MIC23250 Evaluation Board 4MHz Dual 400mA Synchronous Buck Regulator with HyperLight Load™ General Description The MIC23250 is a dual 400mA 4MHz switching regulator with HyperLight Load™ mode. The MIC23250 is highly efficient, consuming 33µA of quiescent current to operate both of its outputs. A Sub-1mm height solution is easily attainable using the tiny package (2mm x 2mm x 0.55mm) and only six external components. Small and fast, the MIC23250 can respond to a load transient at ultra-fast speed while reducing output peak-to-peak voltage. The MIC23250 has two modes of operation that is automatically selected by the internal circuitry. Under light load conditions, the MIC23250 goes into HyperLight Load™ mode. The MIC23250 HyperLight Load™ uses a Pulse-Frequency Modulation (PFM) control scheme that controls the off time at light load. This allows the device to reduce the amount of switching needed at light load, thus reducing the switching losses. The MIC23250 can attain up to 85% efficiency at 1mA output load. At higher output currents of approximately 100mA, HyperLight Load™ mode automatically switches back to Pulse-Width Modulation (PWM) mode to ensure high efficiency up to 94% at higher load. The two modes of operation ensure that the MIC23250 maintains the highest efficiency throughout the entire load range. The MIC23250 operates from a 2.7V to 5.5V input and features internal power MOSFETs that can supply up to 400mA of output current on each channel. It can operate with a maximum duty cycle of 90%. Requirements The MIC23250 evaluation board requires an input power source that is able to deliver greater than 800mA at 2.7V. The output loads can either be an active (electronic) or passive (resistive) load. Getting Started 1. Connect an external supply to the VIN (J1) terminal. Apply desired input voltage to the VIN (J1) and ground (J2) terminal of the evaluation board, paying careful attention to polarity and supply voltage (2.7V < VIN < 5.5V). An ammeter may be placed between the input supply and the VIN (J1) terminal to the evaluation board. Be sure to monitor the supply voltage at the VIN (J1) terminal, as the ammeter and/or power lead resistance can reduce the voltage supplied to the input. 2. Connect a load to the VO1 (J4) and VO2 (J6) outputs and ground terminal (J7). The loads can be either passive (resistive) or active (electronic load). An ammeter can be placed between the load and the output terminal. Ensure that the output voltages are monitored at the VO1 (J4) and VO2 (J6) terminals. 3. Enable the MIC23250 outputs. The MIC23250 evaluation board has pre-installed pull-up resistors (R1 and R2) that enable the device as soon as input voltage is applied. These resistors are optional. To disable the device, apply a voltage below 0.5V to EN1 (J3) or EN2 (J5) terminals. Similarly, if the pull up resistors (R1 and R2) are not used the device may be enabled by applying a voltage greater than 1.2V to the EN1 (J3) or EN2 (J5) terminals. Be sure that the enable voltage never exceeds the input voltage. Output Voltage The MIC23250 evaluation board has fixed output voltage options available per the table below. Ordering Information Part Number Description MIC23250-C4YMT EV 1.2V / 1.0V Output Evaluation Board MIC23250-G4YMT EV 1.2V / 1.8V Output Evaluation Board MIC23250-S4YMT EV 1.2V / 3.3V Output Evaluation Board MIC23250-AAYMT EV Adjustable Output Evaluation Board Note: Other voltage options available upon request. Contact Micrel. 