MIC4724YMME Evaluation Board 3A Buck Regulator General Description The Micrel MIC4724 is a high efficiency PWM buck (step-down) regulator that provides up to 3A of output current. The MIC4724 operates at 2MHz and has proprietary internal compensation that allows a closed loop bandwidth of over 200kHz. The low onresistance internal P-Channel MOSFET of the MIC4724 allows efficiencies up to 94%, reduces external component count and eliminates the need for an expensive external current sense resistor. The MIC4724 operates from a 3V to 6V input and its output is adjustable down to 1V. The devices can operate with a maximum duty cycle of 100% for use in low-dropout applications. Requirements The MIC4724 evaluation board requires an input power source that is able to deliver greater than 3V at over 3A. The output load can either be an active or passive load. Precautions The evaluation board does not have reverse polarity protection. Applying a negative voltage to the VIN terminal may damage the device. In addition, the maximum operating voltage of the MIC4724 evaluation board is 6V. Exceeding 6.5V on the input could damage the device. For short circuit testing, an additional input capacitor over 22µF is required when using the demo board. This is preferably an electrolytic, but may be tantalum or ceramic. The inductance of long test leads connecting the supply voltage to the demo board can be over 1µH. During a short circuit condition, the high peak currents through the test leads may cause the input voltage to spike high and exceed the absolute maximum rating of 6V, possibly damaging the device. Getting Started 1. Connect an external supply to VIN terminal. Apply desired input voltage to the VIN and ground terminals of the evaluation board, paying careful attention to polarity and supply voltage (3V<VIN<6.5V). An ammeter may be placed between the input supply and the VIN terminal to the evaluation board. Ensure the supply voltage is monitored at the VIN terminal. The ammeter and/or power lead resistance can reduce the voltage supplied to the input. 2. Connect the load to the VOUT and ground terminals. The load can be either passive (resistive) or active (as in an electronic load). An ammeter can be placed between the load and the VOUT terminal. Ensure the output voltage is monitored at the VOUT terminal. The default output voltage is set to 1.8V. This can be adjusted by changing the feedback resistors. See “Output Voltage.” 3. Enable the MIC4724. The enable pin is connected to a pull up resistor. The MIC4724 turns on when VIN exceeds the UVLO threshold at the VIN pin. The MIC4724 may be turned off by shorting the pin to ground or bringing the enable pin below the enable threshold. An external connection on the board provides easy access to the enable pin. Micrel, Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 944-0800 • fax 1 (408) 474-1000 • http://www.micrel.com June 2008 M9999-062408-A Micrel, Inc. MIC4724YMME Evaluation Board Output Voltage The output voltage on the MIC4724 evaluation board is adjustable. The output voltage is controlled by the feedback resistors (R1 and R2) and can be calculated as follows: Power OK The POK pin is pulled up to VIN through a pull-up resistor and is asserted low when VOUT is within the regulation band. An external connection on the board provides easy access to the POK pin. R1 ⎞ ⎛ VOUT = VREF × ⎜1 + ⎟ R2 ⎠ ⎝ Ordering Information Where VREF = 1V. The evaluation board is preset at 1.8V, but can easily be modified by removing R2 and