Datenblatt-Suchmaschine für elektronische Bauteile |
|
LM2791 Datenblatt(PDF) 11 Page - Texas Instruments |
|
LM2791 Datenblatt(HTML) 11 Page - Texas Instruments |
11 / 18 page LM2791 www.ti.com SNVS156M – FEBRUARY 2001 – REVISED MAY 2013 PARALLEL Dx OUTPUTS FOR INCREASED CURRENT DRIVE Outputs D1 and D2 may be connected together to drive a single LED. In such a configuration, two parallel current sources of equal value drive the single LED. RSET and VBRGT should be chosen so that the current through each of the outputs is programmed to 50% of the total desired LED current. For example, if 30mA is the desired drive current for the single LED, RSET and VBRGT should be selected so that the current through each of the outputs is 15mA. Connecting the outputs in parallel does not affect internal operation of the LM2791and has no impact on the Electrical Characteristics and limits previously presented. The available Dx output current, maximum Dx voltage, and all other specifications provided in the Electrical Characteristics table apply to this parallel output configuration, just as they do to the standard 2-LED application circuit. THERMAL PROTECTION The LM2791 has internal thermal protection circuitry to disable the charge pump if the junction temperature exceeds 150°C. This feature will protect the device from damage due to excessive power dissipation. The device will recover and operate normally when the junction temperature falls below the maximum operating junction temperature of 100°C. It is important to have good thermal conduction with a proper layout to reduce thermal resistance. POWER EFFICIENCY An ideal power efficiency for a voltage doubler switched capacitor converter is given as the output voltage of the doubler over twice the input voltage as follows: Efficiency = (VDIODE* IDIODE) / ( VIN * IDIODE* Gain) = VDIODE / 2VIN (2) In the case of the LM2791, a more accurate efficiency calculation can be applied as the given formula below. Efficiency = ((VD1* ID1) + (VD2* ID2)) / (ISUPPLY* VIN) (3) It is clear that the efficiency will depend on the supply voltage in the above equation. As such, the lower the supply voltage, the higher the efficiency. POWER DISSIPATION The maximum allowable power dissipation that this package is capable of handling can be determined as follows: PDMax = (TJMax - TA) / θJA (4) where TJMax is the maximum junction temperature, TA is the ambient temperature, and θJA is the junction-to- ambient thermal resistance of the specified package. The actual power dissipation of the device can be calculated using this equation: PDissipation = (2VIN -VDIODE)*ILOAD (5) As an example, if VIN in the target application is 4.2V, VDIODE = 3.0V and worse case current consumption is 32mA (16mA for each diode). PDissipation = ((2*4.2) -3.0)*0.032 = 173mW (6) Power dissipation must be less than that allowed by the package. Please refer to the Absolute Maximum Rating of the LM2791. PCB LAYOUT CONSIDERATIONS The WSON is a leadframe based Chip Scale Package (CSP) with very good thermal properties. This package has an exposed DAP (die attach pad) at the center of the package measuring 2.0mm x 1.2mm. The main advantage of this exposed DAP is to offer lower thermal resistance when it is soldered to the thermal land on the PCB. For PCB layout, a 1:1 ratio between the package and the PCB thermal land is highly recommended. To further enhance thermal conductivity, the PCB thermal land may include vias to a ground plane. For more detailed instructions on mounting WSON packages, please refer to Application Note AN-1187. (SNOA401) Copyright © 2001–2013, Texas Instruments Incorporated Submit Documentation Feedback 11 Product Folder Links: LM2791 Not Recommended For New Designs |
Ähnliche Teilenummer - LM2791 |
|
Ähnliche Beschreibung - LM2791 |
|
|
Link URL |
Privatsphäre und Datenschutz |
ALLDATASHEETDE.COM |
War ALLDATASHEET hilfreich? [ DONATE ] |
Über Alldatasheet | Werbung | Kontakt | Privatsphäre und Datenschutz | Linktausch | Hersteller 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 |