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SS23 Scheda tecnica(PDF) 6 Page - Monolithic Power Systems |
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SS23 Scheda tecnica(HTML) 6 Page - Monolithic Power Systems |
6 / 10 page MP1580 – 2A, 380KHz STEP-DOWN CONVERTER MP1580 Rev. 3.0 www.MonolithicPower.com 6 12/5/2005 MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2005 MPS. All Rights Reserved. TM Input Capacitor The input current to the step-down converter is discontinuous, so a capacitor is required to supply the AC current to the step-down converter while maintaining the DC input voltage. A low ESR capacitor is required to keep the noise at the IC to a minimum. Ceramic capacitors are preferred, but tantalum or low- ESR electrolytic capacitors will also suffice. The input capacitor value should be greater than 10µF. The capacitor can be electrolytic, tantalum or ceramic. However, since it absorbs the input switching current it requires an adequate ripple current rating. Its RMS current rating should be greater than approximately 1/2 of the DC load current. To ensure stable operation, C1 should be placed as close to the IN pin as possible. Alternately, a smaller high quality ceramic 0.1µF capacitor may be placed closer to the IN pin and a larger capacitor placed further away. If using this technique, it is recommended that the larger capacitor be a tantalum or electrolytic type capacitor. All ceramic capacitors should be placed close to the MP1580. Output Capacitor The output capacitor is required to maintain the DC output voltage. Low ESR capacitors are preferred to keep the output voltage ripple low. The characteristics of the output capacitor also affect the stability of the regulation control system. Ceramic, tantalum or low ESR electrolytic capacitors are recommended. In the case of ceramic capacitors, the impedance at the oscillator frequency is dominated by the capacitance, so the output voltage ripple is mostly independent of the ESR. The output voltage ripple is estimated to be: 2 LC IN RIPPLE f f V 4 . 1 V ⎟⎟ ⎠ ⎞ ⎜⎜ ⎝ ⎛ × × ≅ Where VRIPPLE is the output ripple voltage, fLC is the resonant frequency of the LC filter and f is the oscillator frequency. In the case of tantalum or low-ESR electrolytic capacitors, the ESR dominates the impedance at the oscillator frequency, therefore the output ripple is calculated as: ESR RIPPLE R I V × ∆ ≅ Where VRIPPLE is the output voltage ripple and RESR is the equivalent series resistance of the output capacitors. Output Rectifier Diode The output rectifier diode supplies the current to the inductor when the upper transistor M1 is off. To reduce losses due to the diode forward voltage and recovery times, use a Schottky rectifier. Table 2 provides the Schottky rectifier part numbers based on the maximum input voltage and current rating. Table 2—Schottky Rectifier Selection Guide 2A Load Current VIN (Max) Part Number Vendor 15V 30BQ015 4 B220 1 SK23 6 20V SR22 6 20BQ030 4 B230 1 SK23 6 SR23 3, 6 26V SS23 2, 3 Table 3 lists some rectifier manufacturers. Table 3—Schottky Diode Manufacturers Vendor Web Site Diodes, Inc. www.diodes.com Fairchild Semiconductor www.fairchildsemi.com General Semiconductor www.gensemi.com International Rectifier www.irf.com On Semiconductor www.onsemi.com Pan Jit International www.panjit.com.tw Choose a rectifier that has a maximum reverse voltage rating greater than the maximum input voltage, and a current rating greater than the maximum load current. |
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Descrizione simile - SS23 |
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