Datasheet LT1615, LT1615-1 (Analog Devices) - 6

LT1615/LT1615-1
U U W U APPLICATIO S I FOR ATIO
input voltages greater than 5V), the current limit over-
Diode Selection
shoot can be quite high. Although it is internally current For most LT1615 applications, the Motorola MBR0520 limited to 350mA, the power switch of the LT1615 can surface mount Schottky diode (0.5A, 20V) is an ideal handle larger currents without problem, but the overall choice. Schottky diodes, with their low forward voltage efficiency will suffer. Best results will be obtained when drop and fast switching speed, are the best match for the IPEAK is kept below 700mA for the LT1615 and below LT1615. For higher output voltage applications the 30V 400mA for the LT1615-1. MBR0530 can be used. Many different manufacturers make equivalent parts, but make sure that the component
Capacitor Selection
is rated to handle at least 0.35A. For LT1615-1 applica- Low ESR (Equivalent Series Resistance) capacitors should tions, a Philips BAT54 or Central Semiconductor CMDSH-3 be used at the output to minimize the output ripple voltage. works well. Multilayer ceramic capacitors are the best choice, as they have a very low ESR and are available in very small
Lowering Output Voltage Ripple
packages. Their small size makes them a good companion Using low ESR capacitors will help minimize the output to the LT1615’s SOT-23 package. Solid tantalum capaci- ripple voltage, but proper selection of the inductor and the tors (like the AVX TPS, Sprague 593D families) or OS-CON output capacitor also plays a big role. The LT1615 pro- capacitors can be used, but they will occupy more board vides energy to the load in bursts by ramping up the area than a ceramic and will have a higher ESR. Always use inductor current, then delivering that current to the load. a capacitor with a sufficient voltage rating. If too large of an inductor value or too small of a capacitor Ceramic capacitors also make a good choice for the input value is used, the output ripple voltage will increase decoupling capacitor, which should be placed as close as because the capacitor will be slightly overcharged each possible to the LT1615. A 4.7µF input capacitor is suffi- burst cycle. To reduce the output ripple, increase the cient for most applications. Table 2 shows a list of several output capacitor value or add a 4.7pF feed-forward capaci- capacitor manufacturers. Consult the manufacturers for tor in the feedback network of the LT1615 (see the circuits more detailed information and for their entire selection of in the Typical Applications section). Adding this small, related parts. inexpensive 4.7pF capacitor will greatly reduce the output voltage ripple.
Table 2. Recommended Capacitors CAPACITOR TYPE VENDOR
Ceramic Taiyo Yuden (408) 573-4150 www.t-yuden.com Ceramic AVX (803) 448-9411 www.avxcorp.com Ceramic Murata (714) 852-2001 www.murata.com sn16151 16151fas 6