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参数资料
| 型号： | L5993D |
| 厂商： | STMICROELECTRONICS |
| 元件分类： | 稳压器 |
| 英文描述： | 1.5 A SWITCHING REGULATOR, 1000 kHz SWITCHING FREQ-MAX, PDSO16 |
| 封装： | SO-16 |
| 文件页数： | 21/22页 |
| 文件大小： | 200K |
| 代理商： | L5993D |
CONSTANT POWER FUNCTION
Pulse-by-pulse current limitation prevents peak
primary current from exceeding a given level.
This, in turn, limits the maximum power deliver-
able to the output or, in other words, the power
capability of a converter. The capability, however,
depends on switching frequency: for example, in
a discontinuous current mode flyback they are just
proportional.
In SMPS’ of raster-scanned CRT displays the
switching frequency is usually synchronized to the
raster line scan signal of the display in order to in-
crease noise immunity. More and more often,
CRT displays are required to operate within a
range of different video frequencies (e.g. from 31
kHz to 64 kHz), thus also the switching frequency
of the SMPS will vary in that range.
In case of some failure, the power throughput may
be excessive without necessarily tripping the
pulse-by-pulse current limitation circuit because of
a high operating frequency.
For the sake of safety, it would be then desirable
to design the power stage of a converter (power
MOSFET, transformer, catch diode) so as to be
able to withstand the maximum power throughput
under failure conditions. However, this is a con-
siderable increase of size and cost.
The ”Constant Power” function of the L5993 al-
lows to overcome this problem. The device
changes the threshold of its pulse-by-pulse cur-
rent limitation circuit so as to maintain fairly con-
stant the power capability of a flyback converter
despite the changes of the switching frequency.
This is accomplished by clamping the output of
the error amplifier (VCOMP) to a value which de-
creases as the frequency of the signal fed into pin
1 (SYNC) builds up.
The frequency-to-voltage conversion needed to
achieve this functionality is performed by detect-
ing the peak voltage of the (synchronized) oscilla-
tor with a peak-holding circuit. One external ca-
pacitor only is required.
It is important to point out that shape, amplitude
and duration of the synchronization pulses are of
no concern with this technique.
APPLICATION INFORMATION
Detailed Pin Functions Description
Pin 1. SYNC (In/Out Synchronization). This func-
tion allows the IC’s oscillator either to synchronize
other controllers (master) or to be synchronized to
an external frequency (slave).
As a master, the pin delivers positive pulses dur-
ing the falling edge of the oscillator (see pin 2). In
slave operation the circuit is edge triggered. Refer
to fig. 21 to see how it works. When several IC
work in parallel no master-slave designation is
needed because the fastest one becomes auto-
matically the master.
During the ramp-up of the oscillator the pin is
pulled low by a 600
A internal sink current gener-
ator. During the falling edge, that is when the
pulse is released, the 600
A pull-down is discon-
nected. The pin becomes a generator whose
source capability is typically 7mA (with a voltage
still higher than 3.5V).
In fig. 20, some practical examples of synchroniz-
ing the L5993 are given.
Pin 2. RCT (Oscillator). A resistor (RT) and a ca-
pacitor (CT), connected as shown in fig. 21 set the
operating frequency fosc of the oscillator.
CT is charged through RT until its voltage reaches
3V, then is quickly internally discharged. As the
voltage has dropped to 1V it starts being charged
again.
The frequency can be established with the aid of
fig. 13 diagrams or considering the approximate
relationship:
fosc
1
CT
(0.693
RT + KT)
(1)
where KT is defined as:
KT
=
90, V15 = VREF
160 V15 = GND/OPEN
(2)
and is linked to the duration of the falling edge of
the sawtooth:
Td
30 10-9 +KT CT (3)
Td is also the duration of the sync pulses deliv-
L5993
RT
VREF
SYNC
RCT
L4981A
(MASTER)
L5993
(SLAVE)
RT
VREF
SYNC
RCT
ROSC
COSC
CT
L5993
(MASTER)
L4981A
(SLAVE)
SYNC
ROSC
CT
COSC
SYNC
(a)
(b)
(c)
RT
D97IN766B
CT
VREF
4
1
2
1
2
16
18
17
4
2
1
RCT
1
2
4
16
17
18
Figure 20. Sinchronizing the L5993.
L5993
8/22
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相关代理商/技术参数 |
参数描述 |
|---|---|
| L5993D013TR | 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 |
| L5994 | 功能描述:电流型 PWM 控制器 Adj Triple Out Pwr 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 |
| L5994_02 | 制造商:STMICROELECTRONICS 制造商全称:STMicroelectronics 功能描述:ADJUSTABLE TRIPLE OUTPUT POWER SUPPLY CONTROLLER |
| L5994A | 功能描述:监控电路 ADJT TRIPLE OUTPUT POWER SUPPLY CNTLR RoHS:否 制造商:STMicroelectronics 监测电压数: 监测电压: 欠电压阈值: 过电压阈值: 输出类型:Active Low, Open Drain 人工复位:Resettable 监视器:No Watchdog 电池备用开关:No Backup 上电复位延迟（典型值）:10 s 电源电压-最大:5.5 V 最大工作温度:+ 85 C 安装风格:SMD/SMT 封装 / 箱体:UDFN-6 封装:Reel |
| L5995 | 制造商:未知厂家 制造商全称:未知厂家 功能描述:Current-Mode SMPS Controller |
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