LTC3459 OPERATION This is accomplished by varying the tOFF period by ap- 0 8 . pF • 1 2 . 5V proximately 1/(VOUT – VIN). Due to propagation delays t ≈ n 100 s OFF + V – V and a 0.6μA bias current in the timer, the t OUT IN OFF time can be 0 6 . A μ + more accurately predicted as follows: k 500 If VOUT is less than VIN, the tOFF delay is fi xed at approxi- mately 750ns. APPLICATIONS INFORMATION Inductor SelectionCapacitor Selection An inductor with a minimum value of 15μH is recommended The boost converter requires two capacitors. The input for use with the LTC3459. Values larger than 15μH will capacitor should be an X5R type of at least 1.0μF. The VOUT result in lower ripple current and switching frequency. capacitor should also be an X5R type between 2.2μF and High frequency ferrite core materials are strongly recom- 10μF. A larger capacitor should be used if lower peak-to- mended. Some inductors meeting these requirements are peak output ripple and better line regulation is desired. listed in Table 1. Table 2. Capacitor Vendor InformationTable 1. Example InductorsSUPPLIERPHONEWEBSITELDCR (Ω)/DIMENSIONSCONTACT AVX (803) 448-9411 www.avxcorp.com VENDOR/PART(μH) IMAX (mA)(mm)INFORMATION Murata (714) 852-2001 www.murata.com Chip Inductors Taiyo Yuden (408) 573-4150 www.t-yuden.com Murata www.murata.com LQH31C 22 3/160 3.2 × 1.6 × 1.8 TDK (847) 803-6100 www.component.tdk.com LQH32C-Low Profi le 22 0.7/250 3.2 × 2.5 × 1.6 Taiyo Yuden www.t-yuden.com PCB Layout Guidelines LB2016 15 0.7/130 2.0 × 1.6 × 1.6 (408) 573-4150 22 1/105 The high speed operation of the LTC3459 demands care- 33 1.7/85 ful attention to board layout. You will not get advertised Toko www.tokoam.com performance with a careless layout. Figure 4 shows the LLB2520 15 1.7/180 2.5 × 2.0 × 1.6 (847) 297-0070 22 2.5/160 recommended component placement for the TSOT ver- 33 3.8/130 sion of the part. A large ground pin copper area will help Coilcraft www.coilcraft.com to lower the chip temperature. DO3314 15 0.86/650 3.3 × 3.3 × 1.4 (847) 639-6400 22 1.2/500 RECOMMENDED COMPONENT DO1606T 15 0.4/700 6.5 × 5.3 × 2.0 PLACEMENT. TRACES CARRYING CURRENT ARE DIRECT. TRACE 22 0.5/500 AREA AT FB PIN IS SMALL. LEAD 33 0.74/450 LENGTH TO BATTERY IS SHORT Sumida www.sumida.com 1 SW V 6 IN V CMD4D06 15 0.5/400 6.6 × 5.8 × 0.8 (847) 956-0666 IN 22 0.8/300 2 GND V 5 OUT CDRJ2D1BLD 33 1.3/240 SHDN 15 0.175/350 3.2 × 3.2 × 2.0 3 FB SHDN 4 22 0.255/300 33 0.37/240 VOUT 3459 F04 Figure 4. Recommended Component Placement for a Single-Layer Board 3459fc 8
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