MIC33050 Evaluation Board 4MHz Internal Inductor PWM Buck Regulator with HyperLight Load General Description Getting Started The MIC33050 is a 600mA 4MHz switching regulator 1. Connect an external supply to the V (J1) IN featuring HyperLight Load mode. The MIC33050 is terminal. Apply the desired input voltage to V (J1) IN highly efficient throughout the entire output current and ground (J2) terminals of the evaluation board, range, drawing just 20A of quiescent current in paying careful attention to polarity and supply operation. The tiny 3mm x 3mm MLF package, in voltage (2.7V V 5.5V). An ammeter may be IN combination with the 4MHz switching frequency, enables placed between the input supply and the V (J1) IN a compact sub-1mm height solution with only three terminal. Be sure to monitor the supply voltage at external components. The MIC33050 provides accurate the V (J1) terminal, since the ammeter and/or IN output voltage regulation under the most demanding power lead resistance can reduce the voltage conditions and responds extremely quickly to a load supplied to the device. transient with exceptionally small output voltage ripple. 2. Connect a load to the V (J3) and ground OUT Factoring in the output current, the internal circuitry of terminal (J4). The load can be either passive the MIC33050 automatically selects between two modes (resistive) or active (electronic load). An ammeter of operation for optimum efficiency. Under light load may be placed between the load and the output conditions, the MIC33050 goes into HyperLight Load terminal. Ensure the output voltage is monitored at mode. HyperLight Load uses a pulse-frequency the V (J3) terminal. OUT modulation (PFM) control scheme that controls the off time at light load. This proprietary architecture reduces 3. Enable the MIC33050. The MIC33050 evaluation the amount of switching needed at light load, thereby board has a pull-up resistor to V . To disable the IN increasing operating efficiency. The MIC33050 attains device, apply a voltage below 0.5V to the EN (J5) up to 83% efficiency at 1mA output load. As the load terminal. In the absence of the pull-up resistor, the current increases beyond approximately 100mA, the device is enabled by applying a voltage greater than device operates using the pulse-width modulation 1.2V to the EN (J5) terminal. The enable pin must be (PWM) method for up to 93% efficiency at higher load. either pulled high or low for proper operation. The two modes of operation ensure the highest Removing the pull-up resistor and leaving the pin efficiency across the entire load range. floating will cause the regulator to operate in an The MIC33050 operates from an input voltage range of unknown state. 2.7V to 5.5V and features internal power MOSFETs that Output Voltage deliver up to 600mA of output current. This step-down regulator provides an output voltage accuracy of 2.5% The MIC33050 evaluation board is available with the across the junction temperature range of 40C to following output voltage options listed in Ordering +125C. The MIC33050 is available in fixed or adjustable Information. versions supporting an output voltage as low as 0.7V. Ordering Information Requirements Part Number Description The MIC33050 evaluation board requires an input power MIC33050-CYHL EV 1.0V Fixed Output Evaluation Board source that is able to deliver greater than 650mA at MIC33050-4YHL EV 1.2V Fixed Output Evaluation Board 2.7V. The output load can either be an active (electronic) or passive (resistive) load. MIC33050-GYHL EV 1.8V Fixed Output Evaluation Board MIC33050-SYHL EV 3.3V Fixed Output Evaluation Board MIC33050-AYHL EV Adjustable Output Evaluation Board HyperLight Load is a trademark of Micrel, Inc. MLF and MicroLeadFrame are registered 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. MIC33050 Evaluation Board This increases the output voltage. If the output voltage is Output Voltage (Adjustable Option Only) over the regulation threshold, then the error comparator The output voltage of the MIC33050-AYHL is set by the turns the PMOS off for a minimum-off-time until the feedback resistors R2 and R3. Follow the equation and output drops below the threshold. The NMOS acts as an circuit below to determine V : ideal rectifier that conducts when the PMOS is off. Using OUT a NMOS switch instead of a diode allows for lower voltage drop across the switching device when it is on. R2 The asynchronous switching combination between the V 0.4V 1 Eq. 1 OUT PMOS and the NMOS allows the control loop to work in R3 discontinuous mode for light load operations. In discontinuous mode, the MIC33050 works in pulse frequency modulation (PFM) to regulate the output. As the output current increases, the off-time decreases, thus provides more energy to the output. This switching scheme improves the efficiency of MIC33050 during light load currents by only switching when it is needed. As the load current increases, the MIC33050 goes into continuous conduction mode (CCM) and switches at a frequency centered at 4MHz. The equation to calculate the load when the MIC33050 goes into continuous conduction mode may be approximated by the following formula: Figure 1. Typical Circuit for MIC33050-AYHL (V = 1.8V) OUT (V V ) D IN OUT I Eq. 4 LOAD 2L f The default output voltage for the evaluation board is set to 1.8V (R2=348k, R3=100k). A different output voltage can be obtained by removing R2 and replacing it As shown in the previous equation, the load at which MIC33050 transitions from HyperLight Load mode to with the desired resistance. The equation below can be PWM mode is a function of the input voltage (V ), output used to find R2: IN voltage (V ), duty cycle (D), inductance (L) and OUT frequency (f). As shown in Figure 1, as the Output Current increases, the switching frequency also V OUT R2 R3 1 Eq. 2 increases until the MIC33050 goes from HyperLight 0.4V Load mode to PWM mode at approximately 120mA. The MIC33050 will switch at a relatively constant frequency around 4MHz once the output current is over 120mA. Changing the output voltage to 2.5V, assuming R3=100k, can be accomplished via the equation below: SW Frequency vs Output Current 10 2.5V R2 100k 1 Eq. 3 V = 3.0V IN V = 3.6V 0.4V IN 1 V = 4.2V IN 0.1 The result is 523k for R2 which gives an output voltage of 2.5V. L = 4.7H 0.01 V = 1.8V OUT HyperLight Load Mode C = 4.7F OUT MIC33050 uses a minimum on and off time proprietary 0.001 1 10 100 1000 10000 control loop (patented by Micrel). When the output OUTPUT CURRENT (mA) 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 Figure 2. SW Frequency vs. Output Current minimum-on-time. Revision 4.0 March 24, 2014 2 SW FREQUENCY (MHz)