MIC4574 Evaluation Board Micrel MIC4574 Evaluation Board 200kHz Switching Regulator Precautions The MIC4574 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 MIC4574 evaluation board 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 MIC4574 is available in 3.3V fixed, 5.0V fixed, 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, or 6V, by jumper selection. General Description Designed for distributed power systems, the MIC4574 is a monolithic, step-down switching regulator capable of 0.5A output current and can operate from input voltages ranging from 4V to 24V. It has a logic-compatible enable that provides 200µA of quiescent current in shutdown mode. The Micrel MIC4574 is an enhanced version of the popular LM2574, a 52kHz step-down (buck) switching regulator. The MIC4574 features a 200kHz switching frequency that reduces the inductor size by a factor of four, freeing up precious board space. The MIC4574 evaluation board is designed for applications up to 0.5A. MIC4575 and MIC4576 evaluation boards, for 1A and 3A applications respectively, are also available. Requirements The MIC4574 evaluation board requires a power supply capable of at least 0.8A at up to 24V. The load may be up to 0.5A maximum, respectively. Operation 2.5V Output Efficiency 80 10 8V to 24V C1 10µF 35V SHUTDOWN 5 ENABLE SW VIN MIC4574BWM FB SHDN SGND PGND 4 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, current flows through the diode, inductor, and load. Figures 2a through 2c show the efficiency for 5V, 2.5V, and 3.3V outputs versus input voltage and output current. 60 8V 12V 18V 24V 40 20 10 100 500 OUTPUT CURRENT (mA) Figure 2a. 5V Output Efficiency 12 L1 100µH 3 D1 MBRS130 6 5.0V/0.5A R1 3.01k 1% R2 3.01k 1% JP1A 2.5V C3 3300pF R3 1.82k 1% JP1B 3.3V R4 1k 1% JP1C 5V C2* 220µF 10V R5 806Ω 1% JP1D 6V * 330µF required for 2.5V operation Figure 1. Buck Converter (8V–24V to 5V/0.5A) Micrel, Inc. • 1849 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 944-0800 • fax + 1 (408) 944-0970 • http://www.micrel.com October 1997 1 MIC4574 Evaluation Board MIC4574 Evaluation Board Micrel Input Voltage The minimum input voltage rating varies with output voltage. Table 2 lists the lowest input voltage the MIC4574 can operate from. Table 1 shows standard 1% resistor values for jumper selectable output voltages. Jumper Position Output Voltage R1 R2–R5 (nearest 1%) JP1A 2.5V 3.01k 3.01k Output Voltage VIN (Minimum) JP1B 3.3V 3.01k 1.82k 2.5V 5V JP1C 5V 3.01k 1.00k 3.3V 6V JP1D 6V 3.01k 806Ω 5V 8V 6V 9V 12V 15V Table 1. Programming Resistor Values Programming resistors R2, R3, R4, and R5 are used to set the output voltage according to the equation: Table 2. Minimum Input Voltages R1 VOUT = 1.25V 1 + R2 Enable/Shutdown Mode To activate the MIC4574, set the enable switch to the ON position. To put the MIC4574 into its micropower (200µA) shutdown state, set the enable switch to the OFF position. 2.5V Output Option Although the evaluation board will operate normally at 2.5V output, the phase margin falls below 20°. A 330µF output capacitor (C2†) is recommended to increase the phase margin above 20°. The adjustable regulator can be replaced with MIC4574-3.3 or MIC4574-5.0 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. 3.3V Output Efficiency 5V Output Efficiency 100 EFFICIENCY (%) EFFICIENCY (%) 90 70 50 30 10 8V 12V 18V 24V 80 60 8V 12V 18V 24V 40 10 100 500 OUTPUT CURRENT (mA) Figure 2b. 2.5V Output Efficiency 8V 12V 18V 24V 100 500 OUTPUT CURRENT (mA) Figure 2c. 3.3V Output Efficiency Item Part Number Source C1 C2 †C2 C3 TPSD106M035R0300 TPSE227M010R0100 TPSE337M006R0100 3300pF ceramic X7R AVX (803) 448-9411 D1 MBRS130LT3 Motorola (800) 521-6274 L1 D03316P-683 Coilcraft (708) 639-2361 U1 MIC4574BWM Micrel (408) 944-0800 Table 3. Bill of Materials MIC4574 Evaluation Board 2 October 1997 MIC4574 Evaluation Board Micrel Component Side Silk Screen (Component Side) October 1997 3 MIC4574 Evaluation Board MIC4574 Evaluation Board Micrel Solder Side Silk Screen (Solder Side) MICREL INC. 1849 FORTUNE DRIVE SAN JOSE, CA 95131 TEL + 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. © 1997 Micrel Incorporated MIC4574 Evaluation Board 4 October 1997