Datasheet

LM2598
SNVS125C MARCH 1998REVISED APRIL 2013
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Figure 24. Standard Test Circuits and Layout Guides
As in any switching regulator, layout is very important. Rapidly switching currents associated with wiring
inductance can generate voltage transients which can cause problems. For minimal inductance and ground
loops, the wires indicated by heavy lines should be wide printed circuit traces and should be kept as short
as possible. For best results, external components should be located as close to the switcher lC as possible
using ground plane construction or single point grounding.
If open core inductors are used, special care must be taken as to the location and positioning of this type of
inductor. Allowing the inductor flux to intersect sensitive feedback, lC groundpath and C
OUT
wiring can cause
problems.
When using the adjustable version, special care must be taken as to the location of the feedback resistors and
the associated wiring. Physically locate both resistors near the IC, and route the wiring away from the inductor,
especially an open core type of inductor. (See Application Information section for more information.)
Table 1. LM2598 Series Buck Regulator Design Procedure (Fixed Output)
PROCEDURE (Fixed Output Voltage Version) EXAMPLE (Fixed Output Voltage Version)
Given:
Given:
V
OUT
= 5V
V
OUT
= Regulated Output Voltage (3.3V, 5V or 12V)
V
IN
(max) = 12V
V
IN
(max) = Maximum DC Input Voltage
I
LOAD
(max) = Maximum Load Current I
LOAD
(max) = 1A
1. Inductor Selection (L1) 1. Inductor Selection (L1)
A. Select the correct inductor value selection guide from Figures A. Use the inductor selection guide for the 5V version shown in
Figure 25, Figure 26, or Figure 27 (Output voltages of 3.3V, 5V, or Figure 26.
12V respectively.) For all other voltages, see the Design Procedure
for the adjustable version.
B. From the inductor value selection guide, identify the inductance B. From the inductor value selection guide shown in Figure 26, the
region intersected by the Maximum Input Voltage line and the inductance region intersected by the 12V horizontal line and the 1A
Maximum Load Current line. Each region is identified by an vertical line is 68 μH, and the inductor code is L30.
inductance value and an inductor code (LXX).
C. Select an appropriate inductor from the four manufacturer's part C. The inductance value required is 68 μH. From the table in
numbers listed in Table 5. Table 5, go to the L30 line and choose an inductor part number from
any of the four manufacturers shown. (In most instance, both
through hole and surface mount inductors are available.)
2. Output Capacitor Selection (C
OUT
) 2. Output Capacitor Selection (C
OUT
)
A. In the majority of applications, low ESR (Equivalent Series A. See section on output capacitors in Application Information
Resistance) electrolytic capacitors between 47 μF and 330 μF and section.
low ESR solid tantalum capacitors between 56 μF and 270 μF
provide the best results. This capacitor should be located close to
the IC using short capacitor leads and short copper traces. Do not
use capacitors larger than 330 μF.
For additional information, see section on output capacitors in
Application Information section.
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