Electronic Components Datasheet Search |
|
LM3404 Datasheet(PDF) 1 Page - National Semiconductor (TI) |
|
|
LM3404 Datasheet(HTML) 1 Page - National Semiconductor (TI) |
1 / 6 page Thermal Performance of the LM3404/04HV in SO-8 and PSOP-8 Packages National Semiconductor Application Note 1629 Chris Richardson May 2007 Introduction The LM3404/04HV is a buck-regulator designed for driving high powered LEDs at forward currents of up to 1.0A. LED drivers often experience thermal conditions that are extreme even by the standards of switching converters. For example, LED drivers are often placed on the same metal-core PCB (MCPCB) as the LEDs themselves. At 1.0A, a single-die white LED can dissipate more than 3W. The temperature of the MCPCB can easily reach 60°C or more. Even when the driver is placed on a separate PCB, the combination of high power dissipation, small, enclosed spaces, and little-to-no air flow create high ambient temperatures and even higher junction temperatures. Thermal conditions for integrated (MOSFET on-board) LED drivers are made worse by the high duty cycles of LED drivers. For applications that use multiple LEDs, as many LEDs as possible are placed in series to match the current and voltage limitations of the regulator regulator. The result is that output voltage is just below the input voltage. A voltage regulator that provides a 5V output from a 24V input has a duty cycle of 21%, meaning that the internal MOSFET is on for 21% of the time. In contrast, a 24V input is often used to drive five series-con- nected white LEDs, and at 3.5V each this gives an output voltage of 17.5V, forcing the MOSFET to conduct for 73% of the time. The first part of this application note will explore the perfor- mance of the LM3404HV in a high current, high input voltage, high duty cycle application typical of many LED drivers, using lab-tested thermal performance results and simulations. The industry standard SO-8 package and the pin-for-pin compat- ible PSOP-8 package with an exposed thermal pad (also called a die-attach paddle, or DAP) will be compared to help the user estimate the die temperature under various condi- tions, and determine which package is best for their applica- tion. The second part of this application note uses the power dis- sipation calculated in the first section to estimate the LM3404HV’s die temperature under two typical configura- tions of the LEDs relative to the LED driver. The first case is for the LM3404HV mounted on a separate PCB that is con- nected to the LEDs by a wiring harness. This case assumes an ambient temperature influenced by the heating of the LEDs, but no direct heating of the PCB by the LEDs them- selves. The second case assumes the LM3404HV is mounted to the same MCPCB as the LEDs themselves. In this config- uration the temperature of the MCPCB has a much stronger influence over the LM3404HV die temperature than the am- bient temperature, and the tests assume a fixed MCPCB temperature instead of a fixed ambient temperature. Test Circuit The test circuit uses the LM3404HV to drive ten series-con- nected 3W white LEDs from an input voltage of 48V ±5%. The total forward current, I F, is 1A ±5% at a typical forward drop of 36V (in thermal equilibrium). Output current ripple is 70 mA P-P or less. Switching frequency is 550 kHz ±10% and the circuit is surge protected up to 60V. A complete BOM is listed at the back of this document, and performance waveforms are given in Application Note AN-1585. The schematic is shown in Figure 1. 30019201 FIGURE 1. © 2007 National Semiconductor Corporation 300192 www.national.com |
Similar Part No. - LM3404_1 |
|
Similar Description - LM3404_1 |
|
|
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 |