MC33466H-30LT1 View Datasheet(PDF) - Motorola => Freescale
Part Name
Description
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MC33466H-30LT1 Datasheet PDF : 12 Pages
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MC33466
Calculation
L
ton
D
IL(avg)
IL(pk)
Vripple(pp)
Figure 22. Design Equations
Step–Down
Step–Up
t (Vin – VO)(ton)
2IO
D
fs
t (Vin)(ton)
2Iin
D
fs
t (VO)
(Vin)
t * (VO Vin)
(VO)
IO
* (Vin VO)(ton)
L
Iin
* (Vin Vsat)(ton)
L
ȧȱȲǒ Ǔ ȳȴȧ IL(pk)
1
2
2
) 1
8fsCO
(ESR)2
Flyback
t (Vin)(ton)
2Iin
D
fs
ƪǒ Ǔ ƫ t
VO
) Ns
Np
(Vin)
VO
Iin
* (Vin Vsat)(ton)
L
The following converter design characteristics must be chosen:
Vin – Nominal Operating dc input voltage
VO – Desired dc output voltage
IO – Desired dc output current
Vripple(pp) – Desired peak–to–peak output ripple voltage. For best performance the ripple voltage should be kept to a low value since it will directly
affect line and load regulation. Capacitor CO should be a low equivalent series resistance (ESR) electrolytic designed for switching regulator
applications.
D – Operating duty cycle = ton(fs). This parameter must be chosen to be <0.5 for step–up and flyback applications.
NOTES: 1. Vsat – Saturation voltage of the switching transistor.
2. Iin – DC input switch.
3. fs – Switching frequency, nominally 50 kHz.
4. RO – Load resistance. RO = VO/IO.
5. Ns, Np – In flyback applications Ns is the number of turns of the secondary transformer winding; Np is the number of the primary winding turns.
Design Example – Step–down Application
Required: Vin = 8.0 V, an output voltage of 3.3 V at 300 mA is desired with an output ripple of less than 300 mVpp.
+ + W RO
VO
IO
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t + + 1. Because this is a discontinuous mode design, D
VO
Vin
3.3
8
0.41. Choose D = 0.33.
[ + + 2. ton
D
fs
0.33
(50 kHz)
6.6 µs.
t + + 3. L
(Vin – VO)(ton)
2IO
(8 – 3.3)(6.6 µs)
[2(0.3)]
51.7 µH.
Choose L = 47 µH. Coilcraft part number DO3316P–473.
+ + + 4. IL(pk)
(Vin – VO)(ton)
L
(8 – 3.3)(6.6 µs)
(47 µH)
660 mA.
t + + 5. ESR
Vripple(pp)
IL(pk)
(300 mV)
(660 mA)
0.455 W.
Choose CO = two parallel AVX 330 µF tantalum chip capacitors. Part Number TAJE337M006.
Specified maximum ESR for each is 0.9 Ω.
The complete design schematic is shown in Figure 19.
MOTOROLA ANALOG IC DEVICE DATA
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