Electronic Components Datasheet Search |
|
LP3966ESX-5.0 Datasheet(PDF) 11 Page - National Semiconductor (TI) |
|
|
LP3966ESX-5.0 Datasheet(HTML) 11 Page - National Semiconductor (TI) |
11 / 17 page Application Hints EXTERNAL CAPACITORS Like any low-dropout regulator, external capacitors are re- quired to assure stability. these capacitors must be correctly selected for proper performance. INPUT CAPACITOR: The LP3963/6 requires a low source impedance to maintain regulator stability because the inter- nal bias circuitry is connected directly to V IN. The input capacitor must be located less than 1 cm from the LP3963/6 device and connected directly to the input and ground pins using traces which have no other currents flowing through them (see PCB Layout section). The minimum allowable input capacitance for a given appli- cation depends on the type of the capacitor and ESR (equivalent series resistance). A lower ESR capacitor allows the use of less capacitance, while higher ESR types (like aluminum electrolytics) require more capacitance. The lowest value of input capacitance that can be used for stable full-load operation is 68 µF (assuming it is a ceramic or low-ESR Tantalum with ESR less than 100 m Ω). To determine the minimum input capacitance amount and ESR value, an approximation which should be used is: C IN ESR (m Ω)/C IN (µF) ≤ 1.5 This shows that input capacitors with higher ESR values can be used if sufficient total capacitance is provided. Capacitor types (aluminum, ceramic, and tantalum) can be mixed in parallel, but the total equivalent input capacitance/ESR must be defined as above to assure stable operation. IMPORTANT: The input capacitor must maintain its ESR and capacitance in the "stable range" over the entire temperature range of the application to assure stability (see Capacitor Characteristics Section). OUTPUT CAPACITOR: An output capacitor is also required for loop stability. It must be located less than 1 cm from the LP3963/6 device and connected directly to the output and ground pins using traces which have no other currents flow- ing through them (see PCB Layout section). The minimum value of the output capacitance that can be used for stable full-load operation is 33 µF, but it may be increased without limit. The output capacitor’s ESR is critical because it forms a zero to provide phase lead which is required for loop stability. The ESR must fall within the specified range: 0.2 Ω≤ C OUT ESR ≤ 5Ω The lower limit of 200 m Ω means that ceramic capacitors are not suitable for use as LP3963/6 output capacitors (but can be used on the input). Some ceramic capacitance can be used on the output if the total equivalent ESR is in the stable range: when using a 100 µF Tantalum as the output capaci- tor, approximately 3 µF of ceramic capacitance can be ap- plied before stability becomes marginal. IMPORTANT: The output capacitor must meet the require- ments for minimum amount of capacitance and also have an appropriate ESR value over the full temperature range of the application to assure stability (see Capacitor Characteristics Section). SELECTING A CAPACITOR It is important to note that capacitance tolerance and varia- tion with temperature must be taken into consideration when selecting a capacitor so that the minimum required amount of capacitance is provided over the full operating tempera- ture range. In general, a good Tantalum capacitor will show very little capacitance variation with temperature, but a ce- ramic may not be as good (depending on dielectric type). Aluminum electrolytics also typically have large temperature variation of capacitance value. Equally important to consider is a capacitor’s ESR change with temperature: this is not an issue with ceramics, as their ESR is extremely low. However, it is very important in Tan- talum and aluminum electrolytic capacitors. Both show in- creasing ESR at colder temperatures, but the increase in aluminum electrolytic capacitors is so severe they may not be feasible for some applications (see Capacitor Character- istics Section). CAPACITOR CHARACTERISTICS CERAMIC: For values of capacitance in the 10 to 100 µF range, ceramics are usually larger and more costly than tantalums but give superior AC performance for bypassing high frequency noise because of very low ESR (typically less than 10 m Ω). However, some dielectric types do not have good capacitance characteristics as a function of voltage and temperature. Z5U and Y5V dielectric ceramics have capacitance that drops severely with applied voltage. A typical Z5U or Y5V capacitor can lose 60% of its rated capacitance with half of the rated voltage applied to it. The Z5U and Y5V also exhibit a severe temperature effect, losing more than 50% of nomi- nal capacitance at high and low limits of the temperature range. X7R and X5R dielectric ceramic capacitors are strongly rec- ommended if ceramics are used, as they typically maintain a capacitance range within ±20% of nominal over full operat- ing ratings of temperature and voltage. Of course, they are typically larger and more costly than Z5U/Y5U types for a given voltage and capacitance. TANTALUM: Solid Tantalum capacitors are recommended for use on the output because their typical ESR is very close to the ideal value required for loop compensation. They also work well as input capacitors if selected to meet the ESR requirements previously listed. Tantalums also have good temperature stability: a good quality Tantalum will typically show a capacitance value that varies less than 10-15% across the full temperature range of 125˚C to −40˚C. ESR will vary only about 2X going from the high to low temperature limits. The increasing ESR at lower temperatures can cause oscil- lations when marginal quality capacitors are used (if the ESR of the capacitor is near the upper limit of the stability range at room temperature). ALUMINUM: This capacitor type offers the most capaci- tance for the money. The disadvantages are that they are larger in physical size, not widely available in surface mount, and have poor AC performance (especially at higher fre- quencies) due to higher ESR and ESL. Compared by size, the ESR of an aluminum electrolytic is higher than either Tantalum or ceramic, and it also varies greatly with temperature. A typical aluminum electrolytic can exhibit an ESR increase of as much as 50X when going from 25˚C down to −40˚C. It should also be noted that many aluminum electrolytics only specify impedance at a frequency of 120 Hz, which indicates they have poor high frequency performance. Only aluminum electrolytics that have an impedance specified at a higher frequency (between 20 kHz and 100 kHz) should be used for www.national.com 11 |
Similar Part No. - LP3966ESX-5.0 |
|
Similar Description - LP3966ESX-5.0 |
|
|
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 |