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參數資料
| 型號： | L5991 |
| 廠商： | 意法半導體 |
| 英文描述： | PRIMARY CONTROLLER WITH STANDBY |
| 中文描述： | 主控制器具有待機 |
| 文件頁數： | 14/19頁 |
| 文件大小： | 192K |
| 代理商： | L5991 |
now disconnected and C
T
is charged through R
A
only. In this way the oscillator frequency (f
SB
) will
be lower. Refer to pin 2 descriptionto see how to
calculatethe timing components.
Typical values for V
T1
and V
T2
are 2.5 V and 4V
respectively. This 1.5V hysteresis is enough to
prevent undesired frequency change up to a 5.5
to 1 f
osc
/ f
SB
ratio.
The value of V
T1
is such that in a discontinuous
flyback the standby frequency is activated when
the input power is about 13% of the maximum. If
necessary, it is possible to decrease the power
threshold below 13% by adding a DC offset (V
o
)
on the current sense pin (13, ISEN). This will also
allow a frequencychangegreater than 5.5 to 1.
The followingequations,useful for design,apply:
P
inSB
=
1
2
L
P
osc
0.367
V
o
R
sense
2
(
12
)
,
P
inNO
=
1
2
L
P
SB
0.867
V
o
R
sense
2
(
13
)
,
osc
SB
<
0.867
V
o
0.367
V
o
2
(
14
)
,
where P
inSB
is the input power below which the
L5991 recognizes a light load and switches the
oscillator frequency from
osc
to f
SB
, P
inNO
is the
input power above which the L5991 switches
back from
SB
to
osc
and L
p
the primary induc-
tanceof the flybacktransformer.
Connect to Vref or leave open this pin when
stand-by functionis not used.
Layout hints
Generallyspeaking a proper circuitboard layout is
vital for correct operation but is not an easy task.
Carefulcomponent placing,correct traces routing,
appropriate traces widths and, in case of high
voltages, compliance with isolation distances are
the major issues. The L5991 eases this task by
putting two pins at disposal for separate current
returns of bias (SGND) and switch drive currents
(PGND) The matter is complex and only few im-
portant pointswill be here reminded.
1) All current returns (signal ground, power
ground, shielding, etc.) should be routed sepa-
rately and should be connected only at a single
ground point.
2) Noise coupling can be reduced by minimizing
the area circumscribed by current loops. This
applies particularly to loops where high pulsed
currentsflow.
3) For high current paths, the traces should be
doubled on the other side of the PCB whenever
possible: this will reduce both the resistance
and the inductanceof the wiring.
4) Magnetic field radiation (and stray inductance)
can be reduced by keeping all traces carrying
switchedcurrentsas short as possible.
5) In general, traces carrying signal currents
should run far from traces carrying pulsed cur-
rents or with quickly swinging voltages. From
this viewpoint, particular care should be taken
of the high impedance points (current sense in-
put, feedback input, ...).It could be a good idea
to route signal traces on one PCB side and
power traceson theother side.
6) Provide adequate filtering of some crucial
points of the circuit, such as voltagereferences,
IC’s supplypins, etc.
L5991 - L5991A
14/23
相關PDF資料 |
PDF描述 |
|---|---|
| L5991A | PRIMARY CONTROLLER WITH STANDBY |
| L5991AD | PRIMARY CONTROLLER WITH STANDBY |
| L5991D | PRIMARY CONTROLLER WITH STANDBY |
| L5993 | CONSTANT POWER CONTROLLER |
| L5993D | CONSTANT POWER CONTROLLER |
相關代理商/技術參數 |
參數描述 |
|---|---|
| L5991_01 | 制造商:STMICROELECTRONICS 制造商全稱:STMicroelectronics 功能描述:PRIMARY CONTROLLER WITH STANDBY |
| L5991A | 功能描述:電流型 PWM 控制器 Prog Current Mode RoHS:否 制造商:Texas Instruments 開關頻率:27 KHz 上升時間: 下降時間: 工作電源電壓:6 V to 15 V 工作電源電流:1.5 mA 輸出端數量:1 最大工作溫度:+ 105 C 安裝風格:SMD/SMT 封裝 / 箱體:TSSOP-14 |
| L5991AD | 功能描述:開關變換器、穩(wěn)壓器與控制器 Prog Current Mode RoHS:否 制造商:Texas Instruments 輸出電壓:1.2 V to 10 V 輸出電流:300 mA 輸出功率: 輸入電壓:3 V to 17 V 開關頻率:1 MHz 工作溫度范圍: 安裝風格:SMD/SMT 封裝 / 箱體:WSON-8 封裝:Reel |
| L5991AD13TR | 功能描述:電流型 PWM 控制器 Prog Current Mode RoHS:否 制造商:Texas Instruments 開關頻率:27 KHz 上升時間: 下降時間: 工作電源電壓:6 V to 15 V 工作電源電流:1.5 mA 輸出端數量:1 最大工作溫度:+ 105 C 安裝風格:SMD/SMT 封裝 / 箱體:TSSOP-14 |
| L5991D | 功能描述:電流型 PWM 控制器 Prog Current Mode RoHS:否 制造商:Texas Instruments 開關頻率:27 KHz 上升時間: 下降時間: 工作電源電壓:6 V to 15 V 工作電源電流:1.5 mA 輸出端數量:1 最大工作溫度:+ 105 C 安裝風格:SMD/SMT 封裝 / 箱體:TSSOP-14 |
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