lm2575-5 ON Semiconductor, lm2575-5 Datasheet - Page 12

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

Procedure (Adjustable Output Version: LM2575−Adj) (continued)
4. Inductor Selection (L1)
5. Output Capacitor Selection (C
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 mF and 2000 mF will satisfy
C. Due to the fact that the higher voltage electrolytic capacitors
microsecond [V x ms] 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
The inductor current rating can also be determined by
calculating the inductor peak current:
where t
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 + V
I
on
p(max)
C out w 7.785
is the “on” time of the power switch and
in
+
I
t on +
V out
Load(max)
Procedure
V out x L [μH]
V out
V on
V out
V
V
in(max)
in
out
)
x 10
x
)
F[Hz]
V
f osc
in
1
6
V out t on
[μF]
2L
[V x ms]
http://onsemi.com
Ioad
.
12
4. Inductor Selection (L1)
5. Output Capacitor Selection (C
A. Calculate E x T [V x ms] constant:
B. E x T = 51 [V x ms]
C. I
D. Proper inductor value = 220 mH
A.
Inductance Region = L220
Choose the inductor from the Table 1 or Table 2.
To achieve an acceptable ripple voltage, select
C
Load(max)
out
E x T + 12 8.0 x 8.0
= 100 mF electrolytic capacitor.
C out w 7.785
= 1.0 A
8.220
Example
12
12
+ 53 μF
x 1000
out
52
)
+ 51 [V x ms]