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MC34063A

Industrial Standard, Universal DC/DC Converter

Analog Intergrations 

MC34063A

n APPLICATION INFORMATION

• DESIGN FORMULA TABLE

CALCULATION

STEP-DOWN

tON

VOUT + VF

tOFF

V - V - V IN(MIN)

SAT

OUT

(tON + tOFF) MAX

CT

1

FMIN

4x10-5tON

IC (SWITCH)

2IOUT(MAX)

RS

L(MIN)

Co

0.33/IC(SWITCH)

( V - V - V )t IN(MIN)

SAT

OUT

ON(MAX)

IC(SWITCH)

I ( t + t C( SWITCH) ON

OFF)

8 VRIPPLE (P - P )

VSAT - Saturation voltage of the output switch.

VF - Forward voltage drop of the ringback

rectifier

The following power supply characteristics must

be chosen:

VIN - Nominal input voltage.

VOUT - Desired output voltage,

VOUT =1.25 (1 + RB/RA)

IOUT - Desired output current.

STEP-UP

V + V V OUT

F - IN(MIN)

V - V IN(MIN)

SAT

1

FMIN

4 x 10-5tON

2IOUT(MAX)

( t ON + t OFF )

t OFF

0.33/ IC (SWITCH)

( V - V )t IN(MIN)

SAT

ON(MAX)

IC(SWITCH)

I t OUT ON

VRIPPLE(P - P)

VOLTAGE-INVERTING

VOUT + VF

VIN - VSAT

1

FMIN

4 x 10-5tON

2IOUT(MAX)

(

t ON + t OFF )

t OFF

0.33/ IC (SWITCH)

( V - V )t IN(MIN)

SAT

ON(MAX)

IC(SWITCH)

I t OUT ON

VRIPPLE(P - P)

FMIN - Minimum desired output switching

frequency at the selected values for VIN

and IOUT.

VRIPPLE (P-P)- Desired peak-to-peak output ripple

voltage. In practice, the calculated value

will need to be increased due to the

capacitor equivalent series resistance and

board layout. The ripple voltage should be

kept to a low value since it will directly

effect the line and load regulation.

6

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