MIC33153 Evaluation Board 4MHz 1.2A PWM Buck Regulator with HyperLight Load and Power Good Getting Started General Description 1. Connect an external supply to the V (TP4) IN This board enables the evaluation of the MIC33153, a terminal and GND (TP3). With the output of the fully integrated 1.2A, 4MHz switching regulator featuring power supply disabled, set its voltage to the desired HyperLight Load mode, Power Good (PG) output input test voltage (2.7V V 5.5V). An ammeter IN indicator, and programmable soft start. The MIC33153 is may be placed between the input supply and the V IN highly efficient throughout the entire output current (TP4) terminal. Be sure to monitor the supply range, drawing just 22A of quiescent current in voltage at the V (TP4) terminal, as the ammeter IN operation. The tiny 3.5mm x 3.0mm x 0.9mm MLF and/or power lead resistance can reduce the package, in combination with the 4MHz switching voltage supplied to the device. frequency, enables a compact sub 1mm height solution 2. Connect a load to the V (TP1) and ground (TP with only two external input and output capacitors. The OUT 2) terminals. The load can be either active passive MIC33153 provides accurate output voltage regulation (resistive) or active (electronic load). An ammeter under the most demanding conditions and responds may be placed between the load and the output extremely quickly to a load transient with exceptionally terminal. Ensure the output voltage is monitored at small output voltage ripple. the V (TP1) terminal. OUT Datasheets and support documentation can be found on 3. Enable the MIC33153. The MIC33153 evaluation Micrels web site at: www.micrel.com. board has a pull up resistor (R4) to V . By default, IN Requirements the output voltage will be enabled when the input supply of >2.7V is applied. To disable the device, This board needs a single 5W bench power source apply a voltage below 0.5V to the EN (TP6) adjustable from 2.7V to 5.5V. The loads can either be terminal. active (electronic load) or passive (resistor) with the 4. Power Good (PG). A PG test point (TP5) is capability to dissipate 5W. It is ideal to have an provided to monitor the Power Good function. The oscilloscope available to view the circuit waveforms, but PG output will go high (V ) approximately 70s not essential. For the simplest tests two voltage meters OUT after the output voltage reaches 92% of its nominal are required to measure input and output voltage. For voltage. efficiency measurements two voltage meters and two ammeters are required to prevent errors due to Ordering Information measurement inaccuracies. Part Number Description Precautions MIC33153-4YHJ 1.2V Fixed Output Evaluation Board There is no reverse input protection on this board. Be cautious when connecting the input source to ensure MIC33153YHJ Adjustable Output Evaluation Board correct polarity is observed. HyperLight Load is a trademark of Micrel, Inc. MLF and MicroLeadFrame are trademarks of 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. MIC33153 Evaluation Board Soft start Capacitor Power Good (PG) The MIC33153 has a nominal 270k resistor charging The evaluation board has a test point provided to the the capacitor on the SS pin. This enables the output to right of EN for testing PG. This is an open drain follow a controlled soft start characteristic. Setting C3 to connection with an on board pull up resistor of 10k to 100pF sets the startup time to the minimum. The startup the output voltage. This is asserted high approximately time can be determined by: 70s after the output voltage passes 92% of the nominal 3 set voltage. T = 270 x 10 x ln(10) x C SS SS The action of the soft start capacitor is to control the rise HyperLight Load Mode time of the internal reference voltage between 0% and The MIC33153 uses a minimum on and off time 100% of its nominal steady state value. proprietary control loop (patented by Micrel). When the output voltage falls below the regulation threshold, the Feedback Resistors (R1, R2) for Adjustable Output error comparator begins a switching cycle that turns the The output voltage is set nominally to 1.8V. This output PMOS on and keeps it on for the duration of the can be changed by adjusting the upper resistor, R1, in minimum on time. This increases the output voltage. If the feedback potential divider. Therefore: the output voltage is over the regulation threshold, then the error comparator turns the PMOS off for a minimum R1 = R2 V /(V V ) REF O REF off time until the output drops below the threshold. The where V = 0.62V. REF NMOS acts as an ideal rectifier that conducts when the Some example values are: PMOS is off. Using a NMOS switch instead of a diode allows for lower voltage drop across the switching device when it is on. The asynchronous switching V R1 R2 OUT combination between the PMOS and the NMOS allows 1.2V 274k 294k the control loop to work in discontinuous mode for light load operations. In discontinuous mode, the MIC33153 1.5V 316k 221k works in pulse frequency modulation (PFM) to regulate 1.8V 301k 158k the output. As the output current increases, the off time decreases, thus provides more energy to the output. 2.5V 324k 107k This switching scheme improves the efficiency of 3.3V 309k 71.5k MIC33153 during light load currents by only switching when it is needed. As the load current increases, the MIC33153 goes into continuous conduction mode The feed forward capacitor, C4, is typically not fitted (CCM) and switches at a frequency centered at 4MHz. given that transient load regulation is already very good. The equation to calculate the load when the MIC33153 However, it can be improved slightly by fitting a goes into continuous conduction mode may be capacitor at C4 to inject fast output voltage deviations approximated by the following formula: directly into the feedback comparator. This improved load regulation occurs at the expense of slightly ( ) V V D IN OUT increasing the amount of noise on the output at higher I > LOAD 2L f loads. Values between 100pF and 1nF are recommended to prevent instability. As shown in the above equation, the load at which MIC33153 transitions from HyperLight Load mode to PWM mode is a function of the input voltage (V ), IN output voltage (V ), duty cycle (D), inductance (L) and OUT frequency (f). For example, if V = 3.6V, V = 1.8V, D IN OUT = 0.5, f = 4MHz and the internal inductance of MIC33153 is 0.47 H, then the device will enter HyperLight Load mode or PWM mode at approximately 200mA. 2 M9999-121710-A December 2010