LM2574HVN15

Manufacturer Part NumberLM2574HVN15
DescriptionDIP8
ManufacturerNational Semiconductor
LM2574HVN15 datasheet
 


Specifications of LM2574HVN15

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LM2574 Series Buck Regulator Design Procedure
Application Hints
INPUT CAPACITOR (C
)
IN
To maintain stability, the regulator input pin must be by-
passed with at least a 22 µF electrolytic capacitor. The ca-
pacitor’s leads must be kept short, and located near the
regulator.
If the operating temperature range includes temperatures
below −25˚C, the input capacitor value may need to be
larger. With most electrolytic capacitors, the capacitance
value decreases and the ESR increases with lower tempera-
tures and age. Paralleling a ceramic or solid tantalum ca-
pacitor will increase the regulator stability at cold tempera-
tures. For maximum capacitor operating lifetime, the
capacitor’s RMS ripple current rating should be greater than
www.national.com
V
1 Amp Diodes
R
Schottky
Fast Recovery
20V
1N5817
SR102
MBR120P
30V
1N5818
SR103
11DQ03
The
MBR130P
following
10JQ030
diodes
40V
1N5819
are all
SR104
rated to
11DQ04
100V
11JQ04
MBR140P
50V
MBR150
11DF1
SR105
10JF1
11DQ05
MUR110
11JQ05
HER102
60V
MBR160
SR106
11DQ06
11JQ06
90V
11DQ09
FIGURE 9. Diode Selection Guide
INDUCTOR SELECTION
All switching regulators have two basic modes of operation:
continuous and discontinuous. The difference between the
two types relates to the inductor current, whether it is flowing
continuously, or if it drops to zero for a period of time in the
normal switching cycle. Each mode has distinctively different
operating characteristics, which can affect the regulator per-
formance and requirements.
The LM2574 (or any of the Simple Switcher family) can be
used for both continuous and discontinuous modes of opera-
tion.
In many cases the preferred mode of operation is in the con-
tinuous mode. It offers better load regulation, lower peak
switch, inductor and diode currents, and can have lower out-
put ripple voltage. But it does require relatively large inductor
values to keep the inductor current flowing continuously, es-
pecially at low output load currents.
To simplify the inductor selection process, an inductor selec-
tion guide (nomograph) was designed (see Figure 4 through
Figure 8 ). This guide assumes continuous mode operation,
and selects an inductor that will allow a peak-to-peak induc-
tor ripple current ( I
maximum design load current. In the LM2574 SIMPLE
SWITCHER, the peak-to-peak inductor ripple current per-
centage (of load current) is allowed to change as different
design load currents are selected. By allowing the percent-
age of inductor ripple current to increase for lower current
applications, the inductor size and value can be kept rela-
tively low.
16
(Continued)
) to be a certain percentage of the
IND