MIC23450 Evaluation Board 3MHz, PWM, 2A Triple Buck Regulator with HyperLight 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 MIC23450, a fully-integrated, triple-output, 2A, 3MHz terminal and GND (J3). switching regulator that features HyperLight Load mode With the output of the power supply disabled, set its and power good (PG) output indicators. The MIC23450 voltage to the desired input test voltage (2.7V V IN is highly efficient throughout the output current range, 5.5V). An ammeter may be placed between the input drawing just 23A of quiescent current for each channel supply and the V (J1) terminal. Be sure to monitor IN in operation. The tiny 5mm x 5mm MLF package saves the supply voltage at the V (J1) terminal, as the IN board space and requires few external components. The ammeter and/or power lead resistance can reduce MIC23450 provides 2.5% output voltage accuracy and the voltage supplied to the device. each channel responds typically in less than 10s to a 2. Connect a load to the V terminals (J2, J5, J7) OUT load transient with as low as 5mV output voltage ripple. and ground (J4, J6, J8) terminals. Requirements The load can be either active passive (resistive) or active (electronic load). An ammeter may be placed This board needs a single 40W bench power source, between the loads and the output terminals. Make adjustable from 2.7V to 5.5V. The loads can be either sure the output voltage is monitored at V V OUT1, OUT2 active (electronic load) or passive (resistor), and must be and V (J2, J5 and J7) terminals. The board has OUT3 able to dissipate 20W. It is ideal, but not essential, to multiple 2-pin connectors (JP1, JP2 and JP3) to have an oscilloscope available to view the circuit allow for output voltage monitoring of V , V OUT1 OUT2 waveforms. The simplest tests require two voltage and V respectively. OUT3 meters to measure input and output voltage. Efficiency 3. Enable the Supply to MIC23450. measurements for a single channel require two voltage meters and two ammeters to prevent errors caused by The MIC23450 evaluation board has a pull-up measurement inaccuracies. resistor to V for each channel. By default, each IN output voltage is enabled when the input supply of Precautions >2.7V is applied. Each channel 1, 2 or 3 can be There is no reverse input protection on this board. Be disabled by applying a voltage below 0.4V to the EN careful when connecting the input source to make sure terminal J10, J12 or J14 respectively. correct polarity is observed. 4. Power Good. The board provides a power good test point (J9, J11, and J13) to monitor the power good function for each of the channels 1, 2, and 3 respectively. The power good output goes high (V ) nominally 62s OUT after the output voltage reaches 90% of its nominal voltage. Ordering Information Part Number Description 3MHz, PWM, 2A Triple Buck MIC23450-AAAYML EV Regulator Evaluation Board HyperLight 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. MIC23450 Evaluation Board Table 1 Evaluation Board Output Voltage Programming Examples V , V , V R4, R6, R12 R5, R7, R14 OUT1 OUT2 OUT3 1.2V 274k 294k 1.5V 316k 221k 1.8V 301k 158k 2.5V 324k 107k 3.3V 309k 71.5k Power Good (PG1, PG2, PG3) The evaluation board has test points for channels 1, 2, and 3 to monitor the PG1, PG2 and PG3 signals. These are open-drain connections to the corresponding output voltage with on-board pull-up resistors of 100k. The PG signal will be asserted high approximately 62s after the output voltage passes 90% of the nominal set voltage. Other Features Hyper Light Load Mode Soft-Start The MIC23450 uses a minimum on and off time The MIC23450 has an internal soft start for each proprietary control loop (patented by Micrel). When the individual channel and requires no external soft start output voltage falls below the regulation threshold, the capacitor. The typical soft-start time for each channel is error comparator begins a switching cycle that turns the 115s. PMOS on and keeps it on for the duration of the minimum-on-time. This increases the output voltage. If Feedback Resistors (R4-R7, R12, R14) the output voltage is over the regulation threshold, the The feedback pins FB1, FB2, and FB3 are the control error comparator turns the PMOS off for a minimum-off- inputs for programming the output voltages V , V OUT1 OUT2 time until the output drops below the threshold. The and V respectively. Resistor divider networks are OUT3 NMOS acts as an ideal rectifier that conducts when the connected to these pins from the output and are PMOS is off. Using an NMOS switch instead of a diode compared to the internal 0.62V reference within the allows for lower voltage drop across the switching device regulation loop. The output voltage can be programmed when it is on. The asynchronous switching combination between 1V and 3.3V using resistor values calculated by between the PMOS and the NMOS allows the control Equation 1: loop to work in discontinuous mode for light load operations. In discontinuous mode, the MIC23450 works in pulse frequency modulation (PFM) to regulate the R4 V = V 1 + OUT1 REF output. As the output current increases, the off-time R5 decreases, which provides more energy to the output. R6 This switching scheme improves the efficiency of V = V 1 + Eq. 1 OUT2 REF MIC23450 during light load currents by switching only R7 when it is needed. As the load current increases, the R12 V = V 1 + MIC23450 goes into continuous conduction mode (CCM) OUT3 REF R14 and switches at a frequency centered at 3MHz. The equation to calculate the load when the MIC23450 goes into continuous conduction mode is approximated by Example feedback resistor values are provided in Table Equation 2: 1. (V V ) D IN OUT I > Eq. 2 LOAD 2L f Revision 1.0 February 4, 2013 2