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GRM32ER71C226M Datasheet(PDF) 11 Page - Richtek Technology Corporation |
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GRM32ER71C226M Datasheet(HTML) 11 Page - Richtek Technology Corporation |
11 / 14 page RT7272A 11 DS7272A-01 January 2013 www.richtek.com Copyright 2013 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation. © The output ripple will be the highest at the maximum input voltage since ΔIL increases with input voltage. Multiple capacitors placed in parallel may be needed to meet the ESR and RMS current handling requirement. Higher values, lower cost ceramic capacitors are now becoming available in smaller case sizes. Their high ripple current, high voltage rating and low ESR make them ideal for switching regulator applications. However, care must be taken when these capacitors are used at input and output. When a ceramic capacitor is used at the input and the power is supplied by a wall adapter through long wires, a load step at the output can induce ringing at the input, VIN. At best, this ringing can couple to the output and be mistaken as loop instability. At worst, a sudden inrush of current through the long wires can potentially cause a voltage spike at VIN large enough to damage the part. Thermal Considerations For continuous operation, do not exceed the maximum operation junction temperature 125 °C. The maximum power dissipation depends on the thermal resistance of IC package, PCB layout, the rate of surroundings airflow and temperature difference between junction to ambient. The maximum power dissipation can be calculated by following formula : PD(MAX) = (TJ(MAX) − TA) / θJA Where TJ(MAX) is the maximum operation junction temperature , TA is the ambient temperature and the θJAis the junction to ambient thermal resistance. For recommended operating conditions specification of RT7272A, the maximum junction temperature is 125 °C. The junction to ambient thermal resistance θJA is layout dependent. For SOP-8 (Exposed Pad) package, the thermal resistance θJA is 75°C/W on the standard JEDEC 51-7 four-layers thermal test board. The maximum power dissipation at TA = 25 °C can be calculated by following formula : PD(MAX) = (125 °C − 25°C) / (75°C/W) = 1.333W (min.copper area PCB layout) PD(MAX) = (125 °C − 25°C) / (49°C/W) = 2.04W (70mm2copper area PCB layout) The thermal resistance θJA of SOP-8 (Exposed Pad) is determined by the package architecture design and the PCB layout design. However, the package architecture design had been designed. If possible, it's useful to increase thermal performance by the PCB layout copper design. The thermal resistance θJA can be decreased by adding copper area under the exposed pad of SOP-8 (Exposed Pad) package. As shown in Figure 6, the amount of copper area to which the SOP-8 (Exposed Pad) is mounted affects thermal performance. When mounted to the standard SOP-8 (Exposed Pad) pad (Figure 6.a), θJA is 75°C/W. Adding copper area of pad under the SOP-8 (Exposed Pad) (Figure 6.b) reduces the θJA to 64°C/W. Even further, increasing the copper area of pad to 70mm2 (Figure 6.e) reduces the θJA to 49°C/W. The maximum power dissipation depends on operating ambient temperature for fixed TJ(MAX) and thermal resistance θJA. The Figure 7 of derating curves allows the designer to see the effect of rising ambient temperature on the maximum power dissipation allowed. Figure 7. Derating Curve of Maximum Power Dissipation 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 0 25 50 75 100 125 Ambient Temperature (°C) Copper Area 70mm 2 50mm 2 30mm 2 10mm 2 Min.Layout Four-Layer PCB |
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