MIC23153 Evaluation Board 4MHz PWM 2A Buck Regulator with HyperLight Load and Power Good Getting Started General Description 1. Connect an external supply to the V (J4) IN This board enables the evaluation of the MIC23153, a terminal and GND (J3). With the output of the fully integrated 2A, 4MHz switching regulator featuring power supply disabled, set its voltage to the HyperLight Load mode, Power Good output indicator, desired input test voltage (2.7V V 5.5V). An IN and programmable soft-start. The MIC23153 is highly ammeter may be placed between the input efficient throughout the entire output current range, supply and the V (J4) terminal. Be sure to IN drawing just 23A of quiescent current in operation. The monitor the supply voltage at the V (J4) IN tiny 2.5mm x 2.5mm Thin MLF package, in combination terminal, as the ammeter and/or power lead with the 4MHz switching frequency, enables a compact resistance can reduce the voltage supplied to sub-1mm height solution with only four external the device. components. The MIC23153 provides accurate output 2. Connect a load to the V (J1) and ground OUT voltage regulation under the most demanding conditions (J2) terminals. The load can be either active and responds extremely quickly to a load transient with passive (resistive) or active (electronic load). An exceptionally small output voltage ripple. ammeter may be placed between the load and Requirements the output terminal. Ensure the output voltage is monitored at the V (J1) terminal. OUT This board needs a single 10W bench power source adjustable from 2.7V to 5.5V. The loads can either be 3. Enable the MIC23153. The MIC23153 active (electronic load) or passive (resistor) with the evaluation board has a pull-up resistor to V . By IN capability to dissipate 7W. It is ideal to have an default, the output voltage will be enabled when oscilloscope available to view the circuit waveforms, but the input supply of >2.7V is applied. To disable not essential. For the simplest tests, two Voltage meters the device, apply a voltage below 0.5V to the EN are required to measure input and output voltage. For (J6) terminal. efficiency measurements, two Voltage meters and two 4. Power Good. A Power good test point (J5) is Ammeters are required to prevent errors due to provided to monitor the Power Good function. measurement inaccuracies. The Power Good output will go high (Vout) approximately 70s after the output voltage Precautions reaches 92% of its nominal voltage. There is no reverse input protection on this board. Be cautious when connecting the input source to ensure correct polarity is observed. Ordering Information Part Number Description MIC23153-GYMT 1.8V Fixed Output Evaluation Board MIC23153YMT Adjustable Output Evaluation Board HyperLight Load is a 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. MIC23153 Evaluation Board at C4 to inject fast output voltage deviations directly into Evaluation Board the feedback comparator. This improved load regulation is at the expense of slightly increasing the amount of noise on the output at higher loads. Values between 100pF and 1nF are recommended to prevent instability. 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 with an on board pull-up resistor of 10k to the output voltage. This is asserted high approximately 70 s after the output voltage passes 92% of the nominal set voltage. HyperLight Load Mode MIC23153 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, then the error comparator turns the PMOS off for a minimum- Other Features off-time until the output drops below the threshold. The NMOS acts as an ideal rectifier that conducts when the Soft-Start Capacitor (C3) PMOS is off. Using a NMOS switch instead of a diode The MIC23153 has a nominal 270kOhm resistor allows for lower voltage drop across the switching device when it is on. The asynchronous switching combination charging the capacitor on the SS pin. This enables the between the PMOS and the NMOS allows the control output to follow a controlled soft start characteristic. loop to work in discontinuous mode for light load Setting C3 to 100pF sets the startup time to the operations. In discontinuous mode, the MIC23153 works minimum. The start-up time can be determined by: in pulse frequency modulation (PFM) to regulate the 3 T = 270 x 10 x ln(10) x C SS SS output. As the output current increases, the off-time The action of the soft-start capacitor is to control the rise decreases, thus provides more energy to the output. time of the internal reference voltage between 0% and This switching scheme improves the efficiency of 100% of its nominal steady state value. MIC23153 during light load currents by only switching when it is needed. As the load current increases, the Feedback Resistors (R1, R2) for Adjustable Output MIC23153 goes into continuous conduction mode (CCM) and switches at a frequency centered at 4MHz. The The output voltage is set nominally to 1.8V. This output equation to calculate the load when the MIC23153 goes can be changed by adjusting the upper resistor, R1, in into continuous conduction mode may be approximated the feedback potential divider. Therefore: by the following formula: R1 = R2 x V /(V -V ) REF O REF (V V ) D Where V = 0.62V IN OUT REF I > LOAD 2L f Some example values are: V R1 R2 As shown in the previous equation, the load at which OUT MIC23153 transitions from HyperLight Load mode to 1.2V 274k 294k PWM mode is a function of the input voltage (V ), output IN 1.5V 316k 221k voltage (V ), duty cycle (D), inductance (L) and OUT frequency (f). As shown in the Switching Frequency vs 1.8V 301k 158k Load graph, as the Output Current increases, the 2.5V 324k 107k switching frequency also increases until the MIC23153 3.3V 309k 71.5k goes from HyperLight Load mode to PWM mode at approximately 120mA. The MIC23153 will switch at a The Feed-forward capacitor, C4, is typically not fitted relatively constant frequency around 4MHz once the since transient load regulation is already very good, output current is over 120mA. however, it can be improved slightly by fitting a capacitor M9999-020510-A February 2010 2