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SI-8150S 데이터시트(PDF) 5 Page - Sanken electric |
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SI-8150S 데이터시트(HTML) 5 Page - Sanken electric |
5 / 6 page 84 Caution 1. Selecting External Components (1) Choke coil L1 To maintain the stable operation of the regulator, choke coil L1 should be selected appropriately. When selecting choke coil L1, consider the following: a) Suitable for a switching regulator Do not use a coil as a noise filter because it generates excess heat. b) Appropriate inductance The greater the inductance of the choke coil, the smaller the output ripple voltage. However, the size of the coil increases large as the inductance increases. If the inductance is low, a greater peak current flows to the IC and loss increases. This is not favorable for stable operation. The standard external circuit shows reference inductance val- ues suitable for stable operation. However, the appropriate inductance may also be calculated as follows: L= (VIN–VO)•VO ∆IL•VIN•f Where, deltaIL indicates the ripple current of the choke coil that is roughly set as follows: • If the working output current is close to the maximum rating (3 A) of SI-8000S Ripple current = output current × 0.2 to 0.3 • If the working output current is about 1.0A or less Ripple current = output current × 0.3 to 0.4 c) Satisfying the rated current The rated current of a choke coil must be greater than the maximum load current. Note that the inductance decreases drastically and an excess current flows if the load current ex- ceeds the rated current of the coil. d) Good DC current superposition characteristics The current flowing through a choke coil is a triangular wave- form current superimposed on a DC current equal to the load current. The coil inductance decreases as the load current increases. In general, the coil can be used until the induc- tance drops to 50% of the rated value. Use this as the refer- ence value for selection. 100% 50% IO (max.) Inductance Load current e) Less noise A drum-type open magnetic core coil can affect peripheral circuits with noise because the flux passes outside the coil. To avoid this problem, use a toroidal, EI, or EE type open magnetic core coil. qSI-8000S Series (2) Input capacitor C1 Input capacitor C1 operates as a bypass capacitor in the input circuit. When selecting input capacitor C1, consider the following: a) The breakdown voltage is higher than the maximum input volt- age. b) Satisfies the allowable ripple current Exceeding the ratings of this capacitor or using it without de- rating may reduce its service life and also cause the regulator to malfunction. Therefore, an input capacitor with a sufficient margin should be selected. With the SI-8000S Series, the effective ripple current Irms flowing to the input capacitor can be calculated approximately as follows: Irms 1.2 × VO × IO VIN (3) Output capacitor C2 Output capacitor C2 operates as a smoothing capacitor for switch- ing output. The output ripple voltage from the regulator is deter- mined by the product of the pulsating current part ∆IL (=C2 charge- discharge current) of the choke coil current and the equivalent series resistance ESR of the output capacitor C2. Vrip= ∆IL•C2ESR Therefore, a capacitor of low equivalent series resistance ESR should be selected to reduce the output ripple voltage. It is rec- ommended to select a low-impedance capacitor intended for use with switching regulators as C2. (4) Diode D1 Use a Schottky barrier diode for D1. If you use a general rectifier diode or fast recovery diode, the IC may be damaged. (Sanken RK46 recommended) 2. Notes on Pattern Design (1) Large current line Since a large current flows through the bold lines in the standard external circuit make the pattern as wide and as short as pos- sible. 2 1 3 4 SI-8000S VIN GND C1 C2 L1 D1 VOUT GND + + (2) Input capacitor Place the input capacitor C1 and output capacitor C2 as close to the IC as possible. Since a large current flows through the lead wires of the input and output capacitors to charge and discharge them quickly, minimize the lead wire length. The pattern around the capacitors should also be minimized. C1. C2. C1. C2. + + Example of bad pattern Example of good pattern |
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