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參數資料
| 型號： | MC33466H-50LT1 |
| 廠商： | MOTOROLA INC |
| 元件分類： | 穩壓器 |
| 英文描述： | FIXED FREQUENCY PWM MICROPOWER DC-to-DC CONVERTER |
| 中文描述： | SWITCHING CONTROLLER, 120 kHz SWITCHING FREQ-MAX, PSSO3 |
| 封裝： | PLASTIC, SOT-89, 3 PIN |
| 文件頁數： | 11/12頁 |
| 文件大小： | 170K |
| 代理商： | MC33466H-50LT1 |
MC33466
11
MOTOROLA ANALOG IC DEVICE DATA
Figure 22. Design Equations
Calculation
Step–Down
Step–Up
Flyback
L
(Vin– VO)(ton)
2IO
D
fs
(Vin)(ton)
2Iin
(Vin)(ton)
2Iin
ton
D
fs
D
fs
D
(VO)
(Vin)
(VO
Vin)
(VO)
VO
Ns
Np
(Vin)
VO
IL(avg)
IL(pk)
IO
Iin
Iin
(Vin
VO)(ton)
L
(Vin
Vsat)(ton)
L
(Vin
Vsat)(ton)
L
Vripple(pp)
IL(pk)
1
8fsCO
2
(ESR)2
1
2
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.
V
O
I
O
RO
11
1. Because this is a discontinuous mode design, D
V
O
V
in
3.3
8
0.41. Choose D = 0.33.
2. ton
D
fs
0.33
(50 kHz)
6.6
μ
s.
3. L
(Vin– VO)(ton)
2IO
(8 – 3.3)(6.6
μ
s)
[2(0.3)]
51.7
μ
H.
Choose L = 47
μ
H. Coilcraft part number DO3316P–473.
4. IL(pk)
(Vin– VO)(ton)
L
(8 – 3.3)(6.6
μ
s)
(47
μ
H)
660 mA.
5. ESR
Vripple(pp)
IL(pk)
(300 mV)
(660 mA)
0.455
.
Choose CO = two parallel AVX 330
μ
F tantalum chip capacitors. Part Number TAJE337M006.
Specified maximum ESR for each is 0.9
.
The complete design schematic is shown in Figure 19.
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