MC34063A, MC33063A, NCV33063A
Calculation
t
on
/t
off
Step−Up
V out
)
V F
*
V in(min)
V in(min)
*
V sat
1
f
t on
)
t
off
t on
)
1
t
off
t
on
C
T
I
pk(switch)
2I
R
sc
L
(min)
out(max)
(t
on
+ t
off
) − t
off
4.0 x 10
−5
t
on
t on
)
1
t
off
Step−Down
V out
)
V F
V
*
V sat
*
V out
in(min)
1
f
t on
)
t
off
t on
)
1
t
off
(t
on
+ t
off
) − t
off
4.0 x 10
−5
t
on
2I out(max)
0.3/I
pk(switch)
t
(V in(min)
*
V sat
*
V out)
I
pk(switch)
t
2I
Voltage−Inverting
|V out|
)
V F
V
*
V sat
in
1
f
t on
)
t
off
t on
)
1
t
off
(t
on
+ t
off
)
t
off
(t
on
+ t
off
) − t
off
4.0 x 10
−5
t
on
t on
)
1
t
off
out(max)
0.3/I
pk(switch)
(V in(min)
*
V sat)
I
pk(switch)
9
I outt on
V ripple(pp)
0.3/I
pk(switch)
(V in(min)
*
V sat)
I
pk(switch)
9
I outt on
V ripple(pp)
t
on(max)
on(max)
on(max)
C
O
I pk(switch)(t on
)
t off)
8V
ripple(pp)
V
sat
= Saturation voltage of the output switch.
V
F
= Forward voltage drop of the output rectifier.
The following power supply characteristics must be chosen:
V
in
− Nominal input voltage.
V
out
− Desired output voltage, |V
out
|
+
1.25 1
)
R2
R1
I
out
− Desired output current.
f
min
− Minimum desired output switching frequency at the selected values of V
in
and I
O
.
V
ripple(pp)
− Desired peak−to−peak output ripple voltage. In practice, the calculated capacitor value will need to be increased due to its
equivalent series resistance and board layout. The ripple voltage should be kept to a low value since it will directly affect the
line and load regulation.
NOTE:
For further information refer to Application Note AN920A/D and AN954/D.
Figure 15. Design Formula Table
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