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HM8119 bảng dữ liệu(PDF) 11 Page - Shenzhen Huazhimei Semiconductor Co., Ltd |
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HM8119 bảng dữ liệu(HTML) 11 Page - Shenzhen Huazhimei Semiconductor Co., Ltd |
11 / 13 page Standoff 55V 500mA 850KHz Sync Step-Down Regulator Page 11 / 13 Where LLIM_AVG is the average start-up current during the soft-start period, and TSS is the soft- start time. On the other hand, special attention should be paid when selecting these components. The DC bias of these capacitors can result in a capacitance value that falls below the minimum value given in the recommended capacitor specifications table. The ceramic capacitor’s actual capacitance can vary with temperature. The capacitor type X7R, which operates over a temperature range of −55°C to +125°C, will only vary the capacitance to within ±15%. The capacitor type X5R has a similar tolerance over a reduced temperature range of −55°C to +85°C. Many large value ceramic capacitors, larger than 1uF are manufactured with Z5U or Y5V temperature characteristics. Their capacitance can drop by more than 50% as the temperature varies from 25°C to 85°C. Therefore, X5R or X7R is recommended over Z5U and Y5V in applications where the ambient temperature will change significantly above or below 25°C. Feed-Forward Capacitor (CFF) HM8119 has internal loop compensation, so adding CFF is optional. Specifically, for specific applications, if necessary, consider whether to add feed-forward capacitors according to the situation. The use of a feed-forward capacitor (CFF) in the feedback network is to improve the transient response or higher phase margin. For optimizing the feed-forward capacitor, knowing the cross frequency is the first thing. The cross frequency (or the converter bandwidth) can be determined by using a network analyzer. When getting the cross frequency with no feed-forward capacitor identified, the value of feed-forward capacitor (CFF) can be calculated with the following Equation: ������������ = 1 2���� × ������������������������ × √ 1 ����1 × ( 1 ����1 + 1 ����2 ) Where FCROSS is the cross frequency. To reduce transient ripple, the feed-forward capacitor value can be increased to push the cross frequency to higher region. Although this can improve transient response, it also decreases phase margin and cause more ringing. In the other hand, if more phase margin is desired, the feed-forward capacitor value can be decreased to push the cross frequency to lower region. HM8119 |
Số phần tương tự - HM8119 |
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Mô tả tương tự - HM8119 |
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