 |
Electronic Components Datasheet Search |
|
|
Electronic Components Datasheet Search |
|
LP3999ITLX-1.6NOPB Datasheet(PDF) 10 Page - National Semiconductor (TI) |
|
|
||||||||||||||||||||||||||||||
LP3999ITLX-1.6NOPB Datasheet(HTML) 10 Page - National Semiconductor (TI) |
|
|
10 / 12 page  Application Hints POWER DISSIPATION AND DEVICE OPERATION The permissible power dissipation for any package is a measure of the capability of the device to pass heat from the power source, the junctions of the IC, to the ultimate heat sink, the ambient environment. Thus the power dissipation is dependent on the ambient temperature and the thermal resistance across the various interfaces between the die and ambient air. Re-stating the equation given in (Note 7) in the electrical specification section, the allowable power dissipation for the device in a given package can be calculated: With a θ JA = 255˚C/W, the device in the micro SMD package returns a value of 392 mW with a maximum junction tem- perature of 125˚C. The actual power dissipation across the device can be rep- resented by the following equation: P D =(VIN −VOUT)xIOUT. This establishes the relationship between the power dissipa- tion allowed due to thermal consideration, the voltage drop across the device, and the continuous current capability of the device. These two equations should be used to deter- mine the optimum operating conditions for the device in the application. EXTERNAL CAPACITORS In common with most regulators, the LP3999 requires exter- nal capacitors to ensure stable operation. The LP3999 is specifically designed for portable applications requiring mini- mum board space and smallest components. These capaci- tors must be correctly selected for good performance. INPUT CAPACITOR An input capacitor is required for stability. It is recommended that a 1.0 µF capacitor be connected between the LP3999 input pin and ground (this capacitance value may be in- creased without limit). This capacitor must be located a distance of not more than 1 cm from the input pin and returned to a clean analogue ground. Any good quality ceramic, tantalum, or film capacitor may be used at the input. Important: Tantalum capacitors can suffer catastrophic fail- ures due to surge current when connected to a low- impedance source of power (like a battery or a very large capacitor). If a tantalum capacitor is used at the input, it must be guaranteed by the manufacturer to have a surge current rating sufficient for the application. There are no requirements for the ESR (Equivalent Series Resistance) on the input capacitor, but tolerance and tem- perature coefficient must be considered when selecting the capacitor to ensure the capacitance will remain ≅ 1.0 µF over the entire operating temperature range. OUTPUT CAPACITOR The LP3999 is designed specifically to work with very small ceramic output capacitors. A ceramic capacitor (dielectric types Z5U, Y5V or X7R) in the 1.0 [to 10 µF] range, and with ESR between 5 m Ω to 500 mΩ, is suitable in the LP3999 application circuit. For this device the output capacitor should be connected between the V OUT pin and ground. It may also be possible to use tantalum or film capacitors at the device output, V OUT, but these are not as attractive for reasons of size and cost (see the section Capacitor Charac- teristics). The output capacitor must meet the requirement for the minimum value of capacitance and also have an ESR value that is within the range 5 m Ω to 500 mΩ for stability. NO-LOAD STABILITY The LP3999 will remain stable and in regulation with no external load. This is an important consideration in some circuits, for example CMOS RAM keep-alive applications. CAPACITOR CHARACTERISTICS The LP3999 is designed to work with ceramic capacitors on the output to take advantage of the benefits they offer. For capacitance values in the range of 1 µF to 4.7 µF, ceramic capacitors are the smallest, least expensive and have the lowest ESR values, thus making them best for eliminating high frequency noise. The ESR of a typical 1 µF ceramic capacitor is in the range of 20 m Ω to 40 mΩ, which easily meets the ESR requirement for stability for the LP3999. The temperature performance of ceramic capacitors varies by type. Most large value ceramic capacitors ( ≥ 2.2 µF) are manufactured with Z5U or Y5V temperature characteristics, which results in the capacitance dropping by more than 50% as the temperature goes from 25˚C to 85˚C. A better choice for temperature coefficient in a ceramic capacitor is X7R. This type of capacitor is the most stable and holds the capacitance within ±15% over the tempera- ture range. Tantalum capacitors are less desirable than ce- ramic for use as output capacitors because they are more expensive when comparing equivalent capacitance and volt- age ratings in the 1 µF to 4.7 µF range. Another important consideration is that tantalum capacitors have higher ESR values than equivalent size ceramics. This means that while it may be possible to find a tantalum capacitor with an ESR value within the stable range, it would have to be larger in capacitance (which means bigger and more costly) than a ceramic capacitor with the same ESR value. It should also be noted that the ESR of a typical tantalum will increase about 2:1 as the temperature goes from 25˚C down to −40˚C, so some guard band must be allowed. NOISE BYPASS CAPACITOR A bypass capacitor should be connected between the C BY- PASS pin and ground to significantly reduce the noise at the regulator output. This device pin connects directly to a high impedance node within the bandgap reference circuitry. Any significant loading on this node will cause a change on the regulated output voltage. For this reason, DC leakage cur- rent through this pin must be kept as low as possible for best output voltage accuracy. The use of a 0.01µF bypass capacitor is strongly recom- mended to prevent overshoot on the output during start-up. www.national.com 10 |
Similar Part No. - LP3999ITLX-1.6NOPB |
|
Similar Description - LP3999ITLX-1.6NOPB |
|
|
|
Link URL |
| Privacy Policy |
| ALLDATASHEET.COM |
| Does ALLDATASHEET help your business so far? [ DONATE ] |
About Alldatasheet | Advertisement | Datasheet Upload | 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
