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參數資料
| 型號： | FAN5235 |
| 廠商： | FAIRCHILD SEMICONDUCTOR CORP |
| 元件分類： | 穩壓器 |
| 英文描述： | System Electronics Regulator for Mobile PCs |
| 中文描述： | SWITCHED CAPACITOR REGULATOR, 345 kHz SWITCHING FREQ-MAX, PDSO24 |
| 封裝： | QSOP-24 |
| 文件頁數： | 12/15頁 |
| 文件大?。?/td> | 85K |
| 代理商： | FAN5235 |
FAN5235
12
REV. 1.3.3 1/3/02
MOSFET Selection
The notebook application circuit shown in Figure 1 is designed
to run with an input voltage operating range of 5.4-24V.
This wide input range helps determine the selection of the
MOSFETs for the 3.3V and 5V converters, since the high-side
MOSFET is on (V
out
/ V
in
) of the time, and the low-side
MOSFET 1 – (V
out
/ V
in
) of the time. The maxima and minima
are tabulated in Table 2:
Table 2. MOSFET Duty Cycles
High-side FET
Low-side FET
All four MOSFETs have maximum duty cycles greater than
50%. Thus, it is necessary to size all four approximately the
same.
3.3V and 5V Schottky Selection
The maximum current at which the converters operate in PFM
mode determines selection of a Schottky. In the application
shown in Figure 8, since the transition can occur at a current as
high as 28mV * (17.5K
/ 10K
) / 35m
= 1.4A, the diode
(with 24V input) will be conducting 86% of the period (from
Table 2). It thus has an average current of 1.4A * 0.86 = 1.2A,
which requires a Schottky current rating >1A.
3.3V and 5V Inductor Selection
See Table 1.
3.3V and 5V Output Cap Selection
See Table 1.
12V Component Selection
Calculation of the inductor, diode and output capacitor for the
+12V output fly-back is complex, depending on output power
and efficiency. See Applications Bulletin AB-19 for an Excel
spreadsheet calculation tool. See Table 1 also.
Input Capacitor Selection
Input capacitor selection is determined by ripple current rating.
With two converters operating in parallel at differing duty
cycles, calculation of input ripple current is complex; see
Applications Bulletin AB-19 for an Excel spreadsheet
calculation tool.
V
out
3.3V
5V
V
in
5.4V
.61
.43
24V
.14
.21
V
out
3.3V
5V
V
in
5.4V
.39
.07
24V
.86
.79
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| FAN5235MTC_Q | 功能描述:DC/DC 開關控制器 Regulator System Electronics RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關頻率: 輸出電壓:1.215 V to 80 V 輸出電流:3.5 A 輸出端數量:1 最大工作溫度:+ 125 C 安裝風格: 封裝 / 箱體:CPAK |
| FAN5235MTCX | 功能描述:DC/DC 開關控制器 Regulator System Electronics RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關頻率: 輸出電壓:1.215 V to 80 V 輸出電流:3.5 A 輸出端數量:1 最大工作溫度:+ 125 C 安裝風格: 封裝 / 箱體:CPAK |
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