データシートサーチシステム |
|
LMR14006XDDCT データシート(PDF) 11 Page - Texas Instruments |
|
|
LMR14006XDDCT データシート(HTML) 11 Page - Texas Instruments |
11 / 20 page _ _ o ripple ESR L ripple V R I _ _ 1 1 8 K K out o ripple L ripple C V fsw I 2 2 2 2 ( ) ( ) K out o Ioh Iol C L Vf Vi 2 K K out out out I C fsw V LMR14003, LMR14006 www.ti.com SNVSA10 – NOVEMBER 2013 Output Capacitor The selection of COUT is mainly driven by three primary considerations. The output capacitor will determine the modulator pole, the output voltage ripple, and how the regulator responds to a large change in load current. The output capacitance needs to be selected based on the most stringent of these three criteria. The desired response to a large change in the load current is the first criteria. The regulator usually needs two or more clock cycles for the control loop to see the change in load current and output voltage and adjust the duty cycle to react to the change. The output capacitance must be large enough to supply the difference in current for 2 clock cycles while only allowing a tolerable amount of droop in the output voltage. Equation 5 shows the minimum output capacitance necessary to accomplish this. For this example, the transient load response is specified as a 3% change in VOUT for a load step from 0.03A to 0.6A (full load). For this example, ΔIOUT = 0.6 - 0.03 = 0.57A and ΔVOUT = 0.03 × 5 = 0.15V. Using these numbers gives a minimum capacitance of 3.6µF. For ceramic capacitors, the ESR is usually small enough to ignore in this calculation. Aluminum electrolytic and tantalum capacitors have higher ESR that should be taken into account. The stored energy in the inductor will produce an output voltage overshoot when the load current rapidly decreases. The output capacitor must also be sized to absorb energy stored in the inductor when transitioning from a high load current to a lower load current. Equation 6 is used to calculate the minimum capacitance to keep the output voltage overshoot to a desired value. Where L is the value of the inductor, IOH is the output current under heavy load, IOL is the output under light load, Vf is the final peak output voltage, and Vi is the initial capacitor voltage. For this example, the worst case load step will be from 0.6A to 0.03A. The output voltage will increase during this load transition and the stated maximum in our specification is 3% of the output voltage. This will make Vo_overshoot = 1.03 × 5 = 5.15V. Vi is the initial capacitor voltage which is the nominal output voltage of 5V. Using these numbers in Equation 6 yields a minimum capacitance of 2.36µF. Equation 7 calculates the minimum output capacitance needed to meet the output voltage ripple specification. Where fsw is the switching frequency, Vo_ripple is the maximum allowable output voltage ripple, and IL_ripple is the inductor ripple current. Equation 7 yields 0.21µF. Equation 8 calculates the maximum ESR an output capacitor can have to meet the output voltage ripple specification. Equation 8 indicates the ESR should be less than 277m Ω. Additional capacitance de-ratings for aging, temperature and dc bias should be factored in which will increase this minimum value. For this example, 10µF ceramic capacitors will be used. Capacitors in the range of 4.7µF- 100µF are a good starting point with an ESR of 0.1 Ω or less. (5) (6) (7) (8) Schottky Diode The breakdown voltage rating of the diode is preferred to be 25% higher than the maximum input voltage. The current rating for the diode should be equal to the maximum output current for best reliability in most applications. In cases where the input voltage is much greater than the output voltage the average diode current is lower. In this case it is possible to use a diode with a lower average current rating, approximately (1-D) × IOUT however the peak current rating should be higher than the maximum load current. A 0.5A to 1A rated diode is a good starting point. Copyright © 2013, Texas Instruments Incorporated Submit Documentation Feedback 11 Product Folder Links: LMR14003 LMR14006 |
同様の部品番号 - LMR14006XDDCT |
|
同様の説明 - LMR14006XDDCT |
|
|
リンク URL |
プライバシーポリシー |
ALLDATASHEET.JP |
ALLDATASHEETはお客様のビジネスに役立ちますか? [ DONATE ] |
Alldatasheetは | 広告 | お問い合わせ | プライバシーポリシー | リンク交換 | メーカーリスト All Rights Reserved©Alldatasheet.com |
Russian : Alldatasheetru.com | Korean : Alldatasheet.co.kr | Spanish : Alldatasheet.es | French : Alldatasheet.fr | Italian : Alldatasheetit.com Portuguese : Alldatasheetpt.com | Polish : Alldatasheet.pl | Vietnamese : Alldatasheet.vn Indian : Alldatasheet.in | Mexican : Alldatasheet.com.mx | British : Alldatasheet.co.uk | New Zealand : Alldatasheet.co.nz |
Family Site : ic2ic.com |
icmetro.com |