LM2574-12 Motorola Inc, LM2574-12 Datasheet - Page 12

• Manufacturer Part Number: LM2574-12
• Description: EASY SWITCHERE 0.5 A STEP-DOWN VOLTAGE REGULATOR
• Manufacturer: Motorola Inc

Procedure (Adjustable Output Version: LM2574–ADJ)
12
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 LM2574 is a forward–mode switching regulator with
B. Capacitor values between 10 F and 2000 F will satisfy the
C. Due to the fact that the higher voltage electrolytic capacitors
E x T
microsecond [V x s] constant:
number on the vertical axis of the Inductor Value Selection
Guide shown in Figure 23. 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 27.
select an appropriate inductor from 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 Load . 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.
voltage mode control, its open loop 2–pole–1–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:
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 8.0 V is appropriate, and a 10 V
or 16V rating is recommended.
I
p
+
(
max
C out
(V
in
)
+
w
*
t
V out )
I
13, 300
on
Load
+
Procedure
(
max
V out
V
V
V
V out x L
out
in
in
V
)
in
)
x 10
x 1.0
(
max
F[Hz]
f
V
osc
m
in
6
)
H
*
m
V x
2L
F
V
out
m
s
t
on
LM2574
4. Inductor Selection (L1)
5. Output Capacitor Selection (C out )
A.
B.
C. I Load(max) = 0.4 A
D. Proper inductor value = 1000 H
A.
Calculate E x T V x
Inductance Region = 1000
Choose the inductor from Table 2.
To achieve an acceptable ripple voltage, select
C out = 100 F electrolytic capacitor.
E x T
E x T
C out
+
+
w
(40
185 V x
13, 300 x
MOTOROLA ANALOG IC DEVICE DATA
*
24) x 24
m
s
Example
24 x 1000
m
40
s constant :
40
x 1000
52
+
+
22.2
105 V x
m
F
m
s