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SS23 数据表(PDF) 5 Page - Monolithic Power Systems |
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SS23 数据表(HTML) 5 Page - Monolithic Power Systems |
5 / 10 page MP1580 – 2A, 380KHz STEP-DOWN CONVERTER MP1580 Rev. 3.0 www.MonolithicPower.com 5 12/5/2005 MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2005 MPS. All Rights Reserved. TM APPLICATION INFORMATION COMPONENT SELECTION Sync Pin Operation The SYNC pin driving waveform should be a square wave with a rise time less than 20ns. The Minimum High voltage level is 2.7V and the Low level is less than 0.8V. The frequency of the external sync signal needs to be greater than 445KHz. A rising edge on the SYNC pin forces a reset of the oscillator. The upper transistor M1 is switched off immediately if it is not already off. 250ns later M1 turns on connecting SW to VIN. Setting the Output Voltage The output voltage is set using a resistive voltage divider from the output to FB (see Figure 3). The voltage divider divides the output voltage down by the ratio: 2 R 1 R 2 R V V OUT FB + = Where VFB is the feedback voltage and VOUT is the output voltage. Thus the output voltage is: 2 R 2 R 1 R 222 . 1 VOUT + × = R2 can be as high as 100kΩ, but a typical value is 10kΩ. Using this value, R1 is determined by: ) 222 . 1 V ( 18 . 8 1 R OUT − × ≅ For example, for a 3.3V output voltage, R2 is 10kΩ and R1 is 17kΩ. Inductor The inductor is required to supply constant current to the output load while being driven by the switched input voltage. A larger value inductor results in less ripple current that in turn results in lower output ripple voltage. However, the larger value inductor has a larger physical size, higher series resistance and/or lower saturation current. Choose an inductor that does not saturate under the worst-case load conditions. A good rule for determining the inductance is to allow the peak-to-peak ripple current in the inductor to be approximately 30% of the maximum load current. Also, make sure that the peak inductor current (the load current plus half the peak-to-peak inductor ripple current) is below the 2.4A minimum current limit. The inductance value can be calculated by the equation: I f V ) V V ( V L IN OUT IN OUT ∆ × × − × = Where VIN is the input voltage, f is the oscillator frequency and ∆I is the peak-to-peak inductor ripple current. Table 1 lists a number of suitable inductors from various manufacturers. Table 1—Inductor Selection Guide Package Dimensions (mm) Vendor/ Model Core Type Core Material W L H Sumida CR75 Open Ferrite 7.0 7.8 5.5 CDH74 Open Ferrite 7.3 8.0 5.2 CDRH5D28 Shielded Ferrite 5.5 5.7 5.5 CDRH5D28 Shielded Ferrite 5.5 5.7 5.5 CDRH6D28 Shielded Ferrite 6.7 6.7 3.0 CDRH104R Shielded Ferrite 10.1 10.0 3.0 Toko D53LC Type A Shielded Ferrite 5.0 5.0 3.0 D75C Shielded Ferrite 7.6 7.6 5.1 D104C Shielded Ferrite 10.0 10.0 4.3 D10FL Open Ferrite 9.7 11.5 4.0 Coilcraft DO3308 Open Ferrite 9.4 13.0 3.0 DO3316 Open Ferrite 9.4 13.0 5.1 |
类似零件编号 - SS23 |
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类似说明 - SS23 |
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