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 1. Connect an external supply to the V (J1) IN MIC23303, a fully integrated 3A, 4MHz switching terminal and GND (J6). With the output of the regulator that features Hyper Light Load mode, a Power power supply disabled, set its voltage to the desired Good output indicator, and programmable soft-start. The input test voltage (2.9V V 5.5V). The user can IN MIC23303 is highly efficient throughout the output place an ammeter between the input supply and the current range, drawing just 24A of quiescent current in V (J1) terminal. Be sure to monitor the supply IN operation. The tiny 3mm x 3mm DFN package, in voltage at the V (J1) terminal, as the ammeter IN combination with the 4MHz switching frequency, creates and/or power lead resistance can reduce the voltage a compact sub-1mm height solution with only six supplied to the device. external components. The MIC23303 provides accurate 2. Connect a load to the V (J5) and ground (J2) OUT output voltage regulation under the most demanding terminals. The load can be either active passive conditions and responds extremely quickly to a load (resistive) or active (electronic load). The user can transient with exceptionally small output voltage ripple. place an ammeter between the load and the output terminal. Make sure the output voltage is monitored Requirements at the V (J5) terminal. The board has a 2-pin OUT This board needs a single 10W bench power source connector (JP1) to allow for output voltage adjustable from 2.9V to 5.5V. The loads can be either monitoring. active (electronic load) or passive (resistor), and must be 3. Enable the MIC23303. The MIC23303 evaluation able to dissipate 10W. It is ideal, but not essential, to board has a pull-up resistor to V . By default, the IN have an oscilloscope available to view the circuit output voltage is enabled when the input supply of waveforms. The simplest tests require two voltage >2.9V is applied. To disable the device, apply a meters to measure input and output voltage. Efficiency voltage below 0.5V to the EN (J3) terminal. measurements require two voltage meters and two 4. Power Good. The board provides a Power Good ammeters to prevent errors caused by measurement test point (J4) to monitor the Power Good function. inaccuracies. The Power Good output goes high (V ) OUT approximately 160s after the output voltage Precautions reaches 90% of its nominal voltage. There is no reverse input protection on this board. Be careful when connecting the input source to make sure correct polarity is observed. Ordering Information Data sheets and support documentation can be found on Part Number Description Micrels web site at www.micrel.com. 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 Micrel, Inc. MIC23303 Evaluation Board The feed-forward capacitor, C4, can be fitted to improve Evaluation Board 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. 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 10k . This is asserted high approximately 160s 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-off- time until the output drops below the threshold. The Other Features NMOS acts as an ideal rectifier that conducts when the PMOS is off. Using an NMOS switch instead of a diode Soft-Start Capacitor (C2) allows for lower voltage drop across the switching device The soft-start (SS) pin is used to control the output when it is on. The asynchronous switching combination voltage ramp-up time. Setting C2 to 2.2nF sets the start- between the PMOS and the NMOS allows the control up time to the minimum. The start-up time can be loop to work in discontinuous mode for light load determined by: operations. In discontinuous mode, the MIC23303 works 3 in pulse frequency modulation (PFM) to regulate the T = 250x10 x ln(10) x C SS SS output. As the output current increases, the off-time The soft-start capacitor controls the rise time of the decreases, which provides more energy to the output. internal reference voltage between 0% and 100% of its This switching scheme improves the efficiency of nominal steady state value. MIC23303 during light load currents by switching only when it is needed. As the load current increases, the Feedback Resistors (R3, R4) for Adjustable Output MIC23303 goes into continuous conduction mode (CCM) The output voltage is set nominally to 1.8V. This output and switches at a frequency centered at 4MHz. The can be changed by adjusting the upper resistor, R3, in equation to calculate the load when the MIC23303 goes the feedback potential divider. Therefore: into continuous conduction mode is approximated by the following formula: R3 = R4 x V /(V -V ) REF O REF (V V ) D IN OUT I > Where V = 0.62V. LOAD REF 2L f Some example values are: The previous equation shows that the load at which MIC23303 transitions from Hyper Light Load mode to V R3 R4 OUT PWM mode is a function of the input voltage (V ), output IN 1.2V 274k 294k voltage (V ), duty cycle (D), inductance (L), and OUT 1.5V 316k 221k frequency (f). The Switching Frequency vs. Load graph on page 3 shows that, as the output current increases, 1.8V 560k 294k the switching frequency also increases until the 2.5V 324k 107k MIC23303 goes from Hyper Light Load mode to PWM 3.3V 464k 107k mode at approximately 300mA. The MIC23303 will switch at a relatively constant frequency around 4MHz after the output current is over 300mA. M9999-100912-A October 2012 2