MC33463

11

MOTOROLA ANALOG IC DEVICE DATA

Figure 20. Design Equations

Calculation

Step–Down

Step–Up

Flyback

ton

D

D

D

L

t ton

(V

in *

Vsat * VO)

(2I

O

)

t

(n)(V

in

)2(ton)

P

O

t

(n)(V

in

)2(ton)

P

O

IL(avg)

IO

Iin

Iin

IL(pk)

(V

in *

Vsat * VO)(ton)

L

(V

in *

Vsat)(ton)

L

(V

in *

Vsat)(ton)

L

Vripple(pp)

DI

L

1

16foscCO

2

) (ESR)

2

1

2

[

(ton)(IO)

(C

O

)

[

(ton)(IO)

(C

O

)

The following converter design characteristics must be chosen:

Vin – Nominal Operating dc input voltage

VO – Desired dc output voltage

IO – Desired dc output current

Vripple(pp) – Desired peak–to–peak output ripple voltage. For best performance the ripple voltage should be kept to a low value since it will directly

affect line and load regulation. Capacitor CO should be a low equivalent series resistance (ESR) electrolytic designed for switching regulator

applications.

NOTE: 1.

Vsat – Saturation voltage of the switching transistor.

n – Estimated circuit efficiency.