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參數(shù)資料
| 型號： | L6997DTR |
| 廠商： | STMICROELECTRONICS |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | SWITCHING CONTROLLER, PDSO20 |
| 封裝： | MO-153AC, TSSOP-20 |
| 文件頁數(shù)： | 9/30頁 |
| 文件大?。?/td> | 591K |
| 代理商： | L6997DTR |
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17/30
L6997
With our parameters:
Lmin
≥ 2H
The saturation current must be higher then 5A
6.3 Output capacitor and ripple voltage
The output capacitor is selected based on both static and dynamic output voltage accuracy. The static output
voltage accuracy depends mostly on the ERS of the output capacitor, while the dynamic accuracy usually de-
pends both on the ESR and capacitance value.
If the static precision is ±1% for the 1.25V output voltage, the output ripple is ±12.5mV.
To determine the ESR value from the output precision is necessary to calculate the ripple current:
(21)
Where FSW = 270kHz.
From the Eq. above the ripple current is around 1.25A.
So the ESR is given by:
(22)
The dynamic specifications are sometimes more relaxed than the static requirements, Anyway a minimum out-
put capacitance must be ensured to avoid output voltage variation due to the charge and discharge of Cout dur-
ing load transients.
To allow the device control loop to work properly, the zero introduced by the output capacitor ESR (
τ = ESR
Cout) must be at least ten times smaller than switching frequency. Low ESR tantalum capacitors, which ESR
zero is close to ten kHz, are suitable for output filtering. Output capacitor value COUT and its ESR, ESRCOUT,
should be large enough and small enough, respectively, to keep output voltage within the accuracy range during
a load transient, and to give the device a minimum signal to noise ratio.
The current ripple flows through the output capacitors, so the should be calculated also to sustain this ripple:
the RMS current value is given by Eq. 18.
(23)
But this is usually a negligible constrain.
Possible solutions:
Multilayer capacitors can not be used because their very low ESR.
6.4 MOSFET’s and Schottky Diodes
A 3.3V bus powers the gate drivers of the device, the use ultra low level MOSFET is highly recommended, es-
pecially for high current applications. The MOSFET breakdown voltage VBRDSS must be greater than VINMAX
with a certain margin.
The RDSON can be selected once the allowable power dissipation has been established. By selecting identical
330
F
EEFUE0D331R
PANASONIC
220
F2R5TPE220M
POSCAP
I
Vin
Vo
–
L
-----------------------
Vo
Vin
--------- T
sw
=
ESR
V
ripple
I
2
-----
---------------------
25mV
1.25
----------------
=
20m
==
Icout
rms
1
23
----------- I
L
=
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| L6997S | 功能描述:DC/DC 開關(guān)控制器 STEP DOWN CONTROLLER Lo Vltg Operations 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 安裝風格: 封裝 / 箱體:CPAK |
| L6997STR | 功能描述:DC/DC 開關(guān)控制器 3.0 to 5.5V Step-Dwn 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 安裝風格: 封裝 / 箱體:CPAK |
| L6998-0 | 制造商:Johanson Manufacturing 功能描述:TUNING ELEMENT |
| L6998-1 | 制造商:Johanson Manufacturing 功能描述:TUNING ELEMENT |
| L6998-5 | 制造商:Johanson Manufacturing 功能描述:TUNING ELEMENT |
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