 |
Electronic Components Datasheet Search |
|
|
Electronic Components Datasheet Search |
|
LP3874-ADJ Datasheet(PDF) 11 Page - National Semiconductor (TI) |
|
|
||||||||||||||||||||||||||||||
LP3874-ADJ Datasheet(HTML) 11 Page - National Semiconductor (TI) |
|
|
11 / 15 page  Application Hints (Continued) SHUTDOWN OPERATION A CMOS Logic level signal at the shutdown ( SD) pin will turn-off the regulator. Pin SD must be actively terminated through a 10k Ω pull-up resistor for a proper operation. If this pin is driven from a source that actively pulls high and low (such as a CMOS rail to rail comparator), the pull-up resistor is not required. This pin must be tied to Vin if not used. DROPOUT VOLTAGE The dropout voltage of a regulator is defined as the minimum input-to-output differential required to stay within 2% of the nominal output voltage. For CMOS LDOs, the dropout volt- age is the product of the load current and the Rds(on) of the internal MOSFET. REVERSE CURRENT PATH The internal MOSFET in LP3874-ADJ has an inherent para- sitic diode. During normal operation, the input voltage is higher than the output voltage and the parasitic diode is reverse biased. However, if the output is pulled above the input in an application, then current flows from the output to the input as the parasitic diode gets forward biased. The output can be pulled above the input as long as the current in the parasitic diode is limited to 200mA continuous and 1A peak. POWER DISSIPATION/HEATSINKING The LP3874-ADJ can deliver a continuous current of 0.8A over the full operating temperature range. A heatsink may be required depending on the maximum power dissipation and maximum ambient temperature of the application. Under all possible conditions, the junction temperature must be within the range specified under operating conditions. The total power dissipation of the device is given by: P D =(VIN−VOUT)IOUT+(VIN)IGND where I GND is the operating ground current of the device (specified under Electrical Characteristics). The maximum allowable temperature rise (T Rmax) depends on the maximum ambient temperature (T Amax) of the appli- cation, and the maximum allowable junction temperature (T Jmax): T Rmax =TJmax−TAmax The maximum allowable value for junction to ambient Ther- mal Resistance, θ JA, can be calculated using the formula: θ JA =TRmax /PD The LP3874-ADJ is available in TO-220 and TO-263 pack- ages. The thermal resistance depends on amount of copper area or heat sink, and on air flow. If the maximum allowable value of θ JA calculated above is ≥ 60 ˚C/W for TO-220 package and ≥ 60 ˚C/W for TO-263 package no heatsink is needed since the package can dissipate enough heat to satisfy these requirements. If the value for allowable θ JA falls below these limits, a heat sink is required. HEATSINKING TO-220 PACKAGE The thermal resistance of a TO220 package can be reduced by attaching it to a heat sink or a copper plane on a PC board. If a copper plane is to be used, the values of θ JA will be same as shown in next section for TO263 package. The heatsink to be used in the application should have a heatsink to ambient thermal resistance, θ HA ≤θ JA − θ CH − θ JC. In this equation, θ CH is the thermal resistance from the case to the surface of the heat sink and θ JC is the thermal resis- tance from the junction to the surface of the case. θ JC is about 3˚C/W for a TO220 package. The value for θ CH de- pends on method of attachment, insulator, etc. θ CH varies between 1.5˚C/W to 2.5˚C/W. If the exact value is unknown, 2˚C/W can be assumed. HEATSINKING TO-263 PACKAGE The TO-263 package uses the copper plane on the PCB as a heatsink. The tab of these packages are soldered to the copper plane for heat sinking. Figure 1 shows a curve for the θ JA of TO-263 package for different copper area sizes, using a typical PCB with 1 ounce copper and no solder mask over the copper area for heat sinking. As shown in the figure, increasing the copper area beyond 1 square inch produces very little improvement. The minimum value for θ JA for the TO-263 package mounted to a PCB is 32˚C/W. Figure 2 shows the maximum allowable power dissipation for TO-263 packages for different ambient temperatures, assuming θ JA is 35˚C/W and the maximum junction tempera- ture is 125˚C. 20074532 FIGURE 1. θ JA vs Copper (1 Ounce) Area for TO-263 package 20074533 FIGURE 2. Maximum power dissipation vs ambient temperature for TO-263 package www.national.com 11 |
Similar Part No. - LP3874-ADJ |
|
Similar Description - LP3874-ADJ |
|
|
|
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
