MIC2875/6 Evaluation Board 4.8A ISW, Synchronous Boost Regulator with Bi-Directional Load Disconnect General Description Getting Started The MIC2875/6 evaluation board is a compact and highlyefficient 2MHz synchronous boost regulator with a 4.8A switch. It features a bi-directional load disconnect function which prevents any leakage current between the input and output when the device is disabled. 1. Connect an external supply to the VIN terminals. Apply the desired input voltage to the VIN (J1) and GND (J2) terminals of the evaluation board, paying careful attention to polarity and supply range (2.5V to 5.5V). An ammeter can be placed between the power supply and the input terminal of the evaluation board. Ensure that the supply voltage is monitored at the VIN (J1) terminal, as the ammeter and/or power-lead resistance can reduce the voltage supplied to the input. The MIC2875/6 operates in bypass mode automatically when the input voltage is greater than the target output voltage. At light loads, the boost converter goes to PFM mode to improve the efficiency. The part also features an integrated anti-ringing switch to minimize EMI. The MIC2875 is designed to operate with a minimum switching frequency of 45kHz from no load to full load to minimize switching artifacts in the audio band. Datasheets and support documentation are available on Micrel’s web site at: www.micrel.com. Requirements The MIC2875/6 evaluation board requires a bench input power source that is adjustable from 2.5V to 5.5V and is able to deliver greater than 4.5A at 2.5V. Precautions The evaluation board does not have reverse polarity protection. Applying a negative voltage across the VIN terminal to the ground (GND) terminal can damage the device. It should not exceed 5.5V on the input. Input power leads should be kept as short as possible to minimize the inductance. VIN measurements should be made at the VIN and GND terminals, to ensure that the voltage drop on the input power leads are not included. 2. Connect a load to VOUT and GND terminals. The load connected between VOUT (J3) and GND (J4) terminals of the evaluation board can be either passive (resistive) or active (electronic load). In case of electronic load, keep the load disabled until the MIC2875/6 has been powered up. An ammeter may be placed between the load and the output terminal. Ensure the output voltage is monitored across the VOUT (J3) and GND (J4) terminals. 3. Enable/Disable the MIC2875/6. The MIC2875/6 evaluation board has an enable (EN) pin (J8).The MIC2875/6 is in standby mode when the EN pin is asserted high. Setting the jumper at JP1 connects the EN pin to VIN through a 10kΩ pull-up resistor. If this pin is driven low, the IC is shut down. This pin has an internal pull-down resistor and can be left open. 4. Power Good (/PG). A power good (/PG) test pin (J5) is provided to monitor the power good function. It is an open drain active low output power good output. Setting the jumper at JP2 connects the /PG pin to VIN through a 1MΩ pull-up resistor. This pin is asserted low when the output is above the power good threshold. Ordering Information Part Number Description MIC2875-AYMT EV MIC2875 Adjustable Output MIC2875-5.0YMT EV MIC2875-5.0V Fixed Output MIC2876-AYMT EV MIC2876 Adjustable Output MIC2876-5.0YMT EV MIC2876-5.0V Fixed Output Micrel Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel +1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com October 21, 2014 Revision 1.0 Micrel, Inc. MIC2875/6 Evaluation Board Integrated Anti-Ringing Switch The MIC2875/6 includes an anti-ringing switch that eliminates the ringing on the SW node of a conventional boost converter operating in the discontinuous conduction mode (DCM). At the end of a switching cycle during DCM operation, both the NMOS and PMOS are turned off. The anti-ringing switch in the MIC2875/6 clamps the SW pin voltage to IN to dissipate the remaining energy stored in the inductor and the parasitic elements of the