replacing it with the value that yields the desired output voltage. (Removing R2 sets the output to 1V). R2 = R1 × VREF VOUT − VREF Part Number Description Package MIC4724YMME IC 10-Pin MSOP EPAD MIC4724YMME EV Evaluation Board 10-Pin MSOP EPAD For VREF = 1V, this reduces to: R2 = June 2008 R1 VOUT − 1 2 M9999-062408-A Micrel, Inc. MIC4724YMME Evaluation Board U1 MIC4724YMME 2 R6 49.9k R5 10k C1 10µF C2 10µF /6.3V 9 VIN SW VIN SW 1 L1 1µH 10 1 J1 +VIN R3 6 J4 PGOOD 7 EN PGOOD BIAS 8 C3 0.1µF /10V AGND 4 FB C5 82pF R1 10k 5 C4 680pF 3 R PGND 2 J3 EN J5 VOUT 1.8V@3A D1 SSA33L C6 4.7µF R2 12.4K J6 GND J2 GND Bill of Materials Item Part Number C1608 X5R0J106K Manufacturer TDK(1) C1, C2 GRM188R61A106K 08056D106MAT JMK107BJ106MA-T Murata(2) AVX(3) Taiyo Yuden(4) VJ0402Y104KXQCW1BC Vishay(5) 10µF Ceramic Capacitor X5R 6.3V 10µF Ceramic Capacitor X5R 6.3V 0.1µF Ceramic Capacitor X7R 10V C1005X7R1A104K TDK(1) 0.1µF Ceramic Capacitor X7R 10V C3 0402ZD104MAT C4 C5 C6 (3) 680pF Ceramic Capacitor NPO 10V C1005COG1A681J TDK(1) 680pF Ceramic Capacitor 10V VJ0402A82KXXCW1BC Vishay(5) 82pF Ceramic Capacitor NPO 10V (1) C1005COG1A820J TDK C1608X5R0J475K 06036D475MAT TDK(1) AVX(3) JMK107BJ475MA-T GRM188R60J475KE19D Taiyo Yuden(4) Murata(2) SSA33L Vishay(5) MBRM330-13 Diodes, Inc.(6) LTF5022T-1R2N4R2 TDK(1) IHLP2525AHER1R0M01 U1 MIC4724YMME Micrel, Inc.(7) 2 1 3 1 1 3A Schottky 30V 1 1µH Inductor 7A Vishay Dale(5) 1 4.7µF Ceramic Capacitor X5R 6V 1.2µH Inductor 4.3A ±30% Vishay R2 R3 R4 R6 June 2008 82pF Ceramic Capacitor 10V (5) Vishay Dale(5) Qty. 0.1µF Ceramic Capacitor X5R 10V AVX Vishay(5) CRCW04021002FKEYE3 CRCW04021242FKEYE3 CRCW04022R70FKEYE3 CRCW040210R0FKEYE3 CRCW04024992FKEYE3 R1, R5 10µF Ceramic Capacitor X5R 10V VJ0402A681KXXCW1BC D1 L1 Description 10µF Ceramic Capacitor X5R 6.3V 1 10k 1% 0402 1/16W 2 12.4k 1% 0402 1/16W 2.7Ω 1% 0402 1/16W 10Ω 1% 0402 Resistor 1 1 1 49.9k 1% 0402 Resistor 2MHz 3A Buck Regulator 1 1 M9999-062408-A Micrel, Inc. MIC4724YMME Evaluation Board Notes: 1. TDK: www.tdk.com 2. Murata: www.murata.com 3. AVX: www.avx.com 4. Taiyo Yuden: www.t-yuden.com 5. Vishay: www.vishay.com 6. Diodes, Inc.: www.diodes.com 7. Micrel, Inc.: www.micrel.com June 2008 4 M9999-062408-A Micrel, Inc. MIC4724YMME Evaluation Board Printed Circuit Board Layouts Figure 1a. Top Layer Figure 1b. Bottom Layer June 2008 5 M9999-062408-A Micrel, Inc. MIC4724YMME Evaluation Board MICREL, INC. 2180 FORTUNE DRIVE SAN JOSE, CA 95131 USA TEL +1 (408) 944-0800 FAX +1 (408) 474-1000 WEB http:/www.micrel.com This information furnished by Micrel in this data sheet is believed to be accurate and reliable. However no responsibility is assumed by Micrel for its use. Micrel reserves the right to change circuitry and specifications at any time without notification to the customer. Micrel Products are not designed or authorized for use as components in life support appliances, devices or systems where malfunction of a product can reasonably be expected to result in personal injury. Life support devices or systems are devices or systems that (a) are intended for surgical implant into the body or (b) support or sustain life, and whose failure to perform can be reasonably expected to result in a significant injury to the user. A Purchaser's use or sale of Micrel Products for use in life support appliances, devices or systems is a Purchaser's own risk and Purchaser agrees to fully indemnify Micrel for any damages resulting from such use or sale. © 2008 Micrel Incorporated June 2008 6 M9999-062408-A