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參數(shù)資料
| 型號： | L4990 |
| 廠商： | 意法半導(dǎo)體 |
| 英文描述： | PRIMARY CONTROLLER |
| 中文描述： | 主控制器 |
| 文件頁數(shù)： | 11/24頁 |
| 文件大?。?/td> | 322K |
| 代理商： | L4990 |
T
ss
3
R
sense
I
Qpk
I
SSC
C
ss
(6)
where R
sense
is the current sense resistor (see pin
13) and I
Qpk
is the switch peak current (flowing
through R
sense
), which depends on the output
load. Usually, C
SS
is selected for a T
SS
in the or-
der of milliseconds.
As mentioned before, the soft-start intervenes
also in case of severe overload or short circuit on
the output. Referring to fig. 23, pulse-by-pulse
current limitation is somehow effective as long as
the ON-time of the power switch can be reduced
(from A to B). After the minimum ON-time is
reached (from B onwards) the current is out of
control.
To prevent this risk, a comparator trips an over-
current handling procedure, named ’hiccup’ mode
operation, when a voltage above 1.2V (point C) is
detected on current sense input (ISEN, pin 13).
Basically, the IC is turned off and then soft-started
as long as the fault condition is detected. As a re-
sult, the operating point is moved abruptly to D,
creating a foldback effect. Fig. 24 illustrates the
operation.
The oscillation frequency appearing on the soft-
start capacitorin case of permanent fault, referred
to as ’hiccup” period, is approximatelygiven by:
T
hic
4.5
1
I
SSC
+
1
I
SSD
C
ss
(
7
)
Since the system tries restarting each hiccup cy-
cle, there is not any latchoffrisk.
V
OUT
T
ON
D.C.M.
C.C.M.
D
A
B
C
I
Qpk
T
ON(min)
1-2 ·I
Qpk
I
Qpk(max)
I
OUT
I
SHORT
I
OUT(max)
D97IN495
Figure 23. Regulation characteristicand re-
latedquantities
7V
T
hic
time
SHORT
I
OUT
I
SEN
FAULT
SS
5V
0.5V
D97IN496
Figure 24. Hiccupmode operation.
L4990 - L4990A
11/24
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PDF描述 |
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| L4990A | PRIMARY CONTROLLER |
| L4990AD | PRIMARY CONTROLLER |
| L4990D | PRIMARY CONTROLLER |
| L4992 | TRIPLE OUTPUT POWER SUPPLY CONTROLLER |
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| L4990A | 制造商:STMICROELECTRONICS 制造商全稱:STMicroelectronics 功能描述:PRIMARY CONTROLLER |
| L4990AD | 制造商:STMICROELECTRONICS 制造商全稱:STMicroelectronics 功能描述:PRIMARY CONTROLLER |
| L4990D | 制造商:STMICROELECTRONICS 制造商全稱:STMicroelectronics 功能描述:PRIMARY CONTROLLER |
| L4991 | 功能描述:TEST COIL FOR REED SWITCH, 1PC RoHS:是 類別:開關(guān) >> 配件 系列:- 標準包裝:100 系列:- 其它名稱:886.0007886.0007-ND |
| L4992 | 制造商:STMicroelectronics 功能描述: 制造商:STMicroelectronics 功能描述:VOLT SUPERVISOR CNTRLR 5.1V/3.3V 32TQFP - Trays |
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