TC2574 Datasheet, PDF (9/25 Pages) TelCom Semiconductor, Inc – 0.5A Step-Down Switching Regulator

0.5A Step-Down Switching Regulator
TC2574
Procedure (Adjustable Output Version): (TC2574-ADJ) (Continued)
Procedure
Example
3. Catch Diode Selection (D1)
A. Since the diode maximum peak current exceeds the
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 TC2574 to be able to with stand a
continuous output short.
B. The reverse voltage rating of the diode should be at least
1.25 times the maximum input voltage.
3. Catch Diode Selection (D1)
A. For this example, a 1.0A current rating is adequate.
B. Use a 50V MBR150 Schottky diode or any suggested
fast recovery diodes in Table 1.
4. Inductor Selection (L1)
A. Use the following formula to calculate the inductor
Volt x microsecond [V x µs] constant:
ExT=(
V_IN
–
V_OUT)
V_OUT
V_IN
x
10⁶
F[Hz]
[V
x
µsec]
B. Match the calculated E x T value with the corresponding
number on the vertical axis of the Inductor Value
Selection Guide shown in Figure 39. 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.
C. Next step is to identify the inductance region intersected
by the E x T value and the maximum load current value
on the horizontal axis shown in Figure 8.
D. From the inductor code, identify the inductor value. Then
select an appropriate inductor from Table 2. The inductor
chosen must be rated for a switching frequency of 52kHz
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:
4. Inductor Selection (L1)
A. Calculate E x T [V xµsec] constant:
E x T = (40
– 24) x
24
40
x
1000
52
= 105[V x µsec]
B. E x T = 185 [V x µsec]
C. I_LOAD(max) = 0.4 A
Inductance Region = 1000
D. Proper inductor value = 1000µH
Choose the inductor from Table 2.
I_{P (max)} = I_{LOAD(max) +}
(V_IN – V_OUT) t_ON
2L
where t_ON is the "on" time of the power switch and
t_ON
=
(V_OUT
V_IN ^x
1.0 )
f_OSC
For additional information about the inductor, see
the inductor section in the “EXTERNAL COMPONENTS”
section of this data sheet.
TC2574-1 1/6/00
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