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參數(shù)資料
| 型號： | L6997STR |
| 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)： | 6/30頁 |
| 文件大?。?/td> | 515K |
| 代理商： | L6997STR |
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L6997S
6/30
4
DEVICE DESCRIPTION
4.1 Constant On Time PWM topology
Figure 5. 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:
(1)
where K
OSC
= 180ns and
τ
is the internal propagation delay time (typ. 40ns). 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:
V
V
IN
T
ON
K
OSC
(2)
where
(3)
(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 frequen-
cy ideally independent from the input voltage. The delay introduces a light dependence from V
IN
. A mini-
mum Off-Time constraint of about 500ns is introduced in order to assure the boot capacitor charge and to
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
--------------
----------
α
α
OUT
--------------
--------------
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) |
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|---|---|
| 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 |
| L6998-6 | 制造商:Johanson Manufacturing 功能描述:TUNING ELEMENT |
| L6999 | 制造商:HAMAMATSU 制造商全稱:Hamamatsu Corporation 功能描述:The best light source is supported by the best electrode technology |
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