MIC23603 Evaluation Board 4MHz PWM 6A Buck Regulator with Hyper Light Load General Description Getting Started The MIC23603 evaluation board allows the customer to 1. Connect an external supply to the V (J1) terminal IN evaluate the MIC23603, a fully-integrated 6A, 4MHz and GND (J2). switching regulator that features Hyper Light Load mode, With the output of the power supply disabled, set its a power good output indicator, and programmable soft- voltage to the desired input test voltage (2.7V V IN start. The MIC23603 is highly efficient throughout the 5.5V). An ammeter may be placed between the input output current range, drawing just 24A of quiescent supply and the V (J1) terminal. Be sure to monitor IN current in operation. The tiny 4mm 5mm DFN package the supply voltage at the V (J1) terminal, as the IN saves precious board space and requires few external ammeter and/or power lead resistance can reduce the components. The MIC23603 provides accurate output voltage supplied to the device. voltage regulation under the most demanding conditions 2. Connect a load to the V (J4) and ground (J3) OUT and responds extremely quickly to a load transient with terminals. exceptionally small output voltage ripple. The load can be either active passive (resistive) or Requirements active (electronic load). An ammeter may be placed The MIC23603 evaluation board requires a single 40W between the load and the output terminal. Make sure bench power source adjustable from 2.7V to 5.5V. The the output voltage is monitored at the V (J4) OUT loads can be either active (electronic load) or passive terminal. The board has a 2-pin connector (TP1) to (resistor), and must be able to dissipate 30W. It is ideal, allow for output voltage monitoring. but not essential, to have an oscilloscope available to view 3. Enable the MIC23603. the circuit waveforms. The simplest tests require two voltage meters to measure input and output voltage. The MIC23603 evaluation board has a pull-up resistor to V . By default, the output voltage is enabled when Efficiency measurements require two voltage meters and IN two ammeters to prevent errors caused by measurement the input supply of >2.7V is applied. To disable the device, apply a voltage below 0.4V to the EN (J6) inaccuracies. terminal. Precautions 4. Power Good. There is no reverse input protection on this board. Be The board provides a power good test point (J5) to careful when connecting the input source to make sure monitor the power good function. The power good correct polarity is observed. output goes high (V ) approximately 40s after the OUT Datasheets and support documentation are available on output voltage reaches 90% of its nominal voltage. Micrels web site at: www.micrel.com. Ordering Information Part Number Description MIC23603YML EV Adjustable Output Evaluation Board Hyper Light Load is a registered trademark of Micrel, Inc. Micrel Inc. 2180 Fortune Drive San Jose, CA 95131 USA tel +1 (408) 944-0800 fax + 1 (408) 474-1000 Micrel, Inc. MIC23603 Evaluation Board Evaluation Board Examples of values are illustrated in Table 1. Table 1. Example Values for V , R3, and R4 OUT V R3 R4 OUT 1.2V 274k 294k 1.5V 316k 221k 1.8V 560k 294k 2.5V 324k 107k 3.3V 464k 107k The feed-forward capacitor, C10, 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 33pF to 68pF is recommended. Power Good (PG) The evaluation board has a test point provided to the right of EN for testing PG. This is an open-drain connection to Figure 1. MIC23603 Evaluation Board Top Layer the output voltage with an on-board pull-up resistor of 100k. This is asserted high approximately 40s after the output voltage passes 90% of the nominal set voltage. Other Features Hyper Light Load Mode Soft-Start Capacitor MIC23603 uses a minimum on and off time proprietary The soft-start (SS) pin is used to control the output voltage control loop (patented by Micrel). When the output voltage ramp-up time. Setting C4 to 2.2nF sets the start-up time to falls below the regulation threshold, the error comparator the minimum. The start-up time can be determined by: begins a switching cycle that turns the PMOS on and keeps it on for the duration of the minimum-on-time. This 3 increases the output voltage. If the output voltage is over = 250 10 In(10) C Eq.1 T SS SS 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 The soft-start capacitor controls the rise time of the internal that conducts when the PMOS is off. Using an NMOS reference voltage between 0% and 100% of its nominal switch instead of a diode allows for lower voltage drop steady state value. across the switching device when it is on. The Feedback Resistors (R3, R4) for Adjustable Output asynchronous switching combination between the PMOS and the NMOS allows the control loop to work in The output voltage is set nominally to 1.8V. This output discontinuous mode for light load operations. In can be changed by adjusting the upper resistor, R3, in the discontinuous mode, the MIC23603 works in pulse feedback potential divider. Therefore: 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 R3 = R4 (V V )/V Eq. 2 O REF REF scheme improves the efficiency of MIC23603 during light load currents by switching only when it is needed. As the load current increases, the MIC23603 goes into where V = 0.62V. REF continuous conduction mode (CCM) and switches at a frequency centered at 4MHz. Revision 1.1 November 13, 2014 2