MC34063AC datasheet(9/15 Pages) STMICROELECTRONICS

9 / 15 page

Calculation

Parameter

Step-Up

(Discontinuos mode)

Step-Down

(Continuos mode)

Voltage Inverting

(Discontinuos mode)

ton/toff

Vout

+ VF − Vin(min)

Vin(min) − Vsat

Vout

+ VF

Vin(min) − Vsat− Vout

Vout|

+ VF

Vin

− Vsat

(ton + toff)max

1/fmin

4.5x10

-5ton

4.5x10

-5 ton

4.5x10

-5ton

IPK(switch)

2Iout(max)[(ton/toff)+1]

2Iout(max)

2Iout(max)[(ton/toff)+1]

RSC

0.3/IPK(switch)

≅

Iout ton

Vripple (p−p)

IPK (switch) (ton + toff )

8Vripple (p−p)

≅

Iout ton

Vripple (p−p)

L(min)

Vin(min) − Vsat

IPK (switch)

ton (max)

Vin(min) − Vsat − Vout

IPK (switch)

ton (max)

Vin(min) − Vsat

IPK (switch)

ton (max)

NOTES:

Vsat = Saturation voltage of the output switch

VF = Foward voltage drop of the output rectifier

THE FOLLOWING POWER SUPPLY CHARACTERISTICS MUST BE CHOSEN:

Vin = Nominal input voltage

Vout = Desired output voltage, |Vout| = 1.25(1+R2/R1)

Iout = Desired output current

fmin = Minimum desired output switching frequency at the selected values of Vin and Io

Vripple = 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

MC34063A/E

9/15

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