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RT9554A Fiches technique(PDF) 8 Page - Richtek Technology Corporation |
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RT9554A Fiches technique(HTML) 8 Page - Richtek Technology Corporation |
8 / 10 page RT9554A 8 DS9554A-00 June 2014 www.richtek.com © Copyright 2014 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation. Figure 1. Timing Sequence Filter capacitor A 0.1 μF capacitor between CSP and CSN for differential mode filtering is recommended. A 0.1 μF capacitor between CSN and ground is for common mode filtering, and an optional 0.1 μF capacitor between CSP and ground is for common mode filtering. The CSP and CSN pins are used to sense Rsense with default value of 1m Ω. However, resistors of other values can also be used. Using a larger sense resistor, can have higher regulation accuracy, but, it comes with higher conduction loss. Thermal Considerations For continuous operation, do not exceed absolute maximum junction temperature. The maximum power dissipation depends on the thermal resistance of the IC package, PCB layout, rate of surrounding airflow, and difference between junction and ambient temperature. The maximum power dissipation can be calculated by the following formula : PD(MAX) = (TJ(MAX) − TA) / θJA where TJ(MAX) is the maximum junction temperature, TAis the ambient temperature, and θJAis the junction to ambient thermal resistance. For recommended operating condition specifications, the maximum junction temperature is 125 °C. The junction to ambient thermal resistance, θJA, is layout dependent. For WDFN-8L 2x2 package, the thermal resistance, θJA, is 45.5 °C/W on a standard JEDEC 51-7 four-layer thermal test board. The maximum power dissipation at TA = 25 °C can be calculated by the following formula : PD(MAX) = (125 °C − 25°C) / (45.5°C/W) = 2.19W for WDFN-8L 2x2 package The maximum power dissipation depends on the operating ambient temperature for fixed TJ(MAX) and thermal resistance, θJA. The derating curve in Figure 2 allows the designer to see the effect of rising ambient temperature on the maximum power dissipation. SENSE R2 BAT_REF 3.3V R1 R2 I 0.001 200 = BAT_REF 200 is the internal error amp AV. We suggest R1+ R2 = 100k Ω to avoid power consumption. Isense is over-current protection trigger point. For the overall timing sequence, please refer to Figure 1. Application Information The RT9554A provides battery OCP protection functions with FLAG indicator to informs system. It can operate with minimized external components of switching power supply systems to achieve OCP protection. The over- current is detected by monitoring the differential voltage of input current sense resistor. The RT9554A provides a 50 μs system response time for FLAG and there is a 3ms mask time after EN rising edge. Also, the RT9554A provides a comparator with two pins, AC_REAL and AC_REF for users. FLAG The FLAG is an open-drain output and requires a pull-up resistor. When over-current is detected, FLAG is pulled low within 50 μs and maintain until OCP status releases. Over Current Protection( OCP) As an industry standard, high accuracy current sense amplifier is used to monitor the input current that flow through current sense resistor, The RT9554A detects CSP- CSN differential voltage across the current sense resistor to monitor input current from battery. The OCP trigger point equation is shown as below : VCC EN VOC BAT_REF 3ms FLAG |
Numéro de pièce similaire - RT9554A |
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Description similaire - RT9554A |
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