SD14-101-R

Inductor Selection for Switching Regulators Introduction/Basic Operation In switching regulator applications the inductor is used as an energy storage device. When the semiconductor switch is on the current in the inductor ramps up and energy is stored. When the switch turns off energy is released into the load. The amount of energy stored is calculated by the formula Energy = ½L.I² (Joules), where: • L is the inductance in Henrys • I is the peak value of inductor current The amount by which the current changes during a switching cycle is known as the ripple current. Ripple current is defined as Vl = L.di/dt: • Vl is the voltage across the inductor • di is the ripple current • dt is the duration for which the voltage is applied I load dI I inductor 0 1 2 ESR V out Figure 1: Buck Inductor Inductor current is made up of AC and DC components (Figure 1). The AC component is high frequency and will flow through the output capacitor because it has a low HF impedance. A ripple voltage is produced due to the capacitor ‘equivalent series resistance’ (ESR) that will appear at the output of the switching regulator. This ripple voltage needs to be sufficiently low as not to effect the operation of the circuit the regulator is supplying, normally in the order of 10-500mVpk-pk. Selecting the correct ripple current impacts the size of the inductor and output capacitor. The capacitor needs to have a sufficiently high ripple current rating or it will overheat and dry out. To achieve a good compromise between inductor and capacitor size a ripple current value of 10-30% of maximum inductor current should be chosen. The current in the inductor will be continuous for output currents greater that 5-15% of full load. The following parameters need to be defined or calculated to select an inductor: • Maximum input voltage • Output voltage • Switching frequency • Maximum ripple current SD3814 • Duty cycle Inductor Selection: Buck Converters Switch Buck Inductor Inductor Selection: Boost Converters Boost Inductor Diode 12V Input Voltage Freewheeling Diode Output Cap 5V Output Voltage 5V Input Voltage Switch Output Cap 12V Output Voltage Figure 2: Buck Inductor Example Figure 3: Boost Inductor Example Figure 2 Application Parameters: • Switching frequency= 250kHz • Input voltage range= 12V±10% • Max ripple current = 220mA • Output Voltage= 5.0V Step 1. Calculate the Duty Cycle • Vo = output voltage • Vi = Max input voltage • D = Vo / Vi • D = 5/13.2 = 0.379 Step 2. Calculate the Voltage Across the Inductance • V1 = Vi-Vo (Switch on) • V1 = 13.2 - 5 = 8.2V • V1 = -Vo (Switch off) • V1 = - Vo = - 5V Step 3. Calculate the Required Inductance • L = Vl.dt/di • L = (8.2 x 0.379/250 x 103)/0.22 • L = 56μH Figure 3 Application Parameters: • Switching frequency= 100kHz • Input voltage range= 4.5-5.5V • Max ripple current = 100mA • Output Voltage= 12.0V Step 1. Calculate the Duty Cycle: • Vo= output voltage • Vi = Max input voltage • D = 1 - (Vi / Vo) • D = 1 – (5.5/12.0) = 0.542 Step 2. Calculating the voltage across the inductance • V1 = Vi (Switch on) • V1 = 5.5V • V1 = Vo – Vi (Switch off) • V1 = 12 – 5.5 = 6.5V Step 3. Calculating the required inductance • L = Vl.dt/di • L= (5.5 x 0.542/100 x 103)/0.1 • L= 298μH Typical Applications Using Inductors for Switching Regulators Industrial Test Equipment Media Players Digital Cameras Laptop Computers Backlight Displays Mobile Phones SDH3812 Part Number Rated OCL Part SDH3812-1R0-R SDH3812-1R5-R SDH3812-2R2-R SDH3812-3R3-R SDH3812-4R7-R SDH3812-100-R SDH3812-220-R SDH3812-330-R SDH3812-470-R SDH3812-101-R SDH3812-221-R Inductance μH ± 20% Marking (μH) Designator 1.0 0.89 B 1.5 1.49 D 2.2 2.23 E 3.3 3.17 F 4.7 4.96 G 10.0 9.67 J 22.0 22.00 L 33.0 32.90 M 47.0 46.20 N 100.0 97.50 Q 220.0 218.50 S Irms Amps 2.07 1.67 1.37 1.14 0.94 0.69 0.50 0.41 0.34 0.25 0.16 Isat Amps 3.00 2.30 1.90 1.60 1.25 0.88 0.61 0.49 0.41 0.28 0.19 DCR DCR Ω@20°C Ω@20°C (Typical) (Maximum) 0.045 0.054 0.069 0.083 0.104 0.124 0.148 0.177 0.220 0.264 0.398 0.478 0.750 0.900 1.132 1.358 1.583 1.900 3.042 3.650 7.017 8.420 SDH3812 Note: For full product information and a listing of all available inductor values, see http://www.cooperbussmann.com/datasheets/elx, Data Sheet number SDH3812 Series. SDH3812 Dimensions - mm Top View Marking Pin #1 indicator 1.25 Typ. 