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MC34063A Datasheet, PDF (9/12 Pages) ON Semiconductor – DC-to-DC CONVERTER CONTROL CIRCUITS | |||
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MC34063A MC33063A
Calculation
ton/toff
(ton + toff)
toff
ton
CT
Ipk(switch)
Rsc
L(min)
CO
Figure 14. Design Formula Table
StepâUp
) * Vout VF
* Vin(min)
Vin(min)
Vsat
StepâDown
) Vout VF
* * Vin(min) Vsat Vout
1
f
) ton toff
) ton
toff
1
(ton + toff) â toff
Ç ) Ç 4.0 x 10â5 ton
2Iout(max)
ton
toff
1
Ç * Ç0.3/Ipk(switch)
(Vin(min) Vsat)
Ipk(switch)
ton(max)
9
Ioutton
Vripple(pp)
1
f
) ton toff
) ton
toff
1
(ton + toff) â toff
4.0 x 10â5 ton
2Iout(max)
Ç * * Ç 0.3/Ipk(switch)
(Vin(min) Vsat
Ipk(switch)
Vout)
ton(max)
) Ipk(switch)(ton toff)
8Vripple(pp)
VoltageâInverting
) |Vout| VF
* Vin Vsat
1
f
) ton toff
) ton
toff
1
(ton + toff) â toff
Ç ) Ç 4.0 x 10â5 ton
2Iout(max)
ton
toff
1
Ç * Ç0.3/Ipk(switch)
(Vin(min) Vsat)
Ipk(switch)
ton(max)
9
Ioutton
Vripple(pp)
Vsat = Saturation voltage of the output switch.
VF = Forward voltage drop of the output rectifier.
+ Ç ) Ç The following power supply characteristics must be chosen:
Vin â Nominal input voltage.
Vout â Desired output voltage, |Vout|
Iout â Desired output current.
1.25 1
R2
R1
fmin â Minimum desired output switching frequency at the selected values of Vin and IO.
Vripple(pp) â Desired peakâtoâpeak output ripple voltage. In practice, the calculated capacitor value will need to be increased due to its equivalent series
Vripple(pp) â 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.
MOTOROLA ANALOG IC DEVICE DATA
9
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