Electronic Components Datasheet Search |
|
LX8386A-33CDD Datasheet(PDF) 6 Page - Microsemi Corporation |
|
LX8386A-33CDD Datasheet(HTML) 6 Page - Microsemi Corporation |
6 / 7 page 1.5A L OW D ROPOUT P OSITIVE R EGULA TORS LX8386-xx/8386A-xx/8386B-xx PRODUCT DA T ABOOK 1996/1997 Copyright © 1999 Rev. 1.7a 10.00 6 P RODUCTION D ATA S HEET APPLICA TION NOTES Example Given: V IN = 5V V OUT = 2.5V, IOUT = 1.5A Ambient Temp., T A = 50°C Rθ JT = 2.7°C/W for TO-220 Find: Proper Heat Sink to keep IC's junction temperature below 125°C.** Solution: The junction temperature is: T J = PD (R θJT + RθCS + RθSA) + TA where: P D ≡ Dissipated power. Rθ JT ≡ Thermal resistance from the junction to the mounting tab of the package. Rθ CS ≡ Thermal resistance through the interface between the IC and the surface on which it is mounted. (1.0°C/W at 6 in-lbs mounting screw torque.) Rθ SA ≡ Thermal resistance from the mounting surface to ambient (thermal resistance of the heat sink). T S ≡ Heat sink temperature. First, find the maximum allowable thermal resistance of the heat sink: Rθ SA = - (Rθ JT + R θCS) P D =(V IN(MAX) - VOUT) I OUT = (5.0V-2.5V) * 1.5A = 3.75W Rθ SA = - (2.7°C/W + 1.0°C/W) = 16.3°C/W Next, select a suitable heat sink. The selected heat sink must have Rθ SA ≤ 16.3°C/W. Thermalloy heatsink 6230B has R θSA = 12.0°C/W. Finally, verify that junction temperature remains within speci- fication using the selected heat sink: T J = 3.75W (2.7°C/W + 1.0°C/W + 12.0°C/W) + 50°C = 109°C T J T C T S T A RθJT RθCS RθSA T J - TA P D 125°C - 50°C 3.75W ** Although the device can operate up to 150°C junction, it is recom- mended for long term reliability to keep the junction temperature below 125°C whenever possible. LOAD REGULATION (continued) Even when the circuit is optimally configured, parasitic resistance can be a significant source of error. A 20 mil wide PC trace built from 1 oz. copper-clad circuit board material has a parasitic resistance of about 25 milliohms per inch of its length at room temperature. If a 3-terminal regulator used to supply 2.50 volts is connected by 2 inches of this trace to a load which draws 1.5 amps of current, a 75 millivolt drop will appear between the regulator and the load. Even when the regulator output voltage is precisely 2.50 volts, the load will only see 2.43 volts, which is a 3% error. It is important to keep the connection between the regulator output pin and the load as short as possible, and to use wide traces or heavy-gauge wire. The minimum specified output capacitance for the regulator should be located near the reglator package. If several capacitors are used in parallel to construct the power system output capaci- tance, any capacitors beyond the minimum needed to meet the specified requirements of the regulator should be located near the sections of the load that require rapidly-changing amounts of current. Placing capacitors near the sources of load transients will help ensure that power system transient response is not impaired by the effects of trace impedance. To maintain good load regulation, wide traces should be used on the input side of the regulator, especially between the input capacitors and the regulator. Input capacitor ESR must be small enough that the voltage at the input pin does not drop below V IN (MIN) during transients. V IN (MIN) = VOUT + VDROPOUT (MAX) where: V IN (MIN) ≡ the lowest allowable instantaneous voltage at the input pin. V OUT ≡ the designed output voltage for the power supply system. V DROPOUT (MAX) ≡ the specified dropout voltage for the installed regulator. THERMAL CONSIDERATIONS The LX8386/86A/86B regulators have internal power and thermal limiting circuitry designed to protect each device under overload conditions. For continuous normal load conditions, however, maximum junction temperature ratings must not be exceeded. It is important to give careful consideration to all sources of thermal resistance from junction to ambient. This includes junction to case, case to heat sink interface, and heat sink thermal resistance itself. Junction-to-case thermal resistance is specified from the IC junction to the back surface of the case directly opposite the die. This is the lowest resistance path for heat flow. Proper mounting is required to ensure the best possible thermal flow from this area of the package to the heat sink. Thermal compound at the case-to- heat-sink interface is strongly recommended. If the case of the device must be electrically isolated, a thermally conductive spacer can be used, as long as its added contribution to thermal resistance is considered. Note that the case of all devices in this series is electrically connected to the output. |
Similar Part No. - LX8386A-33CDD |
|
Similar Description - LX8386A-33CDD |
|
|
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 |