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RT8560 Datasheet(PDF) 14 Page - Richtek Technology Corporation |
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RT8560 Datasheet(HTML) 14 Page - Richtek Technology Corporation |
14 / 15 page ![]() RT8560 14 DS8560-01 April 2011 www.richtek.com ) OUT IN OUT OUT RIPPLE OUT (V V I C = VV f η −× ×× × Layout Guideline PCB layout is very important for designing power switching converter circuits. Some recommended layout guides that should be strictly be followed are shown as follows : The power components L, D, CVIN, COUT1 and COUT2 must be placed as close as possible to reduce the ac current loop. The PCB trace between power components must be as short and wide as possible due to large current stream flows through these traces during operation. Place L and D connected to SW pin as close as possible. The trace should be short and wide as possible. It is recommended to place CVcc1 and CVcc2 close to VCC1 and VCC2 pins. Pin14 is the compensation point to adjust system stability. Place the compensation components to pin14 as close as possible, no matter the compensation is RC or capacitance. Figure 9. PCB layout OUT OUT IN OUT IN PEAK IN OUT VI V T V V I = V2 L V η ×× − ⎛⎞ + ⎜⎟ ×× × ⎝⎠ Where, VOUT = maximum output voltage. VIN = minimum input voltage. f = operating frequency. IOUT = sum of current from all LED strings. The boost converter operates in discontinuous mode over the entire input voltage range when the L1 inductor value is less than this value L. With an inductance greater than L, the converter operates in continuous mode at the minimum input voltage and may be discontinuous at higher voltages. The inductor must be selected with a saturated current rating that is greater than the peak current provided by the following equation : Where, η is the efficiency of the power converter. Diode Selection Schottky diode is a good choice for an asynchronous Boost converter due to the small forward voltage. However, power dissipation, reverse voltage rating and pulsating peak current are the important parameters for Schottky diode selection. Choose a suitable diode whose reverse voltage rating is greater than the maximum output voltage. Capacitor Selection The input capacitor reduces current spikes from the input supply and minimizes noise injection to the converter. For most applications, a 10uF ceramic capacitor is sufficient. A value higher or lower may be used depending on the noise level from the input supply and the input current to the converter. It is recommended to choose a ceramic capacitor bases on the output voltage ripple requirements. The minimum value of the output capacitor COUT is approximately given by the following equation : 1 2 3 4 5 15 14 13 12 11 6 7 89 10 20 19 18 16 17 LED4 GND GND GND GND SW SW EN OVP SS VC 21 COUT1 COUT2 D VOUT COUT3 GND GND CVIN L CVCC1 CVCC2 RVCC2 RVCC1 GND RVC CVC1 CVC2 VIN Place these components as close as possible. Locate the CVCC1 and CVCC2 as close as possible to VCC1 and VCC2 pin. Locate the compensation components to VC pin as close as possible. |
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