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參數(shù)資料
| 型號： | 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作 |
| 文件頁數(shù)： | 6/23頁 |
| 文件大?。?/td> | 291K |
| 代理商： | L6997DTR |
L6997
6/23
1
DEVICE DESCRIPTION
1.1 Constant On Time PWM topology
Figure 2. Loop block schematic diagram
The device implements a Constant On Time control scheme, where the Ton is the high side MOSFET on time
duration forced by the one-shot generator. The on time is directly proportional to VSENSE pin voltage and in-
verse to OSC pin voltage as in Eq1:
Eq 1
where K
OSC
= 250ns and
τ
is the internal propagation delay time (typ. 70ns). The system imposes in steady
state a minimum on time corresponding to V
OSC
= 1V. In fact if the V
OSC
voltage increases above 1V the cor-
responding Ton will not decrease. Connecting the OSC pin to a voltage partition from V
IN
to GND, it allows a
steady-state switching frequency F
SW
independent of V
IN
. It results:
α
α
OUT
K
OSC
Eq 2
where
Eq 3
Eq 4
The above equations allow setting the frequency divider ratio
α
OSC
once output voltage has been set; note that
such equations hold only if V
OSC
<1V. Further the Eq2 shows how the system has a switching frequency ideally
independent from the input voltage. The delay introduces a light dependence from V
IN
. A minimum off-time con-
strain of about 500ns is introduced in order to assure the boot capacitor charge and to limit the switching fre-
Q
Vsense
R3
R4
R2
R1
R
S
Vout
Vin
HGATE
LGATE
Q
OSC
FB
Vref
HS
LS
DS
PWM comparator
FFSR
One-shot generator
-
+
T
ON
K
OSC
V
V
OSC
---------------------
τ
+
=
f
SW
V
V
IN
--------------
T
ON
----------
--------------
--------------
α
OSC
→
f
SW
K
OSC
α
OUT
=
=
=
α
OSC
V
V
IN
--------------
R
+
R
2
R
1
--------------------
=
=
α
OUT
V
V
OUT
--------------
R
+
R
3
R
4
--------------------
=
=
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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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