063EC datasheet(13/23 Pages) STMICROELECTRONICS

13 / 23 page

MC34063AB - MC34063AC - MC34063EB - MC34063EC

Typical application circuit

13/23

Note:

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, |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 calculated 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.

Table 12.

Calculation

Parameter

Step-Up

(Discontinuous mode)

Step-Down

(Continuous mode)

Voltage Inverting

(Discontinuous mode)

ton/toff

(ton + toff) max

1/fmin

4.5x10-5ton

IPK(switch)

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

2Iout(max)

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

RSC

0.3/IPK(switch)

L(min)

OUT

IN mi

(

–

IN min

() Vsat

–

------------------------------------------------

OUT

Nmin

() Vsat

–

---------------------------------------------------

OUT

sat

–

-------------------------------

outton

ripple p

–

()

-------------------------------

PK switch

() ton

off

()

ripple p

–

()

------------------------------------------------------

outton

ripple p

–

()

-------------------------------

IN min

() Vsat

–

PK switch

()

-----------------------------------

on mi

(

N min

() Vsat

–

out

–

PK switch

()

-------------------------------------------------

(

IN min

() Vsat

–

PK switch

()

-----------------------------------

on mi

(

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