ncp1536 ON Semiconductor, ncp1536 Datasheet - Page 8

• Manufacturer Part Number: ncp1536
• Description: 3.0 A, Step-down Switching Regulator
• Manufacturer: ON Semiconductor

Procedure (continued) In order to simplify the switching regulator design, a step−by−step design procedure and some
examples are provided.
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 NCP1536 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 9. 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 12.
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
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−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:
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 8.0 V is appropriate, and a 10 V
or 16 V rating is recommended.
E x T + V
I
on
p(max)
C out w 13, 300
is the “on” time of the power switch and
in
+
– V out
I
t on +
Load(max)
Procedure
V out x L [μH]
V out
V out
V
V
V
in
in
in(max)
out
)
x 10
x 1.0
)
V
f osc
F[Hz]
in
– V out t on
6
2L
[μF]
[V x ms]
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Load
NCP1536
.
8
4. Inductor Selection (L1)
5. Output Capacitor Selection (C
A. Calculate E x T [V x ms] constant:
B. E x T = 80 [V x ms]
C. I
D. Proper inductor value = 150 mH
A.
Inductance Region = H150
Choose the inductor from Table 2.
To achieve an acceptable ripple voltage, select
C
Load(max)
out
E x T + ( 25 – 8.0 ) x 8.0
= 680 mF electrolytic capacitor.
C out w 13, 300 x
= 2.5 A
Example
8 x 150
25
25
x 1000
out
52
)
+ 332.5 μF
+ 80 [V x ms]