 |
Electronic Components Datasheet Search |
|
|
Electronic Components Datasheet Search |
|
LP3983ITL-1.8 Datasheet(PDF) 8 Page - National Semiconductor (TI) |
|
|
||||||||||||||||||||||||||||||
LP3983ITL-1.8 Datasheet(HTML) 8 Page - National Semiconductor (TI) |
|
|
8 / 10 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. As stated in note 3 in the electrical specification section, the allowable power dissipation for the device in a given pack- age can be calculated using the equation P D =(TJ -TA)/ θ JA With a θ JA = 255˚C/W, the device in the micro SMD package returns a value of 392mW with a maximum junction tempera- ture of 125˚C and an ambient temperature of 25˚C. The actual power dissipation across the device can be repre- sented by the following equation; P D =(VIN -VOUT)*IOUT This establishes the relationship between the power dissipa- tion allowed due to thermal considerations, 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 low-dropout regulators, the LP3983 requires external capacitors to ensure stable operation. The LP3983 is specifically designed for portable applications requiring minimum board space and smallest components. These capacitors must be correctly selected for good perfor- mance. INPUT CAPACITOR An input capacitor is required for stability. It is recommended that a 1.0uF capacitor be connected between the LP3983 input pin and ground (this capacitance value may be in- creased without limit). This capacitor must be located a distance of not more than 1cm from the input pin and returned to a clean analog 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 be ) 1µF over the entire operating temperature range. OUTPUT CAPACITOR The LP3983 is designed specifically to work with very small ceramic output capacitors. A ceramic capacitor (dielectric types Z5U, Y5V or X7R), recommended value 2.2µF and with ESR between 5m Ω to 500mΩ, is suitable in the LP3983 application circuit. For this device the output capacitor should be connected between the VOUT pin and ground. It may also be possible to use tantalum or film capacitors at the output, but these are not as attractive for reasons of size and cost (see the section Capacitor Characteristics). NO-LOAD STABILITY The LP3983 will remain stable and in regulation with no external load. This is specially important in CMOS RAM keep-alive applications. CAPACITOR CHARACTERISTICS The LP3983 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 1µF to 4.7µF range, ceramic capacitors are the smallest, least expensive and have the lowest ESR values (which makes them best for eliminating high frequency noise). The ESR of a typical 1µF ceramic capacitor is in the range of 20 m Ω to 40 mΩ, which easily meets the ESR requirement for stability by the LP3983. The temperature performance of ceramic capacitors varies by type. Larger value ceramic capacitors may be manufac- tured 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, which holds the capacitance within ±15% over the temperature range. Tantalum capacitors are less desirable than ceramic for use as output capacitors because they are more expensive when comparing equivalent capaci- tance and voltage ratings in the 1µF to 4.7µF 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. ENABLE OPERATION The LP3983 may be switched ON or OFF by a logic input at the ENABLE pin, V EN. A high voltage at this pin will turn the device on. When the enable pin is low, the regulator output is off and the device typically consumes < 1µA. If the applica- tion does not require the shutdown feature, the V EN pin should be tied to V IN to keep the regulator output perma- nently on. To ensure proper operation, the signal source used to drive the V EN input must be able to swing above and below the specified turn-on/off voltage thresholds listed in the Electrical Characteristics section under V IL and VIH. MICRO SMD MOUNTING The micro SMD package requires specific mounting tech- niques which are detailed in National Semiconductor Appli- cation Note (AN-1112). Referring to the section Surface Mount Technology (SMT) Assembly Considerations, it should be noted that the pad style which must be used with the 5 pin package is NSMD (non-solder mask defined) type. For best results during assembly, alignment ordinals on the PC board may be used to facilitate placement of the micro SMD device. www.national.com 8 |
Similar Part No. - LP3983ITL-1.8 |
|
Similar Description - LP3983ITL-1.8 |
|
|
|
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
