MC34063A
Calculation
Parameter
t
on
/t
off
(t
on
+ t
off
)max
C
T
I
PK(switch)
R
SC
C
O
L(min)
Step-Up
(Discontinuos mode)
V
out
+
V
F
−
V
in(min)
V
i n(min)
−
V
sa t
1/f
min
4.5x10
- 5
t
on
2I
ou t(max)
[(t
o n
/t
off
)+1]
0.3/I
PK(switc h)
≅
I
out
t
on
V
ri pple
(
p−p)
Step-Down
(Continuos mode)
V
out
+
V
F
V
i n(min)
−
V
sat
−
V
out
1/f
min
4.5x10
-5
t
on
2I
out( max)
0.3/I
PK(switc h)
I
PK
(
s witc h)
(t
on
+
t
off
)
8V
ri pple
(
p−
p
)
V
in(min)
−
V
sa t
−
V
o ut
t
on
(max)
I
PK
(swit
ch)
Voltage Inverting
(Discontinuos mode)
|
V
o ut
|
+
V
F
V
in
−
V
s at
1/f
mi n
4.5x10
-5
t
o n
2I
out(max)
[(t
on
/t
off
)+1]
0.3/I
PK(switch )
≅
I
out
t
o n
V
ripp le
(
p−p
)
V
in(mi n
)
−
V
s at
t
o n
(max)
I
PK
(swit
ch)
V
in(mi n)
−
V
sat
t
on
(ma
x)
I
PK
(s
wi tch)
NOTES:
V
sat
= Saturation voltage of the output switch
V
F
= Foward 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 Vin and Io
V
ripple
= Desired peak to peak output ripple voltage. In practice, the calculaed 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.
Step-up With External NPN Switch
9/15
STMICROELECTRONICS [ STMICROELECTRONICS ]
