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LT3491 Datasheet(PDF) 7 Page - Linear Technology |
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LT3491 Datasheet(HTML) 7 Page - Linear Technology |
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7 / 16 page  7 LT3491 3491fa APPLICATIO S I FOR ATIO INDUCTOR SELECTION A 10 µH inductor is recommended for most LT3491 appli- cations. Although small size and high efficiency are major concerns, the inductor should have low core losses at 2.3MHz and low DCR (copper wire resistance). Some small inductors in this category are listed in Table 1. The efficiency comparison of different inductors is shown in Figure 3. Table 1. Recommended Inductors CURRENT L DCR RATING PART ( µH) ( Ω) (mA) VENDOR LQH32CN100K53 10 0.3 450 Murata LQH2MCN100K02 10 1.2 225 www.murata.com SD3112-100 10 0.446 550 Cooper www.cooperet.com 1001AS-100M 10 0.48 460 Toko (TYPE D312C) www.toko.com CDRH2D11 10 0.5375 280 Sumida CDRH2D14 10 0.294 700 www.sumida.com Table 2 shows a list of several ceramic capacitor manufac- turers. Consult the manufacturers for detailed information on their entire selection of ceramic parts. Table 2. Recommended Ceramic Capacitor Manufacturers Taiyo Yuden (800) 368-2496 www.t-yuden.com AVX (803) 448-9411 www.avxcorp.com Murata (714) 852-2001 www.murata.com OVERVOLTAGE PROTECTION The LT3491 has an internal open-circuit protection circuit. In the cases of output open circuit, when the LEDs are disconnected from the circuit or the LEDs fail open circuit, VCAP is clamped at 27V (typ). The LT3491 will then switch at a very low frequency to minimize input current. The VCAP and input current during output open circuit are shown in the Typical Performance Characteristics. Figure 4 shows the transient response when the LEDs are disconnected. Figure 3. Efficiency Comparison of Different Inductors CAPACITOR SELECTION The small size of ceramic capacitors make them ideal for LT3491 applications. Use only X5R and X7R types be- cause they retain their capacitance over wider temperature ranges than other types such as Y5V or Z5U. A 1 µF input capacitor and a 1 µF output capacitor are sufficient for most applications. INRUSH CURRENT The LT3491 has a built-in Schottky diode. When supply voltage is applied to the VIN pin, an inrush current flows through the inductor and the Schottky diode and charges up the CAP voltage. The Schottky diode inside the LT3491 can sustain a maximum current of 1A. Figure 4. Output Open-Circuit Waveform VCAP 10V/DIV IL 200mA/DIV VIN = 3.6V CIRCUIT OF FRONT PAGE APPLICATION LEDs DISCONNECTED AT THIS INSTANT 500 µs/DIV 3491 F04 LED CURRENT (mA) 0 30 35 45 50 55 80 65 5 10 3491 F03 40 70 75 60 15 20 MURATA LQH2MCN100K02 MURATA LQH32CN100K53 TOKO 10001AS-100M SUMIDA CDRH2D11 SUMIDA CDRH2D14 VIN = 3.6V 4 LEDs FRONT PAGE APPLICATION CIRCUIT |
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