LM2575-15 MOTOROLA [Motorola, Inc], LM2575-15 Datasheet - Page 11

• Manufacturer Part Number: LM2575-15
• Manufacturer: MOTOROLA [Motorola, Inc]

Procedure (Adjustable Output Version: LM2575–Adj) (continued)
MOTOROLA ANALOG IC DEVICE DATA
4. Inductor Selection (L1)
5. Output Capacitor Selection (C out )
A. Use the following formula to calculate the inductor Volt x
B. Match the calculated E x T value with the corresponding
C. Next step is to identify the inductance region intersected by
D. From the inductor code, identify the inductor value. Then
A. Since the LM2575 is a forward–mode switching regulator
B. Capacitor values between 10 F and 2000 F will satisfy
C. Due to the fact that the higher voltage electrolytic capacitors
microsecond [V x s] constant:
number on the vertical axis of the Inductor Value Selection
Guide shown in Figure 21. This E x T constant is a measure
of the energy handling capability of an inductor and is
dependent upon the type of core, the core area, the number
of turns, and the duty cycle.
the E x T value and the maximum load current value on the
horizontal axis shown in Figure 21.
select an appropriate inductor from the Table 1 or Table 2.
The inductor chosen must be rated for a switching
frequency of 52 kHz and for a current rating of 1.15 x I Ioad .
The inductor current rating can also be determined by
calculating the inductor peak current :
where t on is the “on” time of the power switch and
For additional information about the inductor, see the
inductor section in the “External Components” section of
this data sheet.
with voltage mode control, its open loop 2–pole–2–zero
frequency characteristic has the dominant pole–pair
determined by the output capacitor and inductor values.
For stable operation, the capacitor must satisfy the
following requirement:
the loop requirements for stable operation. To achieve an
acceptable output ripple voltage and transient response, the
output capacitor may need to be several times larger than
the above formula yields.
generally have lower ESR (Equivalent Series Resistance)
numbers, the output capacitor’s voltage rating should be at
least 1.5 times greater than the output voltage. For a 5.0 V
regulator, a rating of at least 8V is appropriate, and a 10 V
or 16 V rating is recommended.
E x T
I
p(max)
C out
+
V
w
+
in
7.785
I
– V out
t on
Load(max)
Procedure
+
V out x L [ H]
V out
V
V
V out
V on
in
in(max)
)
x
V
x 10
f osc
in
1
F[Hz]
– V out t on
6
2L
[ F]
[V x
m
s]
LM2575
4. Inductor Selection (L1)
5. Output Capacitor Selection (C out )
A. Calculate E x T [V x s] constant:
B. E x T = 51 [V x s]
C. I Load(max) = 1.0 A
D. Proper inductor value = 220 H
A.
Inductance Region = L220
Choose the inductor from the Table 1 or Table 2.
To achieve an acceptable ripple voltage, select
C out = 100 F electrolytic capacitor.
E x T
C out
+
w
(12 – 8.0) x 8.0
7.785
8.220
12
Example
12
+
53 F
x 1000
52
+
51 [V x
m
s]
11