Datasheet LTC3525L-3 (Analog Devices) - 8

LTC3525L-3
OPERATION
The maximum average load current that can be supported Inductors with lower DC resistance will improve efficiency. is given by: Note that the inductor value does not have a significant 0.3• V effect on ripple current, so while lower values will increase I IN • η O(MAX) = Amps the operating frequency, they do not reduce output volt- VO age ripple. where η is the efficiency (see Typical Performance Char- Some recommended inductor examples are Murata acteristics). LQH32C, Coilcraft LPO4812, LPO3310, DO3314, DS1608 The “burst” frequency (how often the LTC3525L-3 deliv- and MSS4020, Sumida CDRH2D14 and Taiyo Yuden ers a burst of current pulses to the load) is determined NR3015T. by the internal hysteresis (output voltage ripple), the load A ceramic input bypass capacitor should be located as current and the amount of output capacitance. All Burst close as possible to the VIN and GND pins of the IC. A Mode operation or hysteretic converters will enter the minimum value of 1µF is recommended. If the battery is audible frequency range when the load is light enough. more than a few inches away, a bulk tantalum decoupling However, due to the low peak inductor current at light load, cap of at least 10µF is recommended on VIN. circuits using the LTC3525L-3 do not typically generate audible noise. The output capacitor should also be a ceramic, located close to the VOUT and GND pins. A minimum value of 10µF is
Component Selection
recommended. Increasing the value of the output capacitor to 22µF will result in lower output ripple. Higher capacitor Inductor values between 4.7µH and 15µH are recom- values will only offer a small reduction in output ripple, mended. In most applications 10µH will yield the best while reducing light load efficiency by causing the peak compromise between size and efficiency. The inductor inductor current to increase above its minimum value of should be a low-loss ferrite design and must be rated 150mA. The input and output capacitors should be X5R for peak currents of at least 400mA without saturating. or X7R types, not Y5V. 3525lfa 8 Document Outline Features Applications Description Typical Application Absolute Maximum Ratings Pin Configuration Order Information Electrical Characteristics Typical Performance Characteristics Pin Functions Block Diagram Operation Package Description Revision History Typical Applications Related Parts