поискавой системы для электроныых деталей |
|
AME5258-AEV250 датащи(PDF) 9 Page - AMETHERM Circuit Protection Thermistors |
|
AME5258-AEV250 датащи(HTML) 9 Page - AMETHERM Circuit Protection Thermistors |
9 / 17 page AME 9 AME5258 1.5MHz, 600mA Synchronous Buck Converter Rev.A.05 Inductor Core Selection Once the value for L is known, the type of inductor must be selected. High efficiency converters generally cannot afford the core loss found in low cost powdered iron cores, forcing the use of more expensive ferrite or mollypermalloy cores. Actual core loss is independent of core size for a fixed inductor value but it is very depen- dent on the inductance selected. As the inductance in- creases, core losses decrease. Unfortunately, increased inductance requires more turns of wire and therefore cop- per losses will increase. Ferrite designs have very low core losses and are preferred at high switching frequen- cies, so design goals can concentrate on copper loss and preventing saturation. Ferrite core material saturates "hard", which means that inductance collapses abruptly when the peak design current is exceeded. This result in an abrupt increase in inductor ripple current and conse- quent output voltage ripple. Do not allow the core to satu- rate! Different core materials and shapes will change the size/current and price/current relationship of an inductor. Toroid or shielded pot cores in ferrite or permalloy mate- rials are small and don't radiate energy but generally cost more than powdered iron core inductors with similar char- acteristics. The choice of which style inductor to use mainly depends on the price vs. size requirements and any radiated field/EMI requirements. CIN and COUT Selection The input capacitance, CIN, is needed to filter the trap- ezoidal current at the source of the top MOSFET. To pre- vent large ripple voltage, a low ESR input capacitor sized for the maximum RMS current should be used.RMS cur- rent is given by : This formula has a maximum at V IN = 2V OUT, where IRMS = I OUT/2. This simple worst-case condition is commonly used for design because even significant deviations do not offer much relief. Note that ripple current ratings from capacitor manufacturers are often based on only 2000 hours of life which makes it advisable to further derate the capacitor, or choose a capacitor rated at a higher tem- perature than required. Several capacitors may also be paralleled to meet size or height requirements in the design. The selection of COUT is determined by the effective series resistance (ESR) that is required to minimize voltage ripple and load step transients, as well as the amount of bulk capaci- tance that is necessary to ensure that the control loop is stable. Loop stability can be checked by viewing the load transient response as described in a later section. The output ripple, V OUT, is determined by : 1 ) ( − ⋅ ⋅ = VOUT VIN VIN VOUT max IOUT IRMS ⋅ + ∆ ≤ ∆ COUT f ESR IL VOUT 8 1 The output ripple is highest at maximum input voltage since IL increases with input voltage. Multiple capacitors placed in parallel may be needed to meet the ESR and RMS current handling requirements. Dry tantalum, spe- cial polymer, aluminum electrolytic and ceramic capaci- tors are all available in surface mount packages. Special polymer capacitors offer very low ESR but have lower capacitance density than other types. Tantalum capaci- tors have the highest capacitance density but it is impor- tant to only use types that have been surge tested for use in switching power supplies. Aluminum electrolytic capacitors have significantly higher ESR but can be used in cost-sensitive applications provided that consideration is given to ripple current ratings and long term reliability. Ceramic capacitors have excellent low ESR characteris- tics but can have a high voltage coefficient and audible piezoelectric effects. The high Q of ceramic capacitors with trace inductance can also lead to significant ringing Using Ceramic Input and Output Capacitors Higher values, lower cost ceramic capacitors are now becoming available in smaller case sizes. Their high ripple current, high voltage rating and low ESR make them ideal for switching regulator applications. However, care must be taken when these capacitors are used at the input and output. When a ceramic capacitor is used at the input and the power is supplied by a wall adapter through long wires, a load step at the output can induce ringing at the input, V IN. At best, this ringing can couple to the output and be mistaken as loop instability. At worst, a sudden inrush of current through the long wires can potentially cause a voltage spike at V IN large enough to damage the part. |
Аналогичный номер детали - AME5258-AEV250 |
|
Аналогичное описание - AME5258-AEV250 |
|
|
ссылки URL |
Конфиденциальность |
ALLDATASHEETRU.COM |
Вашему бизинису помогли Аллдатащит? [ DONATE ] |
Что такое Аллдатащит | реклама | контакт | Конфиденциальность | обмен ссыками | поиск по производителю 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 |