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參數(shù)資料
| 型號： | L5991D |
| 廠商： | STMICROELECTRONICS |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | 1.5 A SWITCHING CONTROLLER, 1000 kHz SWITCHING FREQ-MAX, PDSO16 |
| 封裝： | SO-16 |
| 文件頁數(shù)： | 22/23頁 |
| 文件大?。?/td> | 414K |
| 代理商： | L5991D |
STANDBY FUNCTION
The standby function, optimized for flyback topol-
ogy, automatically detects a light load condition
for the converter and decreases the oscillator fre-
quency on that occurrence. The normal oscillation
frequency is automatically resumed when the out-
put load builds up and exceeds a defined thresh-
old.
This function allows to minimize power losses re-
lated to switching frequency, which represent the
majority of losses in a lightly loaded flyback, with-
out giving up the advantages of a higher switching
frequency at heavy load.
This is accomplished by monitoring the output of
the Error Amplifier (VCOMP) that depends linearly
on the peak primary current, except for an offset.
If the the peak primary current decreases (as a re-
sult of a decrease of the power demanded by the
load) and VCOMP falls below a fixed threshold
(VT1), the oscillator frequency will be set to a
lower value (fSB). When the peak primary current
increases and VCOMP exceeds a second threshold
(VT2) the oscillator frequency is set to the normal
value (fosc). An appropriate hysteresis (VT2-VT1)
prevents
undesired frequency
change
when
power is such that VCOMP moves close to the
threshold. This operation is shown in fig. 21.
Both the normal and the standby frequency are
externally programmable. VT1 and VT2 are inter-
nally fixed but it is possible to adjust the thresh-
olds in terms of input power level.
APPLICATION INFORMATION
Detailed Pin Function 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. 23 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. 22, some practical examples of synchroniz-
ing the L5991 are given.
Since the device automatically diminishes its op-
erating frequency under light load conditions, it is
reasonable to suppose that synchronization will
refer to normal operation and not to standby.
Pin 2. RCT (Oscillator). Two resistors (RA and RB)
and one capacitor (CT), connected as shown in
fig. 23, allow to set separately the operating fre-
quency of the oscillator in normal operation (fosc)
and in standby mode (fSB).
CT is charged from Vref through RA and RB in nor-
mal operation (STANDBY = HIGH), through RA
only in standby ( STANDBY = LOW). See pin 16
description to see how the STANDBY signal is gen-
erated.
When the voltage on CT reaches 3V, the capaci-
tor is quickly internally discharged. As the voltage
has dropped to 1V it starts being charged again.
1234
VCOMP
Pin
fosc
fSB
Stand-by
Normal operation
VT1
PNO
PSB
VT2
Figure 21. Standby dynamic operation.
L5991
RA
VREF
SYNC
RCT
L4981A
(MASTER)
L5991
(SLAVE)
RA
VREF
SYNC
RCT
ROSC
COSC
CT
L5991
(MASTER)
L4981A
(SLAVE)
SYNC
ROSC
CT
COSC
SYNC
(a)
(b)
(c)
RA
D97IN728A
CT
VREF
4
1
2
1
2
16
18
17
4
2
1
RCT
1
2
4
16
17
18
ST-BY
16
RB
ST-BY
16
RB
16
ST-BY
Figure 22. Synchronizing the L5991.
L5991 - L5991A
8/23
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| L5991D013TR | 功能描述:電流型 PWM 控制器 Prog Current Mode RoHS:否 制造商:Texas Instruments 開關(guān)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(shù)量:1 最大工作溫度:+ 105 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:TSSOP-14 |
| L5993 | 功能描述:開關(guān)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(guān)頻率:1 MHz 工作溫度范圍: 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:WSON-8 封裝:Reel |
| L5993D | 功能描述:開關(guān)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(guān)頻率:1 MHz 工作溫度范圍: 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:WSON-8 封裝:Reel |
| L5993D013TR | 功能描述:開關(guān)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(guān)頻率:1 MHz 工作溫度范圍: 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:WSON-8 封裝:Reel |
| L5994 | 功能描述:電流型 PWM 控制器 Adj Triple Out Pwr RoHS:否 制造商:Texas Instruments 開關(guān)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(shù)量:1 最大工作溫度:+ 105 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:TSSOP-14 |
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