom Layer June 2010 16 M9999-061110-E Micrel, Inc. MIC23250 MIC23250 Typical Application Circuit (Adjustable Output) Bill of Materials Item Part Number C1, C2, C3 C1608X5R0J475K C4 VJ0603Y103KXXAT Manufacturer TDK(1) Description Qty 4.7µF Ceramic Capacitor, 6.3V, X5R, Size 0603 3 (2) 0.01µF Ceramic Capacitor, 25V, X7R, Size 0603 1 (2) Vishay C5, C6 VJ0603Y121KXAAT Vishay 120pF Ceramic Capacitor, 50V, X7R, Size 0603 R1, R2 CRCW06031002FKEA Vishay(2) 10kΩ, 1%, 1/16W, Size 0603 Optional R3, R5 CRCW06036653FKEA Vishay(2) 665kΩ, 1%, 1/16W, Size 0603 2 CRCW06034423FKEA (2) 442kΩ, 1%, 1/16W, Size 0603 2 (3) R4, R6 L1, L2 LQM21PN1R0MC0D Murata 1µH, 0.8A, 190mΩ, L2mm x W1.25mm x H0.5mm LQH32CN1R0M33 Murata(3) 1µH, 1A, 60mΩ, L3.2mm x W2.5mm x H2.0mm LQM31PN1R0M00 (3) GLF251812T1R0M LQM31PNR47M00 MIPF2520D1R5 EPL2010-102 U1 Vishay MIC23250-AAYMT Murata TDK (1) FDK(4) Coilcraft 1µH, 1.2A, 120mΩ, L3.2mm x W1.6mm x H0.95mm 1µH, 0.8A, 100mΩ, L2.5mm x W1.8mm x H1.35mm Murata(3) 2 2 0.47µH, 1.4A, 80mΩ, L3.2mm x W1.6mm x H0.85mm 1.5µH, 1.5A, 70mΩ, L2.5mm x W2mm x H1.0mm (5) Micrel, Inc.(6) 1.0µH, 1.0A, 86mΩ, L2.0mm x W1.8mm x H1.0mm 4MHz Dual 400mA Adjustable Output Buck Regulator with HyperLight Load™ Mode 1 Notes: 1. TDK: www.tdk.com. 2. Vishay: www.vishay.com. 3. Murata: www.murata.com. 4. FDK: www.fdk.co.jp. 5. Coilcraft: www.coilcraft.com. 6. Micrel, Inc: www.micrel.com. June 2010 17 M9999-061110-E Micrel, Inc. MIC23250 PCB Layout Recommendations (Adjustable Output) Top Layer Bottom Layer June 2010 18 M9999-061110-E Micrel, Inc. MIC23250 Package Information (Fixed Output) ® 10-Pin 2mm x 2mm Thin MLF (MT) June 2010 19 M9999-061110-E Micrel, Inc. MIC23250 Package Information (Adjustable Output) ® 12-Pin 2.5mm x 2.5mm Thin MLF (MT) 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. © 2007 Micrel, Incorporated. June 2010 20 M9999-061110-E