MC34063A MC33063A
Figure 14. Design Formula Table
Calculation
ton/toff
V out
)
VF
*
Vin(min)
V
*
Vsat
in(min)
t on
Step–Up
)
VF
V
*
Vsat
*
Vout
in(min)
V out
t on
Step–Down
Voltage–Inverting
|V out|
)
VF
V
*
V sat
in
t on
(ton + toff)
toff
)
toff
ton
)
1
t
off
1
f
)
toff
ton
)
1
t
off
1
f
)
toff
ton
)
1
t
off
1
f
ton
CT
Ipk(switch)
2I
Rsc
L(min)
(V
(ton + toff) – toff
4.0 x 10–5 ton
out(max)
t on
t
off
(ton + toff) – toff
4.0 x 10–5 ton
2I
out(max)
2I
(ton + toff) – toff
4.0 x 10–5 ton
out(max)
t on
t
off
)
1
(V
t
on(max)
)
1
t
0.3/Ipk(switch)
V sat)
in(min)
I
pk(switch)
9
I outt on
V
ripple(pp)
*
V sat
in(min)
I
pk(switch)
I
*
0.3/Ipk(switch)
*
Vout)
)
0.3/Ipk(switch)
(V
t
on(max)
V sat)
in(min)
I
pk(switch)
9
I outt on
V
ripple(pp)
*
on(max)
CO
(t
t )
pk(switch) on
off
8V
ripple(pp)
Vsat = Saturation voltage of the output switch.
VF = Forward voltage drop of the output rectifier.
The following power supply characteristics must be chosen:
Vin – Nominal input voltage.
R2
1.25 1
Vout – Desired output voltage, |V out|
R1
Iout – Desired output current.
fmin – Minimum desired output switching frequency at the selected values of Vin and IO.
Vripple(pp) – Desired peak–to–peak output ripple voltage. In practice, the calculated capacitor value will need to be increased due to its equivalent series
Vripple(pp) –
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.
+
)
MOTOROLA ANALOG IC DEVICE DATA
9
ONSEMI [ ON SEMICONDUCTOR ]
