Datasheet LTC3564 (Analog Devices) - 9
| Manufacturer | Analog Devices |
| Description | 2.25MHz, 1.25A Synchronous Step-Down Regulator |
| Pages / Page | 20 / 9 — APPLICATIO S I FOR ATIO. Figure 1. LTC3564 General Schematic. Inductor … |
| File Format / Size | PDF / 269 Kb |
| Document Language | English |
APPLICATIO S I FOR ATIO. Figure 1. LTC3564 General Schematic. Inductor Selection. Inductor Core Selection
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LTC3564
U U W U APPLICATIO S I FOR ATIO
L The DC current rating of the inductor should be at least VIN VIN SW VOUT CF equal to the maximum load current plus half the ripple CIN LTC3564 current to prevent core saturation. Thus, a 1.5A rated COUT R2 inductor should be enough for most applications (1.25A RUN 3564 F01 VFB + 250mA). For better efficiency, choose a low DC-resis- R1 GND tance inductor. The inductor value also has an effect on Burst Mode
Figure 1. LTC3564 General Schematic
operation. The transition to low current operation begins when the inductor current peaks fall to approximately The basic LTC3564 application circuit is shown in Figure 1. 300mA. Lower inductor values (higher ΔIL) will cause this External component selection is driven by the load require- to occur at lower load currents, which can cause a dip in ment and begins with the selection of L followed by CIN and efficiency in the upper range of low current operation. In COUT. Burst Mode operation, lower inductance values will cause the burst frequency to increase.
Inductor Selection
For most applications, the value of the inductor will fall in
Inductor Core Selection
the range of 0.47μH to 2.2μH. Its value is chosen based on Different core materials and shapes will change the size/ the desired ripple current. Large value inductors lower current and price/current relationship of an inductor. ripple current and small value inductors result in higher Toroid or shielded pot cores in ferrite or permalloy mate- ripple currents. Higher VIN or VOUT also increases the ripple rials are small and don’t radiate much energy, but gener- current as shown in equation 1. A reasonable starting point ally cost more than powdered iron core inductors with for setting ripple current is ΔIL = 500mA (40% of 1.25A). similar electrical characteristics. The choice of which style inductor to use often depends more on the price vs size 1 ⎛ V ⎞ ΔI OUT L = ( V 1 requirements and any radiated field/EMI requirements f)(L) OUT − ⎝⎜ V (1) IN ⎠ ⎟ than on what the LTC3564 requires to operate. Table 1 shows some typical surface mount inductors that work well in LTC3564 applications.
Table 1. Representative Surface Mount Inductors MANUFATURER PART NUMBER VALUE (
μ
H) MAX DC CURRENT (A) DCR (
mΩ
) HEIGHT (mm)
Toko A915AY-1R1M-DC53LC 1.1 3.25 16 3 1070AS-1R0N-DB3020C 1 1.9 47 2 Sumida CDRH4D18C/LD-1R1 1.1 2.1 24 2 CDRH3D14-1R2 1.2 2.2 36 1.5 CR5D11-1R0 1 2.2 40 1.2 CDRH2D18/HP-2R2 2.2 1.6 48 2 FDK MIPW3226D0R9M 0.9 1.4 70 1 Coilcraft LPO6610-122ML 1.2 2.1 80 1 LPS4018-222ML 2.2 2.5 70 1.8 Vishay IHLP1616ABERR47M01 0.47 5 20 1.2 IHLP1616ABER1R0M01 1 4 45 1.2 3564f 9
U U W U APPLICATIO S I FOR ATIO
L The DC current rating of the inductor should be at least VIN VIN SW VOUT CF equal to the maximum load current plus half the ripple CIN LTC3564 current to prevent core saturation. Thus, a 1.5A rated COUT R2 inductor should be enough for most applications (1.25A RUN 3564 F01 VFB + 250mA). For better efficiency, choose a low DC-resis- R1 GND tance inductor. The inductor value also has an effect on Burst Mode
Figure 1. LTC3564 General Schematic
operation. The transition to low current operation begins when the inductor current peaks fall to approximately The basic LTC3564 application circuit is shown in Figure 1. 300mA. Lower inductor values (higher ΔIL) will cause this External component selection is driven by the load require- to occur at lower load currents, which can cause a dip in ment and begins with the selection of L followed by CIN and efficiency in the upper range of low current operation. In COUT. Burst Mode operation, lower inductance values will cause the burst frequency to increase.
Inductor Selection
For most applications, the value of the inductor will fall in
Inductor Core Selection
the range of 0.47μH to 2.2μH. Its value is chosen based on Different core materials and shapes will change the size/ the desired ripple current. Large value inductors lower current and price/current relationship of an inductor. ripple current and small value inductors result in higher Toroid or shielded pot cores in ferrite or permalloy mate- ripple currents. Higher VIN or VOUT also increases the ripple rials are small and don’t radiate much energy, but gener- current as shown in equation 1. A reasonable starting point ally cost more than powdered iron core inductors with for setting ripple current is ΔIL = 500mA (40% of 1.25A). similar electrical characteristics. The choice of which style inductor to use often depends more on the price vs size 1 ⎛ V ⎞ ΔI OUT L = ( V 1 requirements and any radiated field/EMI requirements f)(L) OUT − ⎝⎜ V (1) IN ⎠ ⎟ than on what the LTC3564 requires to operate. Table 1 shows some typical surface mount inductors that work well in LTC3564 applications.
Table 1. Representative Surface Mount Inductors MANUFATURER PART NUMBER VALUE (
μ
H) MAX DC CURRENT (A) DCR (
mΩ
) HEIGHT (mm)
Toko A915AY-1R1M-DC53LC 1.1 3.25 16 3 1070AS-1R0N-DB3020C 1 1.9 47 2 Sumida CDRH4D18C/LD-1R1 1.1 2.1 24 2 CDRH3D14-1R2 1.2 2.2 36 1.5 CR5D11-1R0 1 2.2 40 1.2 CDRH2D18/HP-2R2 2.2 1.6 48 2 FDK MIPW3226D0R9M 0.9 1.4 70 1 Coilcraft LPO6610-122ML 1.2 2.1 80 1 LPS4018-222ML 2.2 2.5 70 1.8 Vishay IHLP1616ABERR47M01 0.47 5 20 1.2 IHLP1616ABER1R0M01 1 4 45 1.2 3564f 9
