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PM6681A Datasheet(PDF) 30 Page - STMicroelectronics |
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PM6681A Datasheet(HTML) 30 Page - STMicroelectronics |
30 / 47 page Design guidelines PM6681A 30/47 9 Design guidelines The design of a switching section starts from two parameters: ● Input voltage range: in notebook applications it varies from the minimum battery voltage, VINmin to the AC adapter voltage, VINmax. ● Maximum load current: it is the maximum required output current, ILOAD(max). 9.1 Switching frequency It's possible to set 3 different working frequency ranges for the two sections with FSEL pin (table 1). Switching frequency mainly influences two parameters: ● Inductor size: for a given saturation current and RMS current, greater frequency allows to use lower inductor values, which means smaller size. ● Efficiency: switching losses are proportional to frequency. High frequency generally involves low efficiency. 9.2 Inductor selection Once that switching frequency is defined, inductor selection depends on the desired inductor ripple current and load transient performance. Low inductance means great ripple current and could generate great output noise. On the other hand, low inductor values involve fast load transient response. A good compromise between the transient response time, the efficiency, the cost and the size is to choose the inductor value in order to maintain the inductor ripple current ∆I L between 20 % and 50 % of the maximum output current ILOAD(max). The maximum ∆IL occurs at the maximum input voltage. With this considerations, the inductor value can be calculated with the following relationship: Equation 13 where fsw is the switching frequency, VIN is the input voltage, VOUT is the output voltage and ∆IL is the selected inductor ripple current. In order to prevent overtemperature working conditions, inductor must be able to provide an RMS current greater than the maximum RMS inductor current ILRMS: Equation 14 Where ∆I L(max) is the maximum ripple current: IN OUT L sw OUT IN V V I f V V L × ∆ × − = 12 (max)) I ( (max)) I ( I 2 L 2 LOAD LRMS ∆ + = |
Similar Part No. - PM6681A_08 |
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Similar Description - PM6681A_08 |
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