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## LTC3409A Datasheet(PDF) 14 Page - Linear Technology

 Part No. LTC3409A Description 600mA Low VIN Buck Regulator in 3mm 3mm DFN Download 16 Pages Scroll/Zoom 100% Maker LINER [Linear Technology] Homepage http://www.linear.com Logo

## LTC3409A Datasheet(HTML) 14 Page - Linear Technology

 14 / 16 page LTC3409A143409afDesign ExampleAs a design example, assume the LTC3409A is used in a2-alkaline cell battery-powered application. The VIN will beoperating from a maximum of 3.2V down to about 1.8V.The load current requirement is a maximum of 600mAbut most of the time it will be in standby mode, requiringonly 2mA. Efﬁciency at both low and high load currents isimportant, so the minimum frequency setting of 1.7MHzis chosen. Output voltage is 1.5V. With this informationwe can calculate L using Equation 3:L=1f•ΔILVOUT 1–VOUTVIN⎛⎝⎜⎞⎠⎟(3)Substituting VOUT = 1.5V, VIN = 3.2V, ΔIL = 240mA andf = 1.7MHz in Equation 2 gives:L=11.7MHz • 240mA1.5V 1–1.5V3.2V⎛⎝⎜⎞⎠⎟ ≅2.2µHFor best efﬁciency choose a 750mA or greater inductorwith less than 0.3Ω series resistance. CIN will requirean RMS current rating of at least 0.3A≅ ILOAD(MAX)/2 attemperature.For the feedback resistors, choose R2 = 137k. R1 is thencalculated to be 200k from Equation 2. Figure 4 shows thecomplete circuit along with its efﬁciency curve.Table 2 below gives 1% resistor values for selected outputvoltages.VOUTR1R20.85V53.6k137k1.2V137k143k1.5V200k137k1.8V267k137kVFBGNDVINVINSYNCRUNSWMODELTC3409AL12.2μHR1200kC110pFCIN4.7μFVIN1.8V TO 3.2VR2137k3409A F04VOUT1.5V0.6ACOUT22μF2L1: SUMIDA CDRH2D18/LDFigure 4Burst Mode Efﬁciency, 1.5VOUTAPPLICATIONS INFORMATIONLOAD CURRENT (mA)3090100201080507060400.11010010003409A F04b011.8VIN3.2VIN2.5VIN