34063API datasheet(11/15 Pages) ONSEMI

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MC34063A, MC33063A, SC34063A, SC33063A, NCV33063A

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Calculation

Step−Up

Step−Down

Voltage−Inverting

ton/toff

Vout ) VF * Vin(min)

Vin(min) * Vsat

Vout ) VF

Vin(min) * Vsat * Vout

|Vout| ) VF

Vin * Vsat

(ton + toff)

toff

ton ) toff

ton

toff

) 1

ton ) toff

ton

toff

) 1

ton ) toff

ton

toff

) 1

ton

(ton + toff) − toff

4.0 x 10−5 ton

Ipk(switch)

2Iout(max)

ton

toff

) 1

2Iout(max)

ton

toff

) 1

Rsc

0.3/Ipk(switch)

L(min)

(Vin(min) * Vsat)

Ipk(switch)

ton(max)

(Vin(min) * Vsat * Vout)

Ipk(switch)

ton(max)

(Vin(min) * Vsat)

Ipk(switch)

ton(max)

Ioutton

Vripple(pp)

Ipk(switch)(ton ) toff)

8Vripple(pp)

Ioutton

Vripple(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 resistance and board layout. The ripple voltage should be kept to a low value since it will directly affect the

line and load regulation.

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

|Vout| + 1.25 1 )

Figure 17. Design Formula Table

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