Electronic Components Datasheet Search 

LM3500 Datasheet(PDF) 15 Page  Texas Instruments 

LM3500 Datasheet(HTML) 15 Page  Texas Instruments 
15 / 25 page IOUT KD' IPK VIND 2LFSW +  D' = VIN =1D VOUT VIN RDSON 0.58 L > D D' 1 VIN RDSON 0.29 L > D D' 1 LM3500 www.ti.com SNVS231F – MAY 2004 – REVISED APRIL 2007 The LM3500 has an internal thermal shutdown function to protect the die from excessive temperatures. The thermal shutdown trip point is typically 150°C. There is a hysteresis of typically 35°C so the die temperature must decrease to approximately 115°C before the LM3500 will return to normal operation. INDUCTOR SELECTION The inductor used with the LM3500 must have a saturation current greater than the cycle by cycle peak inductor current (see Typical Peak Inductor Currents table below). Choosing inductors with low DCR decreases power losses and increases efficiency. The minimum inductor value required for the LM350016 can be calculated using the following equation: (2) The minimum inductor value required for the LM350021 can be calculated using the following equation: (3) For both equations above, L is in µH, VIN is the input supply of the chip in Volts, RDSON is the ON resistance of the NMOS power switch found in the Typical Performance Characteristics section in ohms and D is the duty cycle of the switching regulator. The above equation is only valid for D greater than or equal to 0.5. For applications where the minimum duty cycle is less than 0.5, a 22µH inductor is the typical recommendation for use with most applications. Benchlevel verification of circuit performance is required in these special cases, however. The duty cycle, D, is given by the following equation: (4) where VOUT is the voltage at pin C1. Table 1. Typical Peak Inductor Currents (mA) # LEDs LED Current VIN (in 15 20 30 40 50 60 (V) series) mA mA mA mA mA mA 2.7 2 82 100 134 160 204 234 3 118 138 190 244 294 352 4 142 174 244 322 X X 5 191 232 319 413 X X 3.3 2 76 90 116 136 172 198 3 110 126 168 210 250 290 4 132 158 212 270 320 X 5 183 216 288 365 446 X 4.2 2 64 76 96 116 142 162 3 102 116 148 180 210 246 4 122 146 186 232 272 318 5 179 206 263 324 388 456 The typical cyclebycycle peak inductor current can be calculated from the following equation: (5) where IOUT is the total load current, FSW is the switching frequency, L is the inductance and η is the converter efficiency of the total driven load. A good typical number to use for η is 0.8. The value of η can vary with load and duty cycle. The average inductor current, which is also the average VSW pin current, is given by the following equation: Copyright © 2004–2007, Texas Instruments Incorporated Submit Documentation Feedback 15 Product Folder Links: LM3500 
