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BD9018KV Datasheet(PDF) 8 Page - Rohm |
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BD9018KV Datasheet(HTML) 8 Page - Rohm |
8 / 17 page ![]() Technical Note 8/16 BD9018KV www.rohm.com 2010.02 - Rev.A ○ c 2010 ROHM Co., Ltd. All rights reserved. Over current detection point IL L VIN IL Vo VCCCL CL RCL (6) Setting the soft start time The soft start function is necessary to prevent an inrush of coil current and output voltage overshoot at startup. The figure below shows the relation between soft start delay time and capacitance, which can be calculated using equation (13) at right. 0.8V(typ.)×CSS TSS = [sec]・・・(13) ISS(10μA Typ.) Fig. 19 SS capacitance vs. delay time Recommended capacitance values are between 0.01uF and 0.1uF. There is a possibility that the overshoot is generated in the output according to the phase compensation and the output capacity, etc. , and let me confirm it with a real machine, please. For the case with larger capacitance, the SS-pin may not become fully discharged when the EN becomes from H to L, which might cause the output overshoot when the EN becomes back H. Hence the discharge time (Tdis) needs to be carefully considered. Css × Vss_MAX Tdis = [sec] Idis The insertion of the CR filter is recommended as a noise measures because similar is thought when the noise enters the terminal EN. Please use high accuracy components (such as X5R) when implementing sequential startups involving other power sources. Be sure to test the actual devices and applications to be used, since the soft start time varies, depending on input voltage, output voltage and capacitance, coils and other characteristics. (7) Setting over current detection values The current limit value(ILimit)is determined by the resistance of the RCL established between CL and VCCCL. 90m ILimit = [A]・・・(14) RCL Fig. 20 Fig. 21 The current limit is an auto-recovery type. When the over current is detected, the output Duty is reduced to limit the output current. The output voltage returns to normal when the load returns to the normal state. Fig. 22 0.01 0.1 1 10 0.001 0.01 0.1 SS CAPACITANCE[uF] 0 1 2 3 4 5 6 01 2 3 45 6 Io[A] Vo[V] |
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