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전자부품 데이터시트 검색엔진 |
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전자부품 데이터시트 검색엔진 |
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L6911D 데이터시트(PDF) 13 Page - STMicroelectronics |
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L6911D 데이터시트(HTML) 13 Page - STMicroelectronics |
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13 / 17 page  13/17 L6911D Where Where ZC(s) and ZL(s) are the output capacitor and inductor impedance respectively. The expression of ZI(s) may be simplified as follow: Where: τ1 = R4×C20, τ2 = (R4+R3)×C20 and τd = Rd×C25. The regulator transfer function became now: Figure 8 shows a method to select the regulator components (please note that the frequencies fEC and fCC cor- responds to the singularities introduced by additional ceramic capacitors in parallel to the output main electro- lytic capacitor). s To obtain a flat frequency response of the output impedance, the droop time constant τd has to be equal to the inductor time constant (see the note at the end of the section): s To obtain a constant -20dB/dec Gloop(s) shape the singularity f1 and f2 are placed in proximity of fCE and fLC respectively. This implies that: s To obtain a Gloop bandwidth of fC, results: Note. To understand the reason of the previous assumption, the scheme in figure 9 must be considered. In this scheme, the inductor current has been substituted by the load current, because in the frequencies range of interest for the Droop function these current are substantially the same and it was supposed that the droop network don't represent a charge for the inductor. Gloo p s () Av s () Rs () ⋅ Av s () Zf s () Zi s () -------------- ⋅ == Av s () Vi n V osc ∆ ---------------- Z C s () Z C s () Z L s () + ------------------------------------- ⋅ = Z I s () Rd 1 s --- C25 ⋅⋅ Rd 1 s --- + C25 ⋅ ---------------------------------- R4 1 s --- C20 ⋅ + R3 ⋅ R4 1 s --- C20 ⋅ + R3 + ------------------------------------------------------ + Rd 1 s τ 1 τ d + () s 2 R3 R d -------- τ 1 τ d ⋅⋅ ⋅ + ⋅ + 1s τ 2 ⋅ + () 1s τ d ⋅ + () ⋅ --------------------------------------------------------------------------------------------------- = == Rd 1s R3 R d -------- τ d ⋅ + 1s τ 1 ⋅ + () ⋅ 1s τ 2 ⋅ + () 1s τ d ⋅ + () ⋅ --------------------------------------------------------------------- = Rs () 1s τ 2 ⋅ + () 1s τ d ⋅ + () ⋅ sC 18 R d 1s R3 R d -------- τ d ⋅ + 1s τ 1 ⋅ + () ⋅⋅ ⋅ ⋅ -------------------------------------------------------------------------------------------------------- ≈ τ d R d C25 ⋅ L R L ------- τ L C25 ⇒ L R L R d ⋅ () ----------------------- == = = f 2 f 1 ---- f LC f CE --------- R4 ⇒ R3 f LC f CE --------- 1 – ⋅ == f1 f CE C20 1 2 --- π R4 f CE ⋅ ⋅⋅ = ⇒ = G 0 f LC ⋅ 1f C G 0 ⇒ ⋅ A 0 R 0 ⋅ VIN Vosc ∆ ------------------ C20 // C25 C18 ----------------------------- ⋅ f C f LC -------- C 18 ⇒ VIN Vosc ∆ ------------------ C20 C25 ⋅ C20 C25 + ----------------------------- f LC f C -------- ⋅⋅ == = = = |
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