 |
Electronic Components Datasheet Search |
|
|
Electronic Components Datasheet Search |
|
LT3431 Datasheet(PDF) 10 Page - Linear Technology |
|
||||||||||||||||||||||||||||||
LT3431 Datasheet(HTML) 10 Page - Linear Technology |
|
|
10 / 28 page  10 LT3431 sn3431 3431fs APPLICATIO S I FOR ATIO importance, the subsequent suggestions in Peak Induc- tor and Fault Current and EMI will additionally help in the selection of the inductor value. Peak-to-peak output ripple voltage is the sum of a triwave (created by peak-to-peak ripple current (ILP-P) times ESR) and a square wave (created by parasitic inductance (ESL) and ripple current slew rate). Capacitive reactance is assumed to be small compared to ESR or ESL. V I ESR ESL dI dt RIPPLE LP P = ()( )+() - Σ where: ESR = equivalent series resistance of the output capacitor ESL = equivalent series inductance of the output capacitor dI/dt = slew rate of inductor ripple current = VIN/L Peak-to-peak ripple current (ILP-P) through the inductor and into the output capacitor is typically chosen to be between 20% and 40% of the maximum load current. It is approximated by: I VV V Vf L LP P OUT IN OUT IN - = ()( ) ()( )( ) – Example: with VIN = 12V, VOUT = 5V, L = 10µH, ESR = 0.080 Ω and ESL = 10nH, output ripple voltage can be approximated as follows: IA dI dt VA mV RIPPLE P- P P- P = () − () () ()( ) = == = ()( )+ ()( )() =+= − − − 512 5 12 10 10 500 10 058 12 10 10 10 1 2 0 58 0 08 10 10 10 1 2 0 046 0 012 58 63 6 6 96 •• . • •. .. • . .. Σ To reduce output ripple voltage further requires an in- crease in the inductor value with the trade-off being a physically larger inductor with the possibility of increased component height and cost. Ceramic Output Capacitor An alternative way to further reduce output ripple voltage is to reduce the ESR of the output capacitor by using a ceramic capacitor. Although this reduction of ESR re- moves a useful zero in the overall loop response, this zero can be replaced by inserting a resistor (RC) in series with the VC pin and the compensation capacitor CC. (See Ceramic Capacitors in Applications Information.) Peak Inductor Current and Fault Current To ensure that the inductor will not saturate, the peak inductor current should be calculated knowing the maxi- mum load current. An appropriate inductor should then be chosen. In addition, a decision should be made whether or not the inductor must withstand continuous fault conditions. If maximum load current is 1A, for instance, a 1A inductor may not survive a continuous 4A overload condition. Dead shorts will actually be more gentle on the inductor because the LT3431 has frequency and current limit foldback. Peak inductor and switch current can be significantly higher than output current, especially with smaller induc- tors and lighter loads, so don’t omit this step. Powdered iron cores are forgiving because they saturate softly, whereas ferrite cores saturate abruptly. Other core mate- rials fall somewhere in between. The following formula assumes continuous mode of operation, but errs only slightly on the high side for discontinuous mode, so it can be used for all conditions. II I I VV V Vf L PEAK OUT LP P OUT OUT IN OUT IN =+ =+ ()( ) ()( )( )() () – - 2 2 EMI Decide if the design can tolerate an “open” core geometry like a rod or barrel, which have high magnetic field radiation, or whether it needs a closed core like a toroid to prevent EMI problems. This is a tough decision because the rods or barrels are temptingly cheap and small and |
Similar Part No. - LT3431_15 |
|
Similar Description - LT3431_15 |
|
|
Link URL |
| Privacy Policy |
| ALLDATASHEET.NET |
| Does ALLDATASHEET help your business so far? [ DONATE ] |
About Alldatasheet | Advertisement | Contact us | Privacy Policy | Link Exchange | Manufacturer List 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 |
English ▼
English
Chinese
German
Japanese
Russian
Korean
Spanish
French
Italian
Portuguese
Polish
Vietnamese
Indian
Mexican
British
New Zealand
