MIC23303 Evaluation Board 4MHz PWM 3A Buck Regulator with Hyper Light Load® and Power Good General Description Getting Started This board allows the customer to evaluate the MIC23303, a fully integrated 3A, 4MHz switching regulator that features Hyper Light Load® mode, a Power Good output indicator, and programmable soft-start. The MIC23303 is highly efficient throughout the output current range, drawing just 24µA of quiescent current in operation. The tiny 3mm x 3mm DFN package, in combination with the 4MHz switching frequency, creates a compact sub-1mm height solution with only six external components. The MIC23303 provides accurate output voltage regulation under the most demanding conditions and responds extremely quickly to a load transient with exceptionally small output voltage ripple. 1. Connect an external supply to the VIN (J1) terminal and GND (J6). With the output of the power supply disabled, set its voltage to the desired input test voltage (2.9V ≤ VIN ≤ 5.5V). The user can place an ammeter between the input supply and the VIN (J1) terminal. 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 device. 2. Connect a load to the VOUT (J5) and ground (J2) terminals. The load can be either active passive (resistive) or active (electronic load). The user can place an ammeter between the load and the output terminal. Make sure the output voltage is monitored at the VOUT (J5) terminal. The board has a 2-pin connector (JP1) to allow for output voltage monitoring. 3. Enable the MIC23303. The MIC23303 evaluation board has a pull-up resistor to VIN. By default, the output voltage is enabled when the input supply of >2.9V is applied. To disable the device, apply a voltage below 0.5V to the EN (J3) terminal. 4. Power Good. The board provides a Power Good test point (J4) to monitor the Power Good function. The Power Good output goes high (VOUT) approximately 160µs after the output voltage reaches 90% of its nominal voltage. Requirements This board needs a single 10W bench power source adjustable from 2.9V to 5.5V. The loads can be either active (electronic load) or passive (resistor), and must be able to dissipate 10W. It is ideal, but not essential, to have an oscilloscope available to view the circuit waveforms. The simplest tests require two voltage meters to measure input and output voltage. Efficiency measurements require two voltage meters and two ammeters to prevent errors caused by measurement inaccuracies. Precautions There is no reverse input protection on this board. Be careful when connecting the input source to make sure correct polarity is observed. Data sheets and support documentation can be found on Micrel’s web site at www.micrel.com. Ordering Information Part Number Description MIC23303YML EV Adjustable Output Evaluation Board Hyper Light Load is a registered trademark of Micrel, Inc. MLF and MicroLeadFrame are registered trademark 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 October 2012 M9999-100912-A Micrel, Inc. MIC23303 Evaluation Board The feed-forward capacitor, C4, can be fitted to improve transient performance. This improves transients by injecting fast output voltage deviations directly into the feedback comparator. This improved load regulation is at the expense of slightly increasing the amount of noise on the output at higher loads. A typical value range of 22pF to 68pF is recommended. Evaluation Board Power Good (PG) The evaluation board provides a test point above EN for testing PG. This is an open-drain connection to the output voltage with an on-board pull-up resistor of 10kΩ. This is asserted high approximately 160µs after the output voltage passes 90% of the nominal set voltage. Hyper Light 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, the error comparator turns the PMOS off for a minimum-offtime until the output drops below the threshold. The NMOS acts as an ideal rectifier that conducts when the PMOS is off. Using an 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, which