LM2675 Series Buck Regulator Design Procedure (Adjustable Output)
(Continued)
PROCEDURE (Adjustable Output Voltage Version)
2. Inductor Selection (L1)
EXAMPLE (Adjustable Output Voltage Version)
2. Inductor Selection (L1)
A. Calculate the inductor Volt • microsecond constant E • T (V • A. Calculate the inductor Volt • microsecond constant (E • T),
µs), from the following formula:
where VSAT = internal switch saturation voltage = 0.25V and VD
= diode forward voltage drop = 0.5V
B. Use the E • T value from the previous formula and match it
with the E • T number on the vertical axis of the Inductor Value
Selection Guide shown in Figure 7.
B. E • T = 21.6 (V • µs)
C. ILOAD(max) = 1A
C. On the horizontal axis, select the maximum load current.
D. Identify the inductance region intersected by the E • T value D. From the inductor value selection guide shown in Figure 7,
and the Maximum Load Current value. Each region is identified the inductance region intersected by the 21.6 (V • µs) horizontal
by an inductance value and an inductor code (LXX).
line and the 1A vertical line is 68 µH, and the inductor code is
L30.
E. Select an appropriate inductor from the four manufacturer’s
E. From the table in Figure 8, locate line L30, and select an
part numbers listed in Figure 8. For information on the different inductor part number from the list of manufacturers part
types of inductors, see the inductor selection in the fixed output numbers.
voltage design procedure.
3. Output Capacitor Selection (COUT
A. Select an output capacitor from the capacitor code selection A. Use the appropriate row of the capacitor code selection
guide in Figure 16. Using the inductance value found in the guide, in Figure 16. For this example, use the 15–20V row. The
)
3. Output Capacitor SeIection (COUT)
inductor selection guide, step 1, locate the appropriate capacitor capacitor code corresponding to an inductance of 68 µH is C20.
code corresponding to the desired output voltage.
B. Select an appropriate capacitor value and voltage rating,
B. From the output capacitor selection table in Figure 17,
using the capacitor code, from the output capacitor selection
choose a capacitor value (and voltage rating) that intersects the
table in Figure 17. There are two solid tantalum (surface mount) capacitor code(s) selected in section A, C20.
capacitor manufacturers and four electrolytic (through hole)
The capacitance and voltage rating values corresponding to the
capacitor manufacturers to choose from. It is recommended that capacitor code C20 are the:
both the manufacturers and the manufacturer’s series that are
listed in the table be used. A table listing the manufacturers’
phone numbers is located in Figure 11.
Surface Mount:
33 µF/25V Sprague 594D Series.
33 µF/25V AVX TPS Series.
Through Hole:
33 µF/25V Sanyo OS-CON SC Series.
120 µF/35V Sanyo MV-GX Series.
120 µF/35V Nichicon PL Series.
120 µF/35V Panasonic HFQ Series.
Other manufacturers or other types of capacitors may also be
used, provided the capacitor specifications (especially the 100
kHz ESR) closely match the characteristics of the capacitors
listed in the output capacitor table. Refer to the capacitor
manufacturers’ data sheet for this information.
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