power switches. Evaluation Board Description Automatic Bypass Mode (when VIN > VOUT) The MIC2875/6 automatically operates in bypass mode when the input voltage is higher than the target output voltage. In bypass mode, the NMOS is turned off while the PMOS is fully turned on to provide a very low impedance path from IN to OUT. Soft-Start The MIC2875/6 integrates an internal soft-start circuit to limit the inrush current during start-up. When the device is enabled, the PMOS is turned on slowly to charge the output capacitor to a voltage close to the input voltage. Then, the device begins boost switching cycles to gradually charge up the output voltage to the target VOUT. Figure 1. MIC2875-AYMT Evaluation Board Bi-Directional Output Disconnect The power stage of the MIC2875/6 consists of a NMOS transistor as the main switch and a PMOS transistor as the synchronous rectifier. A control circuit turns off the back gate diode of the PMOS to isolate the output from the input supply when the chip is disabled (VEN = 0V). An “always on” maximum supply selector switches the cathode of the backgate diode to either the IN or the OUT, whichever pin has a higher voltage. As a result, the output of the MIC2875/6 is bi-directionally isolated form the input as long as the device is disabled. The maximum supply selector and hence the output disconnect function requires only 0.3V at the IN pin to operate. Output Voltage Programming The MIC2875/6 has an adjustable version that allows the output voltage to be set by an external resistor divider R2 and R3. The typical feedback voltage is 900mV and the recommended maximum and minimum output voltage is 5.5V and 3.2V respectively. The current through the resistor divider should be significantly larger than the current into the FB pin (0.01µA typical). It is recommended that the total resistance of R2 + R3 should be approximately 1MΩ. The appropriate R2 and R3 values for the desired output voltage are calculated by: Minimum Switching Frequency (MIC2875 Only) When the MIC2875 enters the pulse-skipping mode for more than 20µs, an internal control circuitry forces the PMOS to turn on briefly to discharge VOUT to VIN through the inductor. When the inductor current reaches a predetermined threshold, the PMOS is turned off and the NMOS is turned on so that the inductor current can decrease gradually. Once the inductor current reaches zero, the NMOS is eventually turned off. The above cycle repeats if there is no switching activity for another 20µs, effectively maintaining a minimum switching frequency of 45kHz. The frequency control circuit is disabled when VOUT is less than or within 200mV of VIN. This minimum switching frequency feature is advantageous for applications that are sensitive to low frequency EMI such as audio systems. October 21, 2014 V R 2 = R3 × OUT − 1 0 . 9 V 2 Eq. 1 Revision 1.0 Micrel, Inc. MIC2875/6 Evaluation Board Safe Operating Area (SOA) The safe operating area (SOA) curves represent the boundary of the maximum safe operating current and maximum safe operating junction temperature. Maximum Load Current vs. Ambient Temperature MAXIMUM LOAD CURRENT (A) 3.0 ADJUSTABLE R2 = 910kΩ R3 = 200kΩ 2.5 2.0 1.5 VIN = 3.0V VIN = 3.2V VIN = 3.6V 1.0 VOUT = 5.0V COUT = 22µF L = 1µH 0.5 0.0 0 25 50 75 100 125 150 175 AMBIENT TEMPERATURE (℃) Figure 2. MIC2875/6 Safe Operating Area (SOA) Curves Figure 2 illustrates the SOA for various VIN mounted on the MIC2875/6 EVB from 0°C to +155°C. October 21, 2014 3 Revision 1.0 Micrel, Inc. MIC2875/6 Evaluation Board Evaluation Board Schematics (MIC2875/6-AYMT) MIC2875/6-AYMT (VIN ≤ 5.0V) Bill of Materials Item Part Number C1 C1608X5R1A475K080AC C2 LMK212BJ226MG-T C3 GRM188R61A105KA61J − C4 L1 R1 PIMB042T-1R0MS-39 ERJ-3GEYJ105V Manufacturer (1) TDK Taiyo Yuden Murata (2) (3) − Cyntec (4) Panasonic (5) (6) Qty. Capacitor 4.7μF, 10V, 10%, X5R, 0603 1 Capacitor 22μF, 10V, 20%, X5R, 0805 (VIN ≤ 5.00V) 1 Capacitor 22μF, 10V, 20%, X5R, 0805 (VIN > 5.00V, in