0.5A Step-Down Switching Regulator
TC2574
Procedure (Adjustable Output Version: TC2574-ADJ) (Continued)
Procedure
5. Output Capacitor Selection (C
OUT
)
A.
Since the TC2574 is a forward–mode switching regulator
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:
V
C
OUT
≥
13,000
IN(max)
[µF]
V
OUT
x L[µF]
B.
Capacitor values between 10µF and 2000µF will satisfy
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.
C.
Due to the fact that the higher voltage electrolytic capaci-
tors 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 5.0V regulator, a rating of at least 8.0V is
appropriate, and a 10V or 16V rating is recommended.
Example
5. Output Capacitor Selection (C
OUT
)
A.
40
C
OUT
≥
13,300 x
22.2µF
24 x 1000
To achieve an acceptable ripple voltage, select C
OUT
100µF electrolytic capacitor.
Table 1. Diode Selection Guide gives an overview about through-hole diodes for an effective design.
1.0 Amp Diodes
VR
20V
30V
40V
50V
60V
Schottky
1N5817
MBR120P
1N5818
MBR130P
1N5819
MBR140P
MBR150
MBR160
Fast Recovery
MUR110
(rated to 100V)
TC2574-1 1/6/00
10
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