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参数资料
| 型号： | L5991AD |
| 厂商： | STMICROELECTRONICS |
| 元件分类： | 稳压器 |
| 英文描述： | 1.5 A SWITCHING CONTROLLER, 1000 kHz SWITCHING FREQ-MAX, PDSO16 |
| 封装： | SO-16 |
| 文件页数： | 6/23页 |
| 文件大小： | 414K |
| 代理商： | L5991AD |
now disconnected and CT is charged through RA
only. In this way the oscillator frequency (fSB) will
be lower. Refer to pin 2 description to see how to
calculate the timing components.
Typical values for VT1 and VT2 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 fosc/ fSB ratio.
The value of VT1 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 (Vo)
on the current sense pin (13, ISEN). This will also
allow a frequency change greater than 5.5 to 1.
The following equations, useful for design, apply:
PinSB
=
1
2
LP osc
0.367
Vo
Rsense
2
(12),
PinNO
=
1
2
LP SB
0.867
Vo
Rsense
2
(13),
osc
SB <
0.867
Vo
0.367
Vo
2
(14),
where PinSB is the input power below which the
L5991 recognizes a light load and switches the
oscillator frequency from
osc to fSB, PinNO is the
input power above which the L5991 switches
back from
SB to osc and Lp the primary induc-
tance of the flyback transformer.
Connect to Vref or leave open this pin when
stand-by function is not used.
Layout hints
Generally speaking a proper circuitboard layout is
vital for correct operation but is not an easy task.
Careful component 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 points will 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
currents flow.
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 inductance of the wiring.
4) Magnetic field radiation (and stray inductance)
can be reduced by keeping all traces carrying
switched currents as 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 traces on the other side.
6) Provide adequate filtering of some crucial
points of the circuit, such as voltage references,
IC’s supply pins, etc.
L5991 - L5991A
14/23
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相关代理商/技术参数 |
参数描述 |
|---|---|
| L5991AD13TR | 功能描述:电流型 PWM 控制器 Prog Current Mode RoHS:否 制造商:Texas Instruments 开关频率:27 KHz 上升时间: 下降时间: 工作电源电压:6 V to 15 V 工作电源电流:1.5 mA 输出端数量:1 最大工作温度:+ 105 C 安装风格:SMD/SMT 封装 / 箱体:TSSOP-14 |
| L5991D | 功能描述:电流型 PWM 控制器 Prog Current Mode RoHS:否 制造商:Texas Instruments 开关频率:27 KHz 上升时间: 下降时间: 工作电源电压:6 V to 15 V 工作电源电流:1.5 mA 输出端数量:1 最大工作温度:+ 105 C 安装风格:SMD/SMT 封装 / 箱体:TSSOP-14 |
| L5991D013TR | 功能描述:电流型 PWM 控制器 Prog Current Mode RoHS:否 制造商:Texas Instruments 开关频率:27 KHz 上升时间: 下降时间: 工作电源电压:6 V to 15 V 工作电源电流:1.5 mA 输出端数量:1 最大工作温度:+ 105 C 安装风格:SMD/SMT 封装 / 箱体:TSSOP-14 |
| L5993 | 功能描述:开关变换器、稳压器与控制器 Prog Current Mode RoHS:否 制造商:Texas Instruments 输出电压:1.2 V to 10 V 输出电流:300 mA 输出功率: 输入电压:3 V to 17 V 开关频率:1 MHz 工作温度范围: 安装风格:SMD/SMT 封装 / 箱体:WSON-8 封装:Reel |
| L5993D | 功能描述:开关变换器、稳压器与控制器 Prog Current Mode RoHS:否 制造商:Texas Instruments 输出电压:1.2 V to 10 V 输出电流:300 mA 输出功率: 输入电压:3 V to 17 V 开关频率:1 MHz 工作温度范围: 安装风格:SMD/SMT 封装 / 箱体:WSON-8 封装:Reel |
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