MC34063A MC33063A

9

MOTOROLA ANALOG IC DEVICE DATA

Figure 14. Design Formula Table

Calculation

Step–Up

Step–Down

Voltage–Inverting

ton/toff

Vout ) VF * Vin(min)

V

in(min) *

Vsat

Vout ) VF

V

in(min) *

Vsat * Vout

|Vout| ) VF

V

in *

Vsat

(ton + toff)

1

f

1

f

1

f

toff

ton ) toff

ton

t

off

) 1

ton ) toff

ton

t

off

) 1

ton ) toff

ton

t

off

) 1

ton

(ton + toff) – toff

(ton + toff) – toff

(ton + toff) – toff

CT

4.0 x 10–5 ton

4.0 x 10–5 ton

4.0 x 10–5 ton

Ipk(switch)

2I

out(max)

ton

t

off

) 1

2I

out(max)

2I

out(max)

ton

t

off

) 1

Rsc

0.3/Ipk(switch)

0.3/Ipk(switch)

0.3/Ipk(switch)

L(min)

(V

in(min) *

Vsat)

I

pk(switch)

t

on(max)

(V

in(min) *

Vsat * Vout)

I

pk(switch)

t

on(max)

(V

in(min) *

Vsat)

I

pk(switch)

t

on(max)

CO

9

Ioutton

V

ripple(pp)

I

pk(switch)

(ton ) toff)

8V

ripple(pp)

9

Ioutton

V

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.

Vout – Desired output voltage,

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

NOTE:

For further information refer to Application Note AN920A/D and AN954/D.

|Vout| + 1.25 1 )

R2

R1