lm2575-5 ON Semiconductor, lm2575-5 Datasheet - Page 10

• Manufacturer Part Number: lm2575-5
• Description: 1.0 A, Adjustable Output Voltage, Step-down Switching Regulator
• Manufacturer: ON Semiconductor

Procedure (Fixed Output Voltage Version)
procedure and example is provided.
Given Parameters:
1. Controller IC Selection
2. Input Capacitor Selection (C
4. Inductor Selection (L1)
3. Catch Diode Selection (D1)
V
V
I
According to the required input voltage, output voltage and
current, select the appropriate type of the controller IC output
voltage version.
To prevent large voltage transients from appearing at the input
and for stable operation of the converter, an aluminium or
tantalum electrolytic bypass capacitor is needed between the
input pin +V
located close to the IC using short leads. This capacitor should
have a low ESR (Equivalent Series Resistance) value.
A. According to the required working conditions, select the
B. From the appropriate inductor selection guide, identify the
C. Select an appropriate inductor from the several different
Load(max)
A. Since the diode maximum peak current exceeds the
B. The reverse voltage rating of the diode should be at least
out
in(max)
correct inductor value using the selection guide from
Figures 17 to 21.
inductance region intersected by the Maximum Input
Voltage line and the Maximum Load Current line. Each
region is identified by an inductance value and an inductor
code.
manufacturers part numbers listed in Table 1 or Table 2.
When using Table 2 for selecting the right inductor the
designer must realize that the inductor current rating must
be higher than the maximum peak current flowing through
the inductor. This maximum peak current can be calculated
as follows:
where t
For additional information about the inductor, see the
inductor section in the “External Components” section of
this data sheet.
regulator maximum load current the catch diode current
rating must be at least 1.2 times greater than the maximum
load current. For a robust design the diode should have a
current rating equal to the maximum current limit of the
LM2575 to be able to withstand a continuous output short
1.25 times the maximum input voltage.
= Regulated Output Voltage (3.3 V, 5.0 V, 12 V or 15 V)
= Maximum DC Input Voltage
= Maximum Load Current
I
on
p(max)
in
is the “on” time of the power switch and
and ground pin GND. This capacitor should be
+
I
t on
Load(max)
Procedure
+
V out
V
in
in
)
)
x
f osc
V
1
in
V out t on
2L
In order to simplify the switching regulator design, a step−by−step design
http://onsemi.com
10
Given Parameters:
1. Controller IC Selection
2. Input Capacitor Selection (C
3. Catch Diode Selection (D1)
4. Inductor Selection (L1)
V
V
I
According to the required input voltage, output voltage,
current polarity and current value, use the LM2575−5
controller IC
A 47 mF, 25 V aluminium electrolytic capacitor located near
to the input and ground pins provides sufficient bypassing.
A. For this example the current rating of the diode is 1.0 A.
B. Use a 30 V 1N5818 Schottky diode, or any of the
A. Use the inductor selection guide shown in Figures 17
B. From the selection guide, the inductance area intersected
by the 20 V line and 0.8 A line is L330.
C. Inductor value required is 330 mH. From the Table 1 or
Load(max)
out
in(max)
suggested fast recovery diodes shown in the Table 4.
to 21.
Table 2, choose an inductor from any of the listed
manufacturers.
= 5.0 V
= 20 V
= 0.8 A
Example
in
)