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Zakładka z wyszukiwarką danych komponentów |
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Zakładka z wyszukiwarką danych komponentów |
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SC453 Arkusz danych(PDF) 18 Page - Semtech Corporation |
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SC453 Arkusz danych(HTML) 18 Page - Semtech Corporation |
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18 / 23 page  18 © 2006 Semtech Corp. www.semtech.com POWER MANAGEMENT SC453 Step 4: BOOTV Design The boot-up voltage for V CORE is set at 1.2V. For the SC453 typical application circuit, R3, R4, and R5 form a voltage divider off V REF and are used to set the boot voltage. For simplicity, we define R BOOT : = R3 + R4. VBOOT 1.2V := O. RHYS 1 1 R25 1 RBOOT R5 + + := P. RBOOT VBOOT R5 ⋅ VREF VBOOT − := Step 5: Sleep Voltage Design The sleep voltage is set at 0.750V nominally using the R3 - R4 - R5 divider. Q. VSLP 0.750V := R3, R4 and R5 are calculated using a matrix to solve the simultaneous equations. R14 is set at 1MΩ as a place- holder: R14 1000KΩ := Mx 1 1 1 1 1 VSLP 1 − VREF VSLP − ⋅ 1 VBOOT VREF VBOOT − − VSLP 1 − VREF VSLP − ⋅ ⎛ ⎜ ⎜ ⎜ ⎜ ⎜ ⎜ ⎝ ⎞ ⎟ ⎟ ⎟ ⎟ ⎟ ⎠ := Applications Information (Cont.) From the standard 1% resistor value table, we choose the following values according to the calculation results: R5 = 33.2KΩ. R4 = 30.1KΩ R3 = 49.9KΩ Step 6: Current Limit Calculation Setting the threshold for current limit is a relatively straightforward process. To do this we must calculate the peak current based on the maximum DC value plus the worst-case ripple current. The following calculations apply for a single phase. Worst-case ripple occurs at the high- est input voltage. Since ripple is also inversely proportion- al to inductance, it is recommended that the minimum inductance value be used based on the manufacturer’s specified tolerance: LLOW L1 120% − () ⋅ := LLOW 4.8 10 7 − × H = R. IRIPPLE_MAX VINMAX VMAX_NL − ()dMIN ⋅ LLOW FS ⋅ := v R14 RHYS ⋅ R14 RHYS − 0 0 ⎛⎜ ⎜ ⎜ ⎜ ⎜⎝ ⎞ ⎟ ⎟ ⎟ ⎟⎠ := soln lsolve Mx v , () := soln 5.011 10 4 × 3.007 10 4 × 3.341 10 4 × ⎛ ⎜ ⎜ ⎜ ⎜ ⎝ ⎞ ⎟ ⎟ ⎟ ⎠ Ω = R4 3.007 10 4 ×Ω = R4 010 ( ) soln ⋅ := R5 3.341 10 4 ×Ω = R5 001 ( ) soln ⋅ := R3 100 ( ) soln ⋅ := R3 5.011 10 4 ×Ω = R3 VSLP R4 R5 + () VREF VSLP − ⋅ := IRIPPLE_MAX 6.777 A = |
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