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SS6550COTR датащи(PDF) 11 Page - Silicon Standard Corp. |
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SS6550COTR датащи(HTML) 11 Page - Silicon Standard Corp. |
11 / 13 page www.SiliconStandard.com 11 of 13 SS6550 n APPLICATION INFORMATION (cont.) Layout Consideration To ensure proper operation of the SS6550, the following points should be considered: 1. The input capacitor and VIN should be placed as close as possible to each other to avoid the AC current flow into the internal MOSFET. 2. The output loop, which consists of the inductor, Schottky diode and output capacitor, should be kept as small as possible. 3. The routes carrying large currents should be kept short and wide. 4. Logically the large current of the converter, when SS6550 is on or off, should flow in the same direction. 5. The FB pin should connect to the feedback re- sistors directly, and the route should be away from any noise source, such as the inductance of the LX line. 6. Grounding all components at the same point may effectively reduce the occurrence of loops. A stable ground plane is very important to obtain higher efficiency. When a ground plane is cut apart, it may cause disturbed signals and noise. If possible, two or three through-holes can en- sure the stability of grounding. Fig.2 to 4 shows the layout diagrams of the SS6550. Example Here is an example to illustrate the components selec- tion guide lines above. Let’s assume the SS6550 is to be used for a mobile phone application, which uses a 1-cell Li-Ion battery with 2.7V to 4.2V input voltage for the power source. The required load current is 800mA, and the output voltage is 1.8V. Substituting VOUT=1.8V, VIN=4.2V, ripple =250mA, and f=500 kHz to equation (1) H 23 . 8 V 2 . 4 V 8 . 1 1 mA 250 kHz 500 V 8 . 1 L µ = − × = Therefore, 10 µH is appropriate for the inductor. The in- ductor, series number SLF6025-100M1R0 from TDK, with 57.3m Ω series resistance is recommended for the best efficiency. For the output capacitor, the ESR is more important than its capacitance. Assuming ripple voltage of 100mV, then the ESR can be calculated as: Ω = = ∆ ∆ = 4 . 0 mA 250 mV 100 I V ESR Therefore, a 33 µF/10V capacitor, MCM series from NIPPON, is recommended. Schottky selection is calculated as following. V 2 . 4 V V IN ) OFF ( MAX , D = = ) ON ( MAX , D I 2 I I L MAX , OUT ∆ + = 2 mA 250 mA 800 + = mA 925 = ) ON ( avg , D I OUT I ) D 1 ( × − = mA 800 ) 2 . 4 8 . 1 1 ( × − = mA 14 . 457 = According to the data above, the Schottky diode, SS12, from GS is recommended. For feedback resistors, choose R2=390k Ω, and then R1 can be calculated as follow: Ω = Ω × − = k 546 k 390 1 75 . 0 V 8 . 1 1 R ; use 560k Ω Fig. 22 shows this application circuit for the SS6550. Rev.2.01 6/06/2003 |
Аналогичный номер детали - SS6550COTR |
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Аналогичное описание - SS6550COTR |
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