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LT3472 Datasheet(PDF) 7 Page - Linear Technology |
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LT3472 Datasheet(HTML) 7 Page - Linear Technology |
7 / 12 page LT3472 7 3472f Table 1. Recommended Inductors Part No. Inductance DCR Current Manufacturer (µH) (Ω) Rating (mA) LQH32CN220 22 0.71 250 Murata LQH32CN470 47 1.3 170 (814) 237-1431 LQH2MCN220 22 2.1 185 www.murata.com LQH2MCN470 47 5.1 120 D1067FB-220M 22 2.0 270 TOKO (408) 432-8281 www.tokoam.com ELJPC220KF 22 4.0 160 Panasonic (714) 373-7334 www.panasonic.com CDRH3D16-220 22 0.53 350 Sumida (847) 956-0666 www.sumida.com LB2012B220M 22 1.7 75 Taiyo Yuden LEM2520-220 22 5.5 125 (408) 573-4150 www.t-yuden.com Capacitor Selection The small size of ceramic capacitors makes them suitable for LT3472 applications. X5R and X57 types of ceramic capacitors are recommended because they retain their capacitance over wider voltage and temperature ranges than other types such as Y5V or Z5U. A 2.2µF input capacitor and a 2.2µF output capacitor are sufficient for most LT3472 applications. Table 2. Recommended Ceramic Capacitor Manufacturers Manufacturer Phone URL Taiyo Yuden (408) 573-4150 www.t-yuden.com Murata (814) 237-1431 www.murata.com Kemet (408) 986-0424 www.kemet.com Inrush Current The LT3472 uses internal Schottky diodes. When supply voltage is abruptly applied to VIN pin, for the positive channel, the voltage difference between VIN and VPOS generates inrush current flowing from input through the inductor LP and the internal Schottky diode DP to charge the output capacitor COP. For the inverter channel, there is a similar inrush current flowing from input through the inductor LN1 path, charging the capacitor CNF, and return- ing through the internal Schottky diode DN. The maximum current the Schottky diodes in the LT3472 can sustain is 1A. The selection of inductor and capacitor value should ensure the peak of the inrush current to be below 1A. The peak inrush current can be calculated as follows: I V L EXP SIN r L LC r L P IN = ⎛ ⎝ ⎜ ⎞ ⎠ ⎟ ⎡ ⎣ ⎢ ⎤ ⎦ ⎥ ⎛ ⎝ ⎜ ⎞ ⎠ ⎟ ⎡ ⎣ ⎢ ⎤ ⎦ ⎥ = + = –. • • – • arctan • arctan• . • • – • 06 15 2 1 4 2 ω α ω ω α ω α α ω where L is the inductance, r is the resistance of the inductor and C is the output capacitance. For low DCR inductors, which is usually the case for this application, the peak inrush current can be simplified as follows: I V L EXP P IN = ⎛ ⎝ ⎜ ⎞ ⎠ ⎟ –. • •– • 06 2 ω α ω π Table 3 gives inrush peak currents for some component selections. Note that inrush current is not a concern if the input voltage rises slowly. Table 3. Inrush Peak Current VIN (V) r (Ω)L (µH) C (µF) IP (A) 5 0.5 22 2.2 0.89 3.6 0.7 22 2.2 0.59 3.6 2.1 22 2.2 0.46 3.6 1.3 47 1 0.32 3.6 0.7 22 1 0.46 External Diode Selection As stated previously the LT3472 has internal Schottky diodes. The Schottky diode DP is sufficient for most step- up applications. However, for high current inverter appli- cations, a properly selected external Schottky diode in parallel with DN can improve efficiency. For external diode selection, both forward voltage drop and diode capaci- tance need to be considered. Schottky diodes rated for higher current usually have lower forward voltage drop APPLICATIO S I FOR ATIO |
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