MIC23451 Evaluation Board 3MHz PWM Triple 2A Buck Regulator with HyperLight Load and Power Good General Description Getting Started This board allows the customer to evaluate the MIC23451, 1. Connect an external supply to the V (J1) terminal IN a fully-integrated, triple-output, 2A, 3MHz switching and GND (J2). regulator that features HyperLight Load mode and Power With the output of the power supply disabled, set its Good output indicators. The MIC23451 is highly efficient voltage to the desired input test voltage (2.7V V IN throughout the output current range, drawing just 24A of 5.5V). An ammeter may be placed between the input quiescent current for each channel in operation. The tiny supply and the V (J1) terminal. Be sure to monitor IN 4mm 4mm DFN package saves precious board space the supply voltage at the V (J1) terminal, as the IN and requires few external components. The MIC23451 ammeter and/or power lead resistance can reduce the provides accurate output voltage regulation under the most voltage supplied to the device. demanding conditions, with each channel responding extremely quickly to a load transient with exceptionally 2. Connect a load to the V terminals (J6, J7, J8) OUT small output voltage ripple. and ground (J3, J4, J5) terminals. The load can be either passive (resistive) or active Requirements (electronic load). An ammeter may be placed between This board needs a single 20W bench power source the loads and the output terminals. Make sure the adjustable from 2.7V to 5.5V. The loads can be either output voltage is monitored at the V (J6, J7, J8) OUT active (electronic load) or passive (resistor), and must be terminals. able to dissipate 10W. It is ideal, but not essential, to have an oscilloscope available to view the circuit waveforms. 3. Enable the MIC23451. The simplest tests require two voltage meters to measure The MIC23451 evaluation board has a pull-up resistor input and output voltage. Efficiency measurements for a to V for each channel. By default, each output voltage IN single channel require two voltage meters and two is enabled when an input supply of >2.7V is applied. ammeters to prevent errors caused by measurement To disable the device, apply a voltage below 0.4V to inaccuracies. the EN (J10, J12, J14) terminals. Precautions 4. Power Good. There is no reverse input protection on this board. Be The board provides a Power Good test point (J9, J11, careful when connecting the input source to make sure J13) to monitor the Power Good function for each correct polarity is observed. individual channel. The Power Good output goes high Datasheets and support documentation are available on (V ) approximately 60s after the output voltage OUT Micrels web site at: www.micrel.com. reaches 90% of its nominal voltage. Ordering Information Part Number Description MIC23451-AAAYFL EV Adjustable Output Evaluation Board HyperLight 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. MIC23451 Evaluation Board Evaluation Board Power Good (PG) The evaluation board has a test point for each individual channel to monitor the PG signal. This is an open-drain connection to the output voltage with an on-board pull-up resistor of 10k . This is asserted high approximately 60s after the output voltage passes 90% of the nominal set voltage. HyperLight Load Mode MIC23451 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 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 Other Features asynchronous switching combination between the PMOS and the NMOS allows the control loop to work in Soft-Start Capacitor discontinuous mode for light load operations. In The MIC23451 has an internal soft-start for each individual discontinuous mode, the MIC23451 works in pulse channel and requires no external soft start-capacitor. The frequency modulation (PFM) to regulate the output. As the typical soft-start time for each channel is 150s. output current increases, the off-time decreases, which provides more energy to the output. This switching scheme improves the efficiency of MIC23451 during light Feedback Resistors (R7R12) load currents by switching only when it is needed. As the The feedback (FB) pin is the control input for programming load current increases, the MIC23451 goes into the output voltage. A resistor divider network is connected continuous conduction mode (CCM) and switches at a to this pin from the output and is compared to the internal frequency centered at 3MHz. The equation to calculate the 0.62V reference within the regulation loop. The output load when the MIC23451 goes into continuous conduction voltage can be programmed between 1V and 3.3V using mode is approximated by Equation 2: Equation 1: (V V ) D IN OUT R7 I > Eq. 2 LOAD Eq. 1 V = V 1 + OUT REF 2L f R8 Equation 2 shows that the load at which MIC23451 Where: R7 is the top, V connected resistor, and R8 is OUT transitions from Hyper Light Load mode to PWM mode is a the bottom, AGND connected resistor. function of the input voltage (V ), output voltage (V ), IN OUT duty cycle (D), inductance (L), and frequency (f). The Table 1. Example Feedback Resistor Values Switching Frequency vs. Load graph in the Evaluation V R7 R8 OUT Board Performance section shows that, as the output current increases, the switching frequency also increases 1.2V 274k 294k until the MIC23451 goes from Hyper Light Load mode to 1.5V 316k 221k PWM mode at approximately 120mA. The MIC23451 will 1.8V 301k 158k switch at a relatively constant frequency around 3MHz after the output current is over 120mA. 2.5V 324k 107k 3.3V 309k 71.5k Revision 1.0 October 14, 2013 2