Datasheet LTC3606B (Analog Devices) - 10

LTC3606B
APPLICATIONS INFORMATION
A general LTC3606B application circuit is shown in Figure 2.
Inductor Core Selection
External component selection is driven by the load require- Different core materials and shapes will change the size/ ment, and begins with the selection of the inductor L. Once current and price/current relationship of an inductor. Toroid the inductor is chosen, CIN and COUT can be selected. or shielded pot cores in ferrite or permalloy materials are small and do not radiate much energy, but generally cost
Inductor Selection
more than powdered iron core inductors with similar Although the inductor does not infl uence the operat- electrical characteristics. The choice of which style ing frequency, the inductor value has a direct effect on inductor to use often depends more on the price versus ripple current. The inductor ripple current IL decreases size requirements, and any radiated fi eld/EMI requirements, with higher inductance and increases with higher VIN or than on what the LTC3606B requires to operate. Table 1 VOUT: shows some typical surface mount inductors that work V V well in LTC3606B applications. I OUT OUT L = • 1 (1) f V O • L IN
Table 1. Representative Surface Mount Inductors MANU- MAX DC
Accepting larger values of IL allows the use of low
FACTURER PART NUMBER VALUE CURRENT DCR HEIGHT
inductances, but results in higher output voltage ripple, Coilcraft LPS4012-152ML 1.5μH 2200mA 0.070Ω 1.2mm greater core losses, and lower output current capability. LPS4012-222ML 2.2μH 1750mA 0.100Ω 1.2mm A reasonable starting point for setting ripple current is LPS4012-332ML 3.3μH 1450mA 0.100Ω 1.2mm LPS4012-472ML 4.7μH 1450mA 0.170Ω 1.2mm 40% of the maximum output load current. So, for a 800mA LPS4018-222ML 2.2μH 2300mA 0.070Ω 1.8mm regulator, I LPS4018-332ML 3.3μH 2000mA 0.080Ω 1.8mm L = 320mA (40% of 800mA). LPS4018-472ML 4.7μH 1800mA 0.125Ω 1.8mm The inductor value will also have an effect on Burst Mode FDK FDKMIPF2520D 4.7μH 1100mA 0.11Ω 1mm operation. The transition to low current operation begins FDKMIPF2520D 3.3μH 1200mA 0.1Ω 1mm FDKMIPF2520D 2.2μH 1300mA 0.08Ω 1mm when the peak inductor current falls below a level set by Murata LQH32CN4R7M23 4.7μH 450mA 0.2Ω 2mm the internal burst clamp. Lower inductor values result in higher ripple current which causes the transition to occur Panasonic ELT5KT4R7M 4.7μH 950mA 0.2Ω 1.2mm at lower load currents. This causes a dip in effi ciency in Sumida CDRH2D18/LD 4.7μH 630mA 0.086Ω 2mm CDH38D11SNP- 3.3μH 1560mA 0.115Ω 1.2mm the upper range of low current operation. Furthermore, 3R3M lower inductance values will cause the bursts to occur CDH38D11SNP- 2.2μH 1900mA 0.082Ω 1.2mm 2R2M with increased frequency. Taiyo Yuden CB2016T2R2M 2.2μH 510mA 0.13Ω 1.6mm L1 CB2012T2R2M 2.2μH 530mA 0.33Ω 1.25mm VIN V V IN SW OUT CB2016T3R3M 3.3μH 410mA 0.27Ω 1.6mm 2.5V TO 5.5V LTC3606B CF NR30102R2M 2.2μH 1100mA 0.1Ω 1mm RPGD RUN C NR30104R7M 4.7μH 750mA 0.19Ω 1mm CIN OUT PGOOD TDK VLF3010AT4R7- 4.7μH 700mA 0.28Ω 1mm R2 V RLIM FB MR70 PGOOD VLF3010AT3R3- 3.3μH 870mA 0.17Ω 1mm GND R1 MR87 VLF3010AT2R2- 2.2μH 1000mA 0.12Ω 1mm RLIM CLIM 3606B F02 M1R0 VLF4012AT-2R2 2.2μH 1500mA 0.076Ω 1.2mm M1R5
Figure 2. LTC3606B General Schematic
VLF5012ST-3R3 3.3μH 1700mA 0.095Ω 1.2mm M1R7 VLF5014ST-2R2 2.2μH 2300mA 0.059Ω 1.4mm M2R3 3606bfb 10