Datasheet

DocID5257 Rev 11 13/23
MC34063AB, MC34063AC, MC34063EB, MC34063EC Typical application circuit
Note: 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 + R
2
/R
1
)
I
OUT
= Desired output current
f
MIN
= Minimum desired output switching frequency at the selected values of V
IN
and I
O
V
RIPPLE
= Desired peak to peak output ripple voltage. In practice, the calculated capacitor
value will and 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.
Table 12. Calculation
Parameter
Step-Up
(Discontinuous mode)
Step-Down
(Continuous mode)
Voltage Inverting
(Discontinuous mode)
t
on
/t
off
(t
on
+ t
off
) max 1/f
min
1/f
min
1/f
min
C
T
4.5x10
-5
t
on
4.5x10
-5
t
on
4.5x10
-5
t
on
I
PK(switch)
2I
out(max)
[(t
on
/t
off
)+1] 2I
out(max)
2I
out(max)
[(t
on
/t
off
)+1]
R
SC
0.3/I
PK(switch)
0.3/I
PK(switch)
0.3/I
PK(switch)
C
O
L
(min)
V
OUT
V
F
V
IN min
–+
V
IN min
V
sat
–
-------------------------------------------------------
V
OUT
V
F
+
V
IN min
V
sat
– V
OUT
–
-----------------------------------------------------------
V
OUT
V
F
+
V
IN
V
sat
–
------------------------------ -
I
out
t
on
V
ripple p p–
-------------------------------
I
PK switch
t
on
t
off
+
8V
ripple p p–
----------------------------------------------------- -
I
out
t
on
V
ripple p p–
-------------------------------
V
IN min
V
sat
–
I
PK switch
-------------------------------------- t
on min

V
IN min
V
sat
– V
out
–
I
PK switch
------------------------------------------------------ - t
on min

V
IN min
V
sat
–
I
PK switch
-------------------------------------- t
on min