2.5 2 plcs 5.0 2.03 +/-0.1 Side View 1.2 Max. Bottom View 4.8 Max. 3.65 Typ. Recommended Pad Layout 1.0 2 plcs Schematic 3.8 +.02/-0.1 3.8 +.02/-0.1 0.415 Min. 0.90 Max. no plating SD3814 Part Number Rated OCL Part SD3814-1R2-R SD3814-1R5-R SD3814-2R2-R SD3814-3R3-R SD3814-4R7-R SD3814-100-R SD3814-220-R SD3814-330-R SD3814-470-R Inductance μH ± 15% Marking (μH) Designator 1.2 1.001 C 1.5 1.286 D 2.2 1.962 E 3.3 2.781 F 4.7 4.276 G 10.0 9.830 J 22.0 21.186 L 33.0 32.151 M 47.0 47.210 N Irms Amps 1.85 1.76 1.43 1.31 1.06 0.713 0.519 0.418 0.346 Isat Amps 2.67 2.35 1.90 1.60 1.29 0.851 0.580 0.471 0.388 DCR Ω Typical 0.046 0.051 0.077 0.093 0.141 0.311 0.589 0.908 1.322 SD3814 Note: For full product information and a listing of all available inductor values, see http://www.cooperbussmann.com/datasheets/elx, Data Sheet number SD38 Series. SD3814 Dimensions - mm Top View Pin #1 indicator Marking (see note A) Side View Bottom View 4.8 Max 3.65 Typ 0.09 Max no plating Recommended Pad Layout 1.0 2 plcs Schematic 1.4 Max 2.5 2 plcs 1.25 ±0.12 4.0 typ 5.0 2.03 ±.02 4.0 Max 4.0 Max 0.415 Min SD14 & SD25 Part Number Rated Inductance (μH) 1.2 1.5 3.2 6.9 10 22 33 47 100 220 330 470 1000 1.20 1.50 2.20 3.30 4.70 10.0 22.0 33.0 47.0 100 150 220 330 470 OCL ± 20% μH 1.23 1.63 3.19 6.98 9.93 21.93 32.55 47.57 99.25 222 335.1 471.4 1008 1.15 1.61 2.14 3.43 5.03 10.35 22.81 33.07 47.89 100.79 148.4 222.4 332.2 472.4 Part Marking C D G J L N O P S U V W Z C D E F G K M N O R S T U V Irms Amps 2.7 2.53 1.94 1.35 1.1 0.806 0.654 0.525 0.386 0.258 0.206 0.173 0.126 3.33 3.12 2.93 2.64 2.39 1.80 1.34 1.11 0.919 0.670 0.553 0.446 0.359 0.293 Isat Amps 3.35 2.91 2.08 1.41 1.18 0.793 0.651 0.538 0.373 0.249 0.203 0.171 0.117 3.81 3.23 2.80 2.21 1.83 1.27 0.857 0.711 0.592 0.398 0.328 0.268 0.219 0.184 DCR Ω Typical 0.0344 0.0390 0.0663 0.1363 0.2058 0.3853 0.5852 0.9055 1.68 3.77 5.92 8.34 15.8 0.0240 0.0274 0.0311 0.0384 0.0467 0.0824 0.1478 0.2149 0.3156 0.5937 0.8723 1.34 2.07 3.10 SD14-1R2-R SD14-1R5-R SD14-3R2-R SD14-6R9-R SD14-100-R SD14-220-R SD14-330-R SD14-470-R SD14-101-R SD14-221-R SD14-331-R SD14-471-R SD14-102-R SD25-1R2-R SD25-1R5-R SD25-2R2-R SD25-3R3-R SD25-4R7-R SD25-100-R SD25-220-R SD25-330-R SD25-470-R SD25-101-R SD25-151-R SD25-221-R SD25-331-R SD25-471-R SD Inductor Series Typical SD Series Applications • Mobile phones • Digital cameras • Industrial test equipment • Computers • Uninterruptible power supplies • Televisions Typical SD Series Uses • Buck and boost converters • LED Drivers • EL panel drivers • Backlighting • Noise filtering chokes Note: SD10, 12, 18 and 20 not shown. For full product information and a listing of all available inductor values, see http://www.cooperbussmann.com/datasheets/elx, Data sheet number SD Series SD14 & SD25 Dimensions - mm Top View Pin # 1 identifier Side View Bottom View Recommended Pad Layout 2 Pad Layout 4 Pad Layout 1 Schematic 1 5.2 Max a 1 1.5 Typ. Ref. 5.95 9 1.0 2 2.975 2 2.575 5.15 2.975 2 2.975 5.950 5.950 9 2 R2.250 R2.250 Part marking (Note A) 2 5.2 Max HT SD14 = 1.45mm Max SD25 = 2.5mm Max 2 The Cooper Bussmann Coiltronics® brand of magnetics specializes in standard and custom solutions, offering the latest in state-of-the-art low-profile high power density magnetic components. We remain at the forefront of innovation and new technology to deliver the optimal mix of packaging, high efficiency and unbeatable reliability. Our designs utilize high frequency, low core loss materials, and new and custom core shapes in combination with innovative construction and packaging to provide designers with the highest performance parts available on the market. The Coiltronics Brand product line of power magnetics continually expands to satisfy shifts in technology and related market needs. Standard Product Categories include: • Shielded Drum Inductors • Toroidal Inductors • Unshielded Drum Inductors • Specialty Magnetics • High Current Inductors • Custom Magnetics Please visit http://www.cooperbussmann.com/datasheets/elx to see data sheets on the wide variety of inductor solutions we have to offer. For techncial inquiries e-mail InductorTech@cooperindustries.com. Order samples online - www.cooperbussmann.com © 2008 Cooper B u ssmann S t. Lo u is, MO 63178 636-394-2877 www.cooperb u ssmann.com Reorder # 4031 1008 PDF Only