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參數(shù)資料
| 型號： | L4992 |
| 廠商： | 意法半導(dǎo)體 |
| 英文描述： | TRIPLE OUTPUT POWER SUPPLY CONTROLLER |
| 中文描述： | 三路輸出電源控制器 |
| 文件頁數(shù)： | 13/26頁 |
| 文件大小： | 296K |
| 代理商： | L4992 |
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Basically, the application circuit topology is fixed, and the design procedure concerns only the selection
of the component values suitable for the voltage and current requirements of the specific application.
The design data one needs to know are therefore:
Input voltage range: the minimum (V
inmin
) and the maximum (V
inmax
) voltage under which the applica-
tion is expected to operate;
Maximum load current for each of the three sections:
- I
out3
for the +3.3V section;
- I
out5
for the +5.1V section:
- I
out12
for the +12V section;
Maximum peak-to-peak ripple amplitude of the output voltage for each switching section:
- V
rpp3
for the +3.3V section;
- V
rpp5
for the +5.1V section;
The operating frequency f
sw
(200/300 kHz or externally synchronized).
It is worth doing some preliminary considerations. The selection of the switching frequency depends on
the requirements of the application. If the aim is to minimize the size of the external components, 300
kHz will be chosen. For low input voltage applications 200 kHz is preferred, since it leads to a higher
maximum duty cycle.
As for the switching regulators, the inductance value of the output filter affects the inductor current ripple:
the higher the inductance the lower the ripple. This implies a lower current sense resistor value (for a
given I
out
), lower core losses and a lower output voltage ripple (for a given output capacitor) but, on the
other hand, more copper losses and a worse transient behaviour due to load changes. Usually the maxi-
mum ripple peak-to-peak amplitude (which occurs at V
inmax
) is chosen between 15% and 50% of the full
load current. It is convenient to introduce a ripple factor coefficient, RF, that is therefore a number be-
tween 0.15 and 0.5.
As for the linear regulator, its input voltage V
inlin
should not fall below 13V and therefore the auxiliary
winding should be dimensioned to get this voltage with a certain margin (say, 14V). Conversely, an
higher input voltage leads to higher losses inside the regulator, to the detriment of efficiency, and to
higher total current on the +3.3V inductor. Besides it implies a higher turns ratio and therefore a worse
magnetic coupling, which affect energy transfer during flyback.
SWITCHING REGULATORS
+5.1V Inductor
To define the inductor, it is necessary to determine firstly the inductance value. Its minimum value is
given by:
L
5min
=
V
in max
f
sw
I
out5
RF
5.1
(
V
in
max
5.1
)
and a value L5 > L5
min
should be selected.
Core geometry selection is connected to the requirements of the specific application in terms of space
utilization and other practical issues like ease of mounting, availability and so on. As to the material, the
choice should be directed towards ferrite, molypermalloy or Kool M
μ
, to achieve high efficiency. These
materials provide low core losses (ferrite in particular), so that the design can be concentrated on pre-
venting saturation and limiting copper losses.
Saturation must be avoided even at maximum peak current:
I
L5pk
=
I
out5
+
5.1
(
V
in max
5.1
)
2
f
sw
L
5
V
in max
To limit copper losses, the winding DC resistance, R
L
, should be as low as possible (in the range of m
).
AC losses can usually be neglected. A practical criterion to minimize DC resistance could be to use the
largest wire that fits the selected core.
Anyway the best solution, whenever possible, is to use an off-the-shelf inductor which meets the require-
ments in terms of inductance and maximum DC current. Nowadays there is a broad range of products
DESIGN PROCEDURE
L4992
13/26
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|---|---|
| L4993 | 制造商:STMICROELECTRONICS 制造商全稱:STMicroelectronics 功能描述:Low drop voltage regulator |
| L4993D | 功能描述:低壓差穩(wěn)壓器 - LDO Low drop voltage regulator RoHS:否 制造商:Texas Instruments 最大輸入電壓:36 V 輸出電壓:1.4 V to 20.5 V 回動電壓（最大值）:307 mV 輸出電流:1 A 負(fù)載調(diào)節(jié):0.3 % 輸出端數(shù)量: 輸出類型:Fixed 最大工作溫度:+ 125 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:VQFN-20 |
| L4993DTR | 功能描述:低壓差穩(wěn)壓器 - LDO Low drop voltage regulator RoHS:否 制造商:Texas Instruments 最大輸入電壓:36 V 輸出電壓:1.4 V to 20.5 V 回動電壓（最大值）:307 mV 輸出電流:1 A 負(fù)載調(diào)節(jié):0.3 % 輸出端數(shù)量: 輸出類型:Fixed 最大工作溫度:+ 125 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:VQFN-20 |
| L4993MD | 功能描述:低壓差穩(wěn)壓器 - LDO Low drop voltage regulator RoHS:否 制造商:Texas Instruments 最大輸入電壓:36 V 輸出電壓:1.4 V to 20.5 V 回動電壓（最大值）:307 mV 輸出電流:1 A 負(fù)載調(diào)節(jié):0.3 % 輸出端數(shù)量: 輸出類型:Fixed 最大工作溫度:+ 125 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:VQFN-20 |
| L4993MDTR | 功能描述:低壓差穩(wěn)壓器 - LDO 5V 150mA LW DROP VLT REGULATOR RoHS:否 制造商:Texas Instruments 最大輸入電壓:36 V 輸出電壓:1.4 V to 20.5 V 回動電壓（最大值）:307 mV 輸出電流:1 A 負(fù)載調(diào)節(jié):0.3 % 輸出端數(shù)量: 輸出類型:Fixed 最大工作溫度:+ 125 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:VQFN-20 |
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