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TPS40322 Datasheet(PDF) 28 Page - Texas Instruments |
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TPS40322 Datasheet(HTML) 28 Page - Texas Instruments |
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28 / 47 page  ( ) ( ) ( ) 1 1 OUT1(max) RIPPLE1 CHARGE L1 peak 2 2 I I I I 10 A 2.5A 0.281A 11.53 A = + ´ + = + ´ + = ( ) OUT1 OUT1 CHARGE SS 1.2 V 2 220 F 2 10 F 2 3.3 F 1 F V C I 0.281A t 2ms ´ ´ m + ´ m + ´ m + m ´ = = = RIPPLE1 RIPPLE1 RIPPLE1 RIPPLE(cap) OUT1 SW MAX RIPPLE1 RIPPLE1 I 2.5 A V 24mV V V 8 C f 8 458 F 500kHz ESR 9m I I 2.5 A æ ö æ ö - - ç ÷ ç ÷ - ´ ´ ´ m ´ è ø è ø = = = = W ( ) 2 2 OUT1 OUT1(min) OUT OVER1 I L1 5 0.88 H C 458 F V V 1.2 40mV D ´ ´ m = = = m ´ ´ ( ) ( ) 2 OUT1 OUT1 OUT1 OUT1 UNDER1 OUT1 OUT1 IN OUT1 IN OUT1 OUT1 I L1 I I I L1 V t C C V V V V C D ´ D D D ´ < ´ D = ´ = - - ´ ( ) D ´ D D D ´ < ´ D = ´ = ´ 2 OUT1 OUT1 OUT1 OUT1 OVER1 OUT1 OUT1 OUT1 OUT1 OUT1 I L1 I I I L1 V t C C V V C TPS40322 SLUSAF8E – JULY 2011 – REVISED JANUARY 2016 www.ti.com 8.2.1.2.3 Output Capacitor Selection (C10 through C16) The selection of the output capacitor is typically driven by the output transient response requirement. Equation 10 and Equation 11 over-estimate the voltage deviation to account for delays in the loop bandwidth and can be used to determine the required output capacitance: (10) (11) When VIN(min) > 2 x VOUT1, use the overshoot equation, VOVER1, to calculate minimum output capacitance. When VIN(min) < 2 x VOUT1 use Equation 11, VUNDER1, to calculate minimum output capacitance. In this design example, VIN(min) is much larger than 2 x VOUT1 so Equation 12 is used to determine the required minimum output capacitance. (12) With a minimum capacitance, the maximum allowable ESR is determined by the maximum ripple voltage and is approximated by Equation 13. (13) Two 220-µF, 4-V, aluminum electrolytic capacitors were chosen for load response requirements. Additionally two 0805 10-µF, X7R, along with two 0603, 3.3-µF X5R, and one 1-µF, X5R ceramic capacitors are selected for low ESR and high frequency decoupling. 8.2.1.2.4 Peak Current Rating of Inductor With the output capacitance known, it is possible to calculate the charge current during start-up and determine the minimum saturation current rating for the inductor. The start-up charging current is approximated using Equation 14. (14) (15) Table 5. Inductor Requirements Summary PARAMETER VALUE UNIT L1 Inductance 0.88 µH IL1_RMS RMS current (thermal rating) 10.026 A IL1_PEAK Peak current (saturation rating) 11.53 A A 744314110 from Wurth Electronics with 1.1-µH zero current inductance is selected. Inductance for this part is 0.88-µH at 10-A bias. This 15-A, 3.15-m Ω inductor exceeds the minimum inductor ratings in a 7-mm x 7-mm package. 8.2.1.2.5 Input Capacitor Selection (C3 through C6) The input voltage ripple is divided between the capacitance and ESR of the input capacitor. For this design VRIPPLE(cap) = 200 mV and VRIPPLE(esr) = 50 mV. The minimum capacitance and maximum ESR are estimated using Equation 16. 28 Submit Documentation Feedback Copyright © 2011–2016, Texas Instruments Incorporated Product Folder Links: TPS40322 |
Similar Part No. - TPS40322_16 |
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Similar Description - TPS40322_16 |
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