MIC28510 Evaluation Board 75V/4A Hyper Speed Control Synchronous DC/DC Buck Regulator General Description Getting Started The MIC28510 DC/DC regulator operates over an 1. V Supply. Connect a power supply to the VIN IN input supply range of 4.5V to 75V and provides a and GND terminals, paying careful attention to the regulated output at up to 4A of output current. The polarity and supply voltage range (5V < VIN < output voltage is adjustable down to 0.8V with a 75V). The input current IIN can be monitored with typical accuracy of 1%. The switching frequency is a current meter. Do not apply power until Step 4. adjustable and once adjusted the switching frequency 2. Connect Load and Monitor Output. Connect a remains fairly constant with changes in input voltage load to the V and GND terminals. The load can OUT and output load. be either a passive (resistive) or an active (as in The basic parameters of the evaluation board are: an electronic load) type. A current meter may be placed between the V terminal and load to OUT Input Voltage 5V to 75V monitor the output current. Ensure the output (1) Output Voltage 0.8V to 5V at 4A voltage is monitored at the V terminal. OUT (2) 12V at up to 4A 3. Enable Input. The EN pin has an internal 100k 250kHz Switching Frequency pull-up resistor to VDD, which allows the output to (Adjustable from 100kHz to 500kHz) be turned on when VDD exceeds its UVLO threshold. An EN connector is provided on the evaluation board for users to easily access the Notes: enable feature. Applying an external logic signal 1, 2. Refer to thermal de-rating curves shown in Typical on the EN pin to pull it low or using a jumper to Characteristics section. short the EN pin to GND will shut off the output of the MIC28510 evaluation board. Datasheets and support documentation can be found 4. Turn On the Power. Turn on the VIN supply and on Micrels web site at: www.micrel.com verify that the output voltage is regulated to 3.3V. Requirements The MIC28510 evaluation board requires only a single Ordering Information power supply with at least 10A current capability. A linear regulator, which includes a Zener and an NPN Part Number Description transistor, has been installed on the board to provide MIC28510 5V EV Evaluation Board up to 5V Output housekeeping (V ) for the MIC28510. The output DD MIC28510 12V EV Evaluation Board 12V Output load can either be a passive or an active load. Precautions The MIC28510 evaluation board does not have reverse polarity protection. Applying a negative voltage to the PVIN and GND terminals may damage the device. The maximum PVIN of the board is rated at 75V. Exceeding 75V on the PVIN could damage the device. Hyper Speed Control is a 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. MIC28510 4A Evaluation Board The switching frequency can be adjusted between Features 100kHz and 500kHz by changing the resistor divider Feedback Resistors connected network consisting of R18 and R19 from The output voltage on the MIC28510 evaluation PVIN to PGND. board, which is preset to 3.3V, is determined by the feedback divider, shown in Equation 1: R4 V = V 1 + Eq. 1 OUT REF R BOTTOM where V = 0.8V, and R is one of R5-R12, REF BOTTOM which corresponds to 0.9V, 1.0V, 1.2V, 1.5V, 1.8V, 2.5V, 3.3V, or 5V. Leaving the R open gives a BOTTOM 0.8V output voltage. All other voltages not listed above can be set by modifying R value BOTTOM according to Equation 2: R4 V REF R = Eq. 2 BOTTOM Figure 1. Switching Frequency Adjustment V V OUT REF Equation 3 illustrates the estimated switching frequency: Note that the output voltage should not be set to exceed 5V due to the 6.3V voltage rating on the R19 output capacitors. f = f Eq. 3 SW ADJ O R18 +R19 If higher than 5V output is desired, it is recommended to use the designs shown in the MIC28510 12V/4A output evaluation board schematic, where the output where f = Switching Frequency when R18 is 100k O capacitors, L1, R3, and R17 are optimized for 12V and R19 being open, f should be typically 450kHz. O output. For more precise setting, it is recommended to use SW Node Figure 2: Test point J11 (V ) is placed for monitoring the SW switching waveform, one of the most critical waveforms for the converter. Current Limit The MIC28510 has internal FETs, and the current limit is implemented by sensing the R of bottom FET. DS-ON The MIC28510 has a fixed current limit of 6.5A (typical). Loop Gain Measurement The resistor, R13, is placed in series with the regulator feedback path. The control loop gain can be measured by connecting an impedance analyzer across the resistor and selecting the resistor value in between 20 to 50 . Setting the Switching Frequency Figure 2. Switching Frequency vs. R19 The MIC28510 is an adjustable-frequency, synchronous buck regulator featuring a unique The evaluation board design is optimized for a digitally modified adaptive on-time control switching frequency of 250kHz. If the switching architecture. frequency is programmed to either lower end or higher end, the design needs optimization. 2 M9999-030712 March 2012 hbwhelp micrel.com or (408) 955-1690