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參數(shù)資料
| 型號： | LT1952IGN |
| 廠商： | LINEAR TECHNOLOGY CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | Single Switch Synchronous Forward Controller |
| 中文描述： | 1 A SWITCHING CONTROLLER, 560 kHz SWITCHING FREQ-MAX, PDSO16 |
| 封裝： | 0.150 INCH, PLASTIC, SSOP-16 |
| 文件頁數(shù)： | 12/24頁 |
| 文件大?。?/td> | 252K |
| 代理商： | LT1952IGN |
LT1952
12
1952f
OPERATIOU
Slope Compensation
The current mode architecture requires slope compensa-
tion to be added to the current sensing loop to prevent
subharmonic oscillations which can occur for duty cycles
above 50%. Unlike most current mode converters which
have a slope compensation ramp that is fixed internally,
placing a constraint on inductor value and operating
frequency, the LT1952 has externally adjustable slope
compensation. Slope compensation can be programmed
by inserting an external resistor (R
SLOPE
) in series with the
I
SENSE
pin. The LT1952 has a linear slope compensation
ramp which sources current out of the I
SENSE
pin of
approximately 8
μ
A at 0% duty cycle to 35
μ
A at 80% duty
cycle.
Over-Current Detection and Soft-Start (OC Pin)
An added feature to the LT1952 is a precise 100mV sense
threshold at the OC pin used to detect over-current condi-
tions in the converter and set a soft-start latch. The OC pin
is connected directly to the source of the primary side
MOSFET to monitor peak current in the MOSFET
(Figure 7). The 100mV threshold is constant over the
entire duty cycle range of the converter because it is
unaffected by the slope compensation added to the
I
SENSE
pin.
Synchronizing
A SYNC pin allows the LT1952 oscillator to be synchro-
nized to an external clock. The SYNC pin can be driven
from a logic level output, requiring less than 0.8V for a
logic level low and greater than 2.2V for a logic level high.
Duty cycle should run between 10% and 90%. To avoid
loss of slope compensation during synchronization, the
free running oscillator frequency (f
OSC
) should be pro-
grammed to 80% of the external clock frequency (f
SYNC
).
The R
SLOPE
resistor chosen for non-synchronized opera-
tion should be increased by 1.25x (= f
SYNC
/f
OSC
).
APPLICATIU
W
U
U
Shutdown and Programming Undervoltage Lockout
The LT1952 has an accurate 1.32V shutdown threshold at
the SD_V
SEC
pin. This threshold can be used in conjunc-
tion with a resistor divider to define the undervoltage
lockout threshold (UVLO) of the system input voltage (V
S
)
to the power converter (Figure 3). A pin current hysteresis
(11
μ
A before part turn on, 0
μ
A after part turn on) allows
UVLO hysteresis to be programmed. Calculation of the
ON/OFF thresholds for the supply (SV
IN
) to the power
converter can be made as follows:
V
S OFF
Threshold = 1.32[1 + (R1/R2)]
V
S ON
Threshold = SV
IN OFF
+ (11
μ
A R1)
A simple open drain transistor can be added to the resistor
divider network at the SD_V
SEC
pin to control the turn off
of the LT1952 (Figure 3).
The SD_V
SEC
pin must not be left open since there must
be an external source current >11
μ
A to lift the pin past its
1.32V threshold for part turn on.
Micropower Start-Up: Selection of Start-Up Resistor
and Capacitor for V
IN
The LT1952 uses turn-on voltage hysteresis at the V
IN
pin
and low start-up current to allow micro-power start-up
(Figure 4). The LT1952 monitors V
IN
pin voltage to allow
part turn on at 14.25V and part turn off at 8.75V. Low start-
up current (460
μ
A) allows a large resistor to be connected
Figure 3. Programming Undervoltage Lockout (UVLO)
1.32V
SYSTEM
INPUT (V
S
)
OPTIONAL
SHUTDOWN
TRANSISTOR
1952 F03
SD_V
SEC
11
μ
A
LT1952
R1
R2
+
–
OFF
ON
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相關代理商/技術參數(shù) |
參數(shù)描述 |
|---|---|
| LT1952IGN#PBF | 功能描述:IC REG CTRLR ISO PWM CM 16-SSOP RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 標準包裝:2,500 系列:- PWM 型:電流模式 輸出數(shù):1 頻率 - 最大:500kHz 占空比:96% 電源電壓:4 V ~ 36 V 降壓:無 升壓:是 回掃:無 反相:無 倍增器:無 除法器:無 Cuk:無 隔離:無 工作溫度:-40°C ~ 125°C 封裝/外殼:24-WQFN 裸露焊盤 包裝:帶卷 (TR) |
| LT1952IGN#TR | 制造商:Linear Technology 功能描述:Current Mode PWM Controller 16-Pin SSOP N T/R |
| LT1952IGN#TRPBF | 功能描述:IC REG CTRLR ISO PWM CM 16-SSOP RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 標準包裝:2,500 系列:- PWM 型:電流模式 輸出數(shù):1 頻率 - 最大:500kHz 占空比:96% 電源電壓:4 V ~ 36 V 降壓:無 升壓:是 回掃:無 反相:無 倍增器:無 除法器:無 Cuk:無 隔離:無 工作溫度:-40°C ~ 125°C 封裝/外殼:24-WQFN 裸露焊盤 包裝:帶卷 (TR) |
| LT1952IGN-1 | 制造商:Linear Technology 功能描述:Current Mode PWM Controller 16-Pin SSOP N |
| LT1952IGN-1#PBF | 功能描述:IC REG CTRLR ISO PWM CM 16-SSOP RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 特色產品:LM3753/54 Scalable 2-Phase Synchronous Buck Controllers 標準包裝:1 系列:PowerWise® PWM 型:電壓模式 輸出數(shù):1 頻率 - 最大:1MHz 占空比:81% 電源電壓:4.5 V ~ 18 V 降壓:是 升壓:無 回掃:無 反相:無 倍增器:無 除法器:無 Cuk:無 隔離:無 工作溫度:-5°C ~ 125°C 封裝/外殼:32-WFQFN 裸露焊盤 包裝:Digi-Reel® 產品目錄頁面:1303 (CN2011-ZH PDF) 其它名稱:LM3754SQDKR |
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