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RTQ2533W Arkusz danych(PDF) 16 Page - Richtek Technology Corporation |
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RTQ2533W Arkusz danych(HTML) 16 Page - Richtek Technology Corporation |
16 / 19 page RTQ2533W 16 DSQ2533W-00 April 2019 www.richtek.com © Copyright 2019 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation. Reverse Current Protection Reverse current from VOUT to VIN that flows through the body diode of the pass element instead of the normal conducting channel can happen if the maximum VOUT exceeds VIN + 0.3V; in this case, the pass element may be damaged. For example, if the output is biased above the input supply voltage level or the input supply has an instant drop at light load operation that makes VIN < VOUT. As shown in Figure 7, an external Schottky diode could be added to prevent the pass element be damaged from the reverse current. Figure 7. Application Circuit for Reverse Current Protection Thermal Considerations Thermal protection limits power dissipation in the RTQ2533W. When power dissipation on the pass element (PDIS = (VIN − VOUT) x IOUT) is too high and raises the junction operation temperature over 160 °C, the OTP circuit starts the thermal shutdown function and turns the pass element off. The pass element turns on again after the junction temperature cools down by 20 °C. The output is shorted to ground when there is short circuit at the output. This procedure can reduce the chip temperature and provides maximum safety to end users when output short circuit occurs. The junction temperature should never exceed the absolute maximum junction temperature TJ(MAX), listed under Absolute Maximum Ratings, to avoid permanent damage to the device. The maximum allowable power dissipation depends on the thermal resistance of the IC package, the PCB layout, the rate of surrounding airflow, and the difference between the junction and ambient temperatures. The maximum power dissipation can be calculated using the following formula : PD(MAX) = (TJ(MAX) − TA) / θJA where TJ(MAX) is the maximum junction temperature, TA is the ambient temperature, and θJAis the junction-to-ambient thermal resistance. For continuous operation, the maximum operating junction temperature indicated under Recommended Operating Conditions is 125 °C. The junction-to-ambient thermal resistance, θJA, is highly package dependent. For a VQFN- 20L 3.5x3.5 package, the thermal resistance, θJA, is 36 °C/W on a high effective-thermal-conductivity four-layer test board. The maximum power dissipation at TA = 25 °C can be calculated as below : PD(MAX) = (125 °C − 25°C) / (36°C/W) = 2.78W for a VQFN-20L 3.5x3.5 package. The maximum power dissipation depends on the operating ambient temperature for the fixed TJ(MAX) and the thermal resistance, θJA. The derating curves in Figure 8 allow the designer to see the effect of rising ambient temperature on the maximum power dissipation. VOUT RTQ2533W GND VIN CIN COUT Figure 8. Derating Curve of Maximum Power Dissipation Layout Considerations For best performance of the RTQ2533W, the PCB layout suggestions below are highly recommend. All circuit components placed on the same side and as near to the respective LDO pin as possible. Place the ground return path connection to the input and output capacitor. Connect 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 0 25 50 75 100 125 Ambient Temperature (°C) Four-Layer PCB |
Podobny numer części - RTQ2533W |
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Podobny opis - RTQ2533W |
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