MIC26950 Evaluation Board 26V/12A Hyper Speed Control Synchronous DC/DC Buck Regulator TM SuperSwitcher II If V is not powered from the on-board V regulator, an DD DD General Description external V power supply is required and must be DD The MIC26950 DC/DC regulator operates over an input powered up at the same time or after V to make the soft- IN supply range of 4.5V to 26V and provides a regulated output start function correctly. at up to 12A of output current. The output voltage is Getting Started adjustable down to 0.8V with a typical accuracy of 1% and the device operates at a switching frequency of 300kHz. The 1. Connect an external supply to the V terminal. Apply IN switching frequency remains fairly constant with changes in the desired input voltage to the V and ground terminals of IN input voltage and output load. the evaluation board, paying careful attention to polarity TM Micrels Hyper Speed Control architecture allows for ultra- and supply voltage. An ammeter may be placed between fast transient response while reducing the output capacitance the input supply and the V terminal to the evaluation IN and also makes (High V )/(Low V ) operation possible. board. Ensure that the supply voltage is monitored at the IN OUT The MIC26950 utilizes an adaptive t ripple control V terminal. The ammeter and/or power lead resistance ON IN architecture. An undervoltage lockout feature is provided to can reduce the voltage supplied to the input. ensure proper operation under power-sag conditions. An 2. Connect the load to the V and ground terminals. OUT internal soft-start feature is provided to reduce the inrush The load can be either passive (resistive) or active (as in current. Foldback current limit, hiccup mode short-circuit an electronic load). An ammeter can be placed between protection, and thermal shutdown ensure protection of the IC the load and the V terminal. Ensure that the output OUT during fault conditions. voltage is monitored at the V terminal. V can be set OUT OUT Note: This evaluation board is for 12A applications. to 0.9V, 1.0V, 1.2V, 1.5V, 1.8V, 2.5V, 3.3V, or 5.0V by a jumper. If a different voltage is needed, it can be adjusted Datasheet and supporting documentation can be found on by changing the feedback resistors. See Output Voltage Micrels web site at: www.micrel.com. section. Requirements 3. Enable the MIC26950. The EN pin is provided on the The MIC26950 evaluation board requires two power evaluation board. The output of the MIC26950 turns on supplies: one to provide V and the other to provide V . when V exceeds the UVLO threshold. The output of the IN DD DD The V power supply must be able to deliver greater than MIC26950 may be turned off by shorting the EN pin to IN 3.0V with more than 12A capability. The V power supply ground. An connection on the board provides easy access DD must be greater than 4.5V. The on-board V regulator, to the enable pin. DD using an NPN transistor, provides V power supply. The DD Output Voltage output load can either be an active or passive load. The output voltage on the MIC26950 evaluation board is Precautions adjustable. It is set by adjusting the feedback resistors (R4 The evaluation board does not have reverse polarity and one of R5, R6, R7, R8, R9, R10, R11, or R12) and protection. Applying a negative voltage to the V terminal can be calculated as follows as an example: IN may damage the device. In addition, the maximum V IN operating voltage of the MIC26950 evaluation board is R4 26V. Exceeding 26V on V or exceeding 5.5V on V IN DD V = V (1 + ) OUT REF R7 could damage the device. where V = 0.8V. REF Hyper Speed Control is a trademark of Micrel, Inc. MLF and MicroLead Frame 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. MIC26950 12A Evaluation Board The output voltage above is set at the factory for a 1.2V The output voltage should not be set to exceed 5V due to output, but it can easily be modified by removing R4 and the 6.3V rating of the output capacitor. If an output voltage R7 and replacing them with the values that yield the greater than 5V is desired, the output capacitor must be desired output voltage. Once R4 is selected, R7 can be replaced with another capacitor that has a higher voltage calculated using: rating. R4 V REF R7 = V V OUT REF For V = 0.8V: REF R4 0.8V R7 = V 0.8V OUT Ordering Information Part Number Description Package MIC26950YJL IC 28-Pin 5mm 6mm MLF MIC26950YJL EV Evaluation Board Evaluation Board Schematic Figure 1. MIC26950 Evaluation Board (J13, R13, R15 Are for Testing Purposes) September 2010 2 M9999-092910-A