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công cụ tìm kiếm bảng dữ liệu linh kiện điện tử |
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ACT6390 bảng dữ liệu(PDF) 7 Page - Active-Semi, Inc |
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ACT6390 bảng dữ liệu(HTML) 7 Page - Active-Semi, Inc |
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7 / 12 page  ACT6390/ACT6391 Rev 1, 22-Aug-13 Innovative PowerTM - 7 - www.active-semi.com Copyright © 2013 Active-Semi, Inc. (28) (25) (18) (27) (17) (19) (20) the cross-over frequency (unity gain-frequency) should be less than one-fifth of the right-half-plane zero fZ(RHP), and lower than one-fifteenth of switch- ing frequency fsw. Choose , then calculate CCOMP: Select RCOMP to meet the transient-droop require- ments. Where: α is the transient droop percentage which can be accepted, calculated by: K: is defined in equation (4) η: is the typical efficiency. VFB: is the feedback voltage, 1.24V GM: is the trans-conductance of the error amplifier. The output capacitor is chosen to set the output pole for canceling the RCOMP, CCOMP zero. CCOMP2 is optional and can be used when the output capacitor has significant ESR. The ESR will form a zero as follows: If this zero occurs at a higher frequency than the cross-over frequency, it can be ignored. Otherwise, it should be canceled with the pole set by capacitor CCOMP2, If the value of CCOMP2 calculated by (23) is smaller than 10pF, CCOMP2 can be omitted. For example: Choose CCOMP = 6.8nF Assume that 200mV of transient droop can be accepted: Choose RCOMP = 180kΩ COUT can be chosen to be either 22µF or 33µF, choose 33µF to reduce droop. If a ceramic capacitor is used with an assumed ESR of 20mΩ, fZ(ESR) > fC Since the zero frequency is greater than the pole frequency ,CCOMP2 can be omitted. If a tantalum capacitor is used, whose ESR is about 0.5Ω, () L π V 2 R V f 2 OUT LOAD 2 IN RHP Z × × × = () C CS M LOAD 2 OUT FB IN C M CS LOAD OUT FB COMP f π 2 R G R V V V D 1 f π 2 G R R V V C × × × × = − × × = ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ + × × × × = × × × 2 K 1 η V I V R R G V α IN OUT OUT CS COMP M FB η V G V α 2 K 1 I V R R IN M FB OUT OUT CS COMP × × × × ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ + × × = OUT OUT V V Δ α = LOAD COMP COMP OUT R C R C × = () OUT ESR ESR Z C R π 2 1 f × × = COMP ESR OUT 2 COMP R R C C × = () () () kHz 8 . 57 H μ 10 π V 12 2 mA 250 V 12 V 3 . 3 f 2 2 RHP Z ≈ × × × ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ × = Choose () kHz 56 . 11 f 5 1 f RHP Z C = = () nF 26 . 6 kHz 56 . 11 π 2 S μ 150 Ω 45 . 0 Ω 48 V 12 V 24 . 1 V 3 . 3 C 2 COMP = × × × × = 60 1 V 12 mV 200 α = = Ω k 3 . 186 85 . 0 V 3 . 3 S μ 150 V 24 . 1 60 1 2 4 . 0 1 mA 250 V 12 Ω 45 . 0 R COMP = × × × × ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ + × × = F μ 5 . 25 A 25 . 0 V 12 nF 8 . 6 Ω k 180 R C R C LOAD COMP COMP OUT = ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ × = × = (30) () kHz 241 Ω m 20 F μ 33 π 2 1 f ESR Z = × × = (21) (22) (23) (24) (26) (29) () RHP Z C f 5 1 f = (16) Ω k 233 nF 8 . 6 F μ 33 Ω 48 C C R R COMP OUT LOAD COMP = × = × = |
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