Datasheet LTC3410-1.875 (Analog Devices) - 8

LTC3410-1.875
U U W U APPLICATIO S I FOR ATIO
The basic LTC3410-1.875 application circuit is shown in
Inductor Core Selection
Figure 1. External component selection is driven by the Different core materials and shapes will change the size/ load requirement and begins with the selection of L fol- current and price/current relationship of an inductor. Tor- lowed by CIN and COUT. oid or shielded pot cores in ferrite or permalloy materials are small and do not radiate much energy, but generally VIN 4.7µH V 2.7V V OUT IN SW cost more than powdered iron core inductors with similar 1.875V TO 5.5V CIN C 4.7µF LTC3410-1.875 OUT electrical characteristics. The choice of which style induc- 4.7µF CER RUN CER tor to use often depends more on the price vs size require- VOUT ments and any radiated field/EMI requirements than on GND what the LTC3410-1.875 requires to operate. Table 1 34101875 F01 shows some typical surface mount inductors that work well in LTC3410-1.875 applications.
Figure 1. High Efficiency Step-Down Converter Table 1. Representative Surface Mount Inductors MAX DC MANUFACTURER PART NUMBER VALUE CURRENT DCR HEIGHT Inductor Selection
Taiyo Yuden CB2016T2R2M 2.2µH 510mA 0.13Ω 1.6mm For most applications, the value of the inductor will fall in CB2012T2R2M 2.2µH 530mA 0.33Ω 1.25mm LBC2016T3R3M 3.3µH 410mA 0.27Ω 1.6mm the range of 2.2µH to 4.7µH. Its value is chosen based on Panasonic ELT5KT4R7M 4.7µH 950mA 0.2Ω 1.2mm the desired ripple current. Large value inductors lower Sumida CDRH2D18/LD 4.7µH 630mA 0.086Ω 2mm ripple current and small value inductors result in higher Murata LQH32CN4R7M23 4.7µH 450mA 0.2Ω 2mm ripple currents. Higher VIN or VOUT also increases the ripple Taiyo Yuden NR30102R2M 2.2 current as shown in equation 1. A reasonable starting point µH 1100mA 0.1Ω 1mm NR30104R7M 4.7µH 750mA 0.19Ω 1mm for setting ripple current is ∆IL = 120mA (40% of 300mA). FDK FDKMIPF2520D 4.7µH 1100mA 0.11Ω 1mm FDKMIPF2520D 3.3µH 1200mA 0.1Ω 1mm 1 ⎛ V ⎞ I V OUT 1 (1) FDKMIPF2520D 2.2 ∆ L = µH 1300mA 0.08Ω 1mm (f)( ) OUT − L ⎝⎜ VIN ⎠⎟ The DC current rating of the inductor should be at least equal to the maximum load current plus half the ripple current to prevent core saturation. Thus, a 360mA rated inductor should be enough for most applications (300mA + 60mA). For better efficiency, choose a low DC-resistance inductor. The inductor value also has an effect on Burst Mode operation. The transition to low current operation begins when the inductor current peaks fall to approximately 100mA. Lower inductor values (higher ∆IL) will cause this to occur at lower load currents, which can cause a dip in efficiency in the upper range of low current operation. In Burst Mode operation, lower inductance values will cause the burst frequency to increase. 34101875f 8