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參數(shù)資料
| 型號(hào)： | L6997DTR |
| 廠商： | 意法半導(dǎo)體 |
| 英文描述： | STEP DOWN CONTROLLER FOR LOW VOLTAGE OPERATIONS |
| 中文描述： | 降壓控制器低電壓運(yùn)作 |
| 文件頁數(shù)： | 17/23頁 |
| 文件大小： | 291K |
| 代理商： | L6997DTR |
17/23
L6997
With our parameters:
Lmin
≥
2
μ
H
The saturation current is around 5A
3.3 Output capacitor and ripple voltage
The output capacitor is chosen by the output voltage static precision and also dynamic precision. The static pre-
cision regards the output voltage ripple value rated the output voltage in steady state at the end the ESR value;
while the dynamic precision regards the load step positive and negative load transient.
If the static precision is around ±1% for the 1.25V output voltage, the output precision is ±12.5mV.
To determine the ESR value from the output precision is necessary to calculate the ripple current:
Eq 21
One can consider a switching frequency around 270kHz.
From the Eq. above the ripple current is around 1.25A.
So the ESR is given from: RMS current in output capacitor is given by:
Eq 22
The dynamic specifications are sometimes more relaxed than the static requirements, so one can consider the
ESR value around 20m
enough.
To allow the device control loop to properly work, output capacitor ESR zero 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 C
OUT
and its ESR, ESRC
OUT
, 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.
Eq 23
But this is usually a negligible constrain.
Possible solutions:
3.4 MOSFET’s and Schottky Diodes
Since a 3.3V bus powers the gate drivers of the device, the use ultra low level MOSFET is highly recommended,
especially for high current applications. The MOSFET breakdown voltage V
BRDSS
must be greater than VINMAX
with a certain margin, so the selection will address 20V or 30V devices (depends on applications).
The RDS
ON
can be selected once the allowable power dissipation has been established. By selecting identical
Power MOSFET as the main switch and the synchronous rectifier, the total power they dissipate does not de-
pend on the duty cycle. Thus, if PON is this power loss (few percent of the rated output power), the required
RDS
ON
(@ 25 °C) can be derived from:
330
μ
F
EEFUE0D331R
PANASONIC
2R5TPE220M
POSCAP
220
μ
F
I
-----------–
L
Vin
--------
T
sw
=
ESR
V
I
2
---------------------
----
1.25
---------------
=
20m
=
=
Icout
rms
2 3
----------
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(fēng)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(fēng)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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