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 July 2009 M9999-070909-C Micrel, Inc. MIC23250 Evaluation Board Feedback Resistor Selection (Adjustable 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. VOUT ⎛ RTOP ⎞ = 0.72V ⎜⎜ + 1⎟⎟ R ⎝ BOTTOM ⎠ 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 as high as possible 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 for the MIC23250 adjustable device. RTOP CFF RBOTTOM 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 2 786 442 120 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 Figure 1. Feedback Resistor Network For VO1 the feedback components are: RTOP = R3, RBOTTOM = R4, CFF = C5. For VO2 the feedback components are: RTOP = R5, RBOTTOM = R6, CFF = C6. July 2009 2 M9999-070909-C Micrel, Inc. MIC23250 Evaluation Board 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 4mA. Under the same condition, when the inductance is 1µH, the MIC23250 will transition into PWM mode at approximately 70mA. HyperLight Load Mode™ 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 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 minimumoff-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 provides 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: 10 Switching Frequency vs. Output Current L = 4.7µH 4MHz 1 L = 1µH L = 2.2µH 0.1 0.01 1 VIN = 3.6V VOUT = 1.8V COUT = 4.7µF 10 100 1000 OUTPUT CURRENT (mA) ⎛ V − VOUT × D ⎞ ⎟⎟ I LOAD = ⎜⎜ IN 2L × f ⎠ ⎝ July 2009 3 M9999-070909-C Micrel, Inc. MIC23250 Evaluation Board MIC23250 Evaluation Board Schematic (Fixed Output) Bill of Materials Item C1, C2, C3 Part Number C1608X5R0J475K Manufacturer (1) TDK (2) Qty 4.7µF Ceramic Capacitor, 6.3V, X5R, Size 0603 3 C4 VJ0603Y103KXXAT 0.01µF Ceramic Capacitor, 25V, X7R, Size 0603 1 R1, R2 CRCW060310K0FKEA Vishay(2) 10kΩ Resistor, 1%, 1/16W, Size 0603 Optional LQM21PN1R0M00 Murata(3) 1µH, 0.8A, 190mΩ, L2mm x W1.25mm x H0.5mm LQH32CNR1R0M33 L1, L2 (3) Murata 1µH, 1A, 60mΩ, L3.2mm x W2.5mm x H2.0mm LQM31P1R0M00 Murata(3) 1µH, 1.2A, 120mΩ, L3.2mm x W1.6mm x H0.95mm GLF251812T1R0M TDK(1) 1µH, 0.8A, 100mΩ, L2.5mm x W1.8mm x H1.35mm LQM31PNR47M00 Murata(3) 0.47µH, 1.4A, 80mΩ, L3.2mm x W1.6mm x H0.85mm MIPF2520D1R5 U1 Vishay Description MIC23250-xxYMT FDK (4) Micrel, Inc. 2 1.5µH, 1.5A, 70mΩ, L2.5mm x W2mm x H1.0mm 4MHz Dual 400mA Buck Regulator with HyperLight Load™ Mode (5) 1 Notes: 1. TDK: www.tdk.com 2. Vishay: www.vishay.com 3. Murata: www.murata.com 4. FDK: www.fdk.co.jp 5. Micrel, Inc: www.micrel.com July 2009 4 M9999-070909-C Micrel, Inc. MIC23250 Evaluation Board MIC23250 Evaluation Board Schematic (Adjustable Output) Bill of Materials Item Part Number Manufacturer (1) Qty C1, C2, C3 C1608X5R0J475K 4.7µF Ceramic Capacitor, 6.3V, X5R, Size 0603 3 C4 VJ0603Y103KXXAT Vishay(2) 0.01µF Ceramic Capacitor, 25V, X7R, Size 0603 1 VJ0603Y121KXAAT (2) 120pF Ceramic Capacitor, 50V, X7R, Size 0603 2 C5, C6 TDK Description Vishay (2) R1, R2 CRCW06031002FKEA Vishay 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) 1µH, 0.8A, 190mΩ, L2mm x W1.25mm x H0.5mm R4, R6 LQM21PN1R0M00 LQH32CN1R0M33 L1, L2 Murata (3) Murata 1µH, 1A, 60mΩ, L3.2mm x W2.5mm x H2.0mm LQM31P1R0M00 Murata(3) 1µH, 1.2A, 120mΩ, L3.2mm x W1.6mm x H0.95mm GLF251812T1R0M TDK(1) 1µH, 0.8A, 100mΩ, L2.5mm x W1.8mm x H1.35mm LQM31PNR47M00 MIPF2520D1R5 EPL2010-102 U1 Vishay MIC23250-AAYMT (3) Murata FDK(4) Coilcraft 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 July 2009 5 M9999-070909-C Micrel, Inc. MIC23250 Evaluation Board PCB Layout Recommendations (Fixed Output) Top Layer Bottom Layer July 2009 6 M9999-070909-C Micrel, Inc. MIC23250 Evaluation Board PCB Layout Recommendations (Adjustable Output) Top Layer Bottom Layer July 2009 7 M9999-070909-C Micrel, Inc. MIC23250 Evaluation Board 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. July 2009 8 M9999-070909-C