parallel) 3 Capacitor 1μF, 10V, 10%, X5R, 0603 1 Not Fitted, Size 0603 0 Inductor 1μH, 4.5A, SMD, 4.2mm × 4.0mm × 1.8mm 1 Resistor 1MΩ, 5%, 0603 1 Resistor 910kΩ, 0.1%, 0603 1 R2 1-1879417-8 R3 ERA-3AEB204V Panasonic Resistor 200kΩ, 0.1%, 0603 1 R4 ERJ-3GEYJ103V Panasonic Resistor 10kΩ, 5%, 0603 1 Resistor 0Ω, 0603 2 4.8A ISW, Synchronous Boost Regulator with Bi-Directional Load Disconnect 1 R5, R7 U1 CRCW0603000Z0EA MIC2875-xYMT MIC2876-xYMT TE Description (7) Vishay (8) Micrel, Inc. Notes: 1. TDK: www.tdk.com. 2. Taiyo Yuden: www.t-yuden.com. 3. Murata: www.murata.com. 4. Cyntec: www.cyntec.com 5. Panasonic: www.panasonic.com. 6. TE: www.te.com. 7. Vishay: www.vishay.com. 8. Micrel, Inc.: www.micrel.com. October 21, 2014 4 Revision 1.0 Micrel, Inc. MIC2875/6 Evaluation Board Evaluation Board Schematics (MIC2875/6-5.0YMT) MIC2875/6-5.0YMT (VIN ≤ 5.0V) Bill of Materials Item Part Number C1 C1608X5R1A475K080AC C2 LMK212BJ226MG-T C3 GRM188R61A105KA61J − C4 L1 PIMB042T-1R0MS-39 R1 ERJ-3GEYJ105V R2, R5, R7 CRCW0603000Z0EA − R3 R4 U1 ERJ-3GEYJ103V MIC2875-xYMT MIC2876-xYMT Manufacturer (9) TDK Taiyo Yuden Murata (10) (11) − Cyntec (12) Panasonic (13) (14) Vishay − Panasonic (15) Micrel, Inc. Description Qty. Capacitor 4.7μF, 10V, 10%, X5R, 0603 1 Capacitor 22μF, 10V, 20%, X5R, 0805 (VIN ≤ 5.00V) 1 Capacitor 22μF, 10V, 20%, X5R, 0805 (VIN > 5.00V, in parallel) 3 Capacitor 1μF, 10V, 10%, X5R, 0603 1 Not Fitted, Size 0603 0 Inductor 1μH, 4.5A, SMD, 4.2mm × 4.0mm × 1.8mm 1 Resistor 1MΩ, 5%, 0603 1 Resistor 0Ω, 0603 3 Not Fitted, Size 0603 0 Resistor 10kΩ, 5%, 0603 1 4.8A ISW, Synchronous Boost Regulator with Bi-Directional Load Disconnect 1 Notes: 9. TDK: www.tdk.com. 10. Taiyo Yuden: www.t-yuden.com. 11. Murata: www.murata.com. 12. Cyntec: www.cyntec.com. 13. Panasonic: www.panasonic.com. 14. Vishay: www.vishay.com. 15. Micrel, Inc.: www.micrel.com. October 21, 2014 5 Revision 1.0 Micrel, Inc. MIC2875/6 Evaluation Board PCB Layout Recommendations Top Layer Bottom Layer October 21, 2014 6 Revision 1.0 Micrel, Inc. MIC2875/6 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 Micrel, Inc. is a leading global manufacturer of IC solutions for the worldwide high-performance linear and power, LAN, and timing & communications markets. The Company’s products include advanced mixed-signal, analog & power semiconductors; high-performance communication, clock management, MEMs-based clock oscillators & crystal-less clock generators, Ethernet switches, and physical layer transceiver ICs. Company customers include leading manufacturers of enterprise, consumer, industrial, mobile, telecommunications, automotive, and computer products. Corporation headquarters and state-of-the-art wafer fabrication facilities are located in San Jose, CA, with regional sales and support offices and advanced technology design centers situated throughout the Americas, Europe, and Asia. Additionally, the Company maintains an extensive network of distributors and reps worldwide. Micrel makes no representations or warranties with respect to the accuracy or completeness of the information furnished in this datasheet. This information is not intended as a warranty and Micrel does not assume responsibility for its use. Micrel reserves the right to change circuitry, specifications and descriptions at any time without notice. No license, whether express, implied, arising by estoppel or otherwise, to any intellectual property rights is granted by this document. Except as provided in Micrel’s terms and conditions of sale for such products, Micrel assumes no liability whatsoever, and Micrel disclaims any express or implied warranty relating to the sale and/or use of Micrel products including liability or warranties relating to fitness for a particular purpose, merchantability, or infringement of any patent, copyright, or other intellectual property right. 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. © 2014 Micrel, Incorporated. October 21, 2014 7 Revision 1.0