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參數(shù)資料
| 型號： | L6995STR |
| 廠商： | STMICROELECTRONICS |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | SWITCHING CONTROLLER, PDSO20 |
| 封裝： | MO-153-AC, TSSOP-20 |
| 文件頁數(shù)： | 8/26頁 |
| 文件大?。?/td> | 427K |
| 代理商： | L6995STR |
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L6995S
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6
STEP BY STEP DESIGN
VIN = 20V VOUT = 1.25V IOUT = 20A FSW = 270kHz
In this design it is considered a low profile demoboard, so a great attention is given to the components height.
6.1 Input capacitor.
A pulsed current (with zero average value) flows through the input capacitor of a buck converter. The AC com-
ponent of this current is quite high and dissipates a considerable amount of power on the ESR capacitor:
Eq 17
The IRMS current is given by:
Eq 18
Neglecting the last term, the equation reduces to:
Eq 19
which maximum value corresponds to
δ = 1/2.
ICINRMS, has a maximum equal to δ = 1/2 (@ VIN = 2×VOUT, that is, 50% duty cycle). The input capacitor,
therefore, should be selected with an RMS rated current higher than ICINRMS. Electrolytic capacitors are the
most used because are the cheapest ones and are available with a wide range of RMS current ratings. The only
drawback is that, considering a requested ripple current rating, they are physically larger than other capacitors.
Very good tantalum capacitors are coming available, with very low ESR and small size. The only problem is that
they occasionally can burn out if subjected to very high current during the charge. So, it is better avoid this type
of capacitors for the input filter of the device. In fact, they can be subjected to high surge current when connected
to the power supply. If available for the requested value and voltage rating, the ceramic capacitors have usually
a higher RMS current rating for a given physical size (due to the very low ESR). From the equation 18 it is found:
Icinrms = 4.8A
Considering 10
F capacitors ceramic, that have ICINRMS =1.5A, 6 pzs. are needed.
6.2 Inductor
In order to determine the inductor value is necessary considering the maximum output current to decide the in-
ductor current saturation. Once the inductor current saturation it is found automatically is found the inductor val-
ue. In our design it is considered a very low profile inductor.
L = 0.6
H
The saturation current for this choke is around 25A
6.3 Output capacitor
The output capacitor is chosen by the output voltage static and dynamic accuracy. The static accuracy is related
to the output voltage ripple value, while the dynamic accuracy is related to the output current load step.
If the static precision is around ± 2% for the 1.25V output, the output accuracy is ±25mV.
To determine the ESR value from the output precision is necessary before calculate the ripple current:
P
CIN
ESR
CIN
Iout
2
Vin
Vout
–
()
Vin
2
------------------------------------------------
=
Icin
rms
Iout
2 δ 1 δ
–
()
δ
12
------
I
L
()
2
+
=
Icin
rms
Iout
δ 1 δ
–
()
=
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| L6996 | 功能描述:DC/DC 開關(guān)控制器 Step-Down Contrllr RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關(guān)頻率: 輸出電壓:1.215 V to 80 V 輸出電流:3.5 A 輸出端數(shù)量:1 最大工作溫度:+ 125 C 安裝風(fēng)格: 封裝 / 箱體:CPAK |
| L6996-1 | 制造商:Johanson 功能描述:TUNING ROTOR |
| L6996-13 | 制造商:Johanson Manufacturing 功能描述:TUNING ELEMENT |
| L6996-16 | 制造商:Johanson Manufacturing 功能描述:TUNING ELEMENT |
| L6996-17 | 制造商:Johanson Manufacturing 功能描述:TUNING ELEMENT |
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