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參數(shù)資料
| 型號： | PC33394FC |
| 廠商： | MOTOROLA INC |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | 1.2 A SWITCHING CONTROLLER, 220 kHz SWITCHING FREQ-MAX, PQCC44 |
| 封裝： | PLASTIC, QFN-44 |
| 文件頁數(shù)： | 21/51頁 |
| 文件大?。?/td> | 543K |
| 代理商： | PC33394FC |
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33394
28
MOTOROLA ANALOG INTEGRATED CIRCUIT DEVICE DATA
Where Io is the average output current.
The inductor peak current is given by the following
equation:
IpkL + Io
Vo
Vin
) 1
2
DIL
Figure 14. Basic Boost Converter Operation and its Waveforms
IL
ID
IQ
Q
L
Vin
RLOAD
VO
+
–
+
CO
D
Vin
RLOAD
+
–
+
CO
L
POWER SWITCH ON
ILOAD
Vout
VIN
RLOAD
+
–
+
CO
POWER SWITCH OFF
IOFF
Vout
IL
IO
IL
ID
IQ
VQ
VCo
DIL
ton
toff
T
ION
ILOAD
t
5.2.1. Switching Regulator Component Selection
The selection of the external inductor L2 and capacitor C2
values (see Figure 15) is a compromise between the two
modes of operation of the switching regulator, the pre
regulated voltage VPRE and the dropout voltage of the linear
regulators. Ideal equations describing the peak—peak
inductor current ripple, peak—peak output voltage ripple and
peak inductor current are shown below. Since the switching
regulator will work mostly in the buck mode, the inductor and
the switcher input and output capacitor were selected for
optimum buck controller performance, but also taking into
account the restriction placed by adopting the boost
converter as well.
Figure 15. 33394 Switcher Topology
IL
VRL
Vfwd1
D1
L
Vin
RLOAD
VO
+
–
+
CO
RL
Q2
VRDS(on)
RDS(on)
IQ
Q1
ESR
D2
Vfwd2
The following example shows a procedure for determining
the component values. The VPRE output is set to regulate to
5.6 V and the linear regulators require a minimum of 0.4 V
dropout voltage. This leaves a
±0.2 V window for the
peak—to–peak output voltage ripple. Assuming the following
conditions:
Vin(typ) = 13.5 V
Io = 1.2
VPRE = 5.6 V (+6 V in the boost mode)
f = 200 kHz
Vfwd1 = Vfwd2 = 0.5 V
Maximum allowed output voltage ripple in the buck mode
Vpp(max) = 0.2 V/2 = 0.1 V (to allow for process and
temperature variations).
5.2.1.1. Selecting the Inductor
In order to select the proper inductance value, the inductor
ripple current
IL has to be determined. The usual ratio of IL
to output current Io is:
IL = 0.3 Io
As described in the previous section, and taking into
account the 33394 switcher topology (see Figure 15), the
inductor ripple current can be estimated as:
DIL +
(Vin * Vo * Vfwd2)
L
Vo ) Vfwd2
Vin
f
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