provides more energy to the output. This switching scheme improves the efficiency of MIC23303 during light load currents by switching only 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 is approximated by the following formula: Other Features Soft-Start Capacitor (C2) The soft-start (SS) pin is used to control the output voltage ramp-up time. Setting C2 to 2.2nF sets the startup time to the minimum. The start-up time can be determined by: TSS = 250x103 x ln(10) x CSS The soft-start capacitor controls the rise time of the internal reference voltage between 0% and 100% of its nominal steady state value. Feedback Resistors (R3, R4) for Adjustable Output The output voltage is set nominally to 1.8V. This output can be changed by adjusting the upper resistor, R3, in the feedback potential divider. Therefore: R3 = R4 x VREF/(VO-VREF) ⎛ (V − VOUT ) × D ⎞ ⎟⎟ ILOAD > ⎜⎜ IN 2L × f ⎠ ⎝ The previous equation shows that the load at which MIC23303 transitions from Hyper Light Load mode to PWM mode is a function of the input voltage (VIN), output voltage (VOUT), duty cycle (D), inductance (L), and frequency (f). The “Switching Frequency vs. Load” graph on page 3 shows that, as the output current increases, the switching frequency also increases until the MIC23303 goes from Hyper Light Load mode to PWM mode at approximately 300mA. The MIC23303 will switch at a relatively constant frequency around 4MHz after the output current is over 300mA. Where VREF = 0.62V. Some example values are: VOUT R3 R4 1.2V 274kΩ 294kΩ 1.5V 316kΩ 221kΩ 1.8V 560kΩ 294kΩ 2.5V 324kΩ 107kΩ 3.3V 464kΩ 107kΩ October 2012 2 M9999-100912-A Micrel, Inc. MIC23303 Evaluation Board Evaluation Board Performance Efficiency vs. Load 1.8VOUT @25°C Switching Frequency vs. Load Current VIN = 5V 100 VIN = 3V 10 1 VOUT = 1.8V 0.1 0.0001 0.001 0.01 0.1 1 100 100 90 90 80 80 70 60 VIN = 3.6V 50 40 30 30 0.1 1 10 0 0.0001 0.001 0.01 0.1 1 10 LOAD CURRENT (A) Enable Threshold vs. Input Voltage 1.1 100000 1.0 VEN THRESHOLD (V) RISE TIME (µs) 0.01 VIN = 5V VIN = 3V 40 10 LOAD CURRENT(A) VOUT Rise Time vs. CSS 10000 1000 100 10 0.9 0.8 0.7 0.6 VIN = 3.6V 1 1000 50 20 0.001 VIN = 3.6V 60 10 LOAD CURRENT (A) 1000000 70 20 0 0.0001 10 VIN = 5V EFFICIENCY (%) 1000 EFFICIENCY (%) SW FREQUENCY (kHz) 10000 Efficiency vs. Load 1.2VOUT @25°C TCASE = 25°C 0.5 10000 100000 CSS (pF) 1000000 2.5 3.0 3.5 4.0 4.5 5.0 5.5 INPUT VOLTAGE (V) MIC23303-YML Evaluation Board Schematic October 2012 3 M9999-100912-A Micrel, Inc. MIC23303 Evaluation Board Bill of Materials Item Part Number 06036D475KAT2A C1 GRM188R60J475ME19D C1608X5R0J475M 06035C222KAT2A C2 GRM188R71H222MA01D C3,C8 C4 C6 C7 06035A330KAT2A AVX Murata Panasonic(4) Murata TDK 06035D104KAT2A AVX 0520CDMCDSNP-R33MC 744373240033 1 22µF/6.3V, X5R, 0805 1 33pF/50V, 0603 1 CAP ALUM 220UF 10V 20% RADIAL 1 1µF/6.3V, X5R, 0603 1 0.1µF/6.3V, X5R, 0603 1 AVX C1608X5R0J105K C1608X5R1H104K L1 Murata TDK GRM188R71H104KA930 2.2nF/50V, X7R, 0603 AVX Murata C2012X5R0J226M GRM188R60J105KA01D 1 TDK AVX 06036D105KAT2A 4.7µF/6.3V, X5R, 0603 (3) 08056D226MAT2A ECA-1AHG221 Qty AVX Murata(2) TDK GRM21BR60J226ME39L Description (1) C1608X7R1H222K GRM1885C1H330JA01D C5 Manufacturer Murata TDK Sumida(5) (6) Wurth 0.33µH/5.6A, 8mΩ 1 0.33µH/8.0A, 8.6mΩ R1,R2 CRCW060310K0FKEA Vishay/Dale(7) 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 MIC23303-YML 4MHz 3A Buck Regulator with Hyper Light Load® Mode 1 Micrel, Inc.(8) Notes: 1. AVX: www.avx.com. 2. TDK: www.tdk.com. 3. Murata: www.murata.com. 4. Panasonic: www.panasonic.com. 5. Sumida: www.sumida.com. 6. Wurth: www.we-online.com. 7. Vishay: www.vishay.com. 8. Micrel, Inc.: www.micrel.com. October 2012 4 M9999-100912-A Micrel, Inc. MIC23303 Evaluation Board PCB Layout Recommendations Top Layer Bottom Layer October 2012 5 M9999-100912-A Micrel, Inc. MIC23303 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 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. © 2012 Micrel, Incorporated. October 2012 6 M9999-100912-A