MIC4576 Evaluation Board Micrel MIC4576 Evaluation Board 200kHz Buck Switching Regulator Precautions The MIC4576 has no protection from reversed polarity being applied to its input. Any momentary reversal of the dc power supply connections can cause permanent damage to the circuit. Use extreme care with these connections. The safest way to power up the MIC4576 is to set the power supply to zero volts and then gradually increase the supply voltage. Monitor the input supply current while increasing the input voltage. If the circuit draws excessive current, immediately shut off the main supply and check for proper power supply connections. This simple procedure can avoid most catastrophic failures. Output Voltage Configuration The MIC4576 is available in 3.3V, 5.0V, and adjustable output-voltage versions. The evaluation board uses the adjustable output version to provide industry standard output voltages of 2.5V, 3.3V, 5V, 6V, or 12V, by jumper selection. General Description Designed for distributed power systems, the MIC4576 is a monolithic, step-down switching regulator capable of 3.0A output current and can operate from input voltages ranging from 4V to 36V. It has a logic-compatible enable pin that provides 200µA of quiescent current in shutdown mode. The Micrel MIC4576 is an enhanced version of the popular LM2576, a 52kHz step-down (buck) switching regulator. The MIC4576 features a 200kHz switching frequency that reduces the inductor size by a factor of four, freeing up precious board space. The MIC4576 evaluation board is designed for applications up to 3A. MIC4574 and MIC4575 evaluation boards, for 0.5A and 1A applications respectively, are also available. Requirements The MIC4576 evaluation board requires a power supply capable of at least 5A at up to 40V. The load may be up to 3A maximum. 5V Output Efficiency Operation 100 J1 VIN 4V to 36V EFFICIENCY (%) Figure 1 shows the schematic of the evaluation board circuit. When the internal high-side switch turns on, one side of the inductor is fed from the input voltage. During this period, current flows from the input, through the internal output switch, output inductor, and load. When the output switch turns off, the SW pin voltage drops until the clamp diode is forward biased. During this portion of the cycle, the current flow through the diode, inductor, and load. Figures 2a through 2d show the efficiency for 5V, 2.5V, 3.3V, and 12V outputs versus input voltage and output current. 80 60 40 100 7.5V 12V 24V 36V 1000 3000 OUTPUT CURRENT (mA) Figure 2a. 5V Output Efficiency L1* 1 C1 680 F 63V C2 0.1 F 50V JP3 OFF ON 5 VIN SW MIC4576BT FB SHDN GND 2 33 H 4 3 D1 MBR360RL J2 GND C3 3300pF 50V R1 3.01k 1% R2 3.01k 1% JP1A 2.5V R3 1.82k 1% JP1B 3.3V R4 1k 1% JP1C 5V JP2 Fix VOUT R5 750‰ 1% JP1D 6V C4 1000 F 16V C5 0.1 F 50V J3 VOUT 3A R6 340‰ 1% JP1E 12V J4 GND * Use 68 H for 12V output Figure 1. Buck Converter (8V–36V to 5V/3A) Micrel, Inc. • 1849 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 944-0800 • fax + 1 (408) 944-0970 • http://www.micrel.com June 2001 1 MIC4576 Evaluation Board MIC4576 Evaluation Board Micrel Table 1 shows standard 1% resistor values for jumper selectable output voltages. R1 R1-R5 (nearest 1%) JP1A 2.5V 3.01k 3.01k JP1B 3.3V 3.01k 1.82k JP1C 5.0V 3.01k 1.0k JP1D 6.0V 3.01k 750Ω JP1E 12.0V 3.01k 340Ω 80 EFFICIENCY (%) Jumper Output Position Voltage 2.5V Output Efficiency 60 5V 12V 18V 24V 40 20 100 1000 3000 OUTPUT CURRENT (mA) Figure 2b. 2.5V Output Efficiency Table 1. Programming Resistor Values 3.3V Output Efficiency Programming resistors