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NCP1410 データシート(PDF) 12 Page - ON Semiconductor |
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NCP1410 データシート(HTML) 12 Page - ON Semiconductor |
12 / 14 page NCP1410 http://onsemi.com 12 GENERAL DESIGN PROCEDURES Switching mode converter design is considered as black magic to most engineers, some complicate empirical formulae are available for reference usage. Those formulae are derived form the assumption that the key components, i.e. power inductor and capacitors are available with no tolerance. Practically, its not true, the result is not a matter of how accurate the equations you are using to calculate the component values, the outcome is still somehow away from the optimum point. In below a simple method base on the most basic first order equations to estimate the inductor and capacitor values for NCP1410 operate in Continuous Conduction Mode is introduced. The component value set can be used as a starting point to fine tune the circuit operation. By all means, detail bench testing is needed to get the best performance out of the circuit. Design Parameters: VIN = 1.8 V to 3.0 V, Typical 2.4 V VOUT = 3.3 V IOUT = 200 mA (250 mA max) VLB = 2.0 V VOUT−RIPPLE = 40 mVP−P at IOUT = 250 mA Calculate the feedback network: Select RFB2 = 200 K RFB1 + RFB2 VOUT VREF * 1 RFB1 + 200 K 3.3 V 1.19 V * 1 + 355 K Calculate the Low Battery Detect divider: VLB = 2.0 V Select RLB2 = 330 K RLB1 + RLB2 VLB VREF * 1 RLB1 + 330 K 2.0 V 1.19 V * 1 + 225 K Determine the Steady State Duty Ratio, D for typical VIN, operation will be optimized around this point: VOUT VIN + 1 1 * D D + 1 * VIN VOUT + 1 * 2.4 V 3.3 V + 0.273 Determine the average inductor current, ILAVG at maximum IOUT: ILAVG + IOUT 1 * D + 250 mA 1 * 0.273 + 344 mA Determine the peak inductor ripple current, IRIPPLE−P and calculate the inductor value: Assume IRIPPLE−P is 20% of ILAVG, the inductance of the power inductor can be calculated as in below: IRIPPLE−P = 0.20 x 344 mA = 68.8 mA L + VIN tON 2IRIPPLE * P + 2.4 V 1.4 mS 2(68.8 mA) + 24.4 mH Standard value of 22 mH is selected for initial trial. Determine the output voltage ripple, VOUT−RIPPLE and calculate the output capacitor value: VOUT−RIPPLE = 40 mVP−P at IOUT = 250 mA COUT u IOUT tON VOUT−RIPPLE * IOUT ESRCOUT where tON = 1.4 mS and ESRCOUT = 0.1 W, COUT u 250 mA 1.4 mS 40 mV * 250 mA 0.1 W + 23.33 mF From above calculation, you need at least 23.33 mF in order to achieve the specified ripple level at conditions stated. Practically, a one level larger capacitor will be used to accommodate factors not take into account in the calculation, therefore a capacitor value of 33 mF is selected. |
同様の部品番号 - NCP1410_05 |
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同様の説明 - NCP1410_05 |
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