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參數(shù)資料
| 型號： | L6598 |
| 廠商： | 意法半導體 |
| 英文描述： | HIGH VOLTAGE RESONANT CONTROLLER |
| 中文描述： | 高壓諧振控制器 |
| 文件頁數(shù)： | 7/16頁 |
| 文件大小： | 114K |
| 代理商： | L6598 |
7/16
L6598
Figure 4. Soft Start and frequency shifting block
During the softstart timethe currentI
SS
chargesthe capacitor C
SS
, generating a voltage ramp which is delivered
to a transconductance amplifier, as shown in fig. 4. Thus this voltage signal is converted in a growing current
which is subtracted to I
fstart
. Therefore the current which drives the oscillator to set the frequency during the soft
start is equal to:
[1]
where
[2]
At the start-up (t=0) the L6598 oscillates at f
start
, set by:
[3]
At the end of soft start (t = T
SS
) the second term of eq.1 decreases to zero and the switching frequency is set
only by I
min
(i.e. R
fmin
):
[4]
Since the second term of eq.1 is equal to zero, we have:
[5]
Note that there is not a fixed threshold of the voltage across C
SS
in which the soft start finishes (i.e. the end of
the frequency shifting), and T
SS
depends on C
SS
, I
fstart
, g
m
, and I
SS
(eq. 5). Making T
SS
independent of I
fstart
,
the I
SS
current has been designed to be a fraction of I
fstart
, so:
I
K
g
m
I
fstart
K
[6]
In this way the soft start time depends only on the capacitor C
SS
. The typical value of the k
SS
constant (Soft
Css
Ifmin
Ifstart
Iss
gm
OSC
Iosc
I
osc
I
fmin
I
fstart
g
m
V
Css
t
( )
–
(
)
+
I
fmin
I
fstart
g
I
C
ss
--------------
t
–
+
=
=
I
fmin
V
R
fmin
-------------
I
fsart
,
V
R
fstart
---------------
V
REF
,
2V
=
=
=
I
osc
0
( )
I
fmin
I
fstart
+
V
REF
R
fmin
-------------
R
fstart
----------------
+
=
=
I
osc
T
ss
(
)
I
fmin
V
R
fmin
-------------
=
=
I
fstart
g
I
C
ss
--------------
T
SS
–
0
T
SS
→
C
I
g
m
I
ss
------------------------
=
=
I
SS
-------------
T
SS
→
--------------------------
T
SS
→
C
g
m
K
-----------
T
SS
k
SS
C
SS
–
→
=
=
=
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相關(guān)代理商/技術(shù)參數(shù) |
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| L6598D016TR | 制造商:STMICROELECTRONICS 制造商全稱:STMicroelectronics 功能描述:High voltage resonant controller |
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