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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 = 1/2L.I (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= 12V10% * 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 = 56H
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= 298H
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 H 20% Marking (H) 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
@20C @20C (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 H 15% Marking (H) 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 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 (H) 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% H 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 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(R) 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
(c) 2008 Cooper Bussmann St. Louis, MO 63178 636-394-2877 www.cooperbussmann.com
Reorder # 4031 1008
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