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RT9715BGBG Datasheet(PDF) 11 Page - Richtek Technology Corporation |
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RT9715BGBG Datasheet(HTML) 11 Page - Richtek Technology Corporation |
11 / 15 page RT9715 11 DS9715-03 April 2011 www.richtek.com PCB Layout Guide In order to meet the voltage drop, droop, and EMI requirements, careful PCB layout is necessary. The following guidelines must be followed : Locate the ceramic bypass capacitors as close as possible to the VIN pins of the RT9715. Place a ground plane under all circuitry to lower both resistance and inductance and improve DC and transient performance (Use a separate ground and power plans if possible). Keep all VBUS traces as short as possible and use at least 50-mil, 2 ounce copper for all VBUS traces. Avoid vias as much as possible. If vias are necessary, make them as large as feasible. Place cuts in the ground plane between ports to help reduce the coupling of transients between ports. Locate the output capacitor and ferrite beads as close to the USB connectors as possible to lower impedance (mainly inductance) between the port and the capacitor and improve transient load performance. Locate the RT9715 as close as possible to the output port to limit switching noise. maximum power dissipation can be calculated by following formula : PD(MAX) = (TJ(MAX) − TA) / θJA Where TJ(MAX) is the maximum operation junction temperature 100 °C, TAis the ambient temperature and the θJA is the junction to ambient thermal resistance. For recommended operating conditions specification of RT9715, where TJ(MAX) is the maximum junction temperature of the die (100 °C) and TA is the maximum ambient temperature. The junction to ambient thermal resistance θJA is layout dependent. For SOT-23-5 packages, the thermal resistance θJA is 250°C/W on the standard JEDEC 51-3 single-layer thermal test board. And for SOP-8 and MSOP-8 packages, the thermal resistance θJA is 160°C/W. The maximum power dissipation at TA = 25 °C can be calculated by following formula : PD(MAX) = (100 °C - 25°C) / (250°C/W) = 0.3W for SOT-23-5 packages PD(MAX) = (100 °C - 25°C) / (160°C/W) = 0.469W for SOP-8/MSOP-8 packages PD(MAX) = (100 °C - 25°C) / (108°C/W) = 0.694W for WDFN-8L 3x3 packages The maximum power dissipation depends on operating ambient temperature for fixed TJ(MAX) and thermal resistance θJA. For RT9715 packages, the Figure 2 of derating curves allows the designer to see the effect of rising ambient temperature on the maximum power allowed. Figure 2. Derating Curves for RT9715 Package 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0 1020 3040 5060 7080 90 100 Ambient Temperature (°C) WDFN-8L 3x3 SOP-8/MSOP-8 SOT-23-5 Single Layer PCB GND EN GND_BUS VIN VOUT VBUS VIN FLG The input capacitor should be placed as close as possible to the IC. Figure 3 |
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