Datasheet LTC3547B (Analog Devices) - 8
| Manufacturer | Analog Devices |
| Description | Dual Monolithic 300mA Synchronous Step-Down Regulator |
| Pages / Page | 16 / 8 — APPLICATIO S I FOR ATIO. Inductor Core Selection. Inductor Selection. … |
| File Format / Size | PDF / 260 Kb |
| Document Language | English |
APPLICATIO S I FOR ATIO. Inductor Core Selection. Inductor Selection. Table 1. Representative Surface Mount Inductors. MANU-
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LTC3547B
U U W U APPLICATIO S I FOR ATIO
A general LTC3547B 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 load requirement, and begins with the selection of the size/current and price/current relationship of an induc- inductor L. Once the inductor is chosen, CIN and COUT tor. Toroid or shielded pot cores in ferrite or permalloy can be selected. materials are small and do not radiate much energy, but generally cost more than powdered iron core inductors
Inductor Selection
with similar electrical characteristics. The choice of which Although the inductor does not infl uence the operat- style inductor to use often depends more on the price vs ing frequency, the inductor value has a direct effect on size requirements, and any radiated fi eld/EMI requirements, ripple current. The inductor ripple current ΔIL decreases than on what the LTC3547B requires to operate. Table 1 with higher inductance and increases with higher VIN shows some typical surface mount inductors that work or VOUT: well in LTC3547B applications. I
Table 1. Representative Surface Mount Inductors
L = VOUT • 1 VOUT f V (1) O • L IN
MANU- MAX DC FACTURER PART NUMBER VALUE CURRENT DCR HEIGHT
Accepting larger values of ΔIL allows the use of low Taiyo Yuden CB2016T2R2M 2.2μH 510mA 0.13Ω 1.6mm inductances, but results in higher output voltage ripple, CB2012T2R2M 2.2μH 530mA 0.33Ω 1.25mm CB2016T3R3M 3.3μH 410mA 0.27Ω 1.6mm greater core losses, and lower output current capability. Panasonic ELT5KT4R7M 4.7μH 950mA 0.2Ω 1.2mm A reasonable starting point for setting ripple current Sumida CDRH2D18/LD 4.7μH 630mA 0.086Ω 2mm is 40% of the maximum output load current. So, for a Murata LQH32CN4R7M23 4.7μH 450mA 0.2Ω 2mm 300mA regulator, ΔIL = 120mA (40% of 300mA). Taiyo Yuden NR30102R2M 2.2μH 1100mA 0.1Ω 1mm VIN NR30104R7M 4.7μH 750mA 0.19Ω 1mm 2.5V TO 5.5V C1 FDK FDKMIPF2520D 4.7μH 1100mA 0.11Ω 1mm RUN2 VIN RUN1 FDKMIPF2520D 3.3μH 1200mA 0.1Ω 1mm FDKMIPF2520D 2.2μH 1300mA 0.08Ω 1mm L2 LTC3547B L1 VOUT2 SW2 SW1 VOUT1 TDK VLF3010AT4R7- 4.7μH 700mA 0.24Ω 1mm CF2 CF1 MR70 VLF3010AT3R3- 3.3μH 870mA 0.17Ω 1mm VFB2 VFB1 MR87 R4 GND R2 COUT2 R3 R1 COUT1 VLF3010AT2R2- 2.2μH 1000mA 0.12Ω 1mm M1RD 3547b F01
Figure 1. LTC3547B General Schematic
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U U W U APPLICATIO S I FOR ATIO
A general LTC3547B 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 load requirement, and begins with the selection of the size/current and price/current relationship of an induc- inductor L. Once the inductor is chosen, CIN and COUT tor. Toroid or shielded pot cores in ferrite or permalloy can be selected. materials are small and do not radiate much energy, but generally cost more than powdered iron core inductors
Inductor Selection
with similar electrical characteristics. The choice of which Although the inductor does not infl uence the operat- style inductor to use often depends more on the price vs ing frequency, the inductor value has a direct effect on size requirements, and any radiated fi eld/EMI requirements, ripple current. The inductor ripple current ΔIL decreases than on what the LTC3547B requires to operate. Table 1 with higher inductance and increases with higher VIN shows some typical surface mount inductors that work or VOUT: well in LTC3547B applications. I
Table 1. Representative Surface Mount Inductors
L = VOUT • 1 VOUT f V (1) O • L IN
MANU- MAX DC FACTURER PART NUMBER VALUE CURRENT DCR HEIGHT
Accepting larger values of ΔIL allows the use of low Taiyo Yuden CB2016T2R2M 2.2μH 510mA 0.13Ω 1.6mm inductances, but results in higher output voltage ripple, CB2012T2R2M 2.2μH 530mA 0.33Ω 1.25mm CB2016T3R3M 3.3μH 410mA 0.27Ω 1.6mm greater core losses, and lower output current capability. Panasonic ELT5KT4R7M 4.7μH 950mA 0.2Ω 1.2mm A reasonable starting point for setting ripple current Sumida CDRH2D18/LD 4.7μH 630mA 0.086Ω 2mm is 40% of the maximum output load current. So, for a Murata LQH32CN4R7M23 4.7μH 450mA 0.2Ω 2mm 300mA regulator, ΔIL = 120mA (40% of 300mA). Taiyo Yuden NR30102R2M 2.2μH 1100mA 0.1Ω 1mm VIN NR30104R7M 4.7μH 750mA 0.19Ω 1mm 2.5V TO 5.5V C1 FDK FDKMIPF2520D 4.7μH 1100mA 0.11Ω 1mm RUN2 VIN RUN1 FDKMIPF2520D 3.3μH 1200mA 0.1Ω 1mm FDKMIPF2520D 2.2μH 1300mA 0.08Ω 1mm L2 LTC3547B L1 VOUT2 SW2 SW1 VOUT1 TDK VLF3010AT4R7- 4.7μH 700mA 0.24Ω 1mm CF2 CF1 MR70 VLF3010AT3R3- 3.3μH 870mA 0.17Ω 1mm VFB2 VFB1 MR87 R4 GND R2 COUT2 R3 R1 COUT1 VLF3010AT2R2- 2.2μH 1000mA 0.12Ω 1mm M1RD 3547b F01
Figure 1. LTC3547B General Schematic
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