LTC3499/LTC3499B APPLICATIONS INFORMATIONPCB LAYOUT GUIDELINES The inductor current ripple is typically set to 20% to 40% The high speed operation of the LTC3499/LTC3499B of the maximum inductor current. For high efficiency, demand careful attention to board layout. Advertised per- choose an inductor with high frequency core material, formance will not be achieved with careless layout. Figure 2 such as ferrite, to reduce core losses. The inductor should shows the recommended component placement. A large have low ESR (equivalent series resistance) to reduce the copper area will help to lower the chip temperature. Traces I2R power losses, and must be able to handle the peak carrying high current (SW, V inductor current without saturating. To minimize radiated OUT, GND) are kept short. The lead length to the battery should be kept as short as noise, use a toroidal or shielded inductor. See Table 1 for possible. The V some suggested inductor suppliers. IN and VOUT ceramic capacitors should be placed as close to the IC pins as possible. Table 1. Inductor Vendor Information PART NUMBERSUPPLIERWEB SITE CC2 EXPOSED PAD FOR DD8 MSS5131 and Coilcraft www.coilcraft.com MOS6020 Series CC1 RZ VC SHDN 1 8 SLF7028 and TDK www.component.tdk.com SLF7045 Series LQH55D Series Murata www.murata.com V R2 IN FB 2 7 CDRH4D28 Series Sumida www.sumida.com 9 R1 + CIN L D53LC and Toko www.tokoam.com VBATT VOUT D62CB Series SW 3 6 DT0703 Series CoEV www.coev.net SS COUT MJPF2520 Series FDK www.fdk.com GND 4 5 CSS Output Capacitor Selection 3499 F02 The output voltage ripple has three components to it. The Figure 2: Recommended Component Placement bulk value of the capacitor is set to reduce the ripple due to charge into the capacitor each cycle. The maximum COMPONENT SELECTION ripple voltage due to charge is given by: V Inductor Selection V IN RBULK = IP • ( ) COUT • VOUT • f The LTC3499/LTC3499B allow the use of small surface mount inductors and chip inductors due to the fast 1.2MHz where IP = peak inductor current and f = switching switching frequency. A minimum inductance value of frequency. 2.2µH is required. Larger values of inductance will allow The ESR (equivalent series resistance) is usually the most greater output current capability by reducing the induc- dominant factor for ripple in most power converters. The tor ripple current. Increasing the inductance above 10µH ripple due to capacitor ESR is simply given by: will increase total solution area while providing minimal improvement in output current capability. VRCESR = IP • CESR where CESR = capacitor equivalent series resistance. 3499fc 10
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