R2 through R6 are used to set the output voltage according to the following equation: 90 EFFICIENCY (%) R1 VOUT = 1.25V 1 + R2 The adjustable regulator can be replaced with MIC4576-3.3 or MIC4576-5.0 fixed output voltage devices for evaluation. To configure the board for fixed devices, connect the feedback pin (pin 4) directly to the output voltage by removing the voltage adjustment jumper and placing a zero-ohm jumper across R1. Input Voltage The minimum input voltage rating varies with output voltage. Table 2 lists the lowest input voltage the MIC4576 can operate from. VIN (Minimum) 2.5V 5V 3.3V 6V 5V 8V 50 30 100 6V 12V 24V 36V 1000 3000 OUTPUT CURRENT (mA) Figure 2c. 3.3V Output Efficiency 12V Output Efficiency 100 EFFICIENCY (%) Output Voltage 70 80 60 15.5V 24V 6V 10V 12V 15V 36V 40 100 1000 3000 OUTPUT CURRENT (mA) Figure 2c. 12V Output Efficiency Table 2. Minimum Input Voltages Enable/Shutdown Mode To activate the MIC4576, set the enable switch to the ON position. To put the MIC4576 into its micropower (200µA) shutdown state, set the enable switch to the OFF position. 12V Output Option Although the evaluation board is functional for a 12V/3A output, the 33µH inductor is not rated to handle this amount of current continuously. An alternate 68µH inductor (L1*) is specified for this board which is specifically designed for a 12V/3A continuous load. Item C1 C2 D1 Part Number 63MV680GX 16MV1000GX MBR360RL L1 UP4B-330 HS 533402B02552 U1 MIC4576BT Source Sanyo (619) 661-6835 ON Semi (800) 344-3860 Coiltronics (561) 752-5000 Aavid (603) 223-1723 Micrel (408) 944-0800 Table 3. Abbreviated Bill of Materials MIC4576 Evaluation Board 2 June 2001 MIC4576 Evaluation Board Micrel Printed Circuit Boards Solder Side Component Side Silk Screen (Solder Side) Silk Screen (Component Side) June 2001 3 MIC4576 Evaluation Board MIC4576 Evaluation Board Micrel J1 VIN 4V to 36V L1* 1 C1 390µF 50V C2 0.1µF 50V OFF JP3 5 ON VIN SW MIC4576BT FB SHDN GND 2 33µH 4 D1 MBR360 3 J2 GND R1 3.01k 1% C3 3300pF 50V R2 3.01k 1% JP1A 2.5V R3 1.82k 1% JP1B 3.3V R4 1k 1% JP1C 5V JP2 Fix VOUT R5 750Ω 1% JP1D 6V C4 1000µF 16V J3 VOUT C5 3A 0.1µF 50V R6 340Ω 1% JP1E 12V J4 GND * Use 68µH for 12V output Figure 1. Buck Converter (8V–36V to 5V/3A) Bill of Materials Item Part Number Manufacturer Description Qty. C1 63MV680AX(16X25mm) Sanyo 680µF / 63V 1 C2, C5 VJ0805Y104KXXMB Vitramon 0.1µF / 50V 1 C3 VJ0805Y332AKXAAT Vitramon 3300pF / 50V 1 C4 16MV1000AX Sanyo 1000µF / 16V 1 D1 MBR360RL On Semiconductor 3A / 60V 1 L1 UP4B-330 Coiltronics 33µH, ISAT 6.1A 1 JP1 S2012-05-ND Sullins 2X5 Straight dual header rale 1 JP2 S2012-02-ND Sullins 1X2 Straight dual header rale 1 JP3 S2012-03-ND Sullins 1X3 Straight dual header rale 1 R1, R2 CCF-55 3011 FT-1 Vishay Dale 3.01k, 1%, 1/4W 1 R3 CCF-55 1821 FT-1 Vishay Dale 1.82k, 1%, 1/4W 1 R4 CCF-55 1001 FT-1 Vishay Dale 1k, 1%, 1/4W 1 R5 CCF-55 7500 FT-1 Vishay Dale 750Ω, 1%, 1/4W 1 R6 CCF-55 3400 FT-1 Vishay Dale 340Ω, 1%, 1/4W 1 HTSNK 533402B02552 Aavid Thermal resistance 5.0Ω 1 U1 MIC4576BT Micrel 200kHz,3A, switching regulator 1 MICREL INC. TEL 1849 FORTUNE DRIVE SAN JOSE, CA 95131 + 1 (408) 944-0800 FAX + 1 (408) 944-0970 WEB USA http://www.micrel.com This information is believed to be accurate and reliable, however no responsibility is assumed by Micrel for its use nor for any infringement of patents or other rights of third parties resulting from its use. No license is granted by implication or otherwise under any patent or patent right of Micrel Inc. © 2001 Micrel Incorporated MIC4576 Evaluation Board 